Adding upstream version 124.0.1.upstream/124.0.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

443 files changed, 47778 insertions, 0 deletions

diff --git a/dom/workers/ChromeWorker.cpp b/dom/workers/ChromeWorker.cpp
new file mode 100644
index 0000000000..7fda84f7f5
--- /dev/null
+++ b/dom/workers/ChromeWorker.cpp
@@ -0,0 +1,84 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "ChromeWorker.h"
+
+#include "mozilla/AppShutdown.h"
+#include "mozilla/dom/BindingUtils.h"
+#include "mozilla/dom/WorkerBinding.h"
+#include "nsContentUtils.h"
+#include "nsIXPConnect.h"
+#include "WorkerPrivate.h"
+
+namespace mozilla::dom {
+
+/* static */
+already_AddRefed<ChromeWorker> ChromeWorker::Constructor(
+    const GlobalObject& aGlobal, const nsAString& aScriptURL,
+    const WorkerOptions& aOptions, ErrorResult& aRv) {
+  // Dump the JS stack if somebody's creating a ChromeWorker after shutdown has
+  // begun.  See bug 1813353.
+  if (xpc::IsInAutomation() &&
+      AppShutdown::IsInOrBeyond(ShutdownPhase::AppShutdown)) {
+    NS_WARNING("ChromeWorker construction during shutdown");
+    nsCOMPtr<nsIXPConnect> xpc = nsIXPConnect::XPConnect();
+    Unused << xpc->DebugDumpJSStack(true, true, false);
+  }
+
+  JSContext* cx = aGlobal.Context();
+
+  RefPtr<WorkerPrivate> workerPrivate = WorkerPrivate::Constructor(
+      cx, aScriptURL, true /* aIsChromeWorker */, WorkerKindDedicated,
+      RequestCredentials::Omit, aOptions.mType, aOptions.mName, VoidCString(),
+      nullptr /*aLoadInfo */, aRv);
+  if (NS_WARN_IF(aRv.Failed())) {
+    return nullptr;
+  }
+
+  nsCOMPtr<nsIGlobalObject> globalObject =
+      do_QueryInterface(aGlobal.GetAsSupports());
+
+  RefPtr<ChromeWorker> worker =
+      new ChromeWorker(globalObject, workerPrivate.forget());
+  return worker.forget();
+}
+
+/* static */
+bool ChromeWorker::WorkerAvailable(JSContext* aCx, JSObject* /* unused */) {
+  // Chrome is always allowed to use workers, and content is never
+  // allowed to use ChromeWorker, so all we have to check is the
+  // caller.  However, chrome workers apparently might not have a
+  // system principal, so we have to check for them manually.
+  if (NS_IsMainThread()) {
+    return nsContentUtils::IsSystemCaller(aCx);
+  }
+
+  return GetWorkerPrivateFromContext(aCx)->IsChromeWorker();
+}
+
+ChromeWorker::ChromeWorker(nsIGlobalObject* aGlobalObject,
+                           already_AddRefed<WorkerPrivate> aWorkerPrivate)
+    : Worker(aGlobalObject, std::move(aWorkerPrivate)) {}
+
+ChromeWorker::~ChromeWorker() = default;
+
+JSObject* ChromeWorker::WrapObject(JSContext* aCx,
+                                   JS::Handle<JSObject*> aGivenProto) {
+  JS::Rooted<JSObject*> wrapper(
+      aCx, ChromeWorker_Binding::Wrap(aCx, this, aGivenProto));
+  if (wrapper) {
+    // Most DOM objects don't assume they have a reflector. If they don't have
+    // one and need one, they create it. But in workers code, we assume that the
+    // reflector is always present.  In order to guarantee that it's always
+    // present, we have to preserve it. Otherwise the GC will happily collect it
+    // as needed.
+    MOZ_ALWAYS_TRUE(TryPreserveWrapper(wrapper));
+  }
+
+  return wrapper;
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/workers/ChromeWorker.h b/dom/workers/ChromeWorker.h
new file mode 100644
index 0000000000..04265f4a31
--- /dev/null
+++ b/dom/workers/ChromeWorker.h
@@ -0,0 +1,33 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_ChromeWorker_h
+#define mozilla_dom_ChromeWorker_h
+
+#include "mozilla/dom/Worker.h"
+
+namespace mozilla::dom {
+
+class ChromeWorker final : public Worker {
+ public:
+  static already_AddRefed<ChromeWorker> Constructor(
+      const GlobalObject& aGlobal, const nsAString& aScriptURL,
+      const WorkerOptions& aOptions, ErrorResult& aRv);
+
+  static bool WorkerAvailable(JSContext* aCx, JSObject* /* unused */);
+
+  JSObject* WrapObject(JSContext* aCx,
+                       JS::Handle<JSObject*> aGivenProto) override;
+
+ private:
+  ChromeWorker(nsIGlobalObject* aGlobalObject,
+               already_AddRefed<WorkerPrivate> aWorkerPrivate);
+  ~ChromeWorker();
+};
+
+}  // namespace mozilla::dom
+
+#endif /* mozilla_dom_ChromeWorker_h */
diff --git a/dom/workers/ChromeWorkerScope.cpp b/dom/workers/ChromeWorkerScope.cpp
new file mode 100644
index 0000000000..e2ec334016
--- /dev/null
+++ b/dom/workers/ChromeWorkerScope.cpp
@@ -0,0 +1,67 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "ChromeWorkerScope.h"
+
+#include "jsapi.h"
+#include "js/PropertyAndElement.h"  // JS_GetProperty
+#include "js/experimental/CTypes.h"  // JS::InitCTypesClass, JS::CTypesCallbacks, JS::SetCTypesCallbacks
+#include "js/MemoryFunctions.h"
+
+#include "nsNativeCharsetUtils.h"
+#include "nsString.h"
+
+namespace mozilla::dom {
+
+namespace {
+
+#ifdef BUILD_CTYPES
+
+char* UnicodeToNative(JSContext* aCx, const char16_t* aSource,
+                      size_t aSourceLen) {
+  nsDependentSubstring unicode(aSource, aSourceLen);
+
+  nsAutoCString native;
+  if (NS_FAILED(NS_CopyUnicodeToNative(unicode, native))) {
+    JS_ReportErrorASCII(aCx, "Could not convert string to native charset!");
+    return nullptr;
+  }
+
+  char* result = static_cast<char*>(JS_malloc(aCx, native.Length() + 1));
+  if (!result) {
+    return nullptr;
+  }
+
+  memcpy(result, native.get(), native.Length());
+  result[native.Length()] = 0;
+  return result;
+}
+
+#endif  // BUILD_CTYPES
+
+}  // namespace
+
+bool DefineChromeWorkerFunctions(JSContext* aCx,
+                                 JS::Handle<JSObject*> aGlobal) {
+  // Currently ctypes is the only special property given to ChromeWorkers.
+#ifdef BUILD_CTYPES
+  {
+    JS::Rooted<JS::Value> ctypes(aCx);
+    if (!JS::InitCTypesClass(aCx, aGlobal) ||
+        !JS_GetProperty(aCx, aGlobal, "ctypes", &ctypes)) {
+      return false;
+    }
+
+    static const JS::CTypesCallbacks callbacks = {UnicodeToNative};
+
+    JS::SetCTypesCallbacks(ctypes.toObjectOrNull(), &callbacks);
+  }
+#endif  // BUILD_CTYPES
+
+  return true;
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/workers/ChromeWorkerScope.h b/dom/workers/ChromeWorkerScope.h
new file mode 100644
index 0000000000..be415a0403
--- /dev/null
+++ b/dom/workers/ChromeWorkerScope.h
@@ -0,0 +1,18 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_workers_chromeworkerscope_h__
+#define mozilla_dom_workers_chromeworkerscope_h__
+
+#include "js/TypeDecls.h"
+
+namespace mozilla::dom {
+
+bool DefineChromeWorkerFunctions(JSContext* aCx, JS::Handle<JSObject*> aGlobal);
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_workers_chromeworkerscope_h__
diff --git a/dom/workers/EventWithOptionsRunnable.cpp b/dom/workers/EventWithOptionsRunnable.cpp
new file mode 100644
index 0000000000..2ddc56d946
--- /dev/null
+++ b/dom/workers/EventWithOptionsRunnable.cpp
@@ -0,0 +1,160 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+#include "EventWithOptionsRunnable.h"
+#include "WorkerScope.h"
+#include "mozilla/dom/WorkerRunnable.h"
+#include "mozilla/dom/StructuredCloneHolder.h"
+#include "js/StructuredClone.h"
+#include "js/RootingAPI.h"
+#include "js/Value.h"
+#include "nsJSPrincipals.h"
+#include "nsContentUtils.h"
+#include "nsDebug.h"
+#include "MainThreadUtils.h"
+#include "mozilla/Assertions.h"
+#include "nsGlobalWindowInner.h"
+#include "mozilla/DOMEventTargetHelper.h"
+#include "mozilla/ErrorResult.h"
+#include "nsIGlobalObject.h"
+#include "nsCOMPtr.h"
+#include "js/GlobalObject.h"
+#include "xpcpublic.h"
+#include "mozilla/dom/MessagePortBinding.h"
+#include "mozilla/dom/MessagePort.h"
+#include "mozilla/OwningNonNull.h"
+#include "mozilla/RefPtr.h"
+#include "mozilla/dom/Event.h"
+#include "mozilla/dom/WorkerCommon.h"
+
+namespace mozilla::dom {
+EventWithOptionsRunnable::EventWithOptionsRunnable(Worker& aWorker,
+                                                   const char* aName)
+    : WorkerDebuggeeRunnable(aWorker.mWorkerPrivate, aName,
+                             WorkerRunnable::WorkerThread),
+      StructuredCloneHolder(CloningSupported, TransferringSupported,
+                            StructuredCloneScope::SameProcess) {}
+
+EventWithOptionsRunnable::~EventWithOptionsRunnable() = default;
+
+void EventWithOptionsRunnable::InitOptions(
+    JSContext* aCx, JS::Handle<JS::Value> aOptions,
+    const Sequence<JSObject*>& aTransferable, ErrorResult& aRv) {
+  JS::Rooted<JS::Value> transferable(aCx, JS::UndefinedValue());
+
+  aRv = nsContentUtils::CreateJSValueFromSequenceOfObject(aCx, aTransferable,
+                                                          &transferable);
+  if (NS_WARN_IF(aRv.Failed())) {
+    return;
+  }
+
+  JS::CloneDataPolicy clonePolicy;
+  // DedicatedWorkers are always part of the same agent cluster.
+  clonePolicy.allowIntraClusterClonableSharedObjects();
+
+  MOZ_ASSERT(NS_IsMainThread());
+  nsGlobalWindowInner* win = nsContentUtils::IncumbentInnerWindow();
+  if (win && win->IsSharedMemoryAllowed()) {
+    clonePolicy.allowSharedMemoryObjects();
+  }
+
+  Write(aCx, aOptions, transferable, clonePolicy, aRv);
+}
+
+// Cargo-culted from MesssageEventRunnable.
+bool EventWithOptionsRunnable::BuildAndFireEvent(
+    JSContext* aCx, WorkerPrivate* aWorkerPrivate,
+    DOMEventTargetHelper* aTarget) {
+  IgnoredErrorResult rv;
+  nsCOMPtr<nsIGlobalObject> parent = aTarget->GetParentObject();
+
+  // For some workers without window, parent is null and we try to find it
+  // from the JS Context.
+  if (!parent) {
+    JS::Rooted<JSObject*> globalObject(aCx, JS::CurrentGlobalOrNull(aCx));
+    if (NS_WARN_IF(!globalObject)) {
+      rv.ThrowDataCloneError("failed to get global object");
+      OptionsDeserializeFailed(rv);
+      return false;
+    }
+
+    parent = xpc::NativeGlobal(globalObject);
+    if (NS_WARN_IF(!parent)) {
+      rv.ThrowDataCloneError("failed to get parent");
+      OptionsDeserializeFailed(rv);
+      return false;
+    }
+  }
+
+  MOZ_ASSERT(parent);
+
+  JS::Rooted<JS::Value> options(aCx);
+
+  JS::CloneDataPolicy cloneDataPolicy;
+  if (parent->GetClientInfo().isSome() &&
+      parent->GetClientInfo()->AgentClusterId().isSome() &&
+      parent->GetClientInfo()->AgentClusterId()->Equals(
+          aWorkerPrivate->AgentClusterId())) {
+    cloneDataPolicy.allowIntraClusterClonableSharedObjects();
+  }
+
+  if (aWorkerPrivate->IsSharedMemoryAllowed()) {
+    cloneDataPolicy.allowSharedMemoryObjects();
+  }
+
+  Read(parent, aCx, &options, cloneDataPolicy, rv);
+
+  if (NS_WARN_IF(rv.Failed())) {
+    OptionsDeserializeFailed(rv);
+    return false;
+  }
+
+  Sequence<OwningNonNull<MessagePort>> ports;
+  if (NS_WARN_IF(!TakeTransferredPortsAsSequence(ports))) {
+    // TODO: Is this an appropriate type? What does this actually do?
+    rv.ThrowDataCloneError("TakeTransferredPortsAsSequence failed");
+    OptionsDeserializeFailed(rv);
+    return false;
+  }
+
+  RefPtr<dom::Event> event = BuildEvent(aCx, parent, aTarget, options);
+
+  if (NS_WARN_IF(!event)) {
+    return false;
+  }
+
+  aTarget->DispatchEvent(*event);
+  return true;
+}
+
+bool EventWithOptionsRunnable::WorkerRun(JSContext* aCx,
+                                         WorkerPrivate* aWorkerPrivate) {
+  if (mTarget == ParentThread) {
+    // Don't fire this event if the JS object has been disconnected from the
+    // private object.
+    if (!aWorkerPrivate->IsAcceptingEvents()) {
+      return true;
+    }
+
+    aWorkerPrivate->AssertInnerWindowIsCorrect();
+
+    return BuildAndFireEvent(aCx, aWorkerPrivate,
+                             aWorkerPrivate->ParentEventTargetRef());
+  }
+
+  MOZ_ASSERT(aWorkerPrivate == GetWorkerPrivateFromContext(aCx));
+  MOZ_ASSERT(aWorkerPrivate->GlobalScope());
+
+  // If the worker start shutting down, don't dispatch the event.
+  if (NS_FAILED(
+          aWorkerPrivate->GlobalScope()->CheckCurrentGlobalCorrectness())) {
+    return true;
+  }
+
+  return BuildAndFireEvent(aCx, aWorkerPrivate, aWorkerPrivate->GlobalScope());
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/workers/EventWithOptionsRunnable.h b/dom/workers/EventWithOptionsRunnable.h
new file mode 100644
index 0000000000..de228f2688
--- /dev/null
+++ b/dom/workers/EventWithOptionsRunnable.h
@@ -0,0 +1,56 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+#ifndef MOZILLA_DOM_WORKERS_EVENTWITHOPTIONSRUNNABLE_H_
+#define MOZILLA_DOM_WORKERS_EVENTWITHOPTIONSRUNNABLE_H_
+
+#include "WorkerCommon.h"
+#include "WorkerRunnable.h"
+#include "mozilla/dom/StructuredCloneHolder.h"
+
+namespace mozilla {
+class DOMEventTargetHelper;
+
+namespace dom {
+class Event;
+class EventTarget;
+class Worker;
+class WorkerPrivate;
+
+// Cargo-culted from MesssageEventRunnable.
+// Intended to be used for the idiom where arbitrary options are transferred to
+// the worker thread (with optional transfer functions), which are then used to
+// build an event, which is then fired on the global worker scope.
+class EventWithOptionsRunnable : public WorkerDebuggeeRunnable,
+                                 public StructuredCloneHolder {
+ public:
+  explicit EventWithOptionsRunnable(
+      Worker& aWorker, const char* aName = "EventWithOptionsRunnable");
+  void InitOptions(JSContext* aCx, JS::Handle<JS::Value> aOptions,
+                   const Sequence<JSObject*>& aTransferable, ErrorResult& aRv);
+
+  // Called on the worker thread. The event returned will be fired on the
+  // worker's global scope. If a StrongWorkerRef needs to be retained, the
+  // implementation can do so with the WorkerPrivate.
+  virtual already_AddRefed<Event> BuildEvent(
+      JSContext* aCx, nsIGlobalObject* aGlobal, EventTarget* aTarget,
+      JS::Handle<JS::Value> aOptions) = 0;
+
+  // Called on the worker thread
+  virtual void OptionsDeserializeFailed(ErrorResult& aRv) {}
+
+ protected:
+  virtual ~EventWithOptionsRunnable();
+
+ private:
+  bool WorkerRun(JSContext* aCx, WorkerPrivate* aWorkerPrivate) override;
+  bool BuildAndFireEvent(JSContext* aCx, WorkerPrivate* aWorkerPrivate,
+                         DOMEventTargetHelper* aTarget);
+};
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // MOZILLA_DOM_WORKERS_EVENTWITHOPTIONSRUNNABLE_H_
diff --git a/dom/workers/JSExecutionManager.cpp b/dom/workers/JSExecutionManager.cpp
new file mode 100644
index 0000000000..9482888423
--- /dev/null
+++ b/dom/workers/JSExecutionManager.cpp
@@ -0,0 +1,251 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/JSExecutionManager.h"
+
+#include "WorkerCommon.h"
+#include "WorkerPrivate.h"
+
+#include "mozilla/dom/DocGroup.h"
+#include "mozilla/StaticPrefs_dom.h"
+#include "mozilla/StaticPtr.h"
+
+namespace mozilla::dom {
+
+JSExecutionManager* JSExecutionManager::mCurrentMTManager;
+
+const uint32_t kTimeSliceExpirationMS = 50;
+
+using RequestState = JSExecutionManager::RequestState;
+
+static StaticRefPtr<JSExecutionManager> sSABSerializationManager;
+
+void JSExecutionManager::Initialize() {
+  if (StaticPrefs::dom_workers_serialized_sab_access()) {
+    sSABSerializationManager = MakeRefPtr<JSExecutionManager>(1);
+  }
+}
+
+void JSExecutionManager::Shutdown() { sSABSerializationManager = nullptr; }
+
+JSExecutionManager* JSExecutionManager::GetSABSerializationManager() {
+  return sSABSerializationManager.get();
+}
+
+RequestState JSExecutionManager::RequestJSThreadExecution() {
+  if (NS_IsMainThread()) {
+    return RequestJSThreadExecutionMainThread();
+  }
+
+  WorkerPrivate* workerPrivate = GetCurrentThreadWorkerPrivate();
+
+  if (!workerPrivate || workerPrivate->GetExecutionGranted()) {
+    return RequestState::ExecutingAlready;
+  }
+
+  MutexAutoLock lock(mExecutionQueueMutex);
+  MOZ_ASSERT(mMaxRunning >= mRunning);
+
+  if ((mExecutionQueue.size() + (mMainThreadAwaitingExecution ? 1 : 0)) <
+      size_t(mMaxRunning - mRunning)) {
+    // There's slots ready for things to run, execute right away.
+    workerPrivate->SetExecutionGranted(true);
+    workerPrivate->ScheduleTimeSliceExpiration(kTimeSliceExpirationMS);
+
+    mRunning++;
+    return RequestState::Granted;
+  }
+
+  mExecutionQueue.push_back(workerPrivate);
+
+  TimeStamp waitStart = TimeStamp::Now();
+
+  while (mRunning >= mMaxRunning || (workerPrivate != mExecutionQueue.front() ||
+                                     mMainThreadAwaitingExecution)) {
+    // If there is no slots available, the main thread is awaiting permission
+    // or we are not first in line for execution, wait until notified.
+    mExecutionQueueCondVar.Wait(TimeDuration::FromMilliseconds(500));
+    if ((TimeStamp::Now() - waitStart) > TimeDuration::FromSeconds(20)) {
+      // Crash so that these types of situations are actually caught in the
+      // crash reporter.
+      MOZ_CRASH();
+    }
+  }
+
+  workerPrivate->SetExecutionGranted(true);
+  workerPrivate->ScheduleTimeSliceExpiration(kTimeSliceExpirationMS);
+
+  mExecutionQueue.pop_front();
+  mRunning++;
+  if (mRunning < mMaxRunning) {
+    // If a thread woke up before that wasn't first in line it will have gone
+    // back to sleep, if there's more slots available, wake it now.
+    mExecutionQueueCondVar.NotifyAll();
+  }
+
+  return RequestState::Granted;
+}
+
+void JSExecutionManager::YieldJSThreadExecution() {
+  if (NS_IsMainThread()) {
+    MOZ_ASSERT(mMainThreadIsExecuting);
+    mMainThreadIsExecuting = false;
+
+    MutexAutoLock lock(mExecutionQueueMutex);
+    mRunning--;
+    mExecutionQueueCondVar.NotifyAll();
+    return;
+  }
+
+  WorkerPrivate* workerPrivate = GetCurrentThreadWorkerPrivate();
+
+  if (!workerPrivate) {
+    return;
+  }
+
+  MOZ_ASSERT(workerPrivate->GetExecutionGranted());
+
+  workerPrivate->CancelTimeSliceExpiration();
+
+  MutexAutoLock lock(mExecutionQueueMutex);
+  mRunning--;
+  mExecutionQueueCondVar.NotifyAll();
+  workerPrivate->SetExecutionGranted(false);
+}
+
+bool JSExecutionManager::YieldJSThreadExecutionIfGranted() {
+  if (NS_IsMainThread()) {
+    if (mMainThreadIsExecuting) {
+      YieldJSThreadExecution();
+      return true;
+    }
+    return false;
+  }
+
+  WorkerPrivate* workerPrivate = GetCurrentThreadWorkerPrivate();
+
+  if (workerPrivate && workerPrivate->GetExecutionGranted()) {
+    YieldJSThreadExecution();
+    return true;
+  }
+
+  return false;
+}
+
+RequestState JSExecutionManager::RequestJSThreadExecutionMainThread() {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  if (mMainThreadIsExecuting) {
+    return RequestState::ExecutingAlready;
+  }
+
+  MutexAutoLock lock(mExecutionQueueMutex);
+  MOZ_ASSERT(mMaxRunning >= mRunning);
+
+  if ((mMaxRunning - mRunning) > 0) {
+    // If there's any slots available run, the main thread always takes
+    // precedence over any worker threads.
+    mRunning++;
+    mMainThreadIsExecuting = true;
+    return RequestState::Granted;
+  }
+
+  mMainThreadAwaitingExecution = true;
+
+  TimeStamp waitStart = TimeStamp::Now();
+
+  while (mRunning >= mMaxRunning) {
+    if ((TimeStamp::Now() - waitStart) > TimeDuration::FromSeconds(20)) {
+      // Crash so that these types of situations are actually caught in the
+      // crash reporter.
+      MOZ_CRASH();
+    }
+    mExecutionQueueCondVar.Wait(TimeDuration::FromMilliseconds(500));
+  }
+
+  mMainThreadAwaitingExecution = false;
+  mMainThreadIsExecuting = true;
+
+  mRunning++;
+  if (mRunning < mMaxRunning) {
+    // If a thread woke up before that wasn't first in line it will have gone
+    // back to sleep, if there's more slots available, wake it now.
+    mExecutionQueueCondVar.NotifyAll();
+  }
+
+  return RequestState::Granted;
+}
+
+AutoRequestJSThreadExecution::AutoRequestJSThreadExecution(
+    nsIGlobalObject* aGlobalObject, bool aIsMainThread) {
+  JSExecutionManager* manager = nullptr;
+
+  mIsMainThread = aIsMainThread;
+  if (mIsMainThread) {
+    mOldGrantingManager = JSExecutionManager::mCurrentMTManager;
+
+    nsPIDOMWindowInner* innerWindow = nullptr;
+    if (aGlobalObject) {
+      innerWindow = aGlobalObject->GetAsInnerWindow();
+    }
+
+    DocGroup* docGroup = nullptr;
+    if (innerWindow) {
+      docGroup = innerWindow->GetDocGroup();
+    }
+
+    if (docGroup) {
+      manager = docGroup->GetExecutionManager();
+    }
+
+    if (JSExecutionManager::mCurrentMTManager == manager) {
+      return;
+    }
+
+    if (JSExecutionManager::mCurrentMTManager) {
+      JSExecutionManager::mCurrentMTManager->YieldJSThreadExecution();
+      JSExecutionManager::mCurrentMTManager = nullptr;
+    }
+  } else {
+    WorkerPrivate* workerPrivate = GetCurrentThreadWorkerPrivate();
+
+    if (workerPrivate) {
+      manager = workerPrivate->GetExecutionManager();
+    }
+  }
+
+  if (manager &&
+      (manager->RequestJSThreadExecution() == RequestState::Granted)) {
+    if (NS_IsMainThread()) {
+      // Make sure we restore permission on destruction if needed.
+      JSExecutionManager::mCurrentMTManager = manager;
+    }
+    mExecutionGrantingManager = std::move(manager);
+  }
+}
+
+AutoYieldJSThreadExecution::AutoYieldJSThreadExecution() {
+  JSExecutionManager* manager = nullptr;
+
+  if (NS_IsMainThread()) {
+    manager = JSExecutionManager::mCurrentMTManager;
+  } else {
+    WorkerPrivate* workerPrivate = GetCurrentThreadWorkerPrivate();
+
+    if (workerPrivate) {
+      manager = workerPrivate->GetExecutionManager();
+    }
+  }
+
+  if (manager && manager->YieldJSThreadExecutionIfGranted()) {
+    mExecutionGrantingManager = std::move(manager);
+    if (NS_IsMainThread()) {
+      JSExecutionManager::mCurrentMTManager = nullptr;
+    }
+  }
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/workers/JSExecutionManager.h b/dom/workers/JSExecutionManager.h
new file mode 100644
index 0000000000..132884bf53
--- /dev/null
+++ b/dom/workers/JSExecutionManager.h
@@ -0,0 +1,192 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_workers_jsexecutionmanager_h__
+#define mozilla_dom_workers_jsexecutionmanager_h__
+
+#include <stdint.h>
+#include <deque>
+#include "MainThreadUtils.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/CondVar.h"
+#include "mozilla/Mutex.h"
+#include "mozilla/RefPtr.h"
+#include "nsISupports.h"
+
+class nsIGlobalObject;
+namespace mozilla {
+
+class ErrorResult;
+
+namespace dom {
+class WorkerPrivate;
+
+// The code in this file is responsible for throttling JS execution. It does
+// this by introducing a JSExecutionManager class. An execution manager may be
+// applied to any number of worker threads or a DocGroup on the main thread.
+//
+// JS environments associated with a JS execution manager may only execute on a
+// certain amount of CPU cores in parallel.
+//
+// Whenever the main thread, or a worker thread begins executing JS it should
+// make sure AutoRequestJSThreadExecution is present on the stack, in practice
+// this is done by it being part of AutoEntryScript.
+//
+// Whenever the main thread may end up blocking on the activity of a worker
+// thread, it should make sure to have an AutoYieldJSThreadExecution object
+// on the stack.
+//
+// Whenever a worker thread may end up blocking on the main thread or the
+// activity of another worker thread, it should make sure to have an
+// AutoYieldJSThreadExecution object on the stack.
+//
+// Failure to do this may result in a deadlock. When a deadlock occurs due
+// to these circumstances we will crash after 20 seconds.
+//
+// For the main thread this class should only be used in the case of an
+// emergency surrounding exploitability of SharedArrayBuffers. A single
+// execution manager will then be shared between all Workers and the main
+// thread doc group containing the SharedArrayBuffer and ensure all this code
+// only runs in a serialized manner. On the main thread we therefore may have
+// 1 execution manager per DocGroup, as this is the granularity at which
+// SharedArrayBuffers may be present.
+
+class AutoRequestJSThreadExecution;
+class AutoYieldJSThreadExecution;
+
+// This class is used to regulate JS execution when for whatever reason we wish
+// to throttle execution of multiple JS environments to occur with a certain
+// maximum of synchronously executing threads. This should be used through
+// the stack helper classes.
+class JSExecutionManager {
+ public:
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(JSExecutionManager)
+
+  explicit JSExecutionManager(int32_t aMaxRunning = 1)
+      : mMaxRunning(aMaxRunning) {}
+
+  enum class RequestState { Granted, ExecutingAlready };
+
+  static void Initialize();
+  static void Shutdown();
+
+  static JSExecutionManager* GetSABSerializationManager();
+
+ private:
+  friend class AutoRequestJSThreadExecution;
+  friend class AutoYieldJSThreadExecution;
+  ~JSExecutionManager() = default;
+
+  // Methods used by Auto*JSThreadExecution
+
+  // Request execution permission, returns ExecutingAlready if execution was
+  // already granted or does not apply to this thread.
+  RequestState RequestJSThreadExecution();
+
+  // Yield JS execution, this asserts that permission is actually granted.
+  void YieldJSThreadExecution();
+
+  // Yield JS execution if permission was granted. This returns false if no
+  // permission is granted. This method is needed because an execution manager
+  // may have been set in between the ctor and dtor of
+  // AutoYieldJSThreadExecution.
+  bool YieldJSThreadExecutionIfGranted();
+
+  RequestState RequestJSThreadExecutionMainThread();
+
+  // Execution manager currently managing the main thread.
+  // MainThread access only.
+  static JSExecutionManager* mCurrentMTManager;
+
+  // Workers waiting to be given permission for execution.
+  // Guarded by mExecutionQueueMutex.
+  std::deque<WorkerPrivate*> mExecutionQueue
+      MOZ_GUARDED_BY(mExecutionQueueMutex);
+
+  // Number of threads currently executing concurrently for this manager.
+  // Guarded by mExecutionQueueMutex.
+  int32_t mRunning MOZ_GUARDED_BY(mExecutionQueueMutex) = 0;
+
+  // Number of threads allowed to run concurrently for environments managed
+  // by this manager.
+  // Guarded by mExecutionQueueMutex.
+  int32_t mMaxRunning MOZ_GUARDED_BY(mExecutionQueueMutex) = 1;
+
+  // Mutex that guards the execution queue and associated state.
+  Mutex mExecutionQueueMutex =
+      Mutex{"JSExecutionManager::sExecutionQueueMutex"};
+
+  // ConditionVariables that blocked threads wait for.
+  CondVar mExecutionQueueCondVar =
+      CondVar{mExecutionQueueMutex, "JSExecutionManager::sExecutionQueueMutex"};
+
+  // Whether the main thread is currently executing for this manager.
+  // MainThread access only.
+  bool mMainThreadIsExecuting = false;
+
+  // Whether the main thread is currently awaiting permission to execute. Main
+  // thread execution is always prioritized.
+  // Guarded by mExecutionQueueMutex.
+  bool mMainThreadAwaitingExecution MOZ_GUARDED_BY(mExecutionQueueMutex) =
+      false;
+};
+
+// Helper for managing execution requests and allowing re-entrant permission
+// requests.
+class MOZ_STACK_CLASS AutoRequestJSThreadExecution {
+ public:
+  explicit AutoRequestJSThreadExecution(nsIGlobalObject* aGlobalObject,
+                                        bool aIsMainThread);
+
+  ~AutoRequestJSThreadExecution() {
+    if (mExecutionGrantingManager) {
+      mExecutionGrantingManager->YieldJSThreadExecution();
+    }
+    if (mIsMainThread) {
+      if (mOldGrantingManager) {
+        mOldGrantingManager->RequestJSThreadExecution();
+      }
+      JSExecutionManager::mCurrentMTManager = mOldGrantingManager;
+    }
+  }
+
+ private:
+  // The manager we obtained permission from. nullptr if permission was already
+  // granted.
+  RefPtr<JSExecutionManager> mExecutionGrantingManager;
+  // The manager we had permission from before, and where permission should be
+  // re-requested upon destruction.
+  RefPtr<JSExecutionManager> mOldGrantingManager;
+
+  // We store this for performance reasons.
+  bool mIsMainThread;
+};
+
+// Class used to wrap code which essentially exits JS execution and may block
+// on other threads.
+class MOZ_STACK_CLASS AutoYieldJSThreadExecution {
+ public:
+  AutoYieldJSThreadExecution();
+
+  ~AutoYieldJSThreadExecution() {
+    if (mExecutionGrantingManager) {
+      mExecutionGrantingManager->RequestJSThreadExecution();
+      if (NS_IsMainThread()) {
+        JSExecutionManager::mCurrentMTManager = mExecutionGrantingManager;
+      }
+    }
+  }
+
+ private:
+  // Set to the granting manager if we were granted permission here.
+  RefPtr<JSExecutionManager> mExecutionGrantingManager;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_workers_jsexecutionmanager_h__
diff --git a/dom/workers/JSSettings.h b/dom/workers/JSSettings.h
new file mode 100644
index 0000000000..af2247a847
--- /dev/null
+++ b/dom/workers/JSSettings.h
@@ -0,0 +1,62 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_workerinternals_JSSettings_h
+#define mozilla_dom_workerinternals_JSSettings_h
+
+#include <stdint.h>
+
+#include "js/ContextOptions.h"
+#include "js/GCAPI.h"
+#include "js/RealmOptions.h"
+#include "mozilla/Maybe.h"
+#include "nsString.h"
+#include "nsTArray.h"
+
+namespace mozilla::dom::workerinternals {
+
+// Random unique constant to facilitate JSPrincipal debugging
+const uint32_t kJSPrincipalsDebugToken = 0x7e2df9d2;
+
+struct JSSettings {
+  struct JSGCSetting {
+    JSGCParamKey key;
+    // Nothing() represents the default value, the result of calling
+    // JS_ResetGCParameter.
+    Maybe<uint32_t> value;
+
+    // For the IndexOf call below.
+    bool operator==(JSGCParamKey k) const { return key == k; }
+  };
+
+  JS::RealmOptions chromeRealmOptions;
+  JS::RealmOptions contentRealmOptions;
+  CopyableTArray<JSGCSetting> gcSettings;
+  JS::ContextOptions contextOptions;
+
+#ifdef JS_GC_ZEAL
+  uint8_t gcZeal = 0;
+  uint32_t gcZealFrequency = 0;
+#endif
+
+  // Returns whether there was a change in the setting.
+  bool ApplyGCSetting(JSGCParamKey aKey, Maybe<uint32_t> aValue) {
+    size_t index = gcSettings.IndexOf(aKey);
+    if (index == gcSettings.NoIndex) {
+      gcSettings.AppendElement(JSGCSetting{aKey, aValue});
+      return true;
+    }
+    if (gcSettings[index].value != aValue) {
+      gcSettings[index].value = aValue;
+      return true;
+    }
+    return false;
+  }
+};
+
+}  // namespace mozilla::dom::workerinternals
+
+#endif  // mozilla_dom_workerinternals_JSSettings_h
diff --git a/dom/workers/MessageEventRunnable.cpp b/dom/workers/MessageEventRunnable.cpp
new file mode 100644
index 0000000000..8edc7037cd
--- /dev/null
+++ b/dom/workers/MessageEventRunnable.cpp
@@ -0,0 +1,127 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "MessageEventRunnable.h"
+
+#include "mozilla/dom/MessageEvent.h"
+#include "mozilla/dom/MessageEventBinding.h"
+#include "mozilla/dom/RootedDictionary.h"
+#include "nsQueryObject.h"
+#include "WorkerScope.h"
+
+namespace mozilla::dom {
+
+MessageEventRunnable::MessageEventRunnable(WorkerPrivate* aWorkerPrivate,
+                                           Target aTarget)
+    : WorkerDebuggeeRunnable(aWorkerPrivate, "MessageEventRunnable", aTarget),
+      StructuredCloneHolder(CloningSupported, TransferringSupported,
+                            StructuredCloneScope::SameProcess) {}
+
+bool MessageEventRunnable::DispatchDOMEvent(JSContext* aCx,
+                                            WorkerPrivate* aWorkerPrivate,
+                                            DOMEventTargetHelper* aTarget,
+                                            bool aIsMainThread) {
+  nsCOMPtr<nsIGlobalObject> parent = aTarget->GetParentObject();
+
+  // For some workers without window, parent is null and we try to find it
+  // from the JS Context.
+  if (!parent) {
+    JS::Rooted<JSObject*> globalObject(aCx, JS::CurrentGlobalOrNull(aCx));
+    if (NS_WARN_IF(!globalObject)) {
+      return false;
+    }
+
+    parent = xpc::NativeGlobal(globalObject);
+    if (NS_WARN_IF(!parent)) {
+      return false;
+    }
+  }
+
+  MOZ_ASSERT(parent);
+
+  JS::Rooted<JS::Value> messageData(aCx);
+  IgnoredErrorResult rv;
+
+  JS::CloneDataPolicy cloneDataPolicy;
+  if (parent->GetClientInfo().isSome() &&
+      parent->GetClientInfo()->AgentClusterId().isSome() &&
+      parent->GetClientInfo()->AgentClusterId()->Equals(
+          aWorkerPrivate->AgentClusterId())) {
+    cloneDataPolicy.allowIntraClusterClonableSharedObjects();
+  }
+
+  if (aWorkerPrivate->IsSharedMemoryAllowed()) {
+    cloneDataPolicy.allowSharedMemoryObjects();
+  }
+
+  Read(parent, aCx, &messageData, cloneDataPolicy, rv);
+
+  if (NS_WARN_IF(rv.Failed())) {
+    DispatchError(aCx, aTarget);
+    return false;
+  }
+
+  Sequence<OwningNonNull<MessagePort>> ports;
+  if (!TakeTransferredPortsAsSequence(ports)) {
+    DispatchError(aCx, aTarget);
+    return false;
+  }
+
+  RefPtr<MessageEvent> event = new MessageEvent(aTarget, nullptr, nullptr);
+  event->InitMessageEvent(nullptr, u"message"_ns, CanBubble::eNo,
+                          Cancelable::eNo, messageData, u""_ns, u""_ns, nullptr,
+                          ports);
+
+  event->SetTrusted(true);
+
+  aTarget->DispatchEvent(*event);
+
+  return true;
+}
+
+bool MessageEventRunnable::WorkerRun(JSContext* aCx,
+                                     WorkerPrivate* aWorkerPrivate) {
+  if (mTarget == ParentThread) {
+    // Don't fire this event if the JS object has been disconnected from the
+    // private object.
+    if (!aWorkerPrivate->IsAcceptingEvents()) {
+      return true;
+    }
+
+    aWorkerPrivate->AssertInnerWindowIsCorrect();
+
+    return DispatchDOMEvent(aCx, aWorkerPrivate,
+                            aWorkerPrivate->ParentEventTargetRef(),
+                            !aWorkerPrivate->GetParent());
+  }
+
+  MOZ_ASSERT(aWorkerPrivate == GetWorkerPrivateFromContext(aCx));
+  MOZ_ASSERT(aWorkerPrivate->GlobalScope());
+
+  // If the worker start shutting down, don't dispatch the message event.
+  if (NS_FAILED(
+          aWorkerPrivate->GlobalScope()->CheckCurrentGlobalCorrectness())) {
+    return true;
+  }
+
+  return DispatchDOMEvent(aCx, aWorkerPrivate, aWorkerPrivate->GlobalScope(),
+                          false);
+}
+
+void MessageEventRunnable::DispatchError(JSContext* aCx,
+                                         DOMEventTargetHelper* aTarget) {
+  RootedDictionary<MessageEventInit> init(aCx);
+  init.mBubbles = false;
+  init.mCancelable = false;
+
+  RefPtr<Event> event =
+      MessageEvent::Constructor(aTarget, u"messageerror"_ns, init);
+  event->SetTrusted(true);
+
+  aTarget->DispatchEvent(*event);
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/workers/MessageEventRunnable.h b/dom/workers/MessageEventRunnable.h
new file mode 100644
index 0000000000..c20efb4c55
--- /dev/null
+++ b/dom/workers/MessageEventRunnable.h
@@ -0,0 +1,37 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_workers_MessageEventRunnable_h
+#define mozilla_dom_workers_MessageEventRunnable_h
+
+#include "WorkerCommon.h"
+#include "WorkerRunnable.h"
+#include "mozilla/dom/StructuredCloneHolder.h"
+
+namespace mozilla {
+
+class DOMEventTargetHelper;
+
+namespace dom {
+
+class MessageEventRunnable final : public WorkerDebuggeeRunnable,
+                                   public StructuredCloneHolder {
+ public:
+  MessageEventRunnable(WorkerPrivate* aWorkerPrivate, Target aTarget);
+
+  bool DispatchDOMEvent(JSContext* aCx, WorkerPrivate* aWorkerPrivate,
+                        DOMEventTargetHelper* aTarget, bool aIsMainThread);
+
+ private:
+  bool WorkerRun(JSContext* aCx, WorkerPrivate* aWorkerPrivate) override;
+
+  void DispatchError(JSContext* aCx, DOMEventTargetHelper* aTarget);
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_workers_MessageEventRunnable_h
diff --git a/dom/workers/Queue.h b/dom/workers/Queue.h
new file mode 100644
index 0000000000..cf65932698
--- /dev/null
+++ b/dom/workers/Queue.h
@@ -0,0 +1,151 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_workerinternal_Queue_h
+#define mozilla_dom_workerinternal_Queue_h
+
+#include "mozilla/Mutex.h"
+#include "nsTArray.h"
+
+namespace mozilla::dom::workerinternals {
+
+template <typename T, int TCount>
+struct StorageWithTArray {
+  typedef AutoTArray<T, TCount> StorageType;
+
+  static void Reverse(StorageType& aStorage) {
+    uint32_t length = aStorage.Length();
+    for (uint32_t index = 0; index < length / 2; index++) {
+      uint32_t reverseIndex = length - 1 - index;
+
+      T t1 = aStorage.ElementAt(index);
+      T t2 = aStorage.ElementAt(reverseIndex);
+
+      aStorage.ReplaceElementsAt(index, 1, t2);
+      aStorage.ReplaceElementsAt(reverseIndex, 1, t1);
+    }
+  }
+
+  static bool IsEmpty(const StorageType& aStorage) {
+    return !!aStorage.IsEmpty();
+  }
+
+  static void Push(StorageType& aStorage, const T& aEntry) {
+    aStorage.AppendElement(aEntry);
+  }
+
+  static bool Pop(StorageType& aStorage, T& aEntry) {
+    if (IsEmpty(aStorage)) {
+      return false;
+    }
+
+    aEntry = aStorage.PopLastElement();
+    return true;
+  }
+
+  static void Clear(StorageType& aStorage) { aStorage.Clear(); }
+
+  static void Compact(StorageType& aStorage) { aStorage.Compact(); }
+};
+
+class MOZ_CAPABILITY("mutex") LockingWithMutex {
+  mozilla::Mutex mMutex;
+
+ protected:
+  LockingWithMutex() : mMutex("LockingWithMutex::mMutex") {}
+
+  void Lock() MOZ_CAPABILITY_ACQUIRE() { mMutex.Lock(); }
+
+  void Unlock() MOZ_CAPABILITY_RELEASE() { mMutex.Unlock(); }
+
+  class MOZ_SCOPED_CAPABILITY AutoLock {
+    LockingWithMutex& mHost;
+
+   public:
+    explicit AutoLock(LockingWithMutex& aHost) MOZ_CAPABILITY_ACQUIRE(aHost)
+        : mHost(aHost) {
+      mHost.Lock();
+    }
+
+    ~AutoLock() MOZ_CAPABILITY_RELEASE() { mHost.Unlock(); }
+  };
+
+  friend class AutoLock;
+};
+
+class NoLocking {
+ protected:
+  void Lock() {}
+
+  void Unlock() {}
+
+  class AutoLock {
+   public:
+    explicit AutoLock(NoLocking& aHost) {}
+
+    ~AutoLock() = default;
+  };
+};
+
+template <typename T, int TCount = 256, class LockingPolicy = NoLocking,
+          class StoragePolicy =
+              StorageWithTArray<T, TCount % 2 ? TCount / 2 + 1 : TCount / 2> >
+class Queue : public LockingPolicy {
+  typedef typename StoragePolicy::StorageType StorageType;
+  typedef typename LockingPolicy::AutoLock AutoLock;
+
+  StorageType mStorage1;
+  StorageType mStorage2;
+
+  StorageType* mFront;
+  StorageType* mBack;
+
+ public:
+  Queue() : mFront(&mStorage1), mBack(&mStorage2) {}
+
+  bool IsEmpty() {
+    AutoLock lock(*this);
+    return StoragePolicy::IsEmpty(*mFront) && StoragePolicy::IsEmpty(*mBack);
+  }
+
+  void Push(const T& aEntry) {
+    AutoLock lock(*this);
+    StoragePolicy::Push(*mBack, aEntry);
+  }
+
+  bool Pop(T& aEntry) {
+    AutoLock lock(*this);
+    if (StoragePolicy::IsEmpty(*mFront)) {
+      StoragePolicy::Compact(*mFront);
+      StoragePolicy::Reverse(*mBack);
+      StorageType* tmp = mFront;
+      mFront = mBack;
+      mBack = tmp;
+    }
+    return StoragePolicy::Pop(*mFront, aEntry);
+  }
+
+  void Clear() {
+    AutoLock lock(*this);
+    StoragePolicy::Clear(*mFront);
+    StoragePolicy::Clear(*mBack);
+  }
+
+  // XXX Do we need this?
+  void Lock() { LockingPolicy::Lock(); }
+
+  // XXX Do we need this?
+  void Unlock() { LockingPolicy::Unlock(); }
+
+ private:
+  // Queue is not copyable.
+  Queue(const Queue&);
+  Queue& operator=(const Queue&);
+};
+
+}  // namespace mozilla::dom::workerinternals
+
+#endif /* mozilla_dom_workerinternals_Queue_h*/
diff --git a/dom/workers/RegisterBindings.cpp b/dom/workers/RegisterBindings.cpp
new file mode 100644
index 0000000000..4c33b1e4c5
--- /dev/null
+++ b/dom/workers/RegisterBindings.cpp
@@ -0,0 +1,53 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "WorkerPrivate.h"
+#include "ChromeWorkerScope.h"
+
+#include "jsapi.h"
+#include "mozilla/dom/DebuggerNotificationObserverBinding.h"
+#include "mozilla/dom/RegisterWorkerBindings.h"
+#include "mozilla/dom/RegisterWorkerDebuggerBindings.h"
+
+using namespace mozilla::dom;
+
+bool WorkerPrivate::RegisterBindings(JSContext* aCx,
+                                     JS::Handle<JSObject*> aGlobal) {
+  // Init Web IDL bindings
+  if (!RegisterWorkerBindings(aCx, aGlobal)) {
+    return false;
+  }
+
+  if (IsChromeWorker()) {
+    if (!DefineChromeWorkerFunctions(aCx, aGlobal)) {
+      return false;
+    }
+  }
+
+  return true;
+}
+
+bool WorkerPrivate::RegisterDebuggerBindings(JSContext* aCx,
+                                             JS::Handle<JSObject*> aGlobal) {
+  // Init Web IDL bindings
+  if (!RegisterWorkerDebuggerBindings(aCx, aGlobal)) {
+    return false;
+  }
+
+  if (!ChromeUtils_Binding::GetConstructorObject(aCx)) {
+    return false;
+  }
+
+  if (!DebuggerNotificationObserver_Binding::GetConstructorObject(aCx)) {
+    return false;
+  }
+
+  if (!JS_DefineDebuggerObject(aCx, aGlobal)) {
+    return false;
+  }
+
+  return true;
+}
diff --git a/dom/workers/RuntimeService.cpp b/dom/workers/RuntimeService.cpp
new file mode 100644
index 0000000000..3d6a883867
--- /dev/null
+++ b/dom/workers/RuntimeService.cpp
@@ -0,0 +1,2373 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "RuntimeService.h"
+
+#include "nsContentSecurityUtils.h"
+#include "nsIContentSecurityPolicy.h"
+#include "mozilla/dom/Document.h"
+#include "nsIObserverService.h"
+#include "nsIScriptContext.h"
+#include "nsIStreamTransportService.h"
+#include "nsISupportsPriority.h"
+#include "nsITimer.h"
+#include "nsIURI.h"
+#include "nsIXULRuntime.h"
+#include "nsPIDOMWindow.h"
+
+#include <algorithm>
+#include "mozilla/ipc/BackgroundChild.h"
+#include "GeckoProfiler.h"
+#include "js/ColumnNumber.h"  // JS::ColumnNumberOneOrigin
+#include "js/experimental/CTypes.h"  // JS::CTypesActivityType, JS::SetCTypesActivityCallback
+#include "jsfriendapi.h"
+#include "js/friend/ErrorMessages.h"  // js::GetErrorMessage, JSMSG_*
+#include "js/ContextOptions.h"
+#include "js/Initialization.h"
+#include "js/LocaleSensitive.h"
+#include "js/WasmFeatures.h"
+#include "mozilla/ArrayUtils.h"
+#include "mozilla/Atomics.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/CycleCollectedJSContext.h"
+#include "mozilla/CycleCollectedJSRuntime.h"
+#include "mozilla/Telemetry.h"
+#include "mozilla/TimeStamp.h"
+#include "mozilla/dom/AtomList.h"
+#include "mozilla/dom/BindingUtils.h"
+#include "mozilla/dom/ErrorEventBinding.h"
+#include "mozilla/dom/EventTargetBinding.h"
+#include "mozilla/dom/FetchUtil.h"
+#include "mozilla/dom/MessageChannel.h"
+#include "mozilla/dom/MessageEventBinding.h"
+#include "mozilla/dom/PerformanceService.h"
+#include "mozilla/dom/RemoteWorkerChild.h"
+#include "mozilla/dom/WorkerBinding.h"
+#include "mozilla/dom/ScriptSettings.h"
+#include "mozilla/dom/ShadowRealmGlobalScope.h"
+#include "mozilla/dom/IndexedDatabaseManager.h"
+#include "mozilla/DebugOnly.h"
+#include "mozilla/Preferences.h"
+#include "mozilla/ScopeExit.h"
+#include "mozilla/dom/Navigator.h"
+#include "mozilla/Monitor.h"
+#include "nsContentUtils.h"
+#include "nsCycleCollector.h"
+#include "nsDOMJSUtils.h"
+#include "nsISupportsImpl.h"
+#include "nsLayoutStatics.h"
+#include "nsNetUtil.h"
+#include "nsServiceManagerUtils.h"
+#include "nsThreadUtils.h"
+#include "nsXPCOM.h"
+#include "nsXPCOMPrivate.h"
+#include "xpcpublic.h"
+#include "XPCSelfHostedShmem.h"
+
+#if defined(XP_MACOSX)
+#  include "nsMacUtilsImpl.h"
+#endif
+
+#include "WorkerDebuggerManager.h"
+#include "WorkerError.h"
+#include "WorkerLoadInfo.h"
+#include "WorkerRunnable.h"
+#include "WorkerScope.h"
+#include "WorkerThread.h"
+#include "prsystem.h"
+
+#ifdef DEBUG
+#  include "nsICookieJarSettings.h"
+#endif
+
+#define WORKERS_SHUTDOWN_TOPIC "web-workers-shutdown"
+
+static mozilla::LazyLogModule gWorkerShutdownDumpLog("WorkerShutdownDump");
+
+#ifdef SHUTDOWN_LOG
+#  undef SHUTDOWN_LOG
+#endif
+#define SHUTDOWN_LOG(msg) MOZ_LOG(gWorkerShutdownDumpLog, LogLevel::Debug, msg);
+
+namespace mozilla {
+
+using namespace ipc;
+
+namespace dom {
+
+using namespace workerinternals;
+
+namespace workerinternals {
+
+// The size of the worker runtime heaps in bytes. May be changed via pref.
+#define WORKER_DEFAULT_RUNTIME_HEAPSIZE 32 * 1024 * 1024
+
+// The size of the worker JS allocation threshold in MB. May be changed via
+// pref.
+#define WORKER_DEFAULT_ALLOCATION_THRESHOLD 30
+
+// Half the size of the actual C stack, to be safe.
+#define WORKER_CONTEXT_NATIVE_STACK_LIMIT 128 * sizeof(size_t) * 1024
+
+// The maximum number of threads to use for workers, overridable via pref.
+#define MAX_WORKERS_PER_DOMAIN 512
+
+static_assert(MAX_WORKERS_PER_DOMAIN >= 1,
+              "We should allow at least one worker per domain.");
+
+#define PREF_WORKERS_PREFIX "dom.workers."
+#define PREF_WORKERS_MAX_PER_DOMAIN PREF_WORKERS_PREFIX "maxPerDomain"
+
+#define GC_REQUEST_OBSERVER_TOPIC "child-gc-request"
+#define CC_REQUEST_OBSERVER_TOPIC "child-cc-request"
+#define MEMORY_PRESSURE_OBSERVER_TOPIC "memory-pressure"
+#define LOW_MEMORY_DATA "low-memory"
+#define LOW_MEMORY_ONGOING_DATA "low-memory-ongoing"
+#define MEMORY_PRESSURE_STOP_OBSERVER_TOPIC "memory-pressure-stop"
+
+// Prefixes for observing preference changes.
+#define PREF_JS_OPTIONS_PREFIX "javascript.options."
+#define PREF_MEM_OPTIONS_PREFIX "mem."
+#define PREF_GCZEAL "gczeal"
+
+static NS_DEFINE_CID(kStreamTransportServiceCID, NS_STREAMTRANSPORTSERVICE_CID);
+
+namespace {
+
+const uint32_t kNoIndex = uint32_t(-1);
+
+uint32_t gMaxWorkersPerDomain = MAX_WORKERS_PER_DOMAIN;
+
+// Does not hold an owning reference.
+Atomic<RuntimeService*> gRuntimeService(nullptr);
+
+// Only true during the call to Init.
+bool gRuntimeServiceDuringInit = false;
+
+class LiteralRebindingCString : public nsDependentCString {
+ public:
+  template <int N>
+  void RebindLiteral(const char (&aStr)[N]) {
+    Rebind(aStr, N - 1);
+  }
+};
+
+template <typename T>
+struct PrefTraits;
+
+template <>
+struct PrefTraits<bool> {
+  using PrefValueType = bool;
+
+  static inline PrefValueType Get(const char* aPref) {
+    AssertIsOnMainThread();
+    return Preferences::GetBool(aPref);
+  }
+
+  static inline bool Exists(const char* aPref) {
+    AssertIsOnMainThread();
+    return Preferences::GetType(aPref) == nsIPrefBranch::PREF_BOOL;
+  }
+};
+
+template <>
+struct PrefTraits<int32_t> {
+  using PrefValueType = int32_t;
+
+  static inline PrefValueType Get(const char* aPref) {
+    AssertIsOnMainThread();
+    return Preferences::GetInt(aPref);
+  }
+
+  static inline bool Exists(const char* aPref) {
+    AssertIsOnMainThread();
+    return Preferences::GetType(aPref) == nsIPrefBranch::PREF_INT;
+  }
+};
+
+template <typename T>
+T GetPref(const char* aFullPref, const T aDefault, bool* aPresent = nullptr) {
+  AssertIsOnMainThread();
+
+  using PrefHelper = PrefTraits<T>;
+
+  T result;
+  bool present = true;
+
+  if (PrefHelper::Exists(aFullPref)) {
+    result = PrefHelper::Get(aFullPref);
+  } else {
+    result = aDefault;
+    present = false;
+  }
+
+  if (aPresent) {
+    *aPresent = present;
+  }
+  return result;
+}
+
+void LoadContextOptions(const char* aPrefName, void* /* aClosure */) {
+  AssertIsOnMainThread();
+
+  RuntimeService* rts = RuntimeService::GetService();
+  if (!rts) {
+    // May be shutting down, just bail.
+    return;
+  }
+
+  const nsDependentCString prefName(aPrefName);
+
+  // Several other pref branches will get included here so bail out if there is
+  // another callback that will handle this change.
+  if (StringBeginsWith(
+          prefName,
+          nsLiteralCString(PREF_JS_OPTIONS_PREFIX PREF_MEM_OPTIONS_PREFIX))) {
+    return;
+  }
+
+#ifdef JS_GC_ZEAL
+  if (prefName.EqualsLiteral(PREF_JS_OPTIONS_PREFIX PREF_GCZEAL)) {
+    return;
+  }
+#endif
+
+  JS::ContextOptions contextOptions;
+  xpc::SetPrefableContextOptions(contextOptions);
+
+  nsCOMPtr<nsIXULRuntime> xr = do_GetService("@mozilla.org/xre/runtime;1");
+  if (xr) {
+    bool safeMode = false;
+    xr->GetInSafeMode(&safeMode);
+    if (safeMode) {
+      contextOptions.disableOptionsForSafeMode();
+    }
+  }
+
+  RuntimeService::SetDefaultContextOptions(contextOptions);
+
+  if (rts) {
+    rts->UpdateAllWorkerContextOptions();
+  }
+}
+
+#ifdef JS_GC_ZEAL
+void LoadGCZealOptions(const char* /* aPrefName */, void* /* aClosure */) {
+  AssertIsOnMainThread();
+
+  RuntimeService* rts = RuntimeService::GetService();
+  if (!rts) {
+    // May be shutting down, just bail.
+    return;
+  }
+
+  int32_t gczeal = GetPref<int32_t>(PREF_JS_OPTIONS_PREFIX PREF_GCZEAL, -1);
+  if (gczeal < 0) {
+    gczeal = 0;
+  }
+
+  int32_t frequency =
+      GetPref<int32_t>(PREF_JS_OPTIONS_PREFIX PREF_GCZEAL ".frequency", -1);
+  if (frequency < 0) {
+    frequency = JS_DEFAULT_ZEAL_FREQ;
+  }
+
+  RuntimeService::SetDefaultGCZeal(uint8_t(gczeal), uint32_t(frequency));
+
+  if (rts) {
+    rts->UpdateAllWorkerGCZeal();
+  }
+}
+#endif
+
+void UpdateCommonJSGCMemoryOption(RuntimeService* aRuntimeService,
+                                  const char* aPrefName, JSGCParamKey aKey) {
+  AssertIsOnMainThread();
+  NS_ASSERTION(aPrefName, "Null pref name!");
+
+  int32_t prefValue = GetPref(aPrefName, -1);
+  Maybe<uint32_t> value = (prefValue < 0 || prefValue >= 10000)
+                              ? Nothing()
+                              : Some(uint32_t(prefValue));
+
+  RuntimeService::SetDefaultJSGCSettings(aKey, value);
+
+  if (aRuntimeService) {
+    aRuntimeService->UpdateAllWorkerMemoryParameter(aKey, value);
+  }
+}
+
+void UpdateOtherJSGCMemoryOption(RuntimeService* aRuntimeService,
+                                 JSGCParamKey aKey, Maybe<uint32_t> aValue) {
+  AssertIsOnMainThread();
+
+  RuntimeService::SetDefaultJSGCSettings(aKey, aValue);
+
+  if (aRuntimeService) {
+    aRuntimeService->UpdateAllWorkerMemoryParameter(aKey, aValue);
+  }
+}
+
+void LoadJSGCMemoryOptions(const char* aPrefName, void* /* aClosure */) {
+  AssertIsOnMainThread();
+
+  RuntimeService* rts = RuntimeService::GetService();
+
+  if (!rts) {
+    // May be shutting down, just bail.
+    return;
+  }
+
+  constexpr auto memPrefix =
+      nsLiteralCString{PREF_JS_OPTIONS_PREFIX PREF_MEM_OPTIONS_PREFIX};
+  const nsDependentCString fullPrefName(aPrefName);
+
+  // Pull out the string that actually distinguishes the parameter we need to
+  // change.
+  nsDependentCSubstring memPrefName;
+  if (StringBeginsWith(fullPrefName, memPrefix)) {
+    memPrefName.Rebind(fullPrefName, memPrefix.Length());
+  } else {
+    NS_ERROR("Unknown pref name!");
+    return;
+  }
+
+  struct WorkerGCPref {
+    nsLiteralCString memName;
+    const char* fullName;
+    JSGCParamKey key;
+  };
+
+#define PREF(suffix_, key_)                                          \
+  {                                                                  \
+    nsLiteralCString(PREF_MEM_OPTIONS_PREFIX suffix_),               \
+        PREF_JS_OPTIONS_PREFIX PREF_MEM_OPTIONS_PREFIX suffix_, key_ \
+  }
+  constexpr WorkerGCPref kWorkerPrefs[] = {
+      PREF("max", JSGC_MAX_BYTES),
+      PREF("gc_high_frequency_time_limit_ms", JSGC_HIGH_FREQUENCY_TIME_LIMIT),
+      PREF("gc_low_frequency_heap_growth", JSGC_LOW_FREQUENCY_HEAP_GROWTH),
+      PREF("gc_high_frequency_large_heap_growth",
+           JSGC_HIGH_FREQUENCY_LARGE_HEAP_GROWTH),
+      PREF("gc_high_frequency_small_heap_growth",
+           JSGC_HIGH_FREQUENCY_SMALL_HEAP_GROWTH),
+      PREF("gc_small_heap_size_max_mb", JSGC_SMALL_HEAP_SIZE_MAX),
+      PREF("gc_large_heap_size_min_mb", JSGC_LARGE_HEAP_SIZE_MIN),
+      PREF("gc_balanced_heap_limits", JSGC_BALANCED_HEAP_LIMITS_ENABLED),
+      PREF("gc_heap_growth_factor", JSGC_HEAP_GROWTH_FACTOR),
+      PREF("gc_allocation_threshold_mb", JSGC_ALLOCATION_THRESHOLD),
+      PREF("gc_malloc_threshold_base_mb", JSGC_MALLOC_THRESHOLD_BASE),
+      PREF("gc_small_heap_incremental_limit",
+           JSGC_SMALL_HEAP_INCREMENTAL_LIMIT),
+      PREF("gc_large_heap_incremental_limit",
+           JSGC_LARGE_HEAP_INCREMENTAL_LIMIT),
+      PREF("gc_urgent_threshold_mb", JSGC_URGENT_THRESHOLD_MB),
+      PREF("gc_incremental_slice_ms", JSGC_SLICE_TIME_BUDGET_MS),
+      PREF("gc_min_empty_chunk_count", JSGC_MIN_EMPTY_CHUNK_COUNT),
+      PREF("gc_max_empty_chunk_count", JSGC_MAX_EMPTY_CHUNK_COUNT),
+      PREF("gc_compacting", JSGC_COMPACTING_ENABLED),
+  };
+#undef PREF
+
+  auto pref = kWorkerPrefs;
+  auto end = kWorkerPrefs + ArrayLength(kWorkerPrefs);
+
+  if (gRuntimeServiceDuringInit) {
+    // During init, we want to update every pref in kWorkerPrefs.
+    MOZ_ASSERT(memPrefName.IsEmpty(),
+               "Pref branch prefix only expected during init");
+  } else {
+    // Otherwise, find the single pref that changed.
+    while (pref != end) {
+      if (pref->memName == memPrefName) {
+        end = pref + 1;
+        break;
+      }
+      ++pref;
+    }
+#ifdef DEBUG
+    if (pref == end) {
+      nsAutoCString message("Workers don't support the '");
+      message.Append(memPrefName);
+      message.AppendLiteral("' preference!");
+      NS_WARNING(message.get());
+    }
+#endif
+  }
+
+  while (pref != end) {
+    switch (pref->key) {
+      case JSGC_MAX_BYTES: {
+        int32_t prefValue = GetPref(pref->fullName, -1);
+        Maybe<uint32_t> value = (prefValue <= 0 || prefValue >= 0x1000)
+                                    ? Nothing()
+                                    : Some(uint32_t(prefValue) * 1024 * 1024);
+        UpdateOtherJSGCMemoryOption(rts, pref->key, value);
+        break;
+      }
+      case JSGC_SLICE_TIME_BUDGET_MS: {
+        int32_t prefValue = GetPref(pref->fullName, -1);
+        Maybe<uint32_t> value = (prefValue <= 0 || prefValue >= 100000)
+                                    ? Nothing()
+                                    : Some(uint32_t(prefValue));
+        UpdateOtherJSGCMemoryOption(rts, pref->key, value);
+        break;
+      }
+      case JSGC_COMPACTING_ENABLED:
+      case JSGC_PARALLEL_MARKING_ENABLED:
+      case JSGC_BALANCED_HEAP_LIMITS_ENABLED: {
+        bool present;
+        bool prefValue = GetPref(pref->fullName, false, &present);
+        Maybe<uint32_t> value = present ? Some(prefValue ? 1 : 0) : Nothing();
+        UpdateOtherJSGCMemoryOption(rts, pref->key, value);
+        break;
+      }
+      case JSGC_HIGH_FREQUENCY_TIME_LIMIT:
+      case JSGC_LOW_FREQUENCY_HEAP_GROWTH:
+      case JSGC_HIGH_FREQUENCY_LARGE_HEAP_GROWTH:
+      case JSGC_HIGH_FREQUENCY_SMALL_HEAP_GROWTH:
+      case JSGC_SMALL_HEAP_SIZE_MAX:
+      case JSGC_LARGE_HEAP_SIZE_MIN:
+      case JSGC_ALLOCATION_THRESHOLD:
+      case JSGC_MALLOC_THRESHOLD_BASE:
+      case JSGC_SMALL_HEAP_INCREMENTAL_LIMIT:
+      case JSGC_LARGE_HEAP_INCREMENTAL_LIMIT:
+      case JSGC_URGENT_THRESHOLD_MB:
+      case JSGC_MIN_EMPTY_CHUNK_COUNT:
+      case JSGC_MAX_EMPTY_CHUNK_COUNT:
+      case JSGC_HEAP_GROWTH_FACTOR:
+        UpdateCommonJSGCMemoryOption(rts, pref->fullName, pref->key);
+        break;
+      default:
+        MOZ_ASSERT_UNREACHABLE("Unknown JSGCParamKey value");
+        break;
+    }
+    ++pref;
+  }
+}
+
+bool InterruptCallback(JSContext* aCx) {
+  WorkerPrivate* worker = GetWorkerPrivateFromContext(aCx);
+  MOZ_ASSERT(worker);
+
+  // Now is a good time to turn on profiling if it's pending.
+  PROFILER_JS_INTERRUPT_CALLBACK();
+
+  return worker->InterruptCallback(aCx);
+}
+
+class LogViolationDetailsRunnable final : public WorkerMainThreadRunnable {
+  uint16_t mViolationType;
+  nsString mFileName;
+  uint32_t mLineNum;
+  uint32_t mColumnNum;
+  nsString mScriptSample;
+
+ public:
+  LogViolationDetailsRunnable(WorkerPrivate* aWorker, uint16_t aViolationType,
+                              const nsString& aFileName, uint32_t aLineNum,
+                              uint32_t aColumnNum,
+                              const nsAString& aScriptSample)
+      : WorkerMainThreadRunnable(aWorker,
+                                 "RuntimeService :: LogViolationDetails"_ns),
+        mViolationType(aViolationType),
+        mFileName(aFileName),
+        mLineNum(aLineNum),
+        mColumnNum(aColumnNum),
+        mScriptSample(aScriptSample) {
+    MOZ_ASSERT(aWorker);
+  }
+
+  virtual bool MainThreadRun() override;
+
+ private:
+  ~LogViolationDetailsRunnable() = default;
+};
+
+bool ContentSecurityPolicyAllows(JSContext* aCx, JS::RuntimeCode aKind,
+                                 JS::Handle<JSString*> aCode) {
+  WorkerPrivate* worker = GetWorkerPrivateFromContext(aCx);
+  worker->AssertIsOnWorkerThread();
+
+  bool evalOK;
+  bool reportViolation;
+  uint16_t violationType;
+  nsAutoJSString scriptSample;
+  if (aKind == JS::RuntimeCode::JS) {
+    if (NS_WARN_IF(!scriptSample.init(aCx, aCode))) {
+      JS_ClearPendingException(aCx);
+      return false;
+    }
+
+    if (!nsContentSecurityUtils::IsEvalAllowed(
+            aCx, worker->UsesSystemPrincipal(), scriptSample)) {
+      return false;
+    }
+
+    evalOK = worker->IsEvalAllowed();
+    reportViolation = worker->GetReportEvalCSPViolations();
+    violationType = nsIContentSecurityPolicy::VIOLATION_TYPE_EVAL;
+  } else {
+    evalOK = worker->IsWasmEvalAllowed();
+    reportViolation = worker->GetReportWasmEvalCSPViolations();
+    violationType = nsIContentSecurityPolicy::VIOLATION_TYPE_WASM_EVAL;
+  }
+
+  if (reportViolation) {
+    nsString fileName;
+    uint32_t lineNum = 0;
+    JS::ColumnNumberOneOrigin columnNum;
+
+    JS::AutoFilename file;
+    if (JS::DescribeScriptedCaller(aCx, &file, &lineNum, &columnNum) &&
+        file.get()) {
+      CopyUTF8toUTF16(MakeStringSpan(file.get()), fileName);
+    } else {
+      MOZ_ASSERT(!JS_IsExceptionPending(aCx));
+    }
+
+    RefPtr<LogViolationDetailsRunnable> runnable =
+        new LogViolationDetailsRunnable(worker, violationType, fileName,
+                                        lineNum, columnNum.oneOriginValue(),
+                                        scriptSample);
+
+    ErrorResult rv;
+    runnable->Dispatch(Killing, rv);
+    if (NS_WARN_IF(rv.Failed())) {
+      rv.SuppressException();
+    }
+  }
+
+  return evalOK;
+}
+
+void CTypesActivityCallback(JSContext* aCx, JS::CTypesActivityType aType) {
+  WorkerPrivate* worker = GetWorkerPrivateFromContext(aCx);
+  worker->AssertIsOnWorkerThread();
+
+  switch (aType) {
+    case JS::CTypesActivityType::BeginCall:
+      worker->BeginCTypesCall();
+      break;
+
+    case JS::CTypesActivityType::EndCall:
+      worker->EndCTypesCall();
+      break;
+
+    case JS::CTypesActivityType::BeginCallback:
+      worker->BeginCTypesCallback();
+      break;
+
+    case JS::CTypesActivityType::EndCallback:
+      worker->EndCTypesCallback();
+      break;
+
+    default:
+      MOZ_CRASH("Unknown type flag!");
+  }
+}
+
+// JSDispatchableRunnables are WorkerRunnables used to dispatch JS::Dispatchable
+// back to their worker thread. A WorkerRunnable is used for two reasons:
+//
+// 1. The JS::Dispatchable::run() callback may run JS so we cannot use a control
+// runnable since they use async interrupts and break JS run-to-completion.
+//
+// 2. The DispatchToEventLoopCallback interface is *required* to fail during
+// shutdown (see jsapi.h) which is exactly what WorkerRunnable::Dispatch() will
+// do. Moreover, JS_DestroyContext() does *not* block on JS::Dispatchable::run
+// being called, DispatchToEventLoopCallback failure is expected to happen
+// during shutdown.
+class JSDispatchableRunnable final : public WorkerRunnable {
+  JS::Dispatchable* mDispatchable;
+
+  ~JSDispatchableRunnable() { MOZ_ASSERT(!mDispatchable); }
+
+  // Disable the usual pre/post-dispatch thread assertions since we are
+  // dispatching from some random JS engine internal thread:
+
+  bool PreDispatch(WorkerPrivate* aWorkerPrivate) override { return true; }
+
+  void PostDispatch(WorkerPrivate* aWorkerPrivate,
+                    bool aDispatchResult) override {
+    // For the benefit of the destructor assert.
+    if (!aDispatchResult) {
+      mDispatchable = nullptr;
+    }
+  }
+
+ public:
+  JSDispatchableRunnable(WorkerPrivate* aWorkerPrivate,
+                         JS::Dispatchable* aDispatchable)
+      : WorkerRunnable(aWorkerPrivate, "JSDispatchableRunnable",
+                       WorkerRunnable::WorkerThread),
+        mDispatchable(aDispatchable) {
+    MOZ_ASSERT(mDispatchable);
+  }
+
+  bool WorkerRun(JSContext* aCx, WorkerPrivate* aWorkerPrivate) override {
+    MOZ_ASSERT(aWorkerPrivate == mWorkerPrivate);
+    MOZ_ASSERT(aCx == mWorkerPrivate->GetJSContext());
+    MOZ_ASSERT(mDispatchable);
+
+    AutoJSAPI jsapi;
+    jsapi.Init();
+
+    mDispatchable->run(mWorkerPrivate->GetJSContext(),
+                       JS::Dispatchable::NotShuttingDown);
+    mDispatchable = nullptr;  // mDispatchable may delete itself
+
+    return true;
+  }
+
+  nsresult Cancel() override {
+    MOZ_ASSERT(mDispatchable);
+
+    AutoJSAPI jsapi;
+    jsapi.Init();
+
+    mDispatchable->run(mWorkerPrivate->GetJSContext(),
+                       JS::Dispatchable::ShuttingDown);
+    mDispatchable = nullptr;  // mDispatchable may delete itself
+
+    return NS_OK;
+  }
+};
+
+static bool DispatchToEventLoop(void* aClosure,
+                                JS::Dispatchable* aDispatchable) {
+  // This callback may execute either on the worker thread or a random
+  // JS-internal helper thread.
+
+  // See comment at JS::InitDispatchToEventLoop() below for how we know the
+  // WorkerPrivate is alive.
+  WorkerPrivate* workerPrivate = reinterpret_cast<WorkerPrivate*>(aClosure);
+
+  // Dispatch is expected to fail during shutdown for the reasons outlined in
+  // the JSDispatchableRunnable comment above.
+  RefPtr<JSDispatchableRunnable> r =
+      new JSDispatchableRunnable(workerPrivate, aDispatchable);
+  return r->Dispatch();
+}
+
+static bool ConsumeStream(JSContext* aCx, JS::Handle<JSObject*> aObj,
+                          JS::MimeType aMimeType,
+                          JS::StreamConsumer* aConsumer) {
+  WorkerPrivate* worker = GetWorkerPrivateFromContext(aCx);
+  if (!worker) {
+    JS_ReportErrorNumberASCII(aCx, js::GetErrorMessage, nullptr,
+                              JSMSG_WASM_ERROR_CONSUMING_RESPONSE);
+    return false;
+  }
+
+  return FetchUtil::StreamResponseToJS(aCx, aObj, aMimeType, aConsumer, worker);
+}
+
+bool InitJSContextForWorker(WorkerPrivate* aWorkerPrivate,
+                            JSContext* aWorkerCx) {
+  aWorkerPrivate->AssertIsOnWorkerThread();
+  NS_ASSERTION(!aWorkerPrivate->GetJSContext(), "Already has a context!");
+
+  JSSettings settings;
+  aWorkerPrivate->CopyJSSettings(settings);
+
+  JS::ContextOptionsRef(aWorkerCx) = settings.contextOptions;
+
+  // This is the real place where we set the max memory for the runtime.
+  for (const auto& setting : settings.gcSettings) {
+    if (setting.value) {
+      JS_SetGCParameter(aWorkerCx, setting.key, *setting.value);
+    } else {
+      JS_ResetGCParameter(aWorkerCx, setting.key);
+    }
+  }
+
+  JS_SetNativeStackQuota(aWorkerCx, WORKER_CONTEXT_NATIVE_STACK_LIMIT);
+
+  // Security policy:
+  static const JSSecurityCallbacks securityCallbacks = {
+      ContentSecurityPolicyAllows};
+  JS_SetSecurityCallbacks(aWorkerCx, &securityCallbacks);
+
+  // A WorkerPrivate lives strictly longer than its JSRuntime so we can safely
+  // store a raw pointer as the callback's closure argument on the JSRuntime.
+  JS::InitDispatchToEventLoop(aWorkerCx, DispatchToEventLoop,
+                              (void*)aWorkerPrivate);
+
+  JS::InitConsumeStreamCallback(aWorkerCx, ConsumeStream,
+                                FetchUtil::ReportJSStreamError);
+
+  // When available, set the self-hosted shared memory to be read, so that we
+  // can decode the self-hosted content instead of parsing it.
+  auto& shm = xpc::SelfHostedShmem::GetSingleton();
+  JS::SelfHostedCache selfHostedContent = shm.Content();
+
+  if (!JS::InitSelfHostedCode(aWorkerCx, selfHostedContent)) {
+    NS_WARNING("Could not init self-hosted code!");
+    return false;
+  }
+
+  JS_AddInterruptCallback(aWorkerCx, InterruptCallback);
+
+  JS::SetCTypesActivityCallback(aWorkerCx, CTypesActivityCallback);
+
+#ifdef JS_GC_ZEAL
+  JS_SetGCZeal(aWorkerCx, settings.gcZeal, settings.gcZealFrequency);
+#endif
+
+  return true;
+}
+
+static bool PreserveWrapper(JSContext* cx, JS::Handle<JSObject*> obj) {
+  MOZ_ASSERT(cx);
+  MOZ_ASSERT(obj);
+  MOZ_ASSERT(mozilla::dom::IsDOMObject(obj));
+
+  return mozilla::dom::TryPreserveWrapper(obj);
+}
+
+static bool IsWorkerDebuggerGlobalOrSandbox(JS::Handle<JSObject*> aGlobal) {
+  return IsWorkerDebuggerGlobal(aGlobal) || IsWorkerDebuggerSandbox(aGlobal);
+}
+
+JSObject* Wrap(JSContext* cx, JS::Handle<JSObject*> existing,
+               JS::Handle<JSObject*> obj) {
+  JS::Rooted<JSObject*> targetGlobal(cx, JS::CurrentGlobalOrNull(cx));
+
+  // Note: the JS engine unwraps CCWs before calling this callback.
+  JS::Rooted<JSObject*> originGlobal(cx, JS::GetNonCCWObjectGlobal(obj));
+
+  const js::Wrapper* wrapper = nullptr;
+  if (IsWorkerDebuggerGlobalOrSandbox(targetGlobal) &&
+      IsWorkerDebuggerGlobalOrSandbox(originGlobal)) {
+    wrapper = &js::CrossCompartmentWrapper::singleton;
+  } else {
+    wrapper = &js::OpaqueCrossCompartmentWrapper::singleton;
+  }
+
+  if (existing) {
+    js::Wrapper::Renew(existing, obj, wrapper);
+  }
+  return js::Wrapper::New(cx, obj, wrapper);
+}
+
+static const JSWrapObjectCallbacks WrapObjectCallbacks = {
+    Wrap,
+    nullptr,
+};
+
+class WorkerJSRuntime final : public mozilla::CycleCollectedJSRuntime {
+ public:
+  // The heap size passed here doesn't matter, we will change it later in the
+  // call to JS_SetGCParameter inside InitJSContextForWorker.
+  explicit WorkerJSRuntime(JSContext* aCx, WorkerPrivate* aWorkerPrivate)
+      : CycleCollectedJSRuntime(aCx), mWorkerPrivate(aWorkerPrivate) {
+    MOZ_COUNT_CTOR_INHERITED(WorkerJSRuntime, CycleCollectedJSRuntime);
+    MOZ_ASSERT(aWorkerPrivate);
+
+    {
+      JS::UniqueChars defaultLocale = aWorkerPrivate->AdoptDefaultLocale();
+      MOZ_ASSERT(defaultLocale,
+                 "failure of a WorkerPrivate to have a default locale should "
+                 "have made the worker fail to spawn");
+
+      if (!JS_SetDefaultLocale(Runtime(), defaultLocale.get())) {
+        NS_WARNING("failed to set workerCx's default locale");
+      }
+    }
+  }
+
+  void Shutdown(JSContext* cx) override {
+    // The CC is shut down, and the superclass destructor will GC, so make sure
+    // we don't try to CC again.
+    mWorkerPrivate = nullptr;
+
+    CycleCollectedJSRuntime::Shutdown(cx);
+  }
+
+  ~WorkerJSRuntime() {
+    MOZ_COUNT_DTOR_INHERITED(WorkerJSRuntime, CycleCollectedJSRuntime);
+  }
+
+  virtual void PrepareForForgetSkippable() override {}
+
+  virtual void BeginCycleCollectionCallback(
+      mozilla::CCReason aReason) override {}
+
+  virtual void EndCycleCollectionCallback(
+      CycleCollectorResults& aResults) override {}
+
+  void DispatchDeferredDeletion(bool aContinuation, bool aPurge) override {
+    MOZ_ASSERT(!aContinuation);
+
+    // Do it immediately, no need for asynchronous behavior here.
+    nsCycleCollector_doDeferredDeletion();
+  }
+
+  virtual void CustomGCCallback(JSGCStatus aStatus) override {
+    if (!mWorkerPrivate) {
+      // We're shutting down, no need to do anything.
+      return;
+    }
+
+    mWorkerPrivate->AssertIsOnWorkerThread();
+
+    if (aStatus == JSGC_END) {
+      bool collectedAnything =
+          nsCycleCollector_collect(CCReason::GC_FINISHED, nullptr);
+      mWorkerPrivate->SetCCCollectedAnything(collectedAnything);
+    }
+  }
+
+ private:
+  WorkerPrivate* mWorkerPrivate;
+};
+
+}  // anonymous namespace
+
+}  // namespace workerinternals
+
+class WorkerJSContext final : public mozilla::CycleCollectedJSContext {
+ public:
+  // The heap size passed here doesn't matter, we will change it later in the
+  // call to JS_SetGCParameter inside InitJSContextForWorker.
+  explicit WorkerJSContext(WorkerPrivate* aWorkerPrivate)
+      : mWorkerPrivate(aWorkerPrivate) {
+    MOZ_COUNT_CTOR_INHERITED(WorkerJSContext, CycleCollectedJSContext);
+    MOZ_ASSERT(aWorkerPrivate);
+    // Magical number 2. Workers have the base recursion depth 1, and normal
+    // runnables run at level 2, and we don't want to process microtasks
+    // at any other level.
+    SetTargetedMicroTaskRecursionDepth(2);
+  }
+
+  // MOZ_CAN_RUN_SCRIPT_BOUNDARY because otherwise we have to annotate the
+  // SpiderMonkey JS::JobQueue's destructor as MOZ_CAN_RUN_SCRIPT, which is a
+  // bit of a pain.
+  MOZ_CAN_RUN_SCRIPT_BOUNDARY ~WorkerJSContext() {
+    MOZ_COUNT_DTOR_INHERITED(WorkerJSContext, CycleCollectedJSContext);
+    JSContext* cx = MaybeContext();
+    if (!cx) {
+      return;  // Initialize() must have failed
+    }
+
+    // We expect to come here with the cycle collector already shut down.
+    // The superclass destructor will run the GC one final time and finalize any
+    // JSObjects that were participating in cycles that were broken during CC
+    // shutdown.
+    // Make sure we don't try to CC again.
+    mWorkerPrivate = nullptr;
+  }
+
+  WorkerJSContext* GetAsWorkerJSContext() override { return this; }
+
+  CycleCollectedJSRuntime* CreateRuntime(JSContext* aCx) override {
+    return new WorkerJSRuntime(aCx, mWorkerPrivate);
+  }
+
+  nsresult Initialize(JSRuntime* aParentRuntime) {
+    nsresult rv = CycleCollectedJSContext::Initialize(
+        aParentRuntime, WORKER_DEFAULT_RUNTIME_HEAPSIZE);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    JSContext* cx = Context();
+
+    js::SetPreserveWrapperCallbacks(cx, PreserveWrapper, HasReleasedWrapper);
+    JS_InitDestroyPrincipalsCallback(cx, nsJSPrincipals::Destroy);
+    JS_InitReadPrincipalsCallback(cx, nsJSPrincipals::ReadPrincipals);
+    JS_SetWrapObjectCallbacks(cx, &WrapObjectCallbacks);
+    if (mWorkerPrivate->IsDedicatedWorker()) {
+      JS_SetFutexCanWait(cx);
+    }
+
+    return NS_OK;
+  }
+
+  virtual void DispatchToMicroTask(
+      already_AddRefed<MicroTaskRunnable> aRunnable) override {
+    RefPtr<MicroTaskRunnable> runnable(aRunnable);
+
+    MOZ_ASSERT(!NS_IsMainThread());
+    MOZ_ASSERT(runnable);
+
+    std::deque<RefPtr<MicroTaskRunnable>>* microTaskQueue = nullptr;
+
+    JSContext* cx = Context();
+    NS_ASSERTION(cx, "This should never be null!");
+
+    JS::Rooted<JSObject*> global(cx, JS::CurrentGlobalOrNull(cx));
+    NS_ASSERTION(global, "This should never be null!");
+
+    // On worker threads, if the current global is the worker global or
+    // ShadowRealm global, we use the main micro task queue. Otherwise, the
+    // current global must be either the debugger global or a debugger sandbox,
+    // and we use the debugger micro task queue instead.
+    if (IsWorkerGlobal(global) || IsShadowRealmGlobal(global)) {
+      microTaskQueue = &GetMicroTaskQueue();
+    } else {
+      MOZ_ASSERT(IsWorkerDebuggerGlobal(global) ||
+                 IsWorkerDebuggerSandbox(global));
+
+      microTaskQueue = &GetDebuggerMicroTaskQueue();
+    }
+
+    JS::JobQueueMayNotBeEmpty(cx);
+    microTaskQueue->push_back(std::move(runnable));
+  }
+
+  bool IsSystemCaller() const override {
+    return mWorkerPrivate->UsesSystemPrincipal();
+  }
+
+  void ReportError(JSErrorReport* aReport,
+                   JS::ConstUTF8CharsZ aToStringResult) override {
+    mWorkerPrivate->ReportError(Context(), aToStringResult, aReport);
+  }
+
+  WorkerPrivate* GetWorkerPrivate() const { return mWorkerPrivate; }
+
+ private:
+  WorkerPrivate* mWorkerPrivate;
+};
+
+namespace workerinternals {
+
+namespace {
+
+class WorkerThreadPrimaryRunnable final : public Runnable {
+  WorkerPrivate* mWorkerPrivate;
+  SafeRefPtr<WorkerThread> mThread;
+  JSRuntime* mParentRuntime;
+
+  class FinishedRunnable final : public Runnable {
+    SafeRefPtr<WorkerThread> mThread;
+
+   public:
+    explicit FinishedRunnable(SafeRefPtr<WorkerThread> aThread)
+        : Runnable("WorkerThreadPrimaryRunnable::FinishedRunnable"),
+          mThread(std::move(aThread)) {
+      MOZ_ASSERT(mThread);
+    }
+
+    NS_INLINE_DECL_REFCOUNTING_INHERITED(FinishedRunnable, Runnable)
+
+   private:
+    ~FinishedRunnable() = default;
+
+    NS_DECL_NSIRUNNABLE
+  };
+
+ public:
+  WorkerThreadPrimaryRunnable(WorkerPrivate* aWorkerPrivate,
+                              SafeRefPtr<WorkerThread> aThread,
+                              JSRuntime* aParentRuntime)
+      : mozilla::Runnable("WorkerThreadPrimaryRunnable"),
+        mWorkerPrivate(aWorkerPrivate),
+        mThread(std::move(aThread)),
+        mParentRuntime(aParentRuntime) {
+    MOZ_ASSERT(aWorkerPrivate);
+    MOZ_ASSERT(mThread);
+  }
+
+  NS_INLINE_DECL_REFCOUNTING_INHERITED(WorkerThreadPrimaryRunnable, Runnable)
+
+ private:
+  ~WorkerThreadPrimaryRunnable() = default;
+
+  NS_DECL_NSIRUNNABLE
+};
+
+void PrefLanguagesChanged(const char* /* aPrefName */, void* /* aClosure */) {
+  AssertIsOnMainThread();
+
+  nsTArray<nsString> languages;
+  Navigator::GetAcceptLanguages(languages);
+
+  RuntimeService* runtime = RuntimeService::GetService();
+  if (runtime) {
+    runtime->UpdateAllWorkerLanguages(languages);
+  }
+}
+
+void AppVersionOverrideChanged(const char* /* aPrefName */,
+                               void* /* aClosure */) {
+  AssertIsOnMainThread();
+
+  nsAutoString override;
+  Preferences::GetString("general.appversion.override", override);
+
+  RuntimeService* runtime = RuntimeService::GetService();
+  if (runtime) {
+    runtime->UpdateAppVersionOverridePreference(override);
+  }
+}
+
+void PlatformOverrideChanged(const char* /* aPrefName */,
+                             void* /* aClosure */) {
+  AssertIsOnMainThread();
+
+  nsAutoString override;
+  Preferences::GetString("general.platform.override", override);
+
+  RuntimeService* runtime = RuntimeService::GetService();
+  if (runtime) {
+    runtime->UpdatePlatformOverridePreference(override);
+  }
+}
+
+} /* anonymous namespace */
+
+// This is only touched on the main thread. Initialized in Init() below.
+StaticAutoPtr<JSSettings> RuntimeService::sDefaultJSSettings;
+
+RuntimeService::RuntimeService()
+    : mMutex("RuntimeService::mMutex"),
+      mObserved(false),
+      mShuttingDown(false),
+      mNavigatorPropertiesLoaded(false) {
+  AssertIsOnMainThread();
+  MOZ_ASSERT(!GetService(), "More than one service!");
+}
+
+RuntimeService::~RuntimeService() {
+  AssertIsOnMainThread();
+
+  // gRuntimeService can be null if Init() fails.
+  MOZ_ASSERT(!GetService() || GetService() == this, "More than one service!");
+
+  gRuntimeService = nullptr;
+}
+
+// static
+RuntimeService* RuntimeService::GetOrCreateService() {
+  AssertIsOnMainThread();
+
+  if (!gRuntimeService) {
+    // The observer service now owns us until shutdown.
+    gRuntimeService = new RuntimeService();
+    if (NS_FAILED((*gRuntimeService).Init())) {
+      NS_WARNING("Failed to initialize!");
+      (*gRuntimeService).Cleanup();
+      gRuntimeService = nullptr;
+      return nullptr;
+    }
+  }
+
+  return gRuntimeService;
+}
+
+// static
+RuntimeService* RuntimeService::GetService() { return gRuntimeService; }
+
+bool RuntimeService::RegisterWorker(WorkerPrivate& aWorkerPrivate) {
+  aWorkerPrivate.AssertIsOnParentThread();
+
+  WorkerPrivate* parent = aWorkerPrivate.GetParent();
+  if (!parent) {
+    AssertIsOnMainThread();
+
+    if (mShuttingDown) {
+      return false;
+    }
+  }
+
+  const bool isServiceWorker = aWorkerPrivate.IsServiceWorker();
+  const bool isSharedWorker = aWorkerPrivate.IsSharedWorker();
+  const bool isDedicatedWorker = aWorkerPrivate.IsDedicatedWorker();
+  if (isServiceWorker) {
+    AssertIsOnMainThread();
+    Telemetry::Accumulate(Telemetry::SERVICE_WORKER_SPAWN_ATTEMPTS, 1);
+  }
+
+  nsCString sharedWorkerScriptSpec;
+  if (isSharedWorker) {
+    AssertIsOnMainThread();
+
+    nsCOMPtr<nsIURI> scriptURI = aWorkerPrivate.GetResolvedScriptURI();
+    NS_ASSERTION(scriptURI, "Null script URI!");
+
+    nsresult rv = scriptURI->GetSpec(sharedWorkerScriptSpec);
+    if (NS_FAILED(rv)) {
+      NS_WARNING("GetSpec failed?!");
+      return false;
+    }
+
+    NS_ASSERTION(!sharedWorkerScriptSpec.IsEmpty(), "Empty spec!");
+  }
+
+  bool exemptFromPerDomainMax = false;
+  if (isServiceWorker) {
+    AssertIsOnMainThread();
+    exemptFromPerDomainMax = Preferences::GetBool(
+        "dom.serviceWorkers.exemptFromPerDomainMax", false);
+  }
+
+  const nsCString& domain = aWorkerPrivate.Domain();
+
+  bool queued = false;
+  {
+    MutexAutoLock lock(mMutex);
+
+    auto* const domainInfo =
+        mDomainMap
+            .LookupOrInsertWith(
+                domain,
+                [&domain, parent] {
+                  NS_ASSERTION(!parent, "Shouldn't have a parent here!");
+                  Unused << parent;  // silence clang -Wunused-lambda-capture in
+                                     // opt builds
+                  auto wdi = MakeUnique<WorkerDomainInfo>();
+                  wdi->mDomain = domain;
+                  return wdi;
+                })
+            .get();
+
+    queued = gMaxWorkersPerDomain &&
+             domainInfo->ActiveWorkerCount() >= gMaxWorkersPerDomain &&
+             !domain.IsEmpty() && !exemptFromPerDomainMax;
+
+    if (queued) {
+      domainInfo->mQueuedWorkers.AppendElement(&aWorkerPrivate);
+
+      // Worker spawn gets queued due to hitting max workers per domain
+      // limit so let's log a warning.
+      WorkerPrivate::ReportErrorToConsole("HittingMaxWorkersPerDomain2");
+
+      if (isServiceWorker) {
+        Telemetry::Accumulate(Telemetry::SERVICE_WORKER_SPAWN_GETS_QUEUED, 1);
+      } else if (isSharedWorker) {
+        Telemetry::Accumulate(Telemetry::SHARED_WORKER_SPAWN_GETS_QUEUED, 1);
+      } else if (isDedicatedWorker) {
+        Telemetry::Accumulate(Telemetry::DEDICATED_WORKER_SPAWN_GETS_QUEUED, 1);
+      }
+    } else if (parent) {
+      domainInfo->mChildWorkerCount++;
+    } else if (isServiceWorker) {
+      domainInfo->mActiveServiceWorkers.AppendElement(&aWorkerPrivate);
+    } else {
+      domainInfo->mActiveWorkers.AppendElement(&aWorkerPrivate);
+    }
+  }
+
+  // From here on out we must call UnregisterWorker if something fails!
+  if (parent) {
+    if (!parent->AddChildWorker(aWorkerPrivate)) {
+      UnregisterWorker(aWorkerPrivate);
+      return false;
+    }
+  } else {
+    if (!mNavigatorPropertiesLoaded) {
+      if (NS_FAILED(Navigator::GetAppVersion(
+              mNavigatorProperties.mAppVersion, aWorkerPrivate.GetDocument(),
+              false /* aUsePrefOverriddenValue */)) ||
+          NS_FAILED(Navigator::GetPlatform(
+              mNavigatorProperties.mPlatform, aWorkerPrivate.GetDocument(),
+              false /* aUsePrefOverriddenValue */))) {
+        UnregisterWorker(aWorkerPrivate);
+        return false;
+      }
+
+      // The navigator overridden properties should have already been read.
+
+      Navigator::GetAcceptLanguages(mNavigatorProperties.mLanguages);
+      mNavigatorPropertiesLoaded = true;
+    }
+
+    nsPIDOMWindowInner* window = aWorkerPrivate.GetWindow();
+
+    if (!isServiceWorker) {
+      // Service workers are excluded since their lifetime is separate from
+      // that of dom windows.
+      if (auto* const windowArray = mWindowMap.GetOrInsertNew(window, 1);
+          !windowArray->Contains(&aWorkerPrivate)) {
+        windowArray->AppendElement(&aWorkerPrivate);
+      } else {
+        MOZ_ASSERT(aWorkerPrivate.IsSharedWorker());
+      }
+    }
+  }
+
+  if (!queued && !ScheduleWorker(aWorkerPrivate)) {
+    return false;
+  }
+
+  if (isServiceWorker) {
+    AssertIsOnMainThread();
+    Telemetry::Accumulate(Telemetry::SERVICE_WORKER_WAS_SPAWNED, 1);
+  }
+  return true;
+}
+
+void RuntimeService::UnregisterWorker(WorkerPrivate& aWorkerPrivate) {
+  aWorkerPrivate.AssertIsOnParentThread();
+
+  WorkerPrivate* parent = aWorkerPrivate.GetParent();
+  if (!parent) {
+    AssertIsOnMainThread();
+  }
+
+  const nsCString& domain = aWorkerPrivate.Domain();
+
+  WorkerPrivate* queuedWorker = nullptr;
+  {
+    MutexAutoLock lock(mMutex);
+
+    WorkerDomainInfo* domainInfo;
+    if (!mDomainMap.Get(domain, &domainInfo)) {
+      NS_ERROR("Don't have an entry for this domain!");
+    }
+
+    // Remove old worker from everywhere.
+    uint32_t index = domainInfo->mQueuedWorkers.IndexOf(&aWorkerPrivate);
+    if (index != kNoIndex) {
+      // Was queued, remove from the list.
+      domainInfo->mQueuedWorkers.RemoveElementAt(index);
+    } else if (parent) {
+      MOZ_ASSERT(domainInfo->mChildWorkerCount, "Must be non-zero!");
+      domainInfo->mChildWorkerCount--;
+    } else if (aWorkerPrivate.IsServiceWorker()) {
+      MOZ_ASSERT(domainInfo->mActiveServiceWorkers.Contains(&aWorkerPrivate),
+                 "Don't know about this worker!");
+      domainInfo->mActiveServiceWorkers.RemoveElement(&aWorkerPrivate);
+    } else {
+      MOZ_ASSERT(domainInfo->mActiveWorkers.Contains(&aWorkerPrivate),
+                 "Don't know about this worker!");
+      domainInfo->mActiveWorkers.RemoveElement(&aWorkerPrivate);
+    }
+
+    // See if there's a queued worker we can schedule.
+    if (domainInfo->ActiveWorkerCount() < gMaxWorkersPerDomain &&
+        !domainInfo->mQueuedWorkers.IsEmpty()) {
+      queuedWorker = domainInfo->mQueuedWorkers[0];
+      domainInfo->mQueuedWorkers.RemoveElementAt(0);
+
+      if (queuedWorker->GetParent()) {
+        domainInfo->mChildWorkerCount++;
+      } else if (queuedWorker->IsServiceWorker()) {
+        domainInfo->mActiveServiceWorkers.AppendElement(queuedWorker);
+      } else {
+        domainInfo->mActiveWorkers.AppendElement(queuedWorker);
+      }
+    }
+
+    if (domainInfo->HasNoWorkers()) {
+      MOZ_ASSERT(domainInfo->mQueuedWorkers.IsEmpty());
+      mDomainMap.Remove(domain);
+    }
+  }
+
+  // NB: For Shared Workers we used to call ShutdownOnMainThread on the
+  // RemoteWorkerController; however, that was redundant because
+  // RemoteWorkerChild uses a WeakWorkerRef which notifies at about the
+  // same time as us calling into the code here and would race with us.
+
+  if (parent) {
+    parent->RemoveChildWorker(aWorkerPrivate);
+  } else if (aWorkerPrivate.IsSharedWorker()) {
+    AssertIsOnMainThread();
+
+    mWindowMap.RemoveIf([&aWorkerPrivate](const auto& iter) {
+      const auto& workers = iter.Data();
+      MOZ_ASSERT(workers);
+
+      if (workers->RemoveElement(&aWorkerPrivate)) {
+        MOZ_ASSERT(!workers->Contains(&aWorkerPrivate),
+                   "Added worker more than once!");
+
+        return workers->IsEmpty();
+      }
+
+      return false;
+    });
+  } else if (aWorkerPrivate.IsDedicatedWorker()) {
+    // May be null.
+    nsPIDOMWindowInner* window = aWorkerPrivate.GetWindow();
+    if (auto entry = mWindowMap.Lookup(window)) {
+      MOZ_ALWAYS_TRUE(entry.Data()->RemoveElement(&aWorkerPrivate));
+      if (entry.Data()->IsEmpty()) {
+        entry.Remove();
+      }
+    } else {
+      MOZ_ASSERT_UNREACHABLE("window is not in mWindowMap");
+    }
+  }
+
+  if (queuedWorker && !ScheduleWorker(*queuedWorker)) {
+    UnregisterWorker(*queuedWorker);
+  }
+}
+
+bool RuntimeService::ScheduleWorker(WorkerPrivate& aWorkerPrivate) {
+  if (!aWorkerPrivate.Start()) {
+    // This is ok, means that we didn't need to make a thread for this worker.
+    return true;
+  }
+
+  const WorkerThreadFriendKey friendKey;
+
+  SafeRefPtr<WorkerThread> thread = WorkerThread::Create(friendKey);
+  if (!thread) {
+    UnregisterWorker(aWorkerPrivate);
+    return false;
+  }
+
+  if (NS_FAILED(thread->SetPriority(nsISupportsPriority::PRIORITY_NORMAL))) {
+    NS_WARNING("Could not set the thread's priority!");
+  }
+
+  aWorkerPrivate.SetThread(thread.unsafeGetRawPtr());
+  JSContext* cx = CycleCollectedJSContext::Get()->Context();
+  nsCOMPtr<nsIRunnable> runnable = new WorkerThreadPrimaryRunnable(
+      &aWorkerPrivate, thread.clonePtr(), JS_GetParentRuntime(cx));
+  if (NS_FAILED(
+          thread->DispatchPrimaryRunnable(friendKey, runnable.forget()))) {
+    UnregisterWorker(aWorkerPrivate);
+    return false;
+  }
+
+  return true;
+}
+
+nsresult RuntimeService::Init() {
+  AssertIsOnMainThread();
+
+  nsLayoutStatics::AddRef();
+
+  // Initialize JSSettings.
+  sDefaultJSSettings = new JSSettings();
+  SetDefaultJSGCSettings(JSGC_MAX_BYTES, Some(WORKER_DEFAULT_RUNTIME_HEAPSIZE));
+  SetDefaultJSGCSettings(JSGC_ALLOCATION_THRESHOLD,
+                         Some(WORKER_DEFAULT_ALLOCATION_THRESHOLD));
+
+  // nsIStreamTransportService is thread-safe but it must be initialized on the
+  // main-thread. FileReader needs it, so, let's initialize it now.
+  nsresult rv;
+  nsCOMPtr<nsIStreamTransportService> sts =
+      do_GetService(kStreamTransportServiceCID, &rv);
+  NS_ENSURE_TRUE(sts, NS_ERROR_FAILURE);
+
+  nsCOMPtr<nsIObserverService> obs = services::GetObserverService();
+  NS_ENSURE_TRUE(obs, NS_ERROR_FAILURE);
+
+  rv = obs->AddObserver(this, NS_XPCOM_SHUTDOWN_THREADS_OBSERVER_ID, false);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  rv = obs->AddObserver(this, NS_XPCOM_SHUTDOWN_OBSERVER_ID, false);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  mObserved = true;
+
+  if (NS_FAILED(obs->AddObserver(this, GC_REQUEST_OBSERVER_TOPIC, false))) {
+    NS_WARNING("Failed to register for GC request notifications!");
+  }
+
+  if (NS_FAILED(obs->AddObserver(this, CC_REQUEST_OBSERVER_TOPIC, false))) {
+    NS_WARNING("Failed to register for CC request notifications!");
+  }
+
+  if (NS_FAILED(
+          obs->AddObserver(this, MEMORY_PRESSURE_OBSERVER_TOPIC, false))) {
+    NS_WARNING("Failed to register for memory pressure notifications!");
+  }
+
+  if (NS_FAILED(
+          obs->AddObserver(this, NS_IOSERVICE_OFFLINE_STATUS_TOPIC, false))) {
+    NS_WARNING("Failed to register for offline notification event!");
+  }
+
+  MOZ_ASSERT(!gRuntimeServiceDuringInit, "This should be false!");
+  gRuntimeServiceDuringInit = true;
+
+#define WORKER_PREF(name, callback) \
+  NS_FAILED(Preferences::RegisterCallbackAndCall(callback, name))
+
+  if (NS_FAILED(Preferences::RegisterPrefixCallbackAndCall(
+          LoadJSGCMemoryOptions,
+          PREF_JS_OPTIONS_PREFIX PREF_MEM_OPTIONS_PREFIX)) ||
+#ifdef JS_GC_ZEAL
+      NS_FAILED(Preferences::RegisterCallback(
+          LoadGCZealOptions, PREF_JS_OPTIONS_PREFIX PREF_GCZEAL)) ||
+#endif
+      WORKER_PREF("intl.accept_languages", PrefLanguagesChanged) ||
+      WORKER_PREF("general.appversion.override", AppVersionOverrideChanged) ||
+      WORKER_PREF("general.platform.override", PlatformOverrideChanged) ||
+      NS_FAILED(Preferences::RegisterPrefixCallbackAndCall(
+          LoadContextOptions, PREF_JS_OPTIONS_PREFIX))) {
+    NS_WARNING("Failed to register pref callbacks!");
+  }
+
+#undef WORKER_PREF
+
+  MOZ_ASSERT(gRuntimeServiceDuringInit, "Should be true!");
+  gRuntimeServiceDuringInit = false;
+
+  int32_t maxPerDomain =
+      Preferences::GetInt(PREF_WORKERS_MAX_PER_DOMAIN, MAX_WORKERS_PER_DOMAIN);
+  gMaxWorkersPerDomain = std::max(0, maxPerDomain);
+
+  if (NS_WARN_IF(!IndexedDatabaseManager::GetOrCreate())) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  // PerformanceService must be initialized on the main-thread.
+  PerformanceService::GetOrCreate();
+
+  return NS_OK;
+}
+
+void RuntimeService::Shutdown() {
+  AssertIsOnMainThread();
+
+  MOZ_ASSERT(!mShuttingDown);
+  // That's it, no more workers.
+  mShuttingDown = true;
+
+  nsCOMPtr<nsIObserverService> obs = services::GetObserverService();
+  NS_WARNING_ASSERTION(obs, "Failed to get observer service?!");
+
+  // Tell anyone that cares that they're about to lose worker support.
+  if (obs && NS_FAILED(obs->NotifyObservers(nullptr, WORKERS_SHUTDOWN_TOPIC,
+                                            nullptr))) {
+    NS_WARNING("NotifyObservers failed!");
+  }
+
+  {
+    AutoTArray<WorkerPrivate*, 100> workers;
+
+    {
+      MutexAutoLock lock(mMutex);
+
+      AddAllTopLevelWorkersToArray(workers);
+    }
+
+    // Cancel all top-level workers.
+    for (const auto& worker : workers) {
+      if (!worker->Cancel()) {
+        NS_WARNING("Failed to cancel worker!");
+      }
+    }
+  }
+
+  sDefaultJSSettings = nullptr;
+}
+
+namespace {
+
+class DumpCrashInfoRunnable final : public WorkerControlRunnable {
+ public:
+  explicit DumpCrashInfoRunnable(WorkerPrivate* aWorkerPrivate)
+      : WorkerControlRunnable(aWorkerPrivate, "DumpCrashInfoRunnable",
+                              WorkerThread),
+        mMonitor("DumpCrashInfoRunnable::mMonitor") {}
+
+  bool WorkerRun(JSContext* aCx, WorkerPrivate* aWorkerPrivate) override {
+    MonitorAutoLock lock(mMonitor);
+    if (!mHasMsg) {
+      aWorkerPrivate->DumpCrashInformation(mMsg);
+      mHasMsg.Flip();
+    }
+    lock.Notify();
+    return true;
+  }
+
+  nsresult Cancel() override {
+    MonitorAutoLock lock(mMonitor);
+    if (!mHasMsg) {
+      mMsg.Assign("Canceled");
+      mHasMsg.Flip();
+    }
+    lock.Notify();
+
+    return NS_OK;
+  }
+
+  bool DispatchAndWait() {
+    MonitorAutoLock lock(mMonitor);
+
+    if (!Dispatch()) {
+      // The worker is already dead but the main thread still didn't remove it
+      // from RuntimeService's registry.
+      return false;
+    }
+
+    // To avoid any possibility of process hangs we never receive reports on
+    // we give the worker 1sec to react.
+    lock.Wait(TimeDuration::FromMilliseconds(1000));
+    if (!mHasMsg) {
+      mMsg.Append("NoResponse");
+      mHasMsg.Flip();
+    }
+    return true;
+  }
+
+  const nsCString& MsgData() const { return mMsg; }
+
+ private:
+  bool PreDispatch(WorkerPrivate* aWorkerPrivate) override { return true; }
+
+  void PostDispatch(WorkerPrivate* aWorkerPrivate,
+                    bool aDispatchResult) override {}
+
+  Monitor mMonitor MOZ_UNANNOTATED;
+  nsCString mMsg;
+  FlippedOnce<false> mHasMsg;
+};
+
+struct ActiveWorkerStats {
+  template <uint32_t ActiveWorkerStats::*Category>
+  void Update(const nsTArray<WorkerPrivate*>& aWorkers) {
+    for (const auto worker : aWorkers) {
+      RefPtr<DumpCrashInfoRunnable> runnable =
+          new DumpCrashInfoRunnable(worker);
+      if (runnable->DispatchAndWait()) {
+        ++(this->*Category);
+        mMessage.Append(runnable->MsgData());
+      }
+    }
+  }
+
+  uint32_t mWorkers = 0;
+  uint32_t mServiceWorkers = 0;
+  nsCString mMessage;
+};
+
+}  // namespace
+
+void RuntimeService::CrashIfHanging() {
+  MutexAutoLock lock(mMutex);
+
+  // If we never wanted to shut down we cannot hang.
+  if (!mShuttingDown) {
+    return;
+  }
+
+  ActiveWorkerStats activeStats;
+  uint32_t inactiveWorkers = 0;
+
+  for (const auto& aData : mDomainMap.Values()) {
+    activeStats.Update<&ActiveWorkerStats::mWorkers>(aData->mActiveWorkers);
+    activeStats.Update<&ActiveWorkerStats::mServiceWorkers>(
+        aData->mActiveServiceWorkers);
+
+    // These might not be top-level workers...
+    inactiveWorkers += std::count_if(
+        aData->mQueuedWorkers.begin(), aData->mQueuedWorkers.end(),
+        [](const auto* const worker) { return !worker->GetParent(); });
+  }
+
+  if (activeStats.mWorkers + activeStats.mServiceWorkers + inactiveWorkers ==
+      0) {
+    return;
+  }
+
+  nsCString msg;
+
+  // A: active Workers | S: active ServiceWorkers | Q: queued Workers
+  msg.AppendPrintf("Workers Hanging - %d|A:%d|S:%d|Q:%d", mShuttingDown ? 1 : 0,
+                   activeStats.mWorkers, activeStats.mServiceWorkers,
+                   inactiveWorkers);
+  msg.Append(activeStats.mMessage);
+
+  // This string will be leaked.
+  MOZ_CRASH_UNSAFE(strdup(msg.BeginReading()));
+}
+
+// This spins the event loop until all workers are finished and their threads
+// have been joined.
+void RuntimeService::Cleanup() {
+  AssertIsOnMainThread();
+
+  if (!mShuttingDown) {
+    Shutdown();
+  }
+
+  nsCOMPtr<nsIObserverService> obs = services::GetObserverService();
+  NS_WARNING_ASSERTION(obs, "Failed to get observer service?!");
+
+  {
+    MutexAutoLock lock(mMutex);
+
+    AutoTArray<WorkerPrivate*, 100> workers;
+    AddAllTopLevelWorkersToArray(workers);
+
+    if (!workers.IsEmpty()) {
+      nsIThread* currentThread = NS_GetCurrentThread();
+      NS_ASSERTION(currentThread, "This should never be null!");
+
+      // If the loop below takes too long, we probably have a problematic
+      // worker.  MOZ_LOG some info before the parent process forcibly
+      // terminates us so that in the event we are a content process, the log
+      // output can provide useful context about the workers that did not
+      // cleanly shut down.
+      nsCOMPtr<nsITimer> timer;
+      RefPtr<RuntimeService> self = this;
+      nsresult rv = NS_NewTimerWithCallback(
+          getter_AddRefs(timer),
+          [self](nsITimer*) { self->DumpRunningWorkers(); },
+          TimeDuration::FromSeconds(1), nsITimer::TYPE_ONE_SHOT,
+          "RuntimeService::WorkerShutdownDump");
+      Unused << NS_WARN_IF(NS_FAILED(rv));
+
+      // And make sure all their final messages have run and all their threads
+      // have joined.
+      while (mDomainMap.Count()) {
+        MutexAutoUnlock unlock(mMutex);
+
+        if (!NS_ProcessNextEvent(currentThread)) {
+          NS_WARNING("Something bad happened!");
+          break;
+        }
+      }
+
+      if (NS_SUCCEEDED(rv)) {
+        timer->Cancel();
+      }
+    }
+  }
+
+  NS_ASSERTION(!mWindowMap.Count(), "All windows should have been released!");
+
+#define WORKER_PREF(name, callback) \
+  NS_FAILED(Preferences::UnregisterCallback(callback, name))
+
+  if (mObserved) {
+    if (NS_FAILED(Preferences::UnregisterPrefixCallback(
+            LoadContextOptions, PREF_JS_OPTIONS_PREFIX)) ||
+        WORKER_PREF("intl.accept_languages", PrefLanguagesChanged) ||
+        WORKER_PREF("general.appversion.override", AppVersionOverrideChanged) ||
+        WORKER_PREF("general.platform.override", PlatformOverrideChanged) ||
+#ifdef JS_GC_ZEAL
+        NS_FAILED(Preferences::UnregisterCallback(
+            LoadGCZealOptions, PREF_JS_OPTIONS_PREFIX PREF_GCZEAL)) ||
+#endif
+        NS_FAILED(Preferences::UnregisterPrefixCallback(
+            LoadJSGCMemoryOptions,
+            PREF_JS_OPTIONS_PREFIX PREF_MEM_OPTIONS_PREFIX))) {
+      NS_WARNING("Failed to unregister pref callbacks!");
+    }
+
+#undef WORKER_PREF
+
+    if (obs) {
+      if (NS_FAILED(obs->RemoveObserver(this, GC_REQUEST_OBSERVER_TOPIC))) {
+        NS_WARNING("Failed to unregister for GC request notifications!");
+      }
+
+      if (NS_FAILED(obs->RemoveObserver(this, CC_REQUEST_OBSERVER_TOPIC))) {
+        NS_WARNING("Failed to unregister for CC request notifications!");
+      }
+
+      if (NS_FAILED(
+              obs->RemoveObserver(this, MEMORY_PRESSURE_OBSERVER_TOPIC))) {
+        NS_WARNING("Failed to unregister for memory pressure notifications!");
+      }
+
+      if (NS_FAILED(
+              obs->RemoveObserver(this, NS_IOSERVICE_OFFLINE_STATUS_TOPIC))) {
+        NS_WARNING("Failed to unregister for offline notification event!");
+      }
+      obs->RemoveObserver(this, NS_XPCOM_SHUTDOWN_THREADS_OBSERVER_ID);
+      obs->RemoveObserver(this, NS_XPCOM_SHUTDOWN_OBSERVER_ID);
+      mObserved = false;
+    }
+  }
+
+  nsLayoutStatics::Release();
+}
+
+void RuntimeService::AddAllTopLevelWorkersToArray(
+    nsTArray<WorkerPrivate*>& aWorkers) {
+  for (const auto& aData : mDomainMap.Values()) {
+#ifdef DEBUG
+    for (const auto& activeWorker : aData->mActiveWorkers) {
+      MOZ_ASSERT(!activeWorker->GetParent(),
+                 "Shouldn't have a parent in this list!");
+    }
+    for (const auto& activeServiceWorker : aData->mActiveServiceWorkers) {
+      MOZ_ASSERT(!activeServiceWorker->GetParent(),
+                 "Shouldn't have a parent in this list!");
+    }
+#endif
+
+    aWorkers.AppendElements(aData->mActiveWorkers);
+    aWorkers.AppendElements(aData->mActiveServiceWorkers);
+
+    // These might not be top-level workers...
+    std::copy_if(aData->mQueuedWorkers.begin(), aData->mQueuedWorkers.end(),
+                 MakeBackInserter(aWorkers),
+                 [](const auto& worker) { return !worker->GetParent(); });
+  }
+}
+
+nsTArray<WorkerPrivate*> RuntimeService::GetWorkersForWindow(
+    const nsPIDOMWindowInner& aWindow) const {
+  AssertIsOnMainThread();
+
+  nsTArray<WorkerPrivate*> result;
+  if (nsTArray<WorkerPrivate*>* const workers = mWindowMap.Get(&aWindow)) {
+    NS_ASSERTION(!workers->IsEmpty(), "Should have been removed!");
+    result.AppendElements(*workers);
+  }
+  return result;
+}
+
+void RuntimeService::CancelWorkersForWindow(const nsPIDOMWindowInner& aWindow) {
+  AssertIsOnMainThread();
+
+  for (WorkerPrivate* const worker : GetWorkersForWindow(aWindow)) {
+    MOZ_ASSERT(!worker->IsSharedWorker());
+    worker->Cancel();
+  }
+}
+
+void RuntimeService::FreezeWorkersForWindow(const nsPIDOMWindowInner& aWindow) {
+  AssertIsOnMainThread();
+
+  for (WorkerPrivate* const worker : GetWorkersForWindow(aWindow)) {
+    MOZ_ASSERT(!worker->IsSharedWorker());
+    worker->Freeze(&aWindow);
+  }
+}
+
+void RuntimeService::ThawWorkersForWindow(const nsPIDOMWindowInner& aWindow) {
+  AssertIsOnMainThread();
+
+  for (WorkerPrivate* const worker : GetWorkersForWindow(aWindow)) {
+    MOZ_ASSERT(!worker->IsSharedWorker());
+    worker->Thaw(&aWindow);
+  }
+}
+
+void RuntimeService::SuspendWorkersForWindow(
+    const nsPIDOMWindowInner& aWindow) {
+  AssertIsOnMainThread();
+
+  for (WorkerPrivate* const worker : GetWorkersForWindow(aWindow)) {
+    MOZ_ASSERT(!worker->IsSharedWorker());
+    worker->ParentWindowPaused();
+  }
+}
+
+void RuntimeService::ResumeWorkersForWindow(const nsPIDOMWindowInner& aWindow) {
+  AssertIsOnMainThread();
+
+  for (WorkerPrivate* const worker : GetWorkersForWindow(aWindow)) {
+    MOZ_ASSERT(!worker->IsSharedWorker());
+    worker->ParentWindowResumed();
+  }
+}
+
+void RuntimeService::PropagateStorageAccessPermissionGranted(
+    const nsPIDOMWindowInner& aWindow) {
+  AssertIsOnMainThread();
+  MOZ_ASSERT_IF(aWindow.GetExtantDoc(), aWindow.GetExtantDoc()
+                                            ->CookieJarSettings()
+                                            ->GetRejectThirdPartyContexts());
+
+  for (WorkerPrivate* const worker : GetWorkersForWindow(aWindow)) {
+    worker->PropagateStorageAccessPermissionGranted();
+  }
+}
+
+template <typename Func>
+void RuntimeService::BroadcastAllWorkers(const Func& aFunc) {
+  AssertIsOnMainThread();
+
+  AutoTArray<WorkerPrivate*, 100> workers;
+  {
+    MutexAutoLock lock(mMutex);
+
+    AddAllTopLevelWorkersToArray(workers);
+  }
+
+  for (const auto& worker : workers) {
+    aFunc(*worker);
+  }
+}
+
+void RuntimeService::UpdateAllWorkerContextOptions() {
+  BroadcastAllWorkers([](auto& worker) {
+    worker.UpdateContextOptions(sDefaultJSSettings->contextOptions);
+  });
+}
+
+void RuntimeService::UpdateAppVersionOverridePreference(
+    const nsAString& aValue) {
+  AssertIsOnMainThread();
+  mNavigatorProperties.mAppVersionOverridden = aValue;
+}
+
+void RuntimeService::UpdatePlatformOverridePreference(const nsAString& aValue) {
+  AssertIsOnMainThread();
+  mNavigatorProperties.mPlatformOverridden = aValue;
+}
+
+void RuntimeService::UpdateAllWorkerLanguages(
+    const nsTArray<nsString>& aLanguages) {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  mNavigatorProperties.mLanguages = aLanguages.Clone();
+  BroadcastAllWorkers(
+      [&aLanguages](auto& worker) { worker.UpdateLanguages(aLanguages); });
+}
+
+void RuntimeService::UpdateAllWorkerMemoryParameter(JSGCParamKey aKey,
+                                                    Maybe<uint32_t> aValue) {
+  BroadcastAllWorkers([aKey, aValue](auto& worker) {
+    worker.UpdateJSWorkerMemoryParameter(aKey, aValue);
+  });
+}
+
+#ifdef JS_GC_ZEAL
+void RuntimeService::UpdateAllWorkerGCZeal() {
+  BroadcastAllWorkers([](auto& worker) {
+    worker.UpdateGCZeal(sDefaultJSSettings->gcZeal,
+                        sDefaultJSSettings->gcZealFrequency);
+  });
+}
+#endif
+
+void RuntimeService::SetLowMemoryStateAllWorkers(bool aState) {
+  BroadcastAllWorkers(
+      [aState](auto& worker) { worker.SetLowMemoryState(aState); });
+}
+
+void RuntimeService::GarbageCollectAllWorkers(bool aShrinking) {
+  BroadcastAllWorkers(
+      [aShrinking](auto& worker) { worker.GarbageCollect(aShrinking); });
+}
+
+void RuntimeService::CycleCollectAllWorkers() {
+  BroadcastAllWorkers([](auto& worker) { worker.CycleCollect(); });
+}
+
+void RuntimeService::SendOfflineStatusChangeEventToAllWorkers(bool aIsOffline) {
+  BroadcastAllWorkers([aIsOffline](auto& worker) {
+    worker.OfflineStatusChangeEvent(aIsOffline);
+  });
+}
+
+void RuntimeService::MemoryPressureAllWorkers() {
+  BroadcastAllWorkers([](auto& worker) { worker.MemoryPressure(); });
+}
+
+uint32_t RuntimeService::ClampedHardwareConcurrency(
+    bool aShouldResistFingerprinting) const {
+  // The Firefox Hardware Report says 70% of Firefox users have exactly 2 cores.
+  // When the resistFingerprinting pref is set, we want to blend into the crowd
+  // so spoof navigator.hardwareConcurrency = 2 to reduce user uniqueness.
+  if (MOZ_UNLIKELY(aShouldResistFingerprinting)) {
+    return 2;
+  }
+
+  // This needs to be atomic, because multiple workers, and even mainthread,
+  // could race to initialize it at once.
+  static Atomic<uint32_t> unclampedHardwareConcurrency;
+
+  // No need to loop here: if compareExchange fails, that just means that some
+  // other worker has initialized numberOfProcessors, so we're good to go.
+  if (!unclampedHardwareConcurrency) {
+    int32_t numberOfProcessors = 0;
+#if defined(XP_MACOSX)
+    if (nsMacUtilsImpl::IsTCSMAvailable()) {
+      // On failure, zero is returned from GetPhysicalCPUCount()
+      // and we fallback to PR_GetNumberOfProcessors below.
+      numberOfProcessors = nsMacUtilsImpl::GetPhysicalCPUCount();
+    }
+#endif
+    if (numberOfProcessors == 0) {
+      numberOfProcessors = PR_GetNumberOfProcessors();
+    }
+    if (numberOfProcessors <= 0) {
+      numberOfProcessors = 1;  // Must be one there somewhere
+    }
+    Unused << unclampedHardwareConcurrency.compareExchange(0,
+                                                           numberOfProcessors);
+  }
+
+  return std::min(uint32_t(unclampedHardwareConcurrency),
+                  StaticPrefs::dom_maxHardwareConcurrency());
+}
+
+// nsISupports
+NS_IMPL_ISUPPORTS(RuntimeService, nsIObserver)
+
+// nsIObserver
+NS_IMETHODIMP
+RuntimeService::Observe(nsISupports* aSubject, const char* aTopic,
+                        const char16_t* aData) {
+  AssertIsOnMainThread();
+
+  if (!strcmp(aTopic, NS_XPCOM_SHUTDOWN_OBSERVER_ID)) {
+    Shutdown();
+    return NS_OK;
+  }
+  if (!strcmp(aTopic, NS_XPCOM_SHUTDOWN_THREADS_OBSERVER_ID)) {
+    Cleanup();
+    return NS_OK;
+  }
+  if (!strcmp(aTopic, GC_REQUEST_OBSERVER_TOPIC)) {
+    GarbageCollectAllWorkers(/* shrinking = */ false);
+    return NS_OK;
+  }
+  if (!strcmp(aTopic, CC_REQUEST_OBSERVER_TOPIC)) {
+    CycleCollectAllWorkers();
+    return NS_OK;
+  }
+  if (!strcmp(aTopic, MEMORY_PRESSURE_OBSERVER_TOPIC)) {
+    nsDependentString data(aData);
+    // Don't continue to GC/CC if we are in an ongoing low-memory state since
+    // its very slow and it likely won't help us anyway.
+    if (data.EqualsLiteral(LOW_MEMORY_ONGOING_DATA)) {
+      return NS_OK;
+    }
+    if (data.EqualsLiteral(LOW_MEMORY_DATA)) {
+      SetLowMemoryStateAllWorkers(true);
+    }
+    GarbageCollectAllWorkers(/* shrinking = */ true);
+    CycleCollectAllWorkers();
+    MemoryPressureAllWorkers();
+    return NS_OK;
+  }
+  if (!strcmp(aTopic, MEMORY_PRESSURE_STOP_OBSERVER_TOPIC)) {
+    SetLowMemoryStateAllWorkers(false);
+    return NS_OK;
+  }
+  if (!strcmp(aTopic, NS_IOSERVICE_OFFLINE_STATUS_TOPIC)) {
+    SendOfflineStatusChangeEventToAllWorkers(NS_IsOffline());
+    return NS_OK;
+  }
+
+  MOZ_ASSERT_UNREACHABLE("Unknown observer topic!");
+  return NS_OK;
+}
+
+namespace {
+const char* WorkerKindToString(WorkerKind kind) {
+  switch (kind) {
+    case WorkerKindDedicated:
+      return "dedicated";
+    case WorkerKindShared:
+      return "shared";
+    case WorkerKindService:
+      return "service";
+    default:
+      NS_WARNING("Unknown worker type");
+      return "unknown worker type";
+  }
+}
+
+void LogWorker(WorkerPrivate* worker, const char* category) {
+  AssertIsOnMainThread();
+
+  SHUTDOWN_LOG(("Found %s (%s): %s", category,
+                WorkerKindToString(worker->Kind()),
+                NS_ConvertUTF16toUTF8(worker->ScriptURL()).get()));
+
+  if (worker->Kind() == WorkerKindService) {
+    SHUTDOWN_LOG(("Scope: %s", worker->ServiceWorkerScope().get()));
+  }
+
+  nsCString origin;
+  worker->GetPrincipal()->GetOrigin(origin);
+  SHUTDOWN_LOG(("Principal: %s", origin.get()));
+
+  nsCString loadingOrigin;
+  worker->GetLoadingPrincipal()->GetOrigin(loadingOrigin);
+  SHUTDOWN_LOG(("LoadingPrincipal: %s", loadingOrigin.get()));
+
+  RefPtr<DumpCrashInfoRunnable> runnable = new DumpCrashInfoRunnable(worker);
+  if (runnable->DispatchAndWait()) {
+    SHUTDOWN_LOG(("CrashInfo: %s", runnable->MsgData().get()));
+  } else {
+    SHUTDOWN_LOG(("CrashInfo: dispatch failed"));
+  }
+}
+}  // namespace
+
+void RuntimeService::DumpRunningWorkers() {
+  // Temporarily set the LogLevel high enough to be certain the messages are
+  // visible.
+  LogModule* module = gWorkerShutdownDumpLog;
+  LogLevel prevLevel = module->Level();
+
+  const auto cleanup =
+      MakeScopeExit([module, prevLevel] { module->SetLevel(prevLevel); });
+
+  if (prevLevel < LogLevel::Debug) {
+    module->SetLevel(LogLevel::Debug);
+  }
+
+  MutexAutoLock lock(mMutex);
+
+  for (const auto& info : mDomainMap.Values()) {
+    for (WorkerPrivate* worker : info->mActiveWorkers) {
+      LogWorker(worker, "ActiveWorker");
+    }
+
+    for (WorkerPrivate* worker : info->mActiveServiceWorkers) {
+      LogWorker(worker, "ActiveServiceWorker");
+    }
+
+    for (WorkerPrivate* worker : info->mQueuedWorkers) {
+      LogWorker(worker, "QueuedWorker");
+    }
+  }
+}
+
+bool LogViolationDetailsRunnable::MainThreadRun() {
+  AssertIsOnMainThread();
+
+  nsIContentSecurityPolicy* csp = mWorkerPrivate->GetCsp();
+  if (csp) {
+    csp->LogViolationDetails(mViolationType,
+                             nullptr,  // triggering element
+                             mWorkerPrivate->CSPEventListener(), mFileName,
+                             mScriptSample, mLineNum, mColumnNum, u""_ns,
+                             u""_ns);
+  }
+
+  return true;
+}
+
+// MOZ_CAN_RUN_SCRIPT_BOUNDARY until Runnable::Run is MOZ_CAN_RUN_SCRIPT.  See
+// bug 1535398.
+MOZ_CAN_RUN_SCRIPT_BOUNDARY
+NS_IMETHODIMP
+WorkerThreadPrimaryRunnable::Run() {
+  NS_ConvertUTF16toUTF8 url(mWorkerPrivate->ScriptURL());
+  AUTO_PROFILER_LABEL_DYNAMIC_CSTR("WorkerThreadPrimaryRunnable::Run", OTHER,
+                                   url.get());
+
+  using mozilla::ipc::BackgroundChild;
+
+  {
+    auto failureCleanup = MakeScopeExit([&]() {
+      // The creation of threadHelper above is the point at which a worker is
+      // considered to have run, because the `mPreStartRunnables` are all
+      // re-dispatched after `mThread` is set.  We need to let the WorkerPrivate
+      // know so it can clean up the various event loops and delete the worker.
+      mWorkerPrivate->RunLoopNeverRan();
+    });
+
+    mWorkerPrivate->SetWorkerPrivateInWorkerThread(mThread.unsafeGetRawPtr());
+
+    const auto threadCleanup = MakeScopeExit([&] {
+      // This must be called before ScheduleDeletion, which is either called
+      // from failureCleanup leaving scope, or from the outer scope.
+      mWorkerPrivate->ResetWorkerPrivateInWorkerThread();
+    });
+
+    mWorkerPrivate->AssertIsOnWorkerThread();
+
+    // This needs to be initialized on the worker thread before being used on
+    // the main thread and calling BackgroundChild::GetOrCreateForCurrentThread
+    // exposes it to the main thread.
+    mWorkerPrivate->EnsurePerformanceStorage();
+
+    if (NS_WARN_IF(!BackgroundChild::GetOrCreateForCurrentThread())) {
+      return NS_ERROR_FAILURE;
+    }
+
+    nsWeakPtr globalScopeSentinel;
+    nsWeakPtr debuggerScopeSentinel;
+    // Never use the following pointers without checking their corresponding
+    // nsWeakPtr sentinel, defined above and initialized after DoRunLoop ends.
+    WorkerGlobalScopeBase* globalScopeRawPtr = nullptr;
+    WorkerGlobalScopeBase* debuggerScopeRawPtr = nullptr;
+    {
+      nsCycleCollector_startup();
+
+      auto context = MakeUnique<WorkerJSContext>(mWorkerPrivate);
+      nsresult rv = context->Initialize(mParentRuntime);
+      if (NS_WARN_IF(NS_FAILED(rv))) {
+        return rv;
+      }
+
+      JSContext* cx = context->Context();
+
+      if (!InitJSContextForWorker(mWorkerPrivate, cx)) {
+        return NS_ERROR_FAILURE;
+      }
+
+      failureCleanup.release();
+
+      {
+        PROFILER_SET_JS_CONTEXT(cx);
+
+        {
+          // We're on the worker thread here, and WorkerPrivate's refcounting is
+          // non-threadsafe: you can only do it on the parent thread.  What that
+          // means in practice is that we're relying on it being kept alive
+          // while we run.  Hopefully.
+          MOZ_KnownLive(mWorkerPrivate)->DoRunLoop(cx);
+          // The AutoJSAPI in DoRunLoop should have reported any exceptions left
+          // on cx.
+          MOZ_ASSERT(!JS_IsExceptionPending(cx));
+        }
+
+        mWorkerPrivate->ShutdownModuleLoader();
+
+        mWorkerPrivate->RunShutdownTasks();
+
+        BackgroundChild::CloseForCurrentThread();
+
+        PROFILER_CLEAR_JS_CONTEXT();
+      }
+
+      // There may still be runnables on the debugger event queue that hold a
+      // strong reference to the debugger global scope. These runnables are not
+      // visible to the cycle collector, so we need to make sure to clear the
+      // debugger event queue before we try to destroy the context. If we don't,
+      // the garbage collector will crash.
+      // Note that this just releases the runnables and does not execute them.
+      mWorkerPrivate->ClearDebuggerEventQueue();
+
+      // Before shutting down the cycle collector we need to do one more pass
+      // through the event loop to clean up any C++ objects that need deferred
+      // cleanup.
+      NS_ProcessPendingEvents(nullptr);
+
+      // At this point we expect the scopes to be alive if they were ever
+      // created successfully, keep weak references and set up the sentinels.
+      globalScopeRawPtr = mWorkerPrivate->GlobalScope();
+      if (globalScopeRawPtr) {
+        globalScopeSentinel = do_GetWeakReference(globalScopeRawPtr);
+      }
+      MOZ_ASSERT(!globalScopeRawPtr || globalScopeSentinel);
+      debuggerScopeRawPtr = mWorkerPrivate->DebuggerGlobalScope();
+      if (debuggerScopeRawPtr) {
+        debuggerScopeSentinel = do_GetWeakReference(debuggerScopeRawPtr);
+      }
+      MOZ_ASSERT(!debuggerScopeRawPtr || debuggerScopeSentinel);
+
+      // To our best knowledge nobody should need a reference to our globals
+      // now (NS_ProcessPendingEvents is the last expected potential usage)
+      // and we can unroot them.
+      mWorkerPrivate->UnrootGlobalScopes();
+
+      // Perform a full GC until we collect the main worker global and CC,
+      // which should break all cycles that touch JS.
+      bool repeatGCCC = true;
+      while (repeatGCCC) {
+        JS::PrepareForFullGC(cx);
+        JS::NonIncrementalGC(cx, JS::GCOptions::Shutdown,
+                             JS::GCReason::WORKER_SHUTDOWN);
+
+        // If we CCed something or got new events as a side effect, repeat.
+        repeatGCCC = mWorkerPrivate->isLastCCCollectedAnything() ||
+                     NS_HasPendingEvents(nullptr);
+        NS_ProcessPendingEvents(nullptr);
+      }
+
+      // The worker global should be unrooted and the shutdown of cycle
+      // collection should break all the remaining cycles.
+      nsCycleCollector_shutdown();
+
+      // If ever the CC shutdown run caused side effects, process them.
+      NS_ProcessPendingEvents(nullptr);
+
+      // Now WorkerJSContext goes out of scope. Do not use any cycle
+      // collectable objects nor JS after this point!
+    }
+
+    // Check sentinels if we actually removed all global scope references.
+    // In case use the earlier set-aside raw pointers to not mess with the
+    // ref counting after the cycle collector has gone away.
+    if (globalScopeSentinel) {
+      MOZ_ASSERT(!globalScopeSentinel->IsAlive());
+      if (NS_WARN_IF(globalScopeSentinel->IsAlive())) {
+        globalScopeRawPtr->NoteWorkerTerminated();
+        globalScopeRawPtr = nullptr;
+      }
+    }
+    if (debuggerScopeSentinel) {
+      MOZ_ASSERT(!debuggerScopeSentinel->IsAlive());
+      if (NS_WARN_IF(debuggerScopeSentinel->IsAlive())) {
+        debuggerScopeRawPtr->NoteWorkerTerminated();
+        debuggerScopeRawPtr = nullptr;
+      }
+    }
+  }
+
+  mWorkerPrivate->ScheduleDeletion(WorkerPrivate::WorkerRan);
+
+  // It is no longer safe to touch mWorkerPrivate.
+  mWorkerPrivate = nullptr;
+
+  // Now recycle this thread.
+  nsCOMPtr<nsIEventTarget> mainTarget = GetMainThreadSerialEventTarget();
+  MOZ_ASSERT(mainTarget);
+
+  RefPtr<FinishedRunnable> finishedRunnable =
+      new FinishedRunnable(std::move(mThread));
+  MOZ_ALWAYS_SUCCEEDS(
+      mainTarget->Dispatch(finishedRunnable, NS_DISPATCH_NORMAL));
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WorkerThreadPrimaryRunnable::FinishedRunnable::Run() {
+  AssertIsOnMainThread();
+
+  SafeRefPtr<WorkerThread> thread = std::move(mThread);
+  if (thread->ShutdownRequired()) {
+    MOZ_ALWAYS_SUCCEEDS(thread->Shutdown());
+  }
+
+  return NS_OK;
+}
+
+}  // namespace workerinternals
+
+// This is mostly for invoking within a debugger.
+void DumpRunningWorkers() {
+  RuntimeService* runtimeService = RuntimeService::GetService();
+  if (runtimeService) {
+    runtimeService->DumpRunningWorkers();
+  } else {
+    NS_WARNING("RuntimeService not found");
+  }
+}
+
+void CancelWorkersForWindow(const nsPIDOMWindowInner& aWindow) {
+  AssertIsOnMainThread();
+  RuntimeService* runtime = RuntimeService::GetService();
+  if (runtime) {
+    runtime->CancelWorkersForWindow(aWindow);
+  }
+}
+
+void FreezeWorkersForWindow(const nsPIDOMWindowInner& aWindow) {
+  AssertIsOnMainThread();
+  RuntimeService* runtime = RuntimeService::GetService();
+  if (runtime) {
+    runtime->FreezeWorkersForWindow(aWindow);
+  }
+}
+
+void ThawWorkersForWindow(const nsPIDOMWindowInner& aWindow) {
+  AssertIsOnMainThread();
+  RuntimeService* runtime = RuntimeService::GetService();
+  if (runtime) {
+    runtime->ThawWorkersForWindow(aWindow);
+  }
+}
+
+void SuspendWorkersForWindow(const nsPIDOMWindowInner& aWindow) {
+  AssertIsOnMainThread();
+  RuntimeService* runtime = RuntimeService::GetService();
+  if (runtime) {
+    runtime->SuspendWorkersForWindow(aWindow);
+  }
+}
+
+void ResumeWorkersForWindow(const nsPIDOMWindowInner& aWindow) {
+  AssertIsOnMainThread();
+  RuntimeService* runtime = RuntimeService::GetService();
+  if (runtime) {
+    runtime->ResumeWorkersForWindow(aWindow);
+  }
+}
+
+void PropagateStorageAccessPermissionGrantedToWorkers(
+    const nsPIDOMWindowInner& aWindow) {
+  AssertIsOnMainThread();
+  MOZ_ASSERT_IF(aWindow.GetExtantDoc(), aWindow.GetExtantDoc()
+                                            ->CookieJarSettings()
+                                            ->GetRejectThirdPartyContexts());
+
+  RuntimeService* runtime = RuntimeService::GetService();
+  if (runtime) {
+    runtime->PropagateStorageAccessPermissionGranted(aWindow);
+  }
+}
+
+WorkerPrivate* GetWorkerPrivateFromContext(JSContext* aCx) {
+  MOZ_ASSERT(!NS_IsMainThread());
+  MOZ_ASSERT(aCx);
+
+  CycleCollectedJSContext* ccjscx = CycleCollectedJSContext::GetFor(aCx);
+  if (!ccjscx) {
+    return nullptr;
+  }
+
+  WorkerJSContext* workerjscx = ccjscx->GetAsWorkerJSContext();
+  // GetWorkerPrivateFromContext is called only for worker contexts.  The
+  // context private is cleared early in ~CycleCollectedJSContext() and so
+  // GetFor() returns null above if called after ccjscx is no longer a
+  // WorkerJSContext.
+  MOZ_ASSERT(workerjscx);
+  return workerjscx->GetWorkerPrivate();
+}
+
+WorkerPrivate* GetCurrentThreadWorkerPrivate() {
+  if (NS_IsMainThread()) {
+    return nullptr;
+  }
+
+  CycleCollectedJSContext* ccjscx = CycleCollectedJSContext::Get();
+  if (!ccjscx) {
+    return nullptr;
+  }
+
+  WorkerJSContext* workerjscx = ccjscx->GetAsWorkerJSContext();
+  // Even when GetCurrentThreadWorkerPrivate() is called on worker
+  // threads, the ccjscx will no longer be a WorkerJSContext if called from
+  // stable state events during ~CycleCollectedJSContext().
+  if (!workerjscx) {
+    return nullptr;
+  }
+
+  return workerjscx->GetWorkerPrivate();
+}
+
+bool IsCurrentThreadRunningWorker() {
+  return !NS_IsMainThread() && !!GetCurrentThreadWorkerPrivate();
+}
+
+bool IsCurrentThreadRunningChromeWorker() {
+  WorkerPrivate* wp = GetCurrentThreadWorkerPrivate();
+  return wp && wp->UsesSystemPrincipal();
+}
+
+JSContext* GetCurrentWorkerThreadJSContext() {
+  WorkerPrivate* wp = GetCurrentThreadWorkerPrivate();
+  if (!wp) {
+    return nullptr;
+  }
+  return wp->GetJSContext();
+}
+
+JSObject* GetCurrentThreadWorkerGlobal() {
+  WorkerPrivate* wp = GetCurrentThreadWorkerPrivate();
+  if (!wp) {
+    return nullptr;
+  }
+  WorkerGlobalScope* scope = wp->GlobalScope();
+  if (!scope) {
+    return nullptr;
+  }
+  return scope->GetGlobalJSObject();
+}
+
+JSObject* GetCurrentThreadWorkerDebuggerGlobal() {
+  WorkerPrivate* wp = GetCurrentThreadWorkerPrivate();
+  if (!wp) {
+    return nullptr;
+  }
+  WorkerDebuggerGlobalScope* scope = wp->DebuggerGlobalScope();
+  if (!scope) {
+    return nullptr;
+  }
+  return scope->GetGlobalJSObject();
+}
+
+}  // namespace dom
+}  // namespace mozilla
diff --git a/dom/workers/RuntimeService.h b/dom/workers/RuntimeService.h
new file mode 100644
index 0000000000..f51076ac14
--- /dev/null
+++ b/dom/workers/RuntimeService.h
@@ -0,0 +1,197 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_workers_runtimeservice_h__
+#define mozilla_dom_workers_runtimeservice_h__
+
+#include "mozilla/dom/WorkerCommon.h"
+
+#include "nsIObserver.h"
+
+#include "js/ContextOptions.h"
+#include "MainThreadUtils.h"
+#include "mozilla/dom/BindingDeclarations.h"
+#include "mozilla/dom/SafeRefPtr.h"
+#include "mozilla/dom/workerinternals/JSSettings.h"
+#include "mozilla/Atomics.h"
+#include "mozilla/Mutex.h"
+#include "mozilla/StaticPtr.h"
+#include "nsClassHashtable.h"
+#include "nsHashKeys.h"
+#include "nsTArray.h"
+
+class nsPIDOMWindowInner;
+
+namespace mozilla::dom {
+struct WorkerLoadInfo;
+class WorkerThread;
+
+namespace workerinternals {
+
+class RuntimeService final : public nsIObserver {
+  struct WorkerDomainInfo {
+    nsCString mDomain;
+    nsTArray<WorkerPrivate*> mActiveWorkers;
+    nsTArray<WorkerPrivate*> mActiveServiceWorkers;
+    nsTArray<WorkerPrivate*> mQueuedWorkers;
+    uint32_t mChildWorkerCount;
+
+    WorkerDomainInfo() : mActiveWorkers(1), mChildWorkerCount(0) {}
+
+    uint32_t ActiveWorkerCount() const {
+      return mActiveWorkers.Length() + mChildWorkerCount;
+    }
+
+    uint32_t ActiveServiceWorkerCount() const {
+      return mActiveServiceWorkers.Length();
+    }
+
+    bool HasNoWorkers() const {
+      return ActiveWorkerCount() == 0 && ActiveServiceWorkerCount() == 0;
+    }
+  };
+
+  mozilla::Mutex mMutex;
+
+  // Protected by mMutex.
+  nsClassHashtable<nsCStringHashKey, WorkerDomainInfo> mDomainMap
+      MOZ_GUARDED_BY(mMutex);
+
+  // *Not* protected by mMutex.
+  nsClassHashtable<nsPtrHashKey<const nsPIDOMWindowInner>,
+                   nsTArray<WorkerPrivate*> >
+      mWindowMap;
+
+  static StaticAutoPtr<workerinternals::JSSettings> sDefaultJSSettings;
+
+ public:
+  struct NavigatorProperties {
+    nsString mAppVersion;
+    nsString mAppVersionOverridden;
+    nsString mPlatform;
+    nsString mPlatformOverridden;
+    CopyableTArray<nsString> mLanguages;
+  };
+
+ private:
+  NavigatorProperties mNavigatorProperties;
+
+  // True when the observer service holds a reference to this object.
+  bool mObserved;
+  bool mShuttingDown;
+  bool mNavigatorPropertiesLoaded;
+
+ public:
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIOBSERVER
+
+  static RuntimeService* GetOrCreateService();
+
+  static RuntimeService* GetService();
+
+  bool RegisterWorker(WorkerPrivate& aWorkerPrivate);
+
+  void UnregisterWorker(WorkerPrivate& aWorkerPrivate);
+
+  void CancelWorkersForWindow(const nsPIDOMWindowInner& aWindow);
+
+  void FreezeWorkersForWindow(const nsPIDOMWindowInner& aWindow);
+
+  void ThawWorkersForWindow(const nsPIDOMWindowInner& aWindow);
+
+  void SuspendWorkersForWindow(const nsPIDOMWindowInner& aWindow);
+
+  void ResumeWorkersForWindow(const nsPIDOMWindowInner& aWindow);
+
+  void PropagateStorageAccessPermissionGranted(
+      const nsPIDOMWindowInner& aWindow);
+
+  const NavigatorProperties& GetNavigatorProperties() const {
+    return mNavigatorProperties;
+  }
+
+  static void GetDefaultJSSettings(workerinternals::JSSettings& aSettings) {
+    AssertIsOnMainThread();
+    aSettings = *sDefaultJSSettings;
+  }
+
+  static void SetDefaultContextOptions(
+      const JS::ContextOptions& aContextOptions) {
+    AssertIsOnMainThread();
+    sDefaultJSSettings->contextOptions = aContextOptions;
+  }
+
+  void UpdateAppVersionOverridePreference(const nsAString& aValue);
+
+  void UpdatePlatformOverridePreference(const nsAString& aValue);
+
+  void UpdateAllWorkerContextOptions();
+
+  void UpdateAllWorkerLanguages(const nsTArray<nsString>& aLanguages);
+
+  static void SetDefaultJSGCSettings(JSGCParamKey aKey,
+                                     Maybe<uint32_t> aValue) {
+    AssertIsOnMainThread();
+    sDefaultJSSettings->ApplyGCSetting(aKey, aValue);
+  }
+
+  void UpdateAllWorkerMemoryParameter(JSGCParamKey aKey,
+                                      Maybe<uint32_t> aValue);
+
+#ifdef JS_GC_ZEAL
+  static void SetDefaultGCZeal(uint8_t aGCZeal, uint32_t aFrequency) {
+    AssertIsOnMainThread();
+    sDefaultJSSettings->gcZeal = aGCZeal;
+    sDefaultJSSettings->gcZealFrequency = aFrequency;
+  }
+
+  void UpdateAllWorkerGCZeal();
+#endif
+
+  void SetLowMemoryStateAllWorkers(bool aState);
+
+  void GarbageCollectAllWorkers(bool aShrinking);
+
+  void CycleCollectAllWorkers();
+
+  void SendOfflineStatusChangeEventToAllWorkers(bool aIsOffline);
+
+  void MemoryPressureAllWorkers();
+
+  uint32_t ClampedHardwareConcurrency(bool aShouldResistFingerprinting) const;
+
+  void CrashIfHanging();
+
+  bool IsShuttingDown() const { return mShuttingDown; }
+
+  void DumpRunningWorkers();
+
+ private:
+  RuntimeService();
+  ~RuntimeService();
+
+  nsresult Init();
+
+  void Shutdown();
+
+  void Cleanup();
+
+  void AddAllTopLevelWorkersToArray(nsTArray<WorkerPrivate*>& aWorkers)
+      MOZ_REQUIRES(mMutex);
+
+  nsTArray<WorkerPrivate*> GetWorkersForWindow(
+      const nsPIDOMWindowInner& aWindow) const;
+
+  bool ScheduleWorker(WorkerPrivate& aWorkerPrivate);
+
+  template <typename Func>
+  void BroadcastAllWorkers(const Func& aFunc);
+};
+
+}  // namespace workerinternals
+}  // namespace mozilla::dom
+
+#endif /* mozilla_dom_workers_runtimeservice_h__ */
diff --git a/dom/workers/ScriptLoader.cpp b/dom/workers/ScriptLoader.cpp
new file mode 100644
index 0000000000..73997b2725
--- /dev/null
+++ b/dom/workers/ScriptLoader.cpp
@@ -0,0 +1,1932 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "ScriptLoader.h"
+
+#include <algorithm>
+#include <type_traits>
+
+#include "mozilla/dom/RequestBinding.h"
+#include "nsIChannel.h"
+#include "nsIContentPolicy.h"
+#include "nsIContentSecurityPolicy.h"
+#include "nsICookieJarSettings.h"
+#include "nsIDocShell.h"
+#include "nsIHttpChannel.h"
+#include "nsIHttpChannelInternal.h"
+#include "nsIIOService.h"
+#include "nsIOService.h"
+#include "nsIPrincipal.h"
+#include "nsIProtocolHandler.h"
+#include "nsIScriptError.h"
+#include "nsIScriptSecurityManager.h"
+#include "nsIStreamListenerTee.h"
+#include "nsIThreadRetargetableRequest.h"
+#include "nsIURI.h"
+#include "nsIXPConnect.h"
+
+#include "jsapi.h"
+#include "jsfriendapi.h"
+#include "js/CompilationAndEvaluation.h"
+#include "js/Exception.h"
+#include "js/SourceText.h"
+#include "js/TypeDecls.h"
+#include "nsError.h"
+#include "nsComponentManagerUtils.h"
+#include "nsContentSecurityManager.h"
+#include "nsContentPolicyUtils.h"
+#include "nsContentUtils.h"
+#include "nsDocShellCID.h"
+#include "nsJSEnvironment.h"
+#include "nsNetUtil.h"
+#include "nsIPipe.h"
+#include "nsIOutputStream.h"
+#include "nsPrintfCString.h"
+#include "nsString.h"
+#include "nsTArray.h"
+#include "nsThreadUtils.h"
+#include "nsXPCOM.h"
+#include "xpcpublic.h"
+
+#include "mozilla/AntiTrackingUtils.h"
+#include "mozilla/ArrayAlgorithm.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/Encoding.h"
+#include "mozilla/LoadContext.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/ipc/BackgroundUtils.h"
+#include "mozilla/dom/ClientChannelHelper.h"
+#include "mozilla/dom/ClientInfo.h"
+#include "mozilla/dom/Exceptions.h"
+#include "mozilla/dom/nsCSPService.h"
+#include "mozilla/dom/nsCSPUtils.h"
+#include "mozilla/dom/PerformanceStorage.h"
+#include "mozilla/dom/Response.h"
+#include "mozilla/dom/ReferrerInfo.h"
+#include "mozilla/dom/ScriptSettings.h"
+#include "mozilla/dom/SerializedStackHolder.h"
+#include "mozilla/dom/workerinternals/CacheLoadHandler.h"
+#include "mozilla/dom/workerinternals/NetworkLoadHandler.h"
+#include "mozilla/dom/workerinternals/ScriptResponseHeaderProcessor.h"
+#include "mozilla/Result.h"
+#include "mozilla/ResultExtensions.h"
+#include "mozilla/StaticPrefs_browser.h"
+#include "mozilla/UniquePtr.h"
+#include "WorkerRunnable.h"
+#include "WorkerScope.h"
+
+#define MAX_CONCURRENT_SCRIPTS 1000
+
+using JS::loader::ParserMetadata;
+using JS::loader::ScriptKind;
+using JS::loader::ScriptLoadRequest;
+using mozilla::ipc::PrincipalInfo;
+
+namespace mozilla::dom::workerinternals {
+namespace {
+
+nsresult ConstructURI(const nsAString& aScriptURL, nsIURI* baseURI,
+                      const mozilla::Encoding* aDocumentEncoding,
+                      nsIURI** aResult) {
+  nsresult rv;
+  // Only top level workers' main script use the document charset for the
+  // script uri encoding. Otherwise, default encoding (UTF-8) is applied.
+  if (aDocumentEncoding) {
+    nsAutoCString charset;
+    aDocumentEncoding->Name(charset);
+    rv = NS_NewURI(aResult, aScriptURL, charset.get(), baseURI);
+  } else {
+    rv = NS_NewURI(aResult, aScriptURL, nullptr, baseURI);
+  }
+
+  if (NS_FAILED(rv)) {
+    return NS_ERROR_DOM_SYNTAX_ERR;
+  }
+  return NS_OK;
+}
+
+nsresult ChannelFromScriptURL(
+    nsIPrincipal* principal, Document* parentDoc, WorkerPrivate* aWorkerPrivate,
+    nsILoadGroup* loadGroup, nsIIOService* ios,
+    nsIScriptSecurityManager* secMan, nsIURI* aScriptURL,
+    const Maybe<ClientInfo>& aClientInfo,
+    const Maybe<ServiceWorkerDescriptor>& aController, bool aIsMainScript,
+    WorkerScriptType aWorkerScriptType, nsContentPolicyType aContentPolicyType,
+    nsLoadFlags aLoadFlags, uint32_t aSecFlags,
+    nsICookieJarSettings* aCookieJarSettings, nsIReferrerInfo* aReferrerInfo,
+    nsIChannel** aChannel) {
+  AssertIsOnMainThread();
+
+  nsresult rv;
+  nsCOMPtr<nsIURI> uri = aScriptURL;
+
+  // Only use the document when its principal matches the principal of the
+  // current request. This means scripts fetched using the Workers' own
+  // principal won't inherit properties of the document, in particular the CSP.
+  if (parentDoc && parentDoc->NodePrincipal() != principal) {
+    parentDoc = nullptr;
+  }
+
+  // The main service worker script should never be loaded over the network
+  // in this path.  It should always be offlined by ServiceWorkerScriptCache.
+  // We assert here since this error should also be caught by the runtime
+  // check in CacheLoadHandler.
+  //
+  // Note, if we ever allow service worker scripts to be loaded from network
+  // here we need to configure the channel properly.  For example, it must
+  // not allow redirects.
+  MOZ_DIAGNOSTIC_ASSERT(aContentPolicyType !=
+                        nsIContentPolicy::TYPE_INTERNAL_SERVICE_WORKER);
+
+  nsCOMPtr<nsIChannel> channel;
+  if (parentDoc) {
+    // This is the path for top level dedicated worker scripts with a document
+    rv = NS_NewChannel(getter_AddRefs(channel), uri, parentDoc, aSecFlags,
+                       aContentPolicyType,
+                       nullptr,  // aPerformanceStorage
+                       loadGroup,
+                       nullptr,  // aCallbacks
+                       aLoadFlags, ios);
+    NS_ENSURE_SUCCESS(rv, NS_ERROR_DOM_SECURITY_ERR);
+  } else {
+    // This branch is used in the following cases:
+    //    * Shared and ServiceWorkers (who do not have a doc)
+    //    * Static Module Imports
+    //    * ImportScripts
+
+    // We must have a loadGroup with a load context for the principal to
+    // traverse the channel correctly.
+
+    MOZ_ASSERT(loadGroup);
+    MOZ_ASSERT(NS_LoadGroupMatchesPrincipal(loadGroup, principal));
+
+    RefPtr<PerformanceStorage> performanceStorage;
+    nsCOMPtr<nsICSPEventListener> cspEventListener;
+    if (aWorkerPrivate && !aIsMainScript) {
+      performanceStorage = aWorkerPrivate->GetPerformanceStorage();
+      cspEventListener = aWorkerPrivate->CSPEventListener();
+    }
+
+    if (aClientInfo.isSome()) {
+      // If we have an existing clientInfo (true for all modules and
+      // importScripts), we will use this branch
+      rv = NS_NewChannel(getter_AddRefs(channel), uri, principal,
+                         aClientInfo.ref(), aController, aSecFlags,
+                         aContentPolicyType, aCookieJarSettings,
+                         performanceStorage, loadGroup, nullptr,  // aCallbacks
+                         aLoadFlags, ios);
+    } else {
+      rv = NS_NewChannel(getter_AddRefs(channel), uri, principal, aSecFlags,
+                         aContentPolicyType, aCookieJarSettings,
+                         performanceStorage, loadGroup, nullptr,  // aCallbacks
+                         aLoadFlags, ios);
+    }
+
+    NS_ENSURE_SUCCESS(rv, NS_ERROR_DOM_SECURITY_ERR);
+
+    if (cspEventListener) {
+      nsCOMPtr<nsILoadInfo> loadInfo = channel->LoadInfo();
+      rv = loadInfo->SetCspEventListener(cspEventListener);
+      NS_ENSURE_SUCCESS(rv, rv);
+    }
+  }
+
+  if (aReferrerInfo) {
+    nsCOMPtr<nsIHttpChannel> httpChannel = do_QueryInterface(channel);
+    if (httpChannel) {
+      rv = httpChannel->SetReferrerInfo(aReferrerInfo);
+      if (NS_WARN_IF(NS_FAILED(rv))) {
+        return rv;
+      }
+    }
+  }
+
+  channel.forget(aChannel);
+  return rv;
+}
+
+void LoadAllScripts(WorkerPrivate* aWorkerPrivate,
+                    UniquePtr<SerializedStackHolder> aOriginStack,
+                    const nsTArray<nsString>& aScriptURLs, bool aIsMainScript,
+                    WorkerScriptType aWorkerScriptType, ErrorResult& aRv,
+                    const mozilla::Encoding* aDocumentEncoding = nullptr) {
+  aWorkerPrivate->AssertIsOnWorkerThread();
+  NS_ASSERTION(!aScriptURLs.IsEmpty(), "Bad arguments!");
+
+  AutoSyncLoopHolder syncLoop(aWorkerPrivate, Canceling);
+  nsCOMPtr<nsISerialEventTarget> syncLoopTarget =
+      syncLoop.GetSerialEventTarget();
+  if (!syncLoopTarget) {
+    aRv.Throw(NS_ERROR_DOM_INVALID_STATE_ERR);
+    return;
+  }
+
+  RefPtr<loader::WorkerScriptLoader> loader =
+      loader::WorkerScriptLoader::Create(
+          aWorkerPrivate, std::move(aOriginStack), syncLoopTarget,
+          aWorkerScriptType, aRv);
+
+  if (NS_WARN_IF(aRv.Failed())) {
+    return;
+  }
+
+  bool ok = loader->CreateScriptRequests(aScriptURLs, aDocumentEncoding,
+                                         aIsMainScript);
+
+  if (!ok) {
+    return;
+  }
+  // Bug 1817259 - For now, we force loading the debugger script as Classic,
+  // even if the debugged worker is a Module.
+  if (aWorkerPrivate->WorkerType() == WorkerType::Module &&
+      aWorkerScriptType != DebuggerScript) {
+    if (!StaticPrefs::dom_workers_modules_enabled()) {
+      aRv.Throw(NS_ERROR_DOM_INVALID_STATE_ERR);
+      return;
+    }
+    MOZ_ASSERT(aIsMainScript);
+    // Module Load
+    RefPtr<JS::loader::ScriptLoadRequest> mainScript = loader->GetMainScript();
+    if (mainScript && mainScript->IsModuleRequest()) {
+      if (NS_FAILED(mainScript->AsModuleRequest()->StartModuleLoad())) {
+        return;
+      }
+      syncLoop.Run();
+      return;
+    }
+  }
+
+  if (loader->DispatchLoadScripts()) {
+    syncLoop.Run();
+  }
+}
+
+class ChannelGetterRunnable final : public WorkerMainThreadRunnable {
+  const nsAString& mScriptURL;
+  const WorkerType& mWorkerType;
+  const RequestCredentials& mCredentials;
+  const ClientInfo mClientInfo;
+  WorkerLoadInfo& mLoadInfo;
+  nsresult mResult;
+
+ public:
+  ChannelGetterRunnable(WorkerPrivate* aParentWorker,
+                        const nsAString& aScriptURL,
+                        const WorkerType& aWorkerType,
+                        const RequestCredentials& aCredentials,
+                        WorkerLoadInfo& aLoadInfo)
+      : WorkerMainThreadRunnable(aParentWorker,
+                                 "ScriptLoader :: ChannelGetter"_ns),
+        mScriptURL(aScriptURL)
+        // ClientInfo should always be present since this should not be called
+        // if parent's status is greater than Running.
+        ,
+        mWorkerType(aWorkerType),
+        mCredentials(aCredentials),
+        mClientInfo(aParentWorker->GlobalScope()->GetClientInfo().ref()),
+        mLoadInfo(aLoadInfo),
+        mResult(NS_ERROR_FAILURE) {
+    MOZ_ASSERT(aParentWorker);
+    aParentWorker->AssertIsOnWorkerThread();
+  }
+
+  virtual bool MainThreadRun() override {
+    AssertIsOnMainThread();
+
+    // Initialize the WorkerLoadInfo principal to our triggering principal
+    // before doing anything else.  Normally we do this in the WorkerPrivate
+    // Constructor, but we can't do so off the main thread when creating
+    // a nested worker.  So do it here instead.
+    mLoadInfo.mLoadingPrincipal = mWorkerPrivate->GetPrincipal();
+    MOZ_DIAGNOSTIC_ASSERT(mLoadInfo.mLoadingPrincipal);
+
+    mLoadInfo.mPrincipal = mLoadInfo.mLoadingPrincipal;
+
+    // Figure out our base URI.
+    nsCOMPtr<nsIURI> baseURI = mWorkerPrivate->GetBaseURI();
+    MOZ_ASSERT(baseURI);
+
+    // May be null.
+    nsCOMPtr<Document> parentDoc = mWorkerPrivate->GetDocument();
+
+    mLoadInfo.mLoadGroup = mWorkerPrivate->GetLoadGroup();
+    mLoadInfo.mCookieJarSettings = mWorkerPrivate->CookieJarSettings();
+
+    // Nested workers use default uri encoding.
+    nsCOMPtr<nsIURI> url;
+    mResult = ConstructURI(mScriptURL, baseURI, nullptr, getter_AddRefs(url));
+    NS_ENSURE_SUCCESS(mResult, true);
+
+    Maybe<ClientInfo> clientInfo;
+    clientInfo.emplace(mClientInfo);
+
+    nsCOMPtr<nsIChannel> channel;
+    nsCOMPtr<nsIReferrerInfo> referrerInfo =
+        ReferrerInfo::CreateForFetch(mLoadInfo.mLoadingPrincipal, nullptr);
+    mLoadInfo.mReferrerInfo =
+        static_cast<ReferrerInfo*>(referrerInfo.get())
+            ->CloneWithNewPolicy(mWorkerPrivate->GetReferrerPolicy());
+
+    mResult = workerinternals::ChannelFromScriptURLMainThread(
+        mLoadInfo.mLoadingPrincipal, parentDoc, mLoadInfo.mLoadGroup, url,
+        mWorkerType, mCredentials, clientInfo,
+        // Nested workers are always dedicated.
+        nsIContentPolicy::TYPE_INTERNAL_WORKER, mLoadInfo.mCookieJarSettings,
+        mLoadInfo.mReferrerInfo, getter_AddRefs(channel));
+    NS_ENSURE_SUCCESS(mResult, true);
+
+    mResult = mLoadInfo.SetPrincipalsAndCSPFromChannel(channel);
+    NS_ENSURE_SUCCESS(mResult, true);
+
+    mLoadInfo.mChannel = std::move(channel);
+    return true;
+  }
+
+  nsresult GetResult() const { return mResult; }
+
+ private:
+  virtual ~ChannelGetterRunnable() = default;
+};
+
+nsresult GetCommonSecFlags(bool aIsMainScript, nsIURI* uri,
+                           nsIPrincipal* principal,
+                           WorkerScriptType aWorkerScriptType,
+                           uint32_t& secFlags) {
+  bool inheritAttrs = nsContentUtils::ChannelShouldInheritPrincipal(
+      principal, uri, true /* aInheritForAboutBlank */,
+      false /* aForceInherit */);
+
+  bool isData = uri->SchemeIs("data");
+  if (inheritAttrs && !isData) {
+    secFlags |= nsILoadInfo::SEC_FORCE_INHERIT_PRINCIPAL;
+  }
+
+  if (aWorkerScriptType == DebuggerScript) {
+    // A DebuggerScript needs to be a local resource like chrome: or resource:
+    bool isUIResource = false;
+    nsresult rv = NS_URIChainHasFlags(
+        uri, nsIProtocolHandler::URI_IS_UI_RESOURCE, &isUIResource);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    if (!isUIResource) {
+      return NS_ERROR_DOM_SECURITY_ERR;
+    }
+
+    secFlags |= nsILoadInfo::SEC_ALLOW_CHROME;
+  }
+
+  // Note: this is for backwards compatibility and goes against spec.
+  // We should find a better solution.
+  if (aIsMainScript && isData) {
+    secFlags = nsILoadInfo::SEC_ALLOW_CROSS_ORIGIN_SEC_CONTEXT_IS_NULL;
+  }
+
+  return NS_OK;
+}
+
+nsresult GetModuleSecFlags(bool aIsTopLevel, nsIPrincipal* principal,
+                           WorkerScriptType aWorkerScriptType, nsIURI* aURI,
+                           RequestCredentials aCredentials,
+                           uint32_t& secFlags) {
+  // Implements "To fetch a single module script,"
+  // Step 9. If destination is "worker", "sharedworker", or "serviceworker",
+  //         and the top-level module fetch flag is set, then set request's
+  //         mode to "same-origin".
+
+  // Step 8. Let request be a new request whose [...] mode is "cors" [...]
+  secFlags = aIsTopLevel ? nsILoadInfo::SEC_REQUIRE_SAME_ORIGIN_DATA_IS_BLOCKED
+                         : nsILoadInfo::SEC_REQUIRE_CORS_INHERITS_SEC_CONTEXT;
+
+  // This implements the same Cookie settings as  nsContentSecurityManager's
+  // ComputeSecurityFlags. The main difference is the line above, Step 9,
+  // setting to same origin.
+
+  if (aCredentials == RequestCredentials::Include) {
+    secFlags |= nsILoadInfo::nsILoadInfo::SEC_COOKIES_INCLUDE;
+  } else if (aCredentials == RequestCredentials::Same_origin) {
+    secFlags |= nsILoadInfo::nsILoadInfo::SEC_COOKIES_SAME_ORIGIN;
+  } else if (aCredentials == RequestCredentials::Omit) {
+    secFlags |= nsILoadInfo::nsILoadInfo::SEC_COOKIES_OMIT;
+  }
+
+  return GetCommonSecFlags(aIsTopLevel, aURI, principal, aWorkerScriptType,
+                           secFlags);
+}
+
+nsresult GetClassicSecFlags(bool aIsMainScript, nsIURI* uri,
+                            nsIPrincipal* principal,
+                            WorkerScriptType aWorkerScriptType,
+                            uint32_t& secFlags) {
+  secFlags = aIsMainScript
+                 ? nsILoadInfo::SEC_REQUIRE_SAME_ORIGIN_DATA_IS_BLOCKED
+                 : nsILoadInfo::SEC_ALLOW_CROSS_ORIGIN_INHERITS_SEC_CONTEXT;
+
+  return GetCommonSecFlags(aIsMainScript, uri, principal, aWorkerScriptType,
+                           secFlags);
+}
+
+}  //  anonymous namespace
+
+namespace loader {
+
+class ScriptExecutorRunnable final : public MainThreadWorkerSyncRunnable {
+  RefPtr<WorkerScriptLoader> mScriptLoader;
+  const Span<RefPtr<ThreadSafeRequestHandle>> mLoadedRequests;
+
+ public:
+  ScriptExecutorRunnable(WorkerScriptLoader* aScriptLoader,
+                         WorkerPrivate* aWorkerPrivate,
+                         nsISerialEventTarget* aSyncLoopTarget,
+                         Span<RefPtr<ThreadSafeRequestHandle>> aLoadedRequests);
+
+ private:
+  ~ScriptExecutorRunnable() = default;
+
+  virtual bool IsDebuggerRunnable() const override;
+
+  virtual bool PreRun(WorkerPrivate* aWorkerPrivate) override;
+
+  bool ProcessModuleScript(JSContext* aCx, WorkerPrivate* aWorkerPrivate);
+
+  bool ProcessClassicScripts(JSContext* aCx, WorkerPrivate* aWorkerPrivate);
+
+  virtual bool WorkerRun(JSContext* aCx,
+                         WorkerPrivate* aWorkerPrivate) override;
+
+  nsresult Cancel() override;
+};
+
+static bool EvaluateSourceBuffer(JSContext* aCx, JS::Handle<JSScript*> aScript,
+                                 JS::loader::ClassicScript* aClassicScript) {
+  if (aClassicScript) {
+    aClassicScript->AssociateWithScript(aScript);
+  }
+
+  JS::Rooted<JS::Value> unused(aCx);
+  return JS_ExecuteScript(aCx, aScript, &unused);
+}
+
+WorkerScriptLoader::WorkerScriptLoader(
+    UniquePtr<SerializedStackHolder> aOriginStack,
+    nsISerialEventTarget* aSyncLoopTarget, WorkerScriptType aWorkerScriptType,
+    ErrorResult& aRv)
+    : mOriginStack(std::move(aOriginStack)),
+      mSyncLoopTarget(aSyncLoopTarget),
+      mWorkerScriptType(aWorkerScriptType),
+      mRv(aRv),
+      mLoadingModuleRequestCount(0),
+      mCleanedUp(false),
+      mCleanUpLock("cleanUpLock") {}
+
+already_AddRefed<WorkerScriptLoader> WorkerScriptLoader::Create(
+    WorkerPrivate* aWorkerPrivate,
+    UniquePtr<SerializedStackHolder> aOriginStack,
+    nsISerialEventTarget* aSyncLoopTarget, WorkerScriptType aWorkerScriptType,
+    ErrorResult& aRv) {
+  aWorkerPrivate->AssertIsOnWorkerThread();
+
+  RefPtr<WorkerScriptLoader> self = new WorkerScriptLoader(
+      std::move(aOriginStack), aSyncLoopTarget, aWorkerScriptType, aRv);
+
+  RefPtr<StrongWorkerRef> workerRef = StrongWorkerRef::Create(
+      aWorkerPrivate, "WorkerScriptLoader::Create", [self]() {
+        // Requests that are in flight are covered by the worker references
+        // in DispatchLoadScript(s), so we do not need to do additional
+        // cleanup, but just in case we are ready/aborted we can try to
+        // shutdown here, too.
+        self->TryShutdown();
+      });
+
+  if (workerRef) {
+    self->mWorkerRef = new ThreadSafeWorkerRef(workerRef);
+  } else {
+    self->mRv.Throw(NS_ERROR_FAILURE);
+    return nullptr;
+  }
+
+  nsIGlobalObject* global = self->GetGlobal();
+  self->mController = global->GetController();
+
+  if (!StaticPrefs::dom_workers_modules_enabled()) {
+    return self.forget();
+  }
+
+  // Set up the module loader, if it has not been initialzied yet.
+  if (!aWorkerPrivate->IsServiceWorker()) {
+    self->InitModuleLoader();
+  }
+
+  return self.forget();
+}
+
+ScriptLoadRequest* WorkerScriptLoader::GetMainScript() {
+  mWorkerRef->Private()->AssertIsOnWorkerThread();
+  ScriptLoadRequest* request = mLoadingRequests.getFirst();
+  if (request->GetWorkerLoadContext()->IsTopLevel()) {
+    return request;
+  }
+  return nullptr;
+}
+
+void WorkerScriptLoader::InitModuleLoader() {
+  mWorkerRef->Private()->AssertIsOnWorkerThread();
+  if (GetGlobal()->GetModuleLoader(nullptr)) {
+    return;
+  }
+  RefPtr<WorkerModuleLoader> moduleLoader =
+      new WorkerModuleLoader(this, GetGlobal());
+  if (mWorkerScriptType == WorkerScript) {
+    mWorkerRef->Private()->GlobalScope()->InitModuleLoader(moduleLoader);
+    return;
+  }
+  mWorkerRef->Private()->DebuggerGlobalScope()->InitModuleLoader(moduleLoader);
+}
+
+bool WorkerScriptLoader::CreateScriptRequests(
+    const nsTArray<nsString>& aScriptURLs,
+    const mozilla::Encoding* aDocumentEncoding, bool aIsMainScript) {
+  mWorkerRef->Private()->AssertIsOnWorkerThread();
+  // If a worker has been loaded as a module worker, ImportScripts calls are
+  // disallowed -- then the operation is invalid.
+  //
+  // 10.3.1 Importing scripts and libraries.
+  // Step 1. If worker global scope's type is "module", throw a TypeError
+  //         exception.
+  //
+  // Also, for now, the debugger script is always loaded as Classic,
+  // even if the debugged worker is a Module. We still want to allow
+  // it to use importScripts.
+  if (mWorkerRef->Private()->WorkerType() == WorkerType::Module &&
+      !aIsMainScript && !IsDebuggerScript()) {
+    // This should only run for non-main scripts, as only these are
+    // importScripts
+    mRv.ThrowTypeError(
+        "Using `ImportScripts` inside a Module Worker is "
+        "disallowed.");
+    return false;
+  }
+  for (const nsString& scriptURL : aScriptURLs) {
+    RefPtr<ScriptLoadRequest> request =
+        CreateScriptLoadRequest(scriptURL, aDocumentEncoding, aIsMainScript);
+    if (!request) {
+      return false;
+    }
+    mLoadingRequests.AppendElement(request);
+  }
+
+  return true;
+}
+
+nsTArray<RefPtr<ThreadSafeRequestHandle>> WorkerScriptLoader::GetLoadingList() {
+  mWorkerRef->Private()->AssertIsOnWorkerThread();
+  nsTArray<RefPtr<ThreadSafeRequestHandle>> list;
+  for (ScriptLoadRequest* req = mLoadingRequests.getFirst(); req;
+       req = req->getNext()) {
+    RefPtr<ThreadSafeRequestHandle> handle =
+        new ThreadSafeRequestHandle(req, mSyncLoopTarget.get());
+    list.AppendElement(handle.forget());
+  }
+  return list;
+}
+
+bool WorkerScriptLoader::IsDynamicImport(ScriptLoadRequest* aRequest) {
+  return aRequest->IsModuleRequest() &&
+         aRequest->AsModuleRequest()->IsDynamicImport();
+}
+
+nsContentPolicyType WorkerScriptLoader::GetContentPolicyType(
+    ScriptLoadRequest* aRequest) {
+  if (aRequest->GetWorkerLoadContext()->IsTopLevel()) {
+    // Implements https://html.spec.whatwg.org/#worker-processing-model
+    // Step 13: Let destination be "sharedworker" if is shared is true, and
+    // "worker" otherwise.
+    return mWorkerRef->Private()->ContentPolicyType();
+  }
+  if (aRequest->IsModuleRequest()) {
+    if (aRequest->AsModuleRequest()->IsDynamicImport()) {
+      return nsIContentPolicy::TYPE_INTERNAL_MODULE;
+    }
+
+    // Implements the destination for Step 14 in
+    // https://html.spec.whatwg.org/#worker-processing-model
+    //
+    // We need a special subresource type in order to correctly implement
+    // the graph fetch, where the destination is set to "worker" or
+    // "sharedworker".
+    return nsIContentPolicy::TYPE_INTERNAL_WORKER_STATIC_MODULE;
+  }
+  // For script imported in worker's importScripts().
+  return nsIContentPolicy::TYPE_INTERNAL_WORKER_IMPORT_SCRIPTS;
+}
+
+already_AddRefed<ScriptLoadRequest> WorkerScriptLoader::CreateScriptLoadRequest(
+    const nsString& aScriptURL, const mozilla::Encoding* aDocumentEncoding,
+    bool aIsMainScript) {
+  mWorkerRef->Private()->AssertIsOnWorkerThread();
+  WorkerLoadContext::Kind kind =
+      WorkerLoadContext::GetKind(aIsMainScript, IsDebuggerScript());
+
+  Maybe<ClientInfo> clientInfo = GetGlobal()->GetClientInfo();
+
+  // (For non-serviceworkers, this variable does not matter, but false best
+  // captures their behavior.)
+  bool onlyExistingCachedResourcesAllowed = false;
+  if (mWorkerRef->Private()->IsServiceWorker()) {
+    // https://w3c.github.io/ServiceWorker/#importscripts step 4:
+    // > 4. If serviceWorker’s state is not "parsed" or "installing":
+    // >    1. Return map[url] if it exists and a network error otherwise.
+    //
+    // So if our state is beyond installing, it's too late to make a request
+    // that would perform a new fetch which would be cached.
+    onlyExistingCachedResourcesAllowed =
+        mWorkerRef->Private()->GetServiceWorkerDescriptor().State() >
+        ServiceWorkerState::Installing;
+  }
+  RefPtr<WorkerLoadContext> loadContext = new WorkerLoadContext(
+      kind, clientInfo, this, onlyExistingCachedResourcesAllowed);
+
+  // Create ScriptLoadRequests for this WorkerScriptLoader
+  ReferrerPolicy referrerPolicy = mWorkerRef->Private()->GetReferrerPolicy();
+
+  // Only top level workers' main script use the document charset for the
+  // script uri encoding. Otherwise, default encoding (UTF-8) is applied.
+  MOZ_ASSERT_IF(bool(aDocumentEncoding),
+                aIsMainScript && !mWorkerRef->Private()->GetParent());
+  nsCOMPtr<nsIURI> baseURI = aIsMainScript ? GetInitialBaseURI() : GetBaseURI();
+  nsCOMPtr<nsIURI> uri;
+  bool setErrorResult = false;
+  nsresult rv =
+      ConstructURI(aScriptURL, baseURI, aDocumentEncoding, getter_AddRefs(uri));
+  // If we failed to construct the URI, handle it in the LoadContext so it is
+  // thrown in the right order.
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    setErrorResult = true;
+    loadContext->mLoadResult = rv;
+  }
+
+  // https://html.spec.whatwg.org/multipage/webappapis.html#fetch-a-classic-worker-script
+  // Step 2.5. Let script be the result [...] and the default classic script
+  // fetch options.
+  //
+  // https://html.spec.whatwg.org/multipage/webappapis.html#fetch-a-worklet/module-worker-script-graph
+  // Step 1. Let options be a script fetch options whose cryptographic nonce is
+  // the empty string, integrity metadata is the empty string, parser metadata
+  // is "not-parser-inserted", credentials mode is credentials mode, referrer
+  // policy is the empty string, and fetch priority is "auto".
+  RefPtr<ScriptFetchOptions> fetchOptions = new ScriptFetchOptions(
+      CORSMode::CORS_NONE, /* aNonce = */ u""_ns, RequestPriority::Auto,
+      ParserMetadata::NotParserInserted, nullptr);
+
+  RefPtr<ScriptLoadRequest> request = nullptr;
+  // Bug 1817259 - For now the debugger scripts are always loaded a Classic.
+  if (mWorkerRef->Private()->WorkerType() == WorkerType::Classic ||
+      IsDebuggerScript()) {
+    request = new ScriptLoadRequest(ScriptKind::eClassic, uri, referrerPolicy,
+                                    fetchOptions, SRIMetadata(),
+                                    nullptr,  // mReferrer
+                                    loadContext);
+  } else {
+    // Implements part of "To fetch a worklet/module worker script graph"
+    // including, setting up the request with a credentials mode,
+    // destination.
+
+    // Step 1. Let options be a script fetch options.
+    // We currently don't track credentials in our ScriptFetchOptions
+    // implementation, so we are defaulting the fetchOptions object defined
+    // above. This behavior is handled fully in GetModuleSecFlags.
+
+    if (!StaticPrefs::dom_workers_modules_enabled()) {
+      mRv.ThrowTypeError("Modules in workers are currently disallowed.");
+      return nullptr;
+    }
+    RefPtr<WorkerModuleLoader::ModuleLoaderBase> moduleLoader =
+        GetGlobal()->GetModuleLoader(nullptr);
+
+    // Implements the referrer for "To fetch a single module script"
+    // Our implementation does not have a "client" as a referrer.
+    // However, when client is resolved (per 8.3. Determine request’s
+    // Referrer in
+    // https://w3c.github.io/webappsec-referrer-policy/#determine-requests-referrer)
+    // This should result in the referrer source being the creation URL.
+    //
+    // In subresource modules, the referrer is the importing script.
+    nsCOMPtr<nsIURI> referrer =
+        mWorkerRef->Private()->GetReferrerInfo()->GetOriginalReferrer();
+
+    // Part of Step 2. This sets the Top-level flag to true
+    request = new ModuleLoadRequest(
+        uri, referrerPolicy, fetchOptions, SRIMetadata(), referrer, loadContext,
+        true,  /* is top level */
+        false, /* is dynamic import */
+        moduleLoader, ModuleLoadRequest::NewVisitedSetForTopLevelImport(uri),
+        nullptr);
+  }
+
+  // Set the mURL, it will be used for error handling and debugging.
+  request->mURL = NS_ConvertUTF16toUTF8(aScriptURL);
+
+  if (setErrorResult) {
+    request->SetPendingFetchingError();
+  } else {
+    request->NoCacheEntryFound();
+  }
+
+  return request.forget();
+}
+
+bool WorkerScriptLoader::DispatchLoadScript(ScriptLoadRequest* aRequest) {
+  mWorkerRef->Private()->AssertIsOnWorkerThread();
+
+  IncreaseLoadingModuleRequestCount();
+
+  nsTArray<RefPtr<ThreadSafeRequestHandle>> scriptLoadList;
+  RefPtr<ThreadSafeRequestHandle> handle =
+      new ThreadSafeRequestHandle(aRequest, mSyncLoopTarget.get());
+  scriptLoadList.AppendElement(handle.forget());
+
+  RefPtr<ScriptLoaderRunnable> runnable =
+      new ScriptLoaderRunnable(this, std::move(scriptLoadList));
+
+  RefPtr<StrongWorkerRef> workerRef = StrongWorkerRef::Create(
+      mWorkerRef->Private(), "WorkerScriptLoader::DispatchLoadScript",
+      [runnable]() {
+        NS_DispatchToMainThread(NewRunnableMethod(
+            "ScriptLoaderRunnable::CancelMainThreadWithBindingAborted",
+            runnable,
+            &ScriptLoaderRunnable::CancelMainThreadWithBindingAborted));
+      });
+
+  if (NS_FAILED(NS_DispatchToMainThread(runnable))) {
+    NS_ERROR("Failed to dispatch!");
+    mRv.Throw(NS_ERROR_FAILURE);
+    return false;
+  }
+  return true;
+}
+
+bool WorkerScriptLoader::DispatchLoadScripts() {
+  mWorkerRef->Private()->AssertIsOnWorkerThread();
+
+  nsTArray<RefPtr<ThreadSafeRequestHandle>> scriptLoadList = GetLoadingList();
+
+  RefPtr<ScriptLoaderRunnable> runnable =
+      new ScriptLoaderRunnable(this, std::move(scriptLoadList));
+
+  RefPtr<StrongWorkerRef> workerRef = StrongWorkerRef::Create(
+      mWorkerRef->Private(), "WorkerScriptLoader::DispatchLoadScripts",
+      [runnable]() {
+        NS_DispatchToMainThread(NewRunnableMethod(
+            "ScriptLoaderRunnable::CancelMainThreadWithBindingAborted",
+            runnable,
+            &ScriptLoaderRunnable::CancelMainThreadWithBindingAborted));
+      });
+
+  if (NS_FAILED(NS_DispatchToMainThread(runnable))) {
+    NS_ERROR("Failed to dispatch!");
+    mRv.Throw(NS_ERROR_FAILURE);
+    return false;
+  }
+  return true;
+}
+
+nsIURI* WorkerScriptLoader::GetInitialBaseURI() {
+  MOZ_ASSERT(mWorkerRef->Private());
+  nsIURI* baseURI;
+  WorkerPrivate* parentWorker = mWorkerRef->Private()->GetParent();
+  if (parentWorker) {
+    baseURI = parentWorker->GetBaseURI();
+  } else {
+    // May be null.
+    baseURI = mWorkerRef->Private()->GetBaseURI();
+  }
+
+  return baseURI;
+}
+
+nsIURI* WorkerScriptLoader::GetBaseURI() const {
+  MOZ_ASSERT(mWorkerRef);
+  nsIURI* baseURI;
+  baseURI = mWorkerRef->Private()->GetBaseURI();
+  NS_ASSERTION(baseURI, "Should have been set already!");
+
+  return baseURI;
+}
+
+nsIGlobalObject* WorkerScriptLoader::GetGlobal() {
+  mWorkerRef->Private()->AssertIsOnWorkerThread();
+  return mWorkerScriptType == WorkerScript
+             ? static_cast<nsIGlobalObject*>(
+                   mWorkerRef->Private()->GlobalScope())
+             : mWorkerRef->Private()->DebuggerGlobalScope();
+}
+
+void WorkerScriptLoader::MaybeMoveToLoadedList(ScriptLoadRequest* aRequest) {
+  mWorkerRef->Private()->AssertIsOnWorkerThread();
+  // Only set to ready for regular scripts. Module loader will set the script to
+  // ready if it is a Module Request.
+  if (!aRequest->IsModuleRequest()) {
+    aRequest->SetReady();
+  }
+
+  // If the request is not in a list, we are in an illegal state.
+  MOZ_RELEASE_ASSERT(aRequest->isInList());
+
+  while (!mLoadingRequests.isEmpty()) {
+    ScriptLoadRequest* request = mLoadingRequests.getFirst();
+    // We need to move requests in post order. If prior requests have not
+    // completed, delay execution.
+    if (!request->IsFinished()) {
+      break;
+    }
+
+    RefPtr<ScriptLoadRequest> req = mLoadingRequests.Steal(request);
+    mLoadedRequests.AppendElement(req);
+  }
+}
+
+bool WorkerScriptLoader::StoreCSP() {
+  // We must be on the same worker as we started on.
+  mWorkerRef->Private()->AssertIsOnWorkerThread();
+
+  if (!mWorkerRef->Private()->GetJSContext()) {
+    return false;
+  }
+
+  MOZ_ASSERT(!mRv.Failed());
+
+  // Move the CSP from the workerLoadInfo in the corresponding Client
+  // where the CSP code expects it!
+  mWorkerRef->Private()->StoreCSPOnClient();
+  return true;
+}
+
+bool WorkerScriptLoader::ProcessPendingRequests(JSContext* aCx) {
+  mWorkerRef->Private()->AssertIsOnWorkerThread();
+  // Don't run if something else has already failed.
+  if (mExecutionAborted) {
+    mLoadedRequests.CancelRequestsAndClear();
+    TryShutdown();
+    return true;
+  }
+
+  // If nothing else has failed, our ErrorResult better not be a failure
+  // either.
+  MOZ_ASSERT(!mRv.Failed(), "Who failed it and why?");
+
+  // Slightly icky action at a distance, but there's no better place to stash
+  // this value, really.
+  JS::Rooted<JSObject*> global(aCx, JS::CurrentGlobalOrNull(aCx));
+  MOZ_ASSERT(global);
+
+  while (!mLoadedRequests.isEmpty()) {
+    RefPtr<ScriptLoadRequest> req = mLoadedRequests.StealFirst();
+    // We don't have a ProcessRequest method (like we do on the DOM), as there
+    // isn't much processing that we need to do per request that isn't related
+    // to evaluation (the processsing done for the DOM is handled in
+    // DataRecievedFrom{Cache,Network} for workers.
+    // So, this inner loop calls EvaluateScript directly. This will change
+    // once modules are introduced as we will have some extra work to do.
+    if (!EvaluateScript(aCx, req)) {
+      req->Cancel();
+      mExecutionAborted = true;
+      WorkerLoadContext* loadContext = req->GetWorkerLoadContext();
+      mMutedErrorFlag = loadContext->mMutedErrorFlag.valueOr(true);
+      mLoadedRequests.CancelRequestsAndClear();
+      break;
+    }
+  }
+
+  TryShutdown();
+  return true;
+}
+
+nsresult WorkerScriptLoader::LoadScript(
+    ThreadSafeRequestHandle* aRequestHandle) {
+  AssertIsOnMainThread();
+
+  WorkerLoadContext* loadContext = aRequestHandle->GetContext();
+  ScriptLoadRequest* request = aRequestHandle->GetRequest();
+  MOZ_ASSERT_IF(loadContext->IsTopLevel(), !IsDebuggerScript());
+
+  // The URL passed to us for loading was invalid, stop loading at this point.
+  if (loadContext->mLoadResult != NS_ERROR_NOT_INITIALIZED) {
+    return loadContext->mLoadResult;
+  }
+
+  WorkerPrivate* parentWorker = mWorkerRef->Private()->GetParent();
+
+  // For JavaScript debugging, the devtools server must run on the same
+  // thread as the debuggee, indicating the worker uses content principal.
+  // However, in Bug 863246, web content will no longer be able to load
+  // resource:// URIs by default, so we need system principal to load
+  // debugger scripts.
+  nsIPrincipal* principal = (IsDebuggerScript())
+                                ? nsContentUtils::GetSystemPrincipal()
+                                : mWorkerRef->Private()->GetPrincipal();
+
+  nsCOMPtr<nsILoadGroup> loadGroup = mWorkerRef->Private()->GetLoadGroup();
+  MOZ_DIAGNOSTIC_ASSERT(principal);
+
+  NS_ENSURE_TRUE(NS_LoadGroupMatchesPrincipal(loadGroup, principal),
+                 NS_ERROR_FAILURE);
+
+  // May be null.
+  nsCOMPtr<Document> parentDoc = mWorkerRef->Private()->GetDocument();
+
+  nsCOMPtr<nsIChannel> channel;
+  if (loadContext->IsTopLevel()) {
+    // May be null.
+    channel = mWorkerRef->Private()->ForgetWorkerChannel();
+  }
+
+  nsCOMPtr<nsIIOService> ios(do_GetIOService());
+
+  nsIScriptSecurityManager* secMan = nsContentUtils::GetSecurityManager();
+  NS_ASSERTION(secMan, "This should never be null!");
+
+  nsresult& rv = loadContext->mLoadResult;
+
+  nsLoadFlags loadFlags = mWorkerRef->Private()->GetLoadFlags();
+
+  // Get the top-level worker.
+  WorkerPrivate* topWorkerPrivate = mWorkerRef->Private();
+  WorkerPrivate* parent = topWorkerPrivate->GetParent();
+  while (parent) {
+    topWorkerPrivate = parent;
+    parent = topWorkerPrivate->GetParent();
+  }
+
+  // If the top-level worker is a dedicated worker and has a window, and the
+  // window has a docshell, the caching behavior of this worker should match
+  // that of that docshell.
+  if (topWorkerPrivate->IsDedicatedWorker()) {
+    nsCOMPtr<nsPIDOMWindowInner> window = topWorkerPrivate->GetWindow();
+    if (window) {
+      nsCOMPtr<nsIDocShell> docShell = window->GetDocShell();
+      if (docShell) {
+        nsresult rv = docShell->GetDefaultLoadFlags(&loadFlags);
+        NS_ENSURE_SUCCESS(rv, rv);
+      }
+    }
+  }
+
+  if (!channel) {
+    nsCOMPtr<nsIReferrerInfo> referrerInfo;
+    uint32_t secFlags;
+    if (request->IsModuleRequest()) {
+      // https://fetch.spec.whatwg.org/#concept-main-fetch
+      // Step 8. If request’s referrer policy is the empty string, then set
+      //         request’s referrer policy to request’s policy container’s
+      //         referrer policy.
+      ReferrerPolicy policy =
+          request->ReferrerPolicy() == ReferrerPolicy::_empty
+              ? mWorkerRef->Private()->GetReferrerPolicy()
+              : request->ReferrerPolicy();
+
+      referrerInfo = new ReferrerInfo(request->mReferrer, policy);
+
+      // https://html.spec.whatwg.org/multipage/webappapis.html#default-classic-script-fetch-options
+      // The default classic script fetch options are a script fetch options
+      // whose ... credentials mode is "same-origin", ....
+      RequestCredentials credentials =
+          mWorkerRef->Private()->WorkerType() == WorkerType::Classic
+              ? RequestCredentials::Same_origin
+              : mWorkerRef->Private()->WorkerCredentials();
+
+      rv = GetModuleSecFlags(loadContext->IsTopLevel(), principal,
+                             mWorkerScriptType, request->mURI, credentials,
+                             secFlags);
+    } else {
+      referrerInfo = ReferrerInfo::CreateForFetch(principal, nullptr);
+      if (parentWorker && !loadContext->IsTopLevel()) {
+        referrerInfo =
+            static_cast<ReferrerInfo*>(referrerInfo.get())
+                ->CloneWithNewPolicy(parentWorker->GetReferrerPolicy());
+      }
+      rv = GetClassicSecFlags(loadContext->IsTopLevel(), request->mURI,
+                              principal, mWorkerScriptType, secFlags);
+    }
+
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    nsContentPolicyType contentPolicyType = GetContentPolicyType(request);
+
+    rv = ChannelFromScriptURL(
+        principal, parentDoc, mWorkerRef->Private(), loadGroup, ios, secMan,
+        request->mURI, loadContext->mClientInfo, mController,
+        loadContext->IsTopLevel(), mWorkerScriptType, contentPolicyType,
+        loadFlags, secFlags, mWorkerRef->Private()->CookieJarSettings(),
+        referrerInfo, getter_AddRefs(channel));
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+  }
+
+  // Associate any originating stack with the channel.
+  if (!mOriginStackJSON.IsEmpty()) {
+    NotifyNetworkMonitorAlternateStack(channel, mOriginStackJSON);
+  }
+
+  // We need to know which index we're on in OnStreamComplete so we know
+  // where to put the result.
+  RefPtr<NetworkLoadHandler> listener =
+      new NetworkLoadHandler(this, aRequestHandle);
+
+  RefPtr<ScriptResponseHeaderProcessor> headerProcessor = nullptr;
+
+  // For each debugger script, a non-debugger script load of the same script
+  // should have occured prior that processed the headers.
+  if (!IsDebuggerScript()) {
+    headerProcessor = MakeRefPtr<ScriptResponseHeaderProcessor>(
+        mWorkerRef->Private(),
+        loadContext->IsTopLevel() && !IsDynamicImport(request),
+        GetContentPolicyType(request) ==
+            nsIContentPolicy::TYPE_INTERNAL_WORKER_IMPORT_SCRIPTS);
+  }
+
+  nsCOMPtr<nsIStreamLoader> loader;
+  rv = NS_NewStreamLoader(getter_AddRefs(loader), listener, headerProcessor);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  if (loadContext->IsTopLevel()) {
+    MOZ_DIAGNOSTIC_ASSERT(loadContext->mClientInfo.isSome());
+
+    // In order to get the correct foreign partitioned prinicpal, we need to
+    // set the `IsThirdPartyContextToTopWindow` to the channel's loadInfo.
+    // This flag reflects the fact that if the worker is created under a
+    // third-party context.
+    nsCOMPtr<nsILoadInfo> loadInfo = channel->LoadInfo();
+    loadInfo->SetIsThirdPartyContextToTopWindow(
+        mWorkerRef->Private()->IsThirdPartyContextToTopWindow());
+
+    Maybe<ClientInfo> clientInfo;
+    clientInfo.emplace(loadContext->mClientInfo.ref());
+    rv = AddClientChannelHelper(channel, std::move(clientInfo),
+                                Maybe<ClientInfo>(),
+                                mWorkerRef->Private()->HybridEventTarget());
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+  }
+
+  if (StaticPrefs::browser_tabs_remote_useCrossOriginEmbedderPolicy()) {
+    nsILoadInfo::CrossOriginEmbedderPolicy respectedCOEP =
+        mWorkerRef->Private()->GetEmbedderPolicy();
+    if (mWorkerRef->Private()->IsDedicatedWorker() &&
+        respectedCOEP == nsILoadInfo::EMBEDDER_POLICY_NULL) {
+      respectedCOEP = mWorkerRef->Private()->GetOwnerEmbedderPolicy();
+    }
+
+    nsCOMPtr<nsILoadInfo> channelLoadInfo = channel->LoadInfo();
+    channelLoadInfo->SetLoadingEmbedderPolicy(respectedCOEP);
+  }
+
+  if (loadContext->mCacheStatus != WorkerLoadContext::ToBeCached) {
+    rv = channel->AsyncOpen(loader);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+  } else {
+    nsCOMPtr<nsIOutputStream> writer;
+
+    // In case we return early.
+    loadContext->mCacheStatus = WorkerLoadContext::Cancel;
+
+    NS_NewPipe(getter_AddRefs(loadContext->mCacheReadStream),
+               getter_AddRefs(writer), 0,
+               UINT32_MAX,    // unlimited size to avoid writer WOULD_BLOCK case
+               true, false);  // non-blocking reader, blocking writer
+
+    nsCOMPtr<nsIStreamListenerTee> tee =
+        do_CreateInstance(NS_STREAMLISTENERTEE_CONTRACTID);
+    rv = tee->Init(loader, writer, listener);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    nsresult rv = channel->AsyncOpen(tee);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+  }
+
+  loadContext->mChannel.swap(channel);
+
+  return NS_OK;
+}
+
+nsresult WorkerScriptLoader::FillCompileOptionsForRequest(
+    JSContext* cx, ScriptLoadRequest* aRequest, JS::CompileOptions* aOptions,
+    JS::MutableHandle<JSScript*> aIntroductionScript) {
+  // The full URL shouldn't be exposed to the debugger. See Bug 1634872
+  aOptions->setFileAndLine(aRequest->mURL.get(), 1);
+  aOptions->setNoScriptRval(true);
+
+  aOptions->setMutedErrors(
+      aRequest->GetWorkerLoadContext()->mMutedErrorFlag.value());
+
+  if (aRequest->mSourceMapURL) {
+    aOptions->setSourceMapURL(aRequest->mSourceMapURL->get());
+  }
+
+  return NS_OK;
+}
+
+bool WorkerScriptLoader::EvaluateScript(JSContext* aCx,
+                                        ScriptLoadRequest* aRequest) {
+  mWorkerRef->Private()->AssertIsOnWorkerThread();
+  MOZ_ASSERT(!IsDynamicImport(aRequest));
+
+  WorkerLoadContext* loadContext = aRequest->GetWorkerLoadContext();
+
+  NS_ASSERTION(!loadContext->mChannel, "Should no longer have a channel!");
+  NS_ASSERTION(aRequest->IsFinished(), "Should be scheduled!");
+
+  MOZ_ASSERT(!mRv.Failed(), "Who failed it and why?");
+  mRv.MightThrowJSException();
+  if (NS_FAILED(loadContext->mLoadResult)) {
+    ReportErrorToConsole(aRequest, loadContext->mLoadResult);
+    return false;
+  }
+
+  // If this is a top level script that succeeded, then mark the
+  // Client execution ready and possible controlled by a service worker.
+  if (loadContext->IsTopLevel()) {
+    if (mController.isSome()) {
+      MOZ_ASSERT(mWorkerScriptType == WorkerScript,
+                 "Debugger clients can't be controlled.");
+      mWorkerRef->Private()->GlobalScope()->Control(mController.ref());
+    }
+    mWorkerRef->Private()->ExecutionReady();
+  }
+
+  if (aRequest->IsModuleRequest()) {
+    // Only the top level module of the module graph will be executed from here,
+    // the rest will be executed from SpiderMonkey as part of the execution of
+    // the module graph.
+    MOZ_ASSERT(aRequest->IsTopLevel());
+    ModuleLoadRequest* request = aRequest->AsModuleRequest();
+    if (!request->mModuleScript) {
+      return false;
+    }
+
+    // https://html.spec.whatwg.org/#run-a-worker
+    // if script's error to rethrow is non-null, then:
+    //    Queue a global task on the DOM manipulation task source given worker's
+    //    relevant global object to fire an event named error at worker.
+    //
+    // The event will be dispatched in CompileScriptRunnable.
+    if (request->mModuleScript->HasParseError()) {
+      // Here we assign an error code that is not a JS Exception, so
+      // CompileRunnable can dispatch the event.
+      mRv.Throw(NS_ERROR_DOM_SYNTAX_ERR);
+      return false;
+    }
+
+    // Implements To fetch a worklet/module worker script graph
+    // Step 5. Fetch the descendants of and link result.
+    if (!request->InstantiateModuleGraph()) {
+      return false;
+    }
+
+    if (request->mModuleScript->HasErrorToRethrow()) {
+      // See the comments when we check HasParseError() above.
+      mRv.Throw(NS_ERROR_DOM_SYNTAX_ERR);
+      return false;
+    }
+
+    nsresult rv = request->EvaluateModule();
+    return NS_SUCCEEDED(rv);
+  }
+
+  JS::CompileOptions options(aCx);
+  // The introduction script is used by the DOM script loader as a way
+  // to fill the Debugger Metadata for the JS Execution context. We don't use
+  // the JS Execution context as we are not making use of async compilation
+  // (delegation to another worker to produce bytecode or compile a string to a
+  // JSScript), so it is not used in this context.
+  JS::Rooted<JSScript*> unusedIntroductionScript(aCx);
+  nsresult rv = FillCompileOptionsForRequest(aCx, aRequest, &options,
+                                             &unusedIntroductionScript);
+
+  MOZ_ASSERT(NS_SUCCEEDED(rv), "Filling compile options should not fail");
+
+  // Our ErrorResult still shouldn't be a failure.
+  MOZ_ASSERT(!mRv.Failed(), "Who failed it and why?");
+
+  // Get the source text.
+  ScriptLoadRequest::MaybeSourceText maybeSource;
+  rv = aRequest->GetScriptSource(aCx, &maybeSource,
+                                 aRequest->mLoadContext.get());
+  if (NS_FAILED(rv)) {
+    mRv.StealExceptionFromJSContext(aCx);
+    return false;
+  }
+
+  RefPtr<JS::loader::ClassicScript> classicScript = nullptr;
+  if (StaticPrefs::dom_workers_modules_enabled() &&
+      !mWorkerRef->Private()->IsServiceWorker()) {
+    // We need a LoadedScript to be associated with the JSScript in order to
+    // correctly resolve the referencing private for dynamic imports. In turn
+    // this allows us to correctly resolve the BaseURL.
+    //
+    // Dynamic import is disallowed on service workers.  Additionally, causes
+    // crashes because the life cycle isn't completed for service workers.  To
+    // keep things simple, we don't create a classic script for ServiceWorkers.
+    // If this changes then we will need to ensure that the reference that is
+    // held is released appropriately.
+    nsCOMPtr<nsIURI> requestBaseURI;
+    if (loadContext->mMutedErrorFlag.valueOr(false)) {
+      NS_NewURI(getter_AddRefs(requestBaseURI), "about:blank"_ns);
+    } else {
+      requestBaseURI = aRequest->mBaseURL;
+    }
+    MOZ_ASSERT(aRequest->mLoadedScript->IsClassicScript());
+    MOZ_ASSERT(aRequest->mLoadedScript->GetFetchOptions() ==
+               aRequest->mFetchOptions);
+    aRequest->mLoadedScript->SetBaseURL(requestBaseURI);
+    classicScript = aRequest->mLoadedScript->AsClassicScript();
+  }
+
+  JS::Rooted<JSScript*> script(aCx);
+  script = aRequest->IsUTF8Text()
+               ? JS::Compile(aCx, options,
+                             maybeSource.ref<JS::SourceText<Utf8Unit>>())
+               : JS::Compile(aCx, options,
+                             maybeSource.ref<JS::SourceText<char16_t>>());
+  if (!script) {
+    if (loadContext->IsTopLevel()) {
+      // This is a top-level worker script,
+      //
+      // https://html.spec.whatwg.org/#run-a-worker
+      // If script is null or if script's error to rethrow is non-null, then:
+      //   Queue a global task on the DOM manipulation task source given
+      //   worker's relevant global object to fire an event named error at
+      //   worker.
+      JS_ClearPendingException(aCx);
+      mRv.Throw(NS_ERROR_DOM_SYNTAX_ERR);
+    } else {
+      // This is a script which is loaded by importScripts().
+      //
+      // https://html.spec.whatwg.org/#import-scripts-into-worker-global-scope
+      // For each url in the resulting URL records:
+      //   Fetch a classic worker-imported script given url and settings object,
+      //   passing along performFetch if provided. If this succeeds, let script
+      //   be the result. Otherwise, rethrow the exception.
+      mRv.StealExceptionFromJSContext(aCx);
+    }
+
+    return false;
+  }
+
+  bool successfullyEvaluated = EvaluateSourceBuffer(aCx, script, classicScript);
+  if (aRequest->IsCanceled()) {
+    return false;
+  }
+  if (!successfullyEvaluated) {
+    mRv.StealExceptionFromJSContext(aCx);
+    return false;
+  }
+  // steal the loadContext so that the cycle is broken and cycle collector can
+  // collect the scriptLoadRequest.
+  return true;
+}
+
+void WorkerScriptLoader::TryShutdown() {
+  {
+    MutexAutoLock lock(CleanUpLock());
+    if (CleanedUp()) {
+      return;
+    }
+  }
+
+  if (AllScriptsExecuted() && AllModuleRequestsLoaded()) {
+    ShutdownScriptLoader(!mExecutionAborted, mMutedErrorFlag);
+  }
+}
+
+void WorkerScriptLoader::ShutdownScriptLoader(bool aResult, bool aMutedError) {
+  MOZ_ASSERT(AllScriptsExecuted());
+  MOZ_ASSERT(AllModuleRequestsLoaded());
+  mWorkerRef->Private()->AssertIsOnWorkerThread();
+
+  if (!aResult) {
+    // At this point there are two possibilities:
+    //
+    // 1) mRv.Failed().  In that case we just want to leave it
+    //    as-is, except if it has a JS exception and we need to mute JS
+    //    exceptions.  In that case, we log the exception without firing any
+    //    events and then replace it on the ErrorResult with a NetworkError,
+    //    per spec.
+    //
+    // 2) mRv succeeded.  As far as I can tell, this can only
+    //    happen when loading the main worker script and
+    //    GetOrCreateGlobalScope() fails or if ScriptExecutorRunnable::Cancel
+    //    got called.  Does it matter what we throw in this case?  I'm not
+    //    sure...
+    if (mRv.Failed()) {
+      if (aMutedError && mRv.IsJSException()) {
+        LogExceptionToConsole(mWorkerRef->Private()->GetJSContext(),
+                              mWorkerRef->Private());
+        mRv.Throw(NS_ERROR_DOM_NETWORK_ERR);
+      }
+    } else {
+      mRv.Throw(NS_ERROR_DOM_INVALID_STATE_ERR);
+    }
+  }
+
+  // Lock, shutdown, and cleanup state. After this the Loader is closed.
+  {
+    MutexAutoLock lock(CleanUpLock());
+
+    if (CleanedUp()) {
+      return;
+    }
+
+    mWorkerRef->Private()->AssertIsOnWorkerThread();
+    // Module loader doesn't use sync loop for dynamic import
+    if (mSyncLoopTarget) {
+      mWorkerRef->Private()->MaybeStopSyncLoop(
+          mSyncLoopTarget, aResult ? NS_OK : NS_ERROR_FAILURE);
+      mSyncLoopTarget = nullptr;
+    }
+
+    // Signal cleanup
+    mCleanedUp = true;
+
+    // Allow worker shutdown.
+    mWorkerRef = nullptr;
+  }
+}
+
+void WorkerScriptLoader::ReportErrorToConsole(ScriptLoadRequest* aRequest,
+                                              nsresult aResult) const {
+  nsAutoString url = NS_ConvertUTF8toUTF16(aRequest->mURL);
+  workerinternals::ReportLoadError(mRv, aResult, url);
+}
+
+void WorkerScriptLoader::LogExceptionToConsole(JSContext* aCx,
+                                               WorkerPrivate* aWorkerPrivate) {
+  aWorkerPrivate->AssertIsOnWorkerThread();
+
+  MOZ_ASSERT(mRv.IsJSException());
+
+  JS::Rooted<JS::Value> exn(aCx);
+  if (!ToJSValue(aCx, std::move(mRv), &exn)) {
+    return;
+  }
+
+  // Now the exception state should all be in exn.
+  MOZ_ASSERT(!JS_IsExceptionPending(aCx));
+  MOZ_ASSERT(!mRv.Failed());
+
+  JS::ExceptionStack exnStack(aCx, exn, nullptr);
+  JS::ErrorReportBuilder report(aCx);
+  if (!report.init(aCx, exnStack, JS::ErrorReportBuilder::WithSideEffects)) {
+    JS_ClearPendingException(aCx);
+    return;
+  }
+
+  RefPtr<xpc::ErrorReport> xpcReport = new xpc::ErrorReport();
+  xpcReport->Init(report.report(), report.toStringResult().c_str(),
+                  aWorkerPrivate->IsChromeWorker(), aWorkerPrivate->WindowID());
+
+  RefPtr<AsyncErrorReporter> r = new AsyncErrorReporter(xpcReport);
+  NS_DispatchToMainThread(r);
+}
+
+bool WorkerScriptLoader::AllModuleRequestsLoaded() const {
+  mWorkerRef->Private()->AssertIsOnWorkerThread();
+  return mLoadingModuleRequestCount == 0;
+}
+
+void WorkerScriptLoader::IncreaseLoadingModuleRequestCount() {
+  mWorkerRef->Private()->AssertIsOnWorkerThread();
+  ++mLoadingModuleRequestCount;
+}
+
+void WorkerScriptLoader::DecreaseLoadingModuleRequestCount() {
+  mWorkerRef->Private()->AssertIsOnWorkerThread();
+  --mLoadingModuleRequestCount;
+}
+
+NS_IMPL_ISUPPORTS(ScriptLoaderRunnable, nsIRunnable, nsINamed)
+
+NS_IMPL_ISUPPORTS(WorkerScriptLoader, nsINamed)
+
+ScriptLoaderRunnable::ScriptLoaderRunnable(
+    WorkerScriptLoader* aScriptLoader,
+    nsTArray<RefPtr<ThreadSafeRequestHandle>> aLoadingRequests)
+    : mScriptLoader(aScriptLoader),
+      mWorkerRef(aScriptLoader->mWorkerRef),
+      mLoadingRequests(std::move(aLoadingRequests)),
+      mCancelMainThread(Nothing()) {
+  MOZ_ASSERT(aScriptLoader);
+}
+
+nsresult ScriptLoaderRunnable::Run() {
+  AssertIsOnMainThread();
+
+  // Convert the origin stack to JSON (which must be done on the main
+  // thread) explicitly, so that we can use the stack to notify the net
+  // monitor about every script we load. We do this, rather than pass
+  // the stack directly to the netmonitor, in order to be able to use this
+  // for all subsequent scripts.
+  if (mScriptLoader->mOriginStack &&
+      mScriptLoader->mOriginStackJSON.IsEmpty()) {
+    ConvertSerializedStackToJSON(std::move(mScriptLoader->mOriginStack),
+                                 mScriptLoader->mOriginStackJSON);
+  }
+
+  if (!mWorkerRef->Private()->IsServiceWorker() ||
+      mScriptLoader->IsDebuggerScript()) {
+    for (ThreadSafeRequestHandle* handle : mLoadingRequests) {
+      handle->mRunnable = this;
+    }
+
+    for (ThreadSafeRequestHandle* handle : mLoadingRequests) {
+      nsresult rv = mScriptLoader->LoadScript(handle);
+      if (NS_WARN_IF(NS_FAILED(rv))) {
+        LoadingFinished(handle, rv);
+        CancelMainThread(rv);
+        return rv;
+      }
+    }
+
+    return NS_OK;
+  }
+
+  MOZ_ASSERT(!mCacheCreator);
+  mCacheCreator = new CacheCreator(mWorkerRef->Private());
+
+  for (ThreadSafeRequestHandle* handle : mLoadingRequests) {
+    handle->mRunnable = this;
+    WorkerLoadContext* loadContext = handle->GetContext();
+    mCacheCreator->AddLoader(MakeNotNull<RefPtr<CacheLoadHandler>>(
+        mWorkerRef, handle, loadContext->IsTopLevel(),
+        loadContext->mOnlyExistingCachedResourcesAllowed, mScriptLoader));
+  }
+
+  // The worker may have a null principal on first load, but in that case its
+  // parent definitely will have one.
+  nsIPrincipal* principal = mWorkerRef->Private()->GetPrincipal();
+  if (!principal) {
+    WorkerPrivate* parentWorker = mWorkerRef->Private()->GetParent();
+    MOZ_ASSERT(parentWorker, "Must have a parent!");
+    principal = parentWorker->GetPrincipal();
+  }
+
+  nsresult rv = mCacheCreator->Load(principal);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    CancelMainThread(rv);
+    return rv;
+  }
+
+  return NS_OK;
+}
+
+nsresult ScriptLoaderRunnable::OnStreamComplete(
+    ThreadSafeRequestHandle* aRequestHandle, nsresult aStatus) {
+  AssertIsOnMainThread();
+
+  LoadingFinished(aRequestHandle, aStatus);
+  return NS_OK;
+}
+
+void ScriptLoaderRunnable::LoadingFinished(
+    ThreadSafeRequestHandle* aRequestHandle, nsresult aRv) {
+  AssertIsOnMainThread();
+
+  WorkerLoadContext* loadContext = aRequestHandle->GetContext();
+
+  loadContext->mLoadResult = aRv;
+  MOZ_ASSERT(!loadContext->mLoadingFinished);
+  loadContext->mLoadingFinished = true;
+
+  if (loadContext->IsTopLevel() && NS_SUCCEEDED(aRv)) {
+    MOZ_DIAGNOSTIC_ASSERT(
+        mWorkerRef->Private()->PrincipalURIMatchesScriptURL());
+  }
+
+  MaybeExecuteFinishedScripts(aRequestHandle);
+}
+
+void ScriptLoaderRunnable::MaybeExecuteFinishedScripts(
+    ThreadSafeRequestHandle* aRequestHandle) {
+  AssertIsOnMainThread();
+
+  // We execute the last step if we don't have a pending operation with the
+  // cache and the loading is completed.
+  WorkerLoadContext* loadContext = aRequestHandle->GetContext();
+  if (!loadContext->IsAwaitingPromise()) {
+    if (aRequestHandle->GetContext()->IsTopLevel()) {
+      mWorkerRef->Private()->WorkerScriptLoaded();
+    }
+    DispatchProcessPendingRequests();
+  }
+}
+
+void ScriptLoaderRunnable::CancelMainThreadWithBindingAborted() {
+  AssertIsOnMainThread();
+  CancelMainThread(NS_BINDING_ABORTED);
+}
+
+void ScriptLoaderRunnable::CancelMainThread(nsresult aCancelResult) {
+  AssertIsOnMainThread();
+  if (IsCancelled()) {
+    return;
+  }
+
+  {
+    MutexAutoLock lock(mScriptLoader->CleanUpLock());
+
+    // Check if we have already cancelled, or if the worker has been killed
+    // before we cancel.
+    if (mScriptLoader->CleanedUp()) {
+      return;
+    }
+
+    mCancelMainThread = Some(aCancelResult);
+
+    for (ThreadSafeRequestHandle* handle : mLoadingRequests) {
+      if (handle->IsEmpty()) {
+        continue;
+      }
+
+      bool callLoadingFinished = true;
+
+      WorkerLoadContext* loadContext = handle->GetContext();
+      if (!loadContext) {
+        continue;
+      }
+
+      if (loadContext->IsAwaitingPromise()) {
+        MOZ_ASSERT(mWorkerRef->Private()->IsServiceWorker());
+        loadContext->mCachePromise->MaybeReject(NS_BINDING_ABORTED);
+        loadContext->mCachePromise = nullptr;
+        callLoadingFinished = false;
+      }
+      if (loadContext->mChannel) {
+        if (NS_SUCCEEDED(loadContext->mChannel->Cancel(aCancelResult))) {
+          callLoadingFinished = false;
+        } else {
+          NS_WARNING("Failed to cancel channel!");
+        }
+      }
+      if (callLoadingFinished && !loadContext->mLoadingFinished) {
+        LoadingFinished(handle, aCancelResult);
+      }
+    }
+    DispatchProcessPendingRequests();
+  }
+}
+
+void ScriptLoaderRunnable::DispatchProcessPendingRequests() {
+  AssertIsOnMainThread();
+
+  const auto begin = mLoadingRequests.begin();
+  const auto end = mLoadingRequests.end();
+  using Iterator = decltype(begin);
+  const auto maybeRangeToExecute =
+      [begin, end]() -> Maybe<std::pair<Iterator, Iterator>> {
+    // firstItToExecute is the first loadInfo where mExecutionScheduled is
+    // unset.
+    auto firstItToExecute = std::find_if(
+        begin, end, [](const RefPtr<ThreadSafeRequestHandle>& requestHandle) {
+          return !requestHandle->mExecutionScheduled;
+        });
+
+    if (firstItToExecute == end) {
+      return Nothing();
+    }
+
+    // firstItUnexecutable is the first loadInfo that is not yet finished.
+    // Update mExecutionScheduled on the ones we're about to schedule for
+    // execution.
+    const auto firstItUnexecutable =
+        std::find_if(firstItToExecute, end,
+                     [](RefPtr<ThreadSafeRequestHandle>& requestHandle) {
+                       MOZ_ASSERT(!requestHandle->IsEmpty());
+                       if (!requestHandle->Finished()) {
+                         return true;
+                       }
+
+                       // We can execute this one.
+                       requestHandle->mExecutionScheduled = true;
+
+                       return false;
+                     });
+
+    return firstItUnexecutable == firstItToExecute
+               ? Nothing()
+               : Some(std::pair(firstItToExecute, firstItUnexecutable));
+  }();
+
+  // If there are no unexecutable load infos, we can unuse things before the
+  // execution of the scripts and the stopping of the sync loop.
+  if (maybeRangeToExecute) {
+    if (maybeRangeToExecute->second == end) {
+      mCacheCreator = nullptr;
+    }
+
+    RefPtr<ScriptExecutorRunnable> runnable = new ScriptExecutorRunnable(
+        mScriptLoader, mWorkerRef->Private(), mScriptLoader->mSyncLoopTarget,
+        Span<RefPtr<ThreadSafeRequestHandle>>{maybeRangeToExecute->first,
+                                              maybeRangeToExecute->second});
+
+    if (!runnable->Dispatch() && mScriptLoader->mSyncLoopTarget) {
+      MOZ_ASSERT(false, "This should never fail!");
+    }
+  }
+}
+
+ScriptExecutorRunnable::ScriptExecutorRunnable(
+    WorkerScriptLoader* aScriptLoader, WorkerPrivate* aWorkerPrivate,
+    nsISerialEventTarget* aSyncLoopTarget,
+    Span<RefPtr<ThreadSafeRequestHandle>> aLoadedRequests)
+    : MainThreadWorkerSyncRunnable(aWorkerPrivate, aSyncLoopTarget,
+                                   "ScriptExecutorRunnable"),
+      mScriptLoader(aScriptLoader),
+      mLoadedRequests(aLoadedRequests) {}
+
+bool ScriptExecutorRunnable::IsDebuggerRunnable() const {
+  // ScriptExecutorRunnable is used to execute both worker and debugger scripts.
+  // In the latter case, the runnable needs to be dispatched to the debugger
+  // queue.
+  return mScriptLoader->IsDebuggerScript();
+}
+
+bool ScriptExecutorRunnable::PreRun(WorkerPrivate* aWorkerPrivate) {
+  aWorkerPrivate->AssertIsOnWorkerThread();
+
+  // We must be on the same worker as we started on.
+  MOZ_ASSERT(
+      mScriptLoader->mSyncLoopTarget == mSyncLoopTarget,
+      "Unexpected SyncLoopTarget. Check if the sync loop was closed early");
+
+  {
+    // There is a possibility that we cleaned up while this task was waiting to
+    // run. If this has happened, return and exit.
+    MutexAutoLock lock(mScriptLoader->CleanUpLock());
+    if (mScriptLoader->CleanedUp()) {
+      return true;
+    }
+
+    const auto& requestHandle = mLoadedRequests[0];
+    // Check if the request is still valid.
+    if (requestHandle->IsEmpty() ||
+        !requestHandle->GetContext()->IsTopLevel()) {
+      return true;
+    }
+  }
+
+  return mScriptLoader->StoreCSP();
+}
+
+bool ScriptExecutorRunnable::ProcessModuleScript(
+    JSContext* aCx, WorkerPrivate* aWorkerPrivate) {
+  // We should only ever have one script when processing modules
+  MOZ_ASSERT(mLoadedRequests.Length() == 1);
+  RefPtr<ScriptLoadRequest> request;
+  {
+    // There is a possibility that we cleaned up while this task was waiting to
+    // run. If this has happened, return and exit.
+    MutexAutoLock lock(mScriptLoader->CleanUpLock());
+    if (mScriptLoader->CleanedUp()) {
+      return true;
+    }
+
+    MOZ_ASSERT(mLoadedRequests.Length() == 1);
+    const auto& requestHandle = mLoadedRequests[0];
+    // The request must be valid.
+    MOZ_ASSERT(!requestHandle->IsEmpty());
+
+    // Release the request to the worker. From this point on, the Request Handle
+    // is empty.
+    request = requestHandle->ReleaseRequest();
+
+    // release lock. We will need it later if we cleanup.
+  }
+
+  MOZ_ASSERT(request->IsModuleRequest());
+
+  WorkerLoadContext* loadContext = request->GetWorkerLoadContext();
+  ModuleLoadRequest* moduleRequest = request->AsModuleRequest();
+
+  // DecreaseLoadingModuleRequestCount must be called before OnFetchComplete.
+  // OnFetchComplete will call ProcessPendingRequests, and in
+  // ProcessPendingRequests it will try to shutdown if
+  // AllModuleRequestsLoaded() returns true.
+  mScriptLoader->DecreaseLoadingModuleRequestCount();
+  moduleRequest->OnFetchComplete(loadContext->mLoadResult);
+
+  if (NS_FAILED(loadContext->mLoadResult)) {
+    if (moduleRequest->IsDynamicImport()) {
+      if (request->isInList()) {
+        moduleRequest->CancelDynamicImport(loadContext->mLoadResult);
+        mScriptLoader->TryShutdown();
+      }
+    } else if (!moduleRequest->IsTopLevel()) {
+      moduleRequest->Cancel();
+      mScriptLoader->TryShutdown();
+    } else {
+      moduleRequest->LoadFailed();
+    }
+  }
+  return true;
+}
+
+bool ScriptExecutorRunnable::ProcessClassicScripts(
+    JSContext* aCx, WorkerPrivate* aWorkerPrivate) {
+  // There is a possibility that we cleaned up while this task was waiting to
+  // run. If this has happened, return and exit.
+  {
+    MutexAutoLock lock(mScriptLoader->CleanUpLock());
+    if (mScriptLoader->CleanedUp()) {
+      return true;
+    }
+
+    for (const auto& requestHandle : mLoadedRequests) {
+      // The request must be valid.
+      MOZ_ASSERT(!requestHandle->IsEmpty());
+
+      // Release the request to the worker. From this point on, the Request
+      // Handle is empty.
+      RefPtr<ScriptLoadRequest> request = requestHandle->ReleaseRequest();
+      mScriptLoader->MaybeMoveToLoadedList(request);
+    }
+  }
+  return mScriptLoader->ProcessPendingRequests(aCx);
+}
+
+bool ScriptExecutorRunnable::WorkerRun(JSContext* aCx,
+                                       WorkerPrivate* aWorkerPrivate) {
+  aWorkerPrivate->AssertIsOnWorkerThread();
+
+  // We must be on the same worker as we started on.
+  MOZ_ASSERT(
+      mScriptLoader->mSyncLoopTarget == mSyncLoopTarget,
+      "Unexpected SyncLoopTarget. Check if the sync loop was closed early");
+
+  if (mLoadedRequests.begin()->get()->GetRequest()->IsModuleRequest()) {
+    return ProcessModuleScript(aCx, aWorkerPrivate);
+  }
+
+  return ProcessClassicScripts(aCx, aWorkerPrivate);
+}
+
+nsresult ScriptExecutorRunnable::Cancel() {
+  if (mScriptLoader->AllScriptsExecuted() &&
+      mScriptLoader->AllModuleRequestsLoaded()) {
+    mScriptLoader->ShutdownScriptLoader(false, false);
+  }
+  return NS_OK;
+}
+
+} /* namespace loader */
+
+nsresult ChannelFromScriptURLMainThread(
+    nsIPrincipal* aPrincipal, Document* aParentDoc, nsILoadGroup* aLoadGroup,
+    nsIURI* aScriptURL, const WorkerType& aWorkerType,
+    const RequestCredentials& aCredentials,
+    const Maybe<ClientInfo>& aClientInfo,
+    nsContentPolicyType aMainScriptContentPolicyType,
+    nsICookieJarSettings* aCookieJarSettings, nsIReferrerInfo* aReferrerInfo,
+    nsIChannel** aChannel) {
+  AssertIsOnMainThread();
+
+  nsCOMPtr<nsIIOService> ios(do_GetIOService());
+
+  nsIScriptSecurityManager* secMan = nsContentUtils::GetSecurityManager();
+  NS_ASSERTION(secMan, "This should never be null!");
+
+  uint32_t secFlags;
+  nsresult rv;
+  if (aWorkerType == WorkerType::Module) {
+    rv = GetModuleSecFlags(true, aPrincipal, WorkerScript, aScriptURL,
+                           aCredentials, secFlags);
+  } else {
+    rv = GetClassicSecFlags(true, aScriptURL, aPrincipal, WorkerScript,
+                            secFlags);
+  }
+  if (NS_FAILED(rv)) {
+    return rv;
+  }
+
+  return ChannelFromScriptURL(
+      aPrincipal, aParentDoc, nullptr, aLoadGroup, ios, secMan, aScriptURL,
+      aClientInfo, Maybe<ServiceWorkerDescriptor>(), true, WorkerScript,
+      aMainScriptContentPolicyType, nsIRequest::LOAD_NORMAL, secFlags,
+      aCookieJarSettings, aReferrerInfo, aChannel);
+}
+
+nsresult ChannelFromScriptURLWorkerThread(
+    JSContext* aCx, WorkerPrivate* aParent, const nsAString& aScriptURL,
+    const WorkerType& aWorkerType, const RequestCredentials& aCredentials,
+    WorkerLoadInfo& aLoadInfo) {
+  aParent->AssertIsOnWorkerThread();
+
+  RefPtr<ChannelGetterRunnable> getter = new ChannelGetterRunnable(
+      aParent, aScriptURL, aWorkerType, aCredentials, aLoadInfo);
+
+  ErrorResult rv;
+  getter->Dispatch(Canceling, rv);
+  if (rv.Failed()) {
+    NS_ERROR("Failed to dispatch!");
+    return rv.StealNSResult();
+  }
+
+  return getter->GetResult();
+}
+
+void ReportLoadError(ErrorResult& aRv, nsresult aLoadResult,
+                     const nsAString& aScriptURL) {
+  MOZ_ASSERT(!aRv.Failed());
+
+  nsPrintfCString err("Failed to load worker script at \"%s\"",
+                      NS_ConvertUTF16toUTF8(aScriptURL).get());
+
+  switch (aLoadResult) {
+    case NS_ERROR_FILE_NOT_FOUND:
+    case NS_ERROR_NOT_AVAILABLE:
+    case NS_ERROR_CORRUPTED_CONTENT:
+      aRv.Throw(NS_ERROR_DOM_NETWORK_ERR);
+      break;
+
+    case NS_ERROR_MALFORMED_URI:
+    case NS_ERROR_DOM_SYNTAX_ERR:
+      aRv.ThrowSyntaxError(err);
+      break;
+
+    case NS_BINDING_ABORTED:
+      // Note: we used to pretend like we didn't set an exception for
+      // NS_BINDING_ABORTED, but then ShutdownScriptLoader did it anyway.  The
+      // other callsite, in WorkerPrivate::Constructor, never passed in
+      // NS_BINDING_ABORTED.  So just throw it directly here.  Consumers will
+      // deal as needed.  But note that we do NOT want to use one of the
+      // Throw*Error() methods on ErrorResult for this case, because that will
+      // make it impossible for consumers to realize that our error was
+      // NS_BINDING_ABORTED.
+      aRv.Throw(aLoadResult);
+      return;
+
+    case NS_ERROR_DOM_BAD_URI:
+      // This is actually a security error.
+    case NS_ERROR_DOM_SECURITY_ERR:
+      aRv.ThrowSecurityError(err);
+      break;
+
+    default:
+      // For lack of anything better, go ahead and throw a NetworkError here.
+      // We don't want to throw a JS exception, because for toplevel script
+      // loads that would get squelched.
+      aRv.ThrowNetworkError(nsPrintfCString(
+          "Failed to load worker script at %s (nsresult = 0x%" PRIx32 ")",
+          NS_ConvertUTF16toUTF8(aScriptURL).get(),
+          static_cast<uint32_t>(aLoadResult)));
+      return;
+  }
+}
+
+void LoadMainScript(WorkerPrivate* aWorkerPrivate,
+                    UniquePtr<SerializedStackHolder> aOriginStack,
+                    const nsAString& aScriptURL,
+                    WorkerScriptType aWorkerScriptType, ErrorResult& aRv,
+                    const mozilla::Encoding* aDocumentEncoding) {
+  nsTArray<nsString> scriptURLs;
+
+  scriptURLs.AppendElement(aScriptURL);
+
+  LoadAllScripts(aWorkerPrivate, std::move(aOriginStack), scriptURLs, true,
+                 aWorkerScriptType, aRv, aDocumentEncoding);
+}
+
+void Load(WorkerPrivate* aWorkerPrivate,
+          UniquePtr<SerializedStackHolder> aOriginStack,
+          const nsTArray<nsString>& aScriptURLs,
+          WorkerScriptType aWorkerScriptType, ErrorResult& aRv) {
+  const uint32_t urlCount = aScriptURLs.Length();
+
+  if (!urlCount) {
+    return;
+  }
+
+  if (urlCount > MAX_CONCURRENT_SCRIPTS) {
+    aRv.Throw(NS_ERROR_OUT_OF_MEMORY);
+    return;
+  }
+
+  LoadAllScripts(aWorkerPrivate, std::move(aOriginStack), aScriptURLs, false,
+                 aWorkerScriptType, aRv);
+}
+
+}  // namespace mozilla::dom::workerinternals
diff --git a/dom/workers/ScriptLoader.h b/dom/workers/ScriptLoader.h
new file mode 100644
index 0000000000..010f3d8316
--- /dev/null
+++ b/dom/workers/ScriptLoader.h
@@ -0,0 +1,380 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_workers_scriptloader_h__
+#define mozilla_dom_workers_scriptloader_h__
+
+#include "js/loader/ScriptLoadRequest.h"
+#include "js/loader/ModuleLoadRequest.h"
+#include "js/loader/ModuleLoaderBase.h"
+#include "mozilla/dom/WorkerBinding.h"
+#include "mozilla/dom/WorkerCommon.h"
+#include "mozilla/dom/WorkerLoadContext.h"
+#include "mozilla/dom/WorkerRef.h"
+#include "mozilla/dom/workerinternals/WorkerModuleLoader.h"
+#include "mozilla/Maybe.h"
+#include "nsIContentPolicy.h"
+#include "nsStringFwd.h"
+#include "nsTArrayForwardDeclare.h"
+
+class nsIChannel;
+class nsICookieJarSettings;
+class nsILoadGroup;
+class nsIPrincipal;
+class nsIReferrerInfo;
+class nsIURI;
+
+namespace mozilla {
+
+class ErrorResult;
+
+namespace dom {
+
+class ClientInfo;
+class Document;
+struct WorkerLoadInfo;
+class WorkerPrivate;
+class SerializedStackHolder;
+
+enum WorkerScriptType { WorkerScript, DebuggerScript };
+
+namespace workerinternals {
+
+namespace loader {
+class ScriptExecutorRunnable;
+class ScriptLoaderRunnable;
+class CachePromiseHandler;
+class CacheLoadHandler;
+class CacheCreator;
+class NetworkLoadHandler;
+
+/*
+ * [DOMDOC] WorkerScriptLoader
+ *
+ * The WorkerScriptLoader is the primary class responsible for loading all
+ * Workers, including: ServiceWorkers, SharedWorkers, RemoteWorkers, and
+ * dedicated Workers. Our implementation also includes a subtype of dedicated
+ * workers: ChromeWorker, which exposes information that isn't normally
+ * accessible on a dedicated worker. See [1] for more information.
+ *
+ * Due to constraints around fetching, this class currently delegates the
+ * "Fetch" portion of its work load to the main thread. Unlike the DOM
+ * ScriptLoader, the WorkerScriptLoader is not persistent and is not reused for
+ * subsequent loads. That means for each iteration of loading (for example,
+ * loading the main script, followed by a load triggered by ImportScripts), we
+ * recreate this class, and handle the case independently.
+ *
+ * The flow of requests across the boundaries looks like this:
+ *
+ *    +----------------------------+
+ *    | new WorkerScriptLoader(..) |
+ *    +----------------------------+
+ *                   |
+ *                   V
+ *            +-------------------------------------------+
+ *            | WorkerScriptLoader::DispatchLoadScripts() |
+ *            +-------------------------------------------+
+ *                   |
+ *                   V
+ *            +............................+
+ *            | new ScriptLoaderRunnable() |
+ *            +............................+
+ *                   :
+ *                   V
+ *  #####################################################################
+ *                             Enter Main thread
+ *  #####################################################################
+ *                   :
+ *                   V
+ *  +.............................+     For each: Is a normal Worker?
+ *  | ScriptLoaderRunnable::Run() |----------------------------------+
+ *  +.............................+                                  |
+ *                   |                                               V
+ *                   |               +----------------------------------+
+ *                   |               | WorkerScriptLoader::LoadScript() |
+ *                   |               +----------------------------------+
+ *                   |                                               |
+ *                   | For each request: Is a ServiceWorker?         |
+ *                   |                                               |
+ *                   V                                               V
+ *   +==================+   No script in cache?   +====================+
+ *   | CacheLoadHandler |------------------------>| NetworkLoadHandler |
+ *   +==================+                         +====================+
+ *      :                                                    :
+ *      : Loaded from Cache                                  : Loaded by Network
+ *      :   +..........................................+     :
+ *      +---| ScriptLoaderRunnable::OnStreamComplete() |<----+
+ *          +..........................................+
+ *                             |
+ *                             | A request is ready, is it in post order?
+ *                             |
+ *                             | call DispatchPendingProcessRequests()
+ *                             | This creates ScriptExecutorRunnable
+ *            +..............................+
+ *            | new ScriptLoaderExecutable() |
+ *            +..............................+
+ *                             :
+ *                             V
+ *  #####################################################################
+ *                           Enter worker thread
+ *  #####################################################################
+ *                             :
+ *                             V
+ *          +...............................+         All Scripts Executed?
+ *          | ScriptLoaderExecutable::Run() | -------------+
+ *          +...............................+              :
+ *                                                         :
+ *                                                         : yes. Do execution
+ *                                                         : then shutdown.
+ *                                                         :
+ *                                                         V
+ *                       +--------------------------------------------+
+ *                       | WorkerScriptLoader::ShutdownScriptLoader() |
+ *                       +--------------------------------------------+
+ */
+
+class WorkerScriptLoader : public JS::loader::ScriptLoaderInterface,
+                           public nsINamed {
+  friend class ScriptExecutorRunnable;
+  friend class ScriptLoaderRunnable;
+  friend class CachePromiseHandler;
+  friend class CacheLoadHandler;
+  friend class CacheCreator;
+  friend class NetworkLoadHandler;
+  friend class WorkerModuleLoader;
+
+  RefPtr<ThreadSafeWorkerRef> mWorkerRef;
+  UniquePtr<SerializedStackHolder> mOriginStack;
+  nsString mOriginStackJSON;
+  nsCOMPtr<nsISerialEventTarget> mSyncLoopTarget;
+  ScriptLoadRequestList mLoadingRequests;
+  ScriptLoadRequestList mLoadedRequests;
+  Maybe<ServiceWorkerDescriptor> mController;
+  WorkerScriptType mWorkerScriptType;
+  ErrorResult& mRv;
+  bool mExecutionAborted = false;
+  bool mMutedErrorFlag = false;
+
+  // Count of loading module requests. mLoadingRequests doesn't keep track of
+  // child module requests.
+  // This member should be accessed on worker thread.
+  uint32_t mLoadingModuleRequestCount;
+
+  // Worker cancellation related Mutex
+  //
+  // Modified on the worker thread.
+  // It is ok to *read* this without a lock on the worker.
+  // Main thread must always acquire a lock.
+  bool mCleanedUp MOZ_GUARDED_BY(
+      mCleanUpLock);  // To specify if the cleanUp() has been done.
+
+  Mutex& CleanUpLock() MOZ_RETURN_CAPABILITY(mCleanUpLock) {
+    return mCleanUpLock;
+  }
+
+  bool CleanedUp() const MOZ_REQUIRES(mCleanUpLock) {
+    mCleanUpLock.AssertCurrentThreadOwns();
+    return mCleanedUp;
+  }
+
+  // Ensure the worker and the main thread won't race to access |mCleanedUp|.
+  // Should be a MutexSingleWriter, but that causes a lot of issues when you
+  // expose the lock via Lock().
+  Mutex mCleanUpLock;
+
+ public:
+  NS_DECL_THREADSAFE_ISUPPORTS
+
+  static already_AddRefed<WorkerScriptLoader> Create(
+      WorkerPrivate* aWorkerPrivate,
+      UniquePtr<SerializedStackHolder> aOriginStack,
+      nsISerialEventTarget* aSyncLoopTarget, WorkerScriptType aWorkerScriptType,
+      ErrorResult& aRv);
+
+  bool CreateScriptRequests(const nsTArray<nsString>& aScriptURLs,
+                            const mozilla::Encoding* aDocumentEncoding,
+                            bool aIsMainScript);
+
+  ScriptLoadRequest* GetMainScript();
+
+  already_AddRefed<ScriptLoadRequest> CreateScriptLoadRequest(
+      const nsString& aScriptURL, const mozilla::Encoding* aDocumentEncoding,
+      bool aIsMainScript);
+
+  bool DispatchLoadScript(ScriptLoadRequest* aRequest);
+
+  bool DispatchLoadScripts();
+
+  void TryShutdown();
+
+  WorkerScriptType GetWorkerScriptType() { return mWorkerScriptType; }
+
+ protected:
+  nsIURI* GetBaseURI() const override;
+
+  nsIURI* GetInitialBaseURI();
+
+  nsIGlobalObject* GetGlobal();
+
+  void MaybeMoveToLoadedList(ScriptLoadRequest* aRequest);
+
+  bool StoreCSP();
+
+  bool ProcessPendingRequests(JSContext* aCx);
+
+  bool AllScriptsExecuted() {
+    return mLoadingRequests.isEmpty() && mLoadedRequests.isEmpty();
+  }
+
+  bool IsDebuggerScript() const { return mWorkerScriptType == DebuggerScript; }
+
+  void SetController(const Maybe<ServiceWorkerDescriptor>& aDescriptor) {
+    mController = aDescriptor;
+  }
+
+  Maybe<ServiceWorkerDescriptor>& GetController() { return mController; }
+
+  nsresult LoadScript(ThreadSafeRequestHandle* aRequestHandle);
+
+  void ShutdownScriptLoader(bool aResult, bool aMutedError);
+
+ private:
+  WorkerScriptLoader(UniquePtr<SerializedStackHolder> aOriginStack,
+                     nsISerialEventTarget* aSyncLoopTarget,
+                     WorkerScriptType aWorkerScriptType, ErrorResult& aRv);
+
+  ~WorkerScriptLoader() = default;
+
+  NS_IMETHOD
+  GetName(nsACString& aName) override {
+    aName.AssignLiteral("WorkerScriptLoader");
+    return NS_OK;
+  }
+
+  void InitModuleLoader();
+
+  nsTArray<RefPtr<ThreadSafeRequestHandle>> GetLoadingList();
+
+  bool IsDynamicImport(ScriptLoadRequest* aRequest);
+
+  nsContentPolicyType GetContentPolicyType(ScriptLoadRequest* aRequest);
+
+  bool EvaluateScript(JSContext* aCx, ScriptLoadRequest* aRequest);
+
+  nsresult FillCompileOptionsForRequest(
+      JSContext* cx, ScriptLoadRequest* aRequest, JS::CompileOptions* aOptions,
+      JS::MutableHandle<JSScript*> aIntroductionScript) override;
+
+  void ReportErrorToConsole(ScriptLoadRequest* aRequest,
+                            nsresult aResult) const override;
+
+  // Only used by import maps, crash if we get here.
+  void ReportWarningToConsole(
+      ScriptLoadRequest* aRequest, const char* aMessageName,
+      const nsTArray<nsString>& aParams = nsTArray<nsString>()) const override {
+    MOZ_CRASH("Import maps have not been implemented for this context");
+  }
+
+  void LogExceptionToConsole(JSContext* aCx, WorkerPrivate* aWorkerPrivate);
+
+  bool AllModuleRequestsLoaded() const;
+  void IncreaseLoadingModuleRequestCount();
+  void DecreaseLoadingModuleRequestCount();
+};
+
+/* ScriptLoaderRunnable
+ *
+ * Responsibilities of this class:
+ *   - the actual dispatch
+ *   - delegating the load back to WorkerScriptLoader
+ *   - handling the collections of scripts being requested
+ *   - handling main thread cancellation
+ *   - dispatching back to the worker thread
+ */
+class ScriptLoaderRunnable final : public nsIRunnable, public nsINamed {
+  RefPtr<WorkerScriptLoader> mScriptLoader;
+  RefPtr<ThreadSafeWorkerRef> mWorkerRef;
+  nsTArrayView<RefPtr<ThreadSafeRequestHandle>> mLoadingRequests;
+  Maybe<nsresult> mCancelMainThread;
+  RefPtr<CacheCreator> mCacheCreator;
+
+ public:
+  NS_DECL_THREADSAFE_ISUPPORTS
+
+  explicit ScriptLoaderRunnable(
+      WorkerScriptLoader* aScriptLoader,
+      nsTArray<RefPtr<ThreadSafeRequestHandle>> aLoadingRequests);
+
+  nsresult OnStreamComplete(ThreadSafeRequestHandle* aRequestHandle,
+                            nsresult aStatus);
+
+  void LoadingFinished(ThreadSafeRequestHandle* aRequestHandle, nsresult aRv);
+
+  void MaybeExecuteFinishedScripts(ThreadSafeRequestHandle* aRequestHandle);
+
+  bool IsCancelled() { return mCancelMainThread.isSome(); }
+
+  nsresult GetCancelResult() {
+    return (IsCancelled()) ? mCancelMainThread.ref() : NS_OK;
+  }
+
+  void CancelMainThreadWithBindingAborted();
+
+  CacheCreator* GetCacheCreator() { return mCacheCreator; };
+
+ private:
+  ~ScriptLoaderRunnable() = default;
+
+  void CancelMainThread(nsresult aCancelResult);
+
+  void DispatchProcessPendingRequests();
+
+  NS_IMETHOD
+  Run() override;
+
+  NS_IMETHOD
+  GetName(nsACString& aName) override {
+    aName.AssignLiteral("ScriptLoaderRunnable");
+    return NS_OK;
+  }
+};
+
+}  // namespace loader
+
+nsresult ChannelFromScriptURLMainThread(
+    nsIPrincipal* aPrincipal, Document* aParentDoc, nsILoadGroup* aLoadGroup,
+    nsIURI* aScriptURL, const WorkerType& aWorkerType,
+    const RequestCredentials& aCredentials,
+    const Maybe<ClientInfo>& aClientInfo,
+    nsContentPolicyType aContentPolicyType,
+    nsICookieJarSettings* aCookieJarSettings, nsIReferrerInfo* aReferrerInfo,
+    nsIChannel** aChannel);
+
+nsresult ChannelFromScriptURLWorkerThread(
+    JSContext* aCx, WorkerPrivate* aParent, const nsAString& aScriptURL,
+    const WorkerType& aWorkerType, const RequestCredentials& aCredentials,
+    WorkerLoadInfo& aLoadInfo);
+
+void ReportLoadError(ErrorResult& aRv, nsresult aLoadResult,
+                     const nsAString& aScriptURL);
+
+void LoadMainScript(WorkerPrivate* aWorkerPrivate,
+                    UniquePtr<SerializedStackHolder> aOriginStack,
+                    const nsAString& aScriptURL,
+                    WorkerScriptType aWorkerScriptType, ErrorResult& aRv,
+                    const mozilla::Encoding* aDocumentEncoding);
+
+void Load(WorkerPrivate* aWorkerPrivate,
+          UniquePtr<SerializedStackHolder> aOriginStack,
+          const nsTArray<nsString>& aScriptURLs,
+          WorkerScriptType aWorkerScriptType, ErrorResult& aRv);
+
+}  // namespace workerinternals
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif /* mozilla_dom_workers_scriptloader_h__ */
diff --git a/dom/workers/Worker.cpp b/dom/workers/Worker.cpp
new file mode 100644
index 0000000000..2348572e65
--- /dev/null
+++ b/dom/workers/Worker.cpp
@@ -0,0 +1,222 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "Worker.h"
+
+#include "MessageEventRunnable.h"
+#include "mozilla/dom/WorkerBinding.h"
+#include "mozilla/ProfilerLabels.h"
+#include "mozilla/ProfilerMarkers.h"
+#include "mozilla/Unused.h"
+#include "nsContentUtils.h"
+#include "nsGlobalWindowInner.h"
+#include "WorkerPrivate.h"
+#include "EventWithOptionsRunnable.h"
+#include "js/RootingAPI.h"
+#include "mozilla/dom/BindingDeclarations.h"
+#include "nsISupports.h"
+#include "nsDebug.h"
+#include "mozilla/dom/WorkerStatus.h"
+#include "mozilla/RefPtr.h"
+
+#ifdef XP_WIN
+#  undef PostMessage
+#endif
+
+namespace mozilla::dom {
+
+/* static */
+already_AddRefed<Worker> Worker::Constructor(const GlobalObject& aGlobal,
+                                             const nsAString& aScriptURL,
+                                             const WorkerOptions& aOptions,
+                                             ErrorResult& aRv) {
+  JSContext* cx = aGlobal.Context();
+
+  nsCOMPtr<nsIGlobalObject> globalObject =
+      do_QueryInterface(aGlobal.GetAsSupports());
+
+  if (globalObject->GetAsInnerWindow() &&
+      !globalObject->GetAsInnerWindow()->IsCurrentInnerWindow()) {
+    aRv.ThrowInvalidStateError(
+        "Cannot create worker for a going to be discarded document");
+    return nullptr;
+  }
+
+  RefPtr<WorkerPrivate> workerPrivate = WorkerPrivate::Constructor(
+      cx, aScriptURL, false /* aIsChromeWorker */, WorkerKindDedicated,
+      aOptions.mCredentials, aOptions.mType, aOptions.mName, VoidCString(),
+      nullptr /*aLoadInfo */, aRv);
+  if (NS_WARN_IF(aRv.Failed())) {
+    return nullptr;
+  }
+
+  RefPtr<Worker> worker = new Worker(globalObject, workerPrivate.forget());
+  return worker.forget();
+}
+
+Worker::Worker(nsIGlobalObject* aGlobalObject,
+               already_AddRefed<WorkerPrivate> aWorkerPrivate)
+    : DOMEventTargetHelper(aGlobalObject),
+      mWorkerPrivate(std::move(aWorkerPrivate)) {
+  MOZ_ASSERT(mWorkerPrivate);
+  mWorkerPrivate->SetParentEventTargetRef(this);
+}
+
+Worker::~Worker() { Terminate(); }
+
+JSObject* Worker::WrapObject(JSContext* aCx,
+                             JS::Handle<JSObject*> aGivenProto) {
+  JS::Rooted<JSObject*> wrapper(aCx,
+                                Worker_Binding::Wrap(aCx, this, aGivenProto));
+  if (wrapper) {
+    // Most DOM objects don't assume they have a reflector. If they don't have
+    // one and need one, they create it. But in workers code, we assume that the
+    // reflector is always present.  In order to guarantee that it's always
+    // present, we have to preserve it. Otherwise the GC will happily collect it
+    // as needed.
+    MOZ_ALWAYS_TRUE(TryPreserveWrapper(wrapper));
+  }
+
+  return wrapper;
+}
+
+void Worker::PostMessage(JSContext* aCx, JS::Handle<JS::Value> aMessage,
+                         const Sequence<JSObject*>& aTransferable,
+                         ErrorResult& aRv) {
+  NS_ASSERT_OWNINGTHREAD(Worker);
+
+  if (!mWorkerPrivate || mWorkerPrivate->ParentStatusProtected() > Running) {
+    return;
+  }
+  RefPtr<WorkerPrivate> workerPrivate = mWorkerPrivate;
+  Unused << workerPrivate;
+
+  JS::Rooted<JS::Value> transferable(aCx, JS::UndefinedValue());
+
+  aRv = nsContentUtils::CreateJSValueFromSequenceOfObject(aCx, aTransferable,
+                                                          &transferable);
+  if (NS_WARN_IF(aRv.Failed())) {
+    return;
+  }
+
+  NS_ConvertUTF16toUTF8 nameOrScriptURL(
+      mWorkerPrivate->WorkerName().IsEmpty()
+          ? Substring(
+                mWorkerPrivate->ScriptURL(), 0,
+                std::min(size_t(1024), mWorkerPrivate->ScriptURL().Length()))
+          : Substring(
+                mWorkerPrivate->WorkerName(), 0,
+                std::min(size_t(1024), mWorkerPrivate->WorkerName().Length())));
+  AUTO_PROFILER_MARKER_TEXT("Worker.postMessage", DOM, {}, nameOrScriptURL);
+  uint32_t flags = uint32_t(js::ProfilingStackFrame::Flags::RELEVANT_FOR_JS);
+  if (mWorkerPrivate->IsChromeWorker()) {
+    flags |= uint32_t(js::ProfilingStackFrame::Flags::NONSENSITIVE);
+  }
+  mozilla::AutoProfilerLabel PROFILER_RAII(
+      "Worker.postMessage", nameOrScriptURL.get(),
+      JS::ProfilingCategoryPair::DOM, flags);
+
+  RefPtr<MessageEventRunnable> runnable =
+      new MessageEventRunnable(mWorkerPrivate, WorkerRunnable::WorkerThread);
+
+  JS::CloneDataPolicy clonePolicy;
+  // DedicatedWorkers are always part of the same agent cluster.
+  clonePolicy.allowIntraClusterClonableSharedObjects();
+
+  if (NS_IsMainThread()) {
+    nsGlobalWindowInner* win = nsContentUtils::IncumbentInnerWindow();
+    if (win && win->IsSharedMemoryAllowed()) {
+      clonePolicy.allowSharedMemoryObjects();
+    }
+  } else {
+    WorkerPrivate* worker = GetCurrentThreadWorkerPrivate();
+    if (worker && worker->IsSharedMemoryAllowed()) {
+      clonePolicy.allowSharedMemoryObjects();
+    }
+  }
+
+  runnable->Write(aCx, aMessage, transferable, clonePolicy, aRv);
+
+  if (!mWorkerPrivate || mWorkerPrivate->ParentStatusProtected() > Running) {
+    return;
+  }
+
+  if (NS_WARN_IF(aRv.Failed())) {
+    return;
+  }
+
+  // The worker could have closed between the time we entered this function and
+  // checked ParentStatusProtected and now, which could cause the dispatch to
+  // fail.
+  Unused << NS_WARN_IF(!runnable->Dispatch());
+}
+
+void Worker::PostMessage(JSContext* aCx, JS::Handle<JS::Value> aMessage,
+                         const StructuredSerializeOptions& aOptions,
+                         ErrorResult& aRv) {
+  PostMessage(aCx, aMessage, aOptions.mTransfer, aRv);
+}
+
+void Worker::PostEventWithOptions(JSContext* aCx,
+                                  JS::Handle<JS::Value> aOptions,
+                                  const Sequence<JSObject*>& aTransferable,
+                                  EventWithOptionsRunnable* aRunnable,
+                                  ErrorResult& aRv) {
+  NS_ASSERT_OWNINGTHREAD(Worker);
+
+  if (NS_WARN_IF(!mWorkerPrivate ||
+                 mWorkerPrivate->ParentStatusProtected() > Running)) {
+    return;
+  }
+  RefPtr<WorkerPrivate> workerPrivate = mWorkerPrivate;
+  Unused << workerPrivate;
+
+  aRunnable->InitOptions(aCx, aOptions, aTransferable, aRv);
+
+  if (NS_WARN_IF(!mWorkerPrivate ||
+                 mWorkerPrivate->ParentStatusProtected() > Running)) {
+    return;
+  }
+
+  if (NS_WARN_IF(aRv.Failed())) {
+    return;
+  }
+
+  Unused << NS_WARN_IF(!aRunnable->Dispatch());
+}
+
+void Worker::Terminate() {
+  NS_ASSERT_OWNINGTHREAD(Worker);
+
+  if (mWorkerPrivate) {
+    mWorkerPrivate->Cancel();
+    mWorkerPrivate = nullptr;
+  }
+}
+
+NS_IMPL_CYCLE_COLLECTION_CLASS(Worker)
+
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(Worker, DOMEventTargetHelper)
+  if (tmp->mWorkerPrivate) {
+    tmp->mWorkerPrivate->Traverse(cb);
+  }
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED(Worker, DOMEventTargetHelper)
+  tmp->Terminate();
+  NS_IMPL_CYCLE_COLLECTION_UNLINK_WEAK_PTR
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+
+NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN_INHERITED(Worker, DOMEventTargetHelper)
+NS_IMPL_CYCLE_COLLECTION_TRACE_END
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(Worker)
+NS_INTERFACE_MAP_END_INHERITING(DOMEventTargetHelper)
+
+NS_IMPL_ADDREF_INHERITED(Worker, DOMEventTargetHelper)
+NS_IMPL_RELEASE_INHERITED(Worker, DOMEventTargetHelper)
+
+}  // namespace mozilla::dom
diff --git a/dom/workers/Worker.h b/dom/workers/Worker.h
new file mode 100644
index 0000000000..14d0630f28
--- /dev/null
+++ b/dom/workers/Worker.h
@@ -0,0 +1,74 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_Worker_h
+#define mozilla_dom_Worker_h
+
+#include "mozilla/Attributes.h"
+#include "mozilla/dom/DebuggerNotificationBinding.h"
+#include "mozilla/DOMEventTargetHelper.h"
+#include "mozilla/RefPtr.h"
+#include "mozilla/WeakPtr.h"
+
+#ifdef XP_WIN
+#  undef PostMessage
+#endif
+
+namespace mozilla::dom {
+
+class EventWithOptionsRunnable;
+struct StructuredSerializeOptions;
+struct WorkerOptions;
+class WorkerPrivate;
+
+class Worker : public DOMEventTargetHelper, public SupportsWeakPtr {
+ public:
+  NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS_INHERITED(Worker,
+                                                         DOMEventTargetHelper)
+  static already_AddRefed<Worker> Constructor(const GlobalObject& aGlobal,
+                                              const nsAString& aScriptURL,
+                                              const WorkerOptions& aOptions,
+                                              ErrorResult& aRv);
+
+  JSObject* WrapObject(JSContext* aCx,
+                       JS::Handle<JSObject*> aGivenProto) override;
+
+  Maybe<EventCallbackDebuggerNotificationType> GetDebuggerNotificationType()
+      const override {
+    return Some(EventCallbackDebuggerNotificationType::Worker);
+  }
+
+  void PostMessage(JSContext* aCx, JS::Handle<JS::Value> aMessage,
+                   const Sequence<JSObject*>& aTransferable, ErrorResult& aRv);
+
+  void PostMessage(JSContext* aCx, JS::Handle<JS::Value> aMessage,
+                   const StructuredSerializeOptions& aOptions,
+                   ErrorResult& aRv);
+
+  void PostEventWithOptions(JSContext* aCx, JS::Handle<JS::Value> aOptions,
+                            const Sequence<JSObject*>& aTransferable,
+                            EventWithOptionsRunnable* aRunnable,
+                            ErrorResult& aRv);
+
+  void Terminate();
+
+  IMPL_EVENT_HANDLER(error)
+  IMPL_EVENT_HANDLER(message)
+  IMPL_EVENT_HANDLER(messageerror)
+
+ protected:
+  Worker(nsIGlobalObject* aGlobalObject,
+         already_AddRefed<WorkerPrivate> aWorkerPrivate);
+  ~Worker();
+
+  friend class EventWithOptionsRunnable;
+  RefPtr<WorkerPrivate> mWorkerPrivate;
+};
+
+}  // namespace mozilla::dom
+
+#endif /* mozilla_dom_Worker_h */
diff --git a/dom/workers/WorkerCSPEventListener.cpp b/dom/workers/WorkerCSPEventListener.cpp
new file mode 100644
index 0000000000..c693928486
--- /dev/null
+++ b/dom/workers/WorkerCSPEventListener.cpp
@@ -0,0 +1,105 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "WorkerCSPEventListener.h"
+#include "WorkerRef.h"
+#include "WorkerRunnable.h"
+#include "WorkerScope.h"
+#include "mozilla/dom/SecurityPolicyViolationEvent.h"
+#include "mozilla/dom/SecurityPolicyViolationEventBinding.h"
+#include "mozilla/dom/WorkerRunnable.h"
+
+using namespace mozilla::dom;
+
+namespace {
+
+class WorkerCSPEventRunnable final : public MainThreadWorkerRunnable {
+ public:
+  WorkerCSPEventRunnable(WorkerPrivate* aWorkerPrivate, const nsAString& aJSON)
+      : MainThreadWorkerRunnable(aWorkerPrivate, "WorkerCSPEventRunnable"),
+        mJSON(aJSON) {}
+
+ private:
+  bool WorkerRun(JSContext* aCx, WorkerPrivate* aWorkerPrivate) {
+    SecurityPolicyViolationEventInit violationEventInit;
+    if (NS_WARN_IF(!violationEventInit.Init(mJSON))) {
+      return true;
+    }
+
+    RefPtr<mozilla::dom::Event> event =
+        mozilla::dom::SecurityPolicyViolationEvent::Constructor(
+            aWorkerPrivate->GlobalScope(), u"securitypolicyviolation"_ns,
+            violationEventInit);
+    event->SetTrusted(true);
+
+    aWorkerPrivate->GlobalScope()->DispatchEvent(*event);
+    return true;
+  }
+
+  const nsString mJSON;
+};
+
+}  // namespace
+
+NS_IMPL_ISUPPORTS(WorkerCSPEventListener, nsICSPEventListener)
+
+/* static */
+already_AddRefed<WorkerCSPEventListener> WorkerCSPEventListener::Create(
+    WorkerPrivate* aWorkerPrivate) {
+  MOZ_ASSERT(aWorkerPrivate);
+  aWorkerPrivate->AssertIsOnWorkerThread();
+
+  RefPtr<WorkerCSPEventListener> listener = new WorkerCSPEventListener();
+
+  MutexAutoLock lock(listener->mMutex);
+  listener->mWorkerRef = WeakWorkerRef::Create(aWorkerPrivate, [listener]() {
+    MutexAutoLock lock(listener->mMutex);
+    listener->mWorkerRef = nullptr;
+  });
+
+  if (NS_WARN_IF(!listener->mWorkerRef)) {
+    return nullptr;
+  }
+
+  return listener.forget();
+}
+
+WorkerCSPEventListener::WorkerCSPEventListener()
+    : mMutex("WorkerCSPEventListener::mMutex") {}
+
+NS_IMETHODIMP
+WorkerCSPEventListener::OnCSPViolationEvent(const nsAString& aJSON) {
+  MutexAutoLock lock(mMutex);
+  if (!mWorkerRef) {
+    return NS_OK;
+  }
+
+  WorkerPrivate* workerPrivate = mWorkerRef->GetUnsafePrivate();
+  MOZ_ASSERT(workerPrivate);
+
+  if (NS_IsMainThread()) {
+    RefPtr<WorkerCSPEventRunnable> runnable =
+        new WorkerCSPEventRunnable(workerPrivate, aJSON);
+    runnable->Dispatch();
+
+    return NS_OK;
+  }
+
+  SecurityPolicyViolationEventInit violationEventInit;
+  if (NS_WARN_IF(!violationEventInit.Init(aJSON))) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  RefPtr<mozilla::dom::Event> event =
+      mozilla::dom::SecurityPolicyViolationEvent::Constructor(
+          workerPrivate->GlobalScope(), u"securitypolicyviolation"_ns,
+          violationEventInit);
+  event->SetTrusted(true);
+
+  workerPrivate->GlobalScope()->DispatchEvent(*event);
+
+  return NS_OK;
+}
diff --git a/dom/workers/WorkerCSPEventListener.h b/dom/workers/WorkerCSPEventListener.h
new file mode 100644
index 0000000000..1265f0ed17
--- /dev/null
+++ b/dom/workers/WorkerCSPEventListener.h
@@ -0,0 +1,40 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_WorkerCSPEventListener_h
+#define mozilla_dom_WorkerCSPEventListener_h
+
+#include "mozilla/dom/WorkerRef.h"
+#include "mozilla/Mutex.h"
+#include "nsIContentSecurityPolicy.h"
+
+namespace mozilla::dom {
+
+class WeakWorkerRef;
+class WorkerRef;
+class WorkerPrivate;
+
+class WorkerCSPEventListener final : public nsICSPEventListener {
+ public:
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSICSPEVENTLISTENER
+
+  static already_AddRefed<WorkerCSPEventListener> Create(
+      WorkerPrivate* aWorkerPrivate);
+
+ private:
+  WorkerCSPEventListener();
+  ~WorkerCSPEventListener() = default;
+
+  Mutex mMutex;
+
+  // Protected by mutex.
+  RefPtr<WeakWorkerRef> mWorkerRef MOZ_GUARDED_BY(mMutex);
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_WorkerCSPEventListener_h
diff --git a/dom/workers/WorkerChannelInfo.cpp b/dom/workers/WorkerChannelInfo.cpp
new file mode 100644
index 0000000000..cea6acf1ef
--- /dev/null
+++ b/dom/workers/WorkerChannelInfo.cpp
@@ -0,0 +1,66 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "WorkerChannelInfo.h"
+#include "mozilla/dom/BrowsingContext.h"
+
+namespace mozilla::dom {
+
+// WorkerChannelLoadInfo
+
+NS_IMPL_ISUPPORTS(WorkerChannelLoadInfo, nsIWorkerChannelLoadInfo)
+
+NS_IMETHODIMP
+WorkerChannelLoadInfo::GetWorkerAssociatedBrowsingContextID(uint64_t* aResult) {
+  *aResult = mWorkerAssociatedBrowsingContextID;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WorkerChannelLoadInfo::SetWorkerAssociatedBrowsingContextID(uint64_t aID) {
+  mWorkerAssociatedBrowsingContextID = aID;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WorkerChannelLoadInfo::GetWorkerAssociatedBrowsingContext(
+    dom::BrowsingContext** aResult) {
+  *aResult = BrowsingContext::Get(mWorkerAssociatedBrowsingContextID).take();
+  return NS_OK;
+}
+
+// WorkerChannelInfo
+
+NS_IMPL_ISUPPORTS(WorkerChannelInfo, nsIWorkerChannelInfo)
+
+WorkerChannelInfo::WorkerChannelInfo(uint64_t aChannelID,
+                                     uint64_t aBrowsingContextID)
+    : mChannelID(aChannelID) {
+  mLoadInfo = new WorkerChannelLoadInfo();
+  mLoadInfo->SetWorkerAssociatedBrowsingContextID(aBrowsingContextID);
+}
+
+NS_IMETHODIMP
+WorkerChannelInfo::SetLoadInfo(nsIWorkerChannelLoadInfo* aLoadInfo) {
+  MOZ_ASSERT(aLoadInfo);
+  mLoadInfo = aLoadInfo;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WorkerChannelInfo::GetLoadInfo(nsIWorkerChannelLoadInfo** aLoadInfo) {
+  *aLoadInfo = do_AddRef(mLoadInfo).take();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WorkerChannelInfo::GetChannelId(uint64_t* aChannelID) {
+  NS_ENSURE_ARG_POINTER(aChannelID);
+  *aChannelID = mChannelID;
+  return NS_OK;
+}
+
+}  // end of namespace mozilla::dom
diff --git a/dom/workers/WorkerChannelInfo.h b/dom/workers/WorkerChannelInfo.h
new file mode 100644
index 0000000000..66b28bf685
--- /dev/null
+++ b/dom/workers/WorkerChannelInfo.h
@@ -0,0 +1,50 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_WorkerChannel_h
+#define mozilla_dom_WorkerChannel_h
+
+#include "nsIWorkerChannelInfo.h"
+#include "nsILoadInfo.h"
+#include "nsIChannel.h"
+#include "nsTArray.h"
+#include "nsIURI.h"
+#include "mozilla/dom/ClientInfo.h"
+#include "mozilla/dom/ServiceWorkerDescriptor.h"
+#include "mozilla/OriginAttributes.h"
+
+namespace mozilla::dom {
+
+class WorkerChannelLoadInfo final : public nsIWorkerChannelLoadInfo {
+ public:
+  NS_DECL_THREADSAFE_ISUPPORTS;
+  NS_DECL_NSIWORKERCHANNELLOADINFO;
+
+ private:
+  ~WorkerChannelLoadInfo() = default;
+
+  uint64_t mWorkerAssociatedBrowsingContextID;
+};
+
+class WorkerChannelInfo final : public nsIWorkerChannelInfo {
+ public:
+  NS_DECL_THREADSAFE_ISUPPORTS;
+  NS_DECL_NSIWORKERCHANNELINFO;
+
+  WorkerChannelInfo(uint64_t aChannelID,
+                    uint64_t aWorkerAssociatedBrowsingContextID);
+  WorkerChannelInfo() = delete;
+
+ private:
+  ~WorkerChannelInfo() = default;
+
+  nsCOMPtr<nsIWorkerChannelLoadInfo> mLoadInfo;
+  uint64_t mChannelID;
+};
+
+}  // end of namespace mozilla::dom
+
+#endif
diff --git a/dom/workers/WorkerCommon.h b/dom/workers/WorkerCommon.h
new file mode 100644
index 0000000000..d10dabb5c5
--- /dev/null
+++ b/dom/workers/WorkerCommon.h
@@ -0,0 +1,57 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_workers_WorkerCommon_h
+#define mozilla_dom_workers_WorkerCommon_h
+
+#include "js/TypeDecls.h"
+
+class nsPIDOMWindowInner;
+
+namespace mozilla::dom {
+
+class WorkerPrivate;
+
+// All of these are implemented in RuntimeService.cpp
+
+WorkerPrivate* GetWorkerPrivateFromContext(JSContext* aCx);
+
+WorkerPrivate* GetCurrentThreadWorkerPrivate();
+
+bool IsCurrentThreadRunningWorker();
+
+bool IsCurrentThreadRunningChromeWorker();
+
+JSContext* GetCurrentWorkerThreadJSContext();
+
+JSObject* GetCurrentThreadWorkerGlobal();
+
+JSObject* GetCurrentThreadWorkerDebuggerGlobal();
+
+void CancelWorkersForWindow(const nsPIDOMWindowInner& aWindow);
+
+void FreezeWorkersForWindow(const nsPIDOMWindowInner& aWindow);
+
+void ThawWorkersForWindow(const nsPIDOMWindowInner& aWindow);
+
+void SuspendWorkersForWindow(const nsPIDOMWindowInner& aWindow);
+
+void ResumeWorkersForWindow(const nsPIDOMWindowInner& aWindow);
+
+void PropagateStorageAccessPermissionGrantedToWorkers(
+    const nsPIDOMWindowInner& aWindow);
+
+// All of these are implemented in WorkerScope.cpp
+
+bool IsWorkerGlobal(JSObject* global);
+
+bool IsWorkerDebuggerGlobal(JSObject* global);
+
+bool IsWorkerDebuggerSandbox(JSObject* object);
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_workers_WorkerCommon_h
diff --git a/dom/workers/WorkerDebugger.cpp b/dom/workers/WorkerDebugger.cpp
new file mode 100644
index 0000000000..a3e0af7a38
--- /dev/null
+++ b/dom/workers/WorkerDebugger.cpp
@@ -0,0 +1,501 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/BrowsingContext.h"
+#include "mozilla/dom/Document.h"
+#include "mozilla/dom/MessageEvent.h"
+#include "mozilla/dom/MessageEventBinding.h"
+#include "mozilla/dom/RemoteWorkerChild.h"
+#include "mozilla/dom/WindowContext.h"
+#include "mozilla/AbstractThread.h"
+#include "mozilla/Encoding.h"
+#include "nsProxyRelease.h"
+#include "nsQueryObject.h"
+#include "nsThreadUtils.h"
+#include "ScriptLoader.h"
+#include "WorkerCommon.h"
+#include "WorkerError.h"
+#include "WorkerRunnable.h"
+#include "WorkerDebugger.h"
+
+#if defined(XP_WIN)
+#  include <processthreadsapi.h>  // for GetCurrentProcessId()
+#else
+#  include <unistd.h>  // for getpid()
+#endif                 // defined(XP_WIN)
+
+namespace mozilla::dom {
+
+namespace {
+
+class DebuggerMessageEventRunnable final : public WorkerDebuggerRunnable {
+  nsString mMessage;
+
+ public:
+  DebuggerMessageEventRunnable(WorkerPrivate* aWorkerPrivate,
+                               const nsAString& aMessage)
+      : WorkerDebuggerRunnable(aWorkerPrivate, "DebuggerMessageEventRunnable"),
+        mMessage(aMessage) {}
+
+ private:
+  virtual bool WorkerRun(JSContext* aCx,
+                         WorkerPrivate* aWorkerPrivate) override {
+    WorkerDebuggerGlobalScope* globalScope =
+        aWorkerPrivate->DebuggerGlobalScope();
+    MOZ_ASSERT(globalScope);
+
+    JS::Rooted<JSString*> message(
+        aCx, JS_NewUCStringCopyN(aCx, mMessage.get(), mMessage.Length()));
+    if (!message) {
+      return false;
+    }
+    JS::Rooted<JS::Value> data(aCx, JS::StringValue(message));
+
+    RefPtr<MessageEvent> event =
+        new MessageEvent(globalScope, nullptr, nullptr);
+    event->InitMessageEvent(nullptr, u"message"_ns, CanBubble::eNo,
+                            Cancelable::eYes, data, u""_ns, u""_ns, nullptr,
+                            Sequence<OwningNonNull<MessagePort>>());
+    event->SetTrusted(true);
+
+    globalScope->DispatchEvent(*event);
+    return true;
+  }
+};
+
+class CompileDebuggerScriptRunnable final : public WorkerDebuggerRunnable {
+  nsString mScriptURL;
+  const mozilla::Encoding* mDocumentEncoding;
+
+ public:
+  CompileDebuggerScriptRunnable(WorkerPrivate* aWorkerPrivate,
+                                const nsAString& aScriptURL,
+                                const mozilla::Encoding* aDocumentEncoding)
+      : WorkerDebuggerRunnable(aWorkerPrivate, "CompileDebuggerScriptRunnable"),
+        mScriptURL(aScriptURL),
+        mDocumentEncoding(aDocumentEncoding) {}
+
+ private:
+  virtual bool WorkerRun(JSContext* aCx,
+                         WorkerPrivate* aWorkerPrivate) override {
+    aWorkerPrivate->AssertIsOnWorkerThread();
+
+    WorkerDebuggerGlobalScope* globalScope =
+        aWorkerPrivate->CreateDebuggerGlobalScope(aCx);
+    if (!globalScope) {
+      NS_WARNING("Failed to make global!");
+      return false;
+    }
+
+    if (NS_WARN_IF(!aWorkerPrivate->EnsureCSPEventListener())) {
+      return false;
+    }
+
+    JS::Rooted<JSObject*> global(aCx, globalScope->GetWrapper());
+
+    ErrorResult rv;
+    JSAutoRealm ar(aCx, global);
+    workerinternals::LoadMainScript(aWorkerPrivate, nullptr, mScriptURL,
+                                    DebuggerScript, rv, mDocumentEncoding);
+    rv.WouldReportJSException();
+    // Explicitly ignore NS_BINDING_ABORTED on rv.  Or more precisely, still
+    // return false and don't SetWorkerScriptExecutedSuccessfully() in that
+    // case, but don't throw anything on aCx.  The idea is to not dispatch error
+    // events if our load is canceled with that error code.
+    if (rv.ErrorCodeIs(NS_BINDING_ABORTED)) {
+      rv.SuppressException();
+      return false;
+    }
+    // Make sure to propagate exceptions from rv onto aCx, so that they will get
+    // reported after we return.  We do this for all failures on rv, because now
+    // we're using rv to track all the state we care about.
+    if (rv.MaybeSetPendingException(aCx)) {
+      return false;
+    }
+
+    return true;
+  }
+};
+
+}  // namespace
+
+class WorkerDebugger::PostDebuggerMessageRunnable final : public Runnable {
+  WorkerDebugger* mDebugger;
+  nsString mMessage;
+
+ public:
+  PostDebuggerMessageRunnable(WorkerDebugger* aDebugger,
+                              const nsAString& aMessage)
+      : mozilla::Runnable("PostDebuggerMessageRunnable"),
+        mDebugger(aDebugger),
+        mMessage(aMessage) {}
+
+ private:
+  ~PostDebuggerMessageRunnable() = default;
+
+  NS_IMETHOD
+  Run() override {
+    mDebugger->PostMessageToDebuggerOnMainThread(mMessage);
+
+    return NS_OK;
+  }
+};
+
+class WorkerDebugger::ReportDebuggerErrorRunnable final : public Runnable {
+  WorkerDebugger* mDebugger;
+  nsString mFilename;
+  uint32_t mLineno;
+  nsString mMessage;
+
+ public:
+  ReportDebuggerErrorRunnable(WorkerDebugger* aDebugger,
+                              const nsAString& aFilename, uint32_t aLineno,
+                              const nsAString& aMessage)
+      : Runnable("ReportDebuggerErrorRunnable"),
+        mDebugger(aDebugger),
+        mFilename(aFilename),
+        mLineno(aLineno),
+        mMessage(aMessage) {}
+
+ private:
+  ~ReportDebuggerErrorRunnable() = default;
+
+  NS_IMETHOD
+  Run() override {
+    mDebugger->ReportErrorToDebuggerOnMainThread(mFilename, mLineno, mMessage);
+
+    return NS_OK;
+  }
+};
+
+WorkerDebugger::WorkerDebugger(WorkerPrivate* aWorkerPrivate)
+    : mWorkerPrivate(aWorkerPrivate), mIsInitialized(false) {
+  AssertIsOnMainThread();
+}
+
+WorkerDebugger::~WorkerDebugger() {
+  MOZ_ASSERT(!mWorkerPrivate);
+
+  if (!NS_IsMainThread()) {
+    for (auto& listener : mListeners) {
+      NS_ReleaseOnMainThread("WorkerDebugger::mListeners", listener.forget());
+    }
+  }
+}
+
+NS_IMPL_ISUPPORTS(WorkerDebugger, nsIWorkerDebugger)
+
+NS_IMETHODIMP
+WorkerDebugger::GetIsClosed(bool* aResult) {
+  AssertIsOnMainThread();
+
+  *aResult = !mWorkerPrivate;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WorkerDebugger::GetIsChrome(bool* aResult) {
+  AssertIsOnMainThread();
+
+  if (!mWorkerPrivate) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  *aResult = mWorkerPrivate->IsChromeWorker();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WorkerDebugger::GetIsInitialized(bool* aResult) {
+  AssertIsOnMainThread();
+
+  if (!mWorkerPrivate) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  *aResult = mIsInitialized;
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WorkerDebugger::GetParent(nsIWorkerDebugger** aResult) {
+  AssertIsOnMainThread();
+
+  if (!mWorkerPrivate) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  WorkerPrivate* parent = mWorkerPrivate->GetParent();
+  if (!parent) {
+    *aResult = nullptr;
+    return NS_OK;
+  }
+
+  MOZ_ASSERT(mWorkerPrivate->IsDedicatedWorker());
+
+  nsCOMPtr<nsIWorkerDebugger> debugger = parent->Debugger();
+  debugger.forget(aResult);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WorkerDebugger::GetType(uint32_t* aResult) {
+  AssertIsOnMainThread();
+
+  if (!mWorkerPrivate) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  *aResult = mWorkerPrivate->Kind();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WorkerDebugger::GetUrl(nsAString& aResult) {
+  AssertIsOnMainThread();
+
+  if (!mWorkerPrivate) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  aResult = mWorkerPrivate->ScriptURL();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WorkerDebugger::GetWindow(mozIDOMWindow** aResult) {
+  AssertIsOnMainThread();
+
+  if (!mWorkerPrivate) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  nsCOMPtr<nsPIDOMWindowInner> window = DedicatedWorkerWindow();
+  window.forget(aResult);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WorkerDebugger::GetWindowIDs(nsTArray<uint64_t>& aResult) {
+  AssertIsOnMainThread();
+
+  if (!mWorkerPrivate) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  if (mWorkerPrivate->IsDedicatedWorker()) {
+    if (const auto window = DedicatedWorkerWindow()) {
+      aResult.AppendElement(window->WindowID());
+    }
+  } else if (mWorkerPrivate->IsSharedWorker()) {
+    const RemoteWorkerChild* const controller =
+        mWorkerPrivate->GetRemoteWorkerController();
+    MOZ_ASSERT(controller);
+    aResult = controller->WindowIDs().Clone();
+  }
+
+  return NS_OK;
+}
+
+nsCOMPtr<nsPIDOMWindowInner> WorkerDebugger::DedicatedWorkerWindow() {
+  MOZ_ASSERT(mWorkerPrivate);
+
+  WorkerPrivate* worker = mWorkerPrivate;
+  while (worker->GetParent()) {
+    worker = worker->GetParent();
+  }
+
+  if (!worker->IsDedicatedWorker()) {
+    return nullptr;
+  }
+
+  return worker->GetWindow();
+}
+
+NS_IMETHODIMP
+WorkerDebugger::GetPrincipal(nsIPrincipal** aResult) {
+  AssertIsOnMainThread();
+  MOZ_ASSERT(aResult);
+
+  if (!mWorkerPrivate) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  nsCOMPtr<nsIPrincipal> prin = mWorkerPrivate->GetPrincipal();
+  prin.forget(aResult);
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WorkerDebugger::GetServiceWorkerID(uint32_t* aResult) {
+  AssertIsOnMainThread();
+  MOZ_ASSERT(aResult);
+
+  if (!mWorkerPrivate || !mWorkerPrivate->IsServiceWorker()) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  *aResult = mWorkerPrivate->ServiceWorkerID();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WorkerDebugger::GetId(nsAString& aResult) {
+  AssertIsOnMainThread();
+
+  if (!mWorkerPrivate) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  aResult = mWorkerPrivate->Id();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WorkerDebugger::Initialize(const nsAString& aURL) {
+  AssertIsOnMainThread();
+
+  if (!mWorkerPrivate) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  // This should be non-null for dedicated workers and null for Shared and
+  // Service workers. All Encoding values are static and will live as long
+  // as the process and the convention is to therefore use raw pointers.
+  const mozilla::Encoding* aDocumentEncoding =
+      NS_IsMainThread() && !mWorkerPrivate->GetParent() &&
+              mWorkerPrivate->GetDocument()
+          ? mWorkerPrivate->GetDocument()->GetDocumentCharacterSet().get()
+          : nullptr;
+
+  if (!mIsInitialized) {
+    RefPtr<CompileDebuggerScriptRunnable> runnable =
+        new CompileDebuggerScriptRunnable(mWorkerPrivate, aURL,
+                                          aDocumentEncoding);
+    if (!runnable->Dispatch()) {
+      return NS_ERROR_FAILURE;
+    }
+
+    mIsInitialized = true;
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WorkerDebugger::PostMessageMoz(const nsAString& aMessage) {
+  AssertIsOnMainThread();
+
+  if (!mWorkerPrivate || !mIsInitialized) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  RefPtr<DebuggerMessageEventRunnable> runnable =
+      new DebuggerMessageEventRunnable(mWorkerPrivate, aMessage);
+  if (!runnable->Dispatch()) {
+    return NS_ERROR_FAILURE;
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WorkerDebugger::AddListener(nsIWorkerDebuggerListener* aListener) {
+  AssertIsOnMainThread();
+
+  if (mListeners.Contains(aListener)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  mListeners.AppendElement(aListener);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WorkerDebugger::RemoveListener(nsIWorkerDebuggerListener* aListener) {
+  AssertIsOnMainThread();
+
+  if (!mListeners.Contains(aListener)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  mListeners.RemoveElement(aListener);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WorkerDebugger::SetDebuggerReady(bool aReady) {
+  return mWorkerPrivate->SetIsDebuggerReady(aReady);
+}
+
+void WorkerDebugger::Close() {
+  MOZ_ASSERT(mWorkerPrivate);
+  mWorkerPrivate = nullptr;
+
+  for (const auto& listener : mListeners.Clone()) {
+    listener->OnClose();
+  }
+}
+
+void WorkerDebugger::PostMessageToDebugger(const nsAString& aMessage) {
+  mWorkerPrivate->AssertIsOnWorkerThread();
+
+  RefPtr<PostDebuggerMessageRunnable> runnable =
+      new PostDebuggerMessageRunnable(this, aMessage);
+  if (NS_FAILED(mWorkerPrivate->DispatchToMainThreadForMessaging(
+          runnable.forget()))) {
+    NS_WARNING("Failed to post message to debugger on main thread!");
+  }
+}
+
+void WorkerDebugger::PostMessageToDebuggerOnMainThread(
+    const nsAString& aMessage) {
+  AssertIsOnMainThread();
+
+  for (const auto& listener : mListeners.Clone()) {
+    listener->OnMessage(aMessage);
+  }
+}
+
+void WorkerDebugger::ReportErrorToDebugger(const nsAString& aFilename,
+                                           uint32_t aLineno,
+                                           const nsAString& aMessage) {
+  mWorkerPrivate->AssertIsOnWorkerThread();
+
+  RefPtr<ReportDebuggerErrorRunnable> runnable =
+      new ReportDebuggerErrorRunnable(this, aFilename, aLineno, aMessage);
+  if (NS_FAILED(mWorkerPrivate->DispatchToMainThreadForMessaging(
+          runnable.forget()))) {
+    NS_WARNING("Failed to report error to debugger on main thread!");
+  }
+}
+
+void WorkerDebugger::ReportErrorToDebuggerOnMainThread(
+    const nsAString& aFilename, uint32_t aLineno, const nsAString& aMessage) {
+  AssertIsOnMainThread();
+
+  for (const auto& listener : mListeners.Clone()) {
+    listener->OnError(aFilename, aLineno, aMessage);
+  }
+
+  AutoJSAPI jsapi;
+  // We're only using this context to deserialize a stack to report to the
+  // console, so the scope we use doesn't matter. Stack frame filtering happens
+  // based on the principal encoded into the frame and the caller compartment,
+  // not the compartment of the frame object, and the console reporting code
+  // will not be using our context, and therefore will not care what compartment
+  // it has entered.
+  DebugOnly<bool> ok = jsapi.Init(xpc::PrivilegedJunkScope());
+  MOZ_ASSERT(ok, "PrivilegedJunkScope should exist");
+
+  WorkerErrorReport report;
+  report.mMessage = aMessage;
+  report.mFilename = aFilename;
+  WorkerErrorReport::LogErrorToConsole(jsapi.cx(), report, 0);
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/workers/WorkerDebugger.h b/dom/workers/WorkerDebugger.h
new file mode 100644
index 0000000000..3be7ef4203
--- /dev/null
+++ b/dom/workers/WorkerDebugger.h
@@ -0,0 +1,59 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_workers_WorkerDebugger_h
+#define mozilla_dom_workers_WorkerDebugger_h
+
+#include "mozilla/dom/WorkerScope.h"
+#include "nsCOMPtr.h"
+#include "nsIWorkerDebugger.h"
+
+class mozIDOMWindow;
+class nsIPrincipal;
+class nsPIDOMWindowInner;
+
+namespace mozilla::dom {
+
+class WorkerPrivate;
+
+class WorkerDebugger : public nsIWorkerDebugger {
+  class ReportDebuggerErrorRunnable;
+  class PostDebuggerMessageRunnable;
+
+  CheckedUnsafePtr<WorkerPrivate> mWorkerPrivate;
+  bool mIsInitialized;
+  nsTArray<nsCOMPtr<nsIWorkerDebuggerListener>> mListeners;
+
+ public:
+  explicit WorkerDebugger(WorkerPrivate* aWorkerPrivate);
+
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIWORKERDEBUGGER
+
+  void AssertIsOnParentThread();
+
+  void Close();
+
+  void PostMessageToDebugger(const nsAString& aMessage);
+
+  void ReportErrorToDebugger(const nsAString& aFilename, uint32_t aLineno,
+                             const nsAString& aMessage);
+
+ private:
+  virtual ~WorkerDebugger();
+
+  void PostMessageToDebuggerOnMainThread(const nsAString& aMessage);
+
+  void ReportErrorToDebuggerOnMainThread(const nsAString& aFilename,
+                                         uint32_t aLineno,
+                                         const nsAString& aMessage);
+
+  nsCOMPtr<nsPIDOMWindowInner> DedicatedWorkerWindow();
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_workers_WorkerDebugger_h
diff --git a/dom/workers/WorkerDebuggerManager.cpp b/dom/workers/WorkerDebuggerManager.cpp
new file mode 100644
index 0000000000..dfca4748b7
--- /dev/null
+++ b/dom/workers/WorkerDebuggerManager.cpp
@@ -0,0 +1,330 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "WorkerDebuggerManager.h"
+
+#include "nsSimpleEnumerator.h"
+
+#include "mozilla/dom/JSExecutionManager.h"
+#include "mozilla/ClearOnShutdown.h"
+#include "mozilla/Services.h"
+#include "mozilla/StaticPtr.h"
+
+#include "WorkerDebugger.h"
+#include "WorkerPrivate.h"
+#include "nsIObserverService.h"
+
+namespace mozilla::dom {
+
+namespace {
+
+class RegisterDebuggerMainThreadRunnable final : public mozilla::Runnable {
+  WorkerPrivate* mWorkerPrivate;
+  bool mNotifyListeners;
+
+ public:
+  RegisterDebuggerMainThreadRunnable(WorkerPrivate* aWorkerPrivate,
+                                     bool aNotifyListeners)
+      : mozilla::Runnable("RegisterDebuggerMainThreadRunnable"),
+        mWorkerPrivate(aWorkerPrivate),
+        mNotifyListeners(aNotifyListeners) {}
+
+ private:
+  ~RegisterDebuggerMainThreadRunnable() = default;
+
+  NS_IMETHOD
+  Run() override {
+    WorkerDebuggerManager* manager = WorkerDebuggerManager::Get();
+    MOZ_ASSERT(manager);
+
+    manager->RegisterDebuggerMainThread(mWorkerPrivate, mNotifyListeners);
+    return NS_OK;
+  }
+};
+
+class UnregisterDebuggerMainThreadRunnable final : public mozilla::Runnable {
+  WorkerPrivate* mWorkerPrivate;
+
+ public:
+  explicit UnregisterDebuggerMainThreadRunnable(WorkerPrivate* aWorkerPrivate)
+      : mozilla::Runnable("UnregisterDebuggerMainThreadRunnable"),
+        mWorkerPrivate(aWorkerPrivate) {}
+
+ private:
+  ~UnregisterDebuggerMainThreadRunnable() = default;
+
+  NS_IMETHOD
+  Run() override {
+    WorkerDebuggerManager* manager = WorkerDebuggerManager::Get();
+    MOZ_ASSERT(manager);
+
+    manager->UnregisterDebuggerMainThread(mWorkerPrivate);
+    return NS_OK;
+  }
+};
+
+static StaticRefPtr<WorkerDebuggerManager> gWorkerDebuggerManager;
+
+} /* anonymous namespace */
+
+class WorkerDebuggerEnumerator final : public nsSimpleEnumerator {
+  nsTArray<RefPtr<WorkerDebugger>> mDebuggers;
+  uint32_t mIndex;
+
+ public:
+  explicit WorkerDebuggerEnumerator(
+      const nsTArray<RefPtr<WorkerDebugger>>& aDebuggers)
+      : mDebuggers(aDebuggers.Clone()), mIndex(0) {}
+
+  NS_DECL_NSISIMPLEENUMERATOR
+
+  const nsID& DefaultInterface() override {
+    return NS_GET_IID(nsIWorkerDebugger);
+  }
+
+ private:
+  ~WorkerDebuggerEnumerator() override = default;
+};
+
+NS_IMETHODIMP
+WorkerDebuggerEnumerator::HasMoreElements(bool* aResult) {
+  *aResult = mIndex < mDebuggers.Length();
+  return NS_OK;
+};
+
+NS_IMETHODIMP
+WorkerDebuggerEnumerator::GetNext(nsISupports** aResult) {
+  if (mIndex == mDebuggers.Length()) {
+    return NS_ERROR_FAILURE;
+  }
+
+  mDebuggers.ElementAt(mIndex++).forget(aResult);
+  return NS_OK;
+};
+
+WorkerDebuggerManager::WorkerDebuggerManager()
+    : mMutex("WorkerDebuggerManager::mMutex") {
+  AssertIsOnMainThread();
+}
+
+WorkerDebuggerManager::~WorkerDebuggerManager() { AssertIsOnMainThread(); }
+
+// static
+already_AddRefed<WorkerDebuggerManager> WorkerDebuggerManager::GetInstance() {
+  RefPtr<WorkerDebuggerManager> manager = WorkerDebuggerManager::GetOrCreate();
+  return manager.forget();
+}
+
+// static
+WorkerDebuggerManager* WorkerDebuggerManager::GetOrCreate() {
+  AssertIsOnMainThread();
+
+  if (!gWorkerDebuggerManager) {
+    // The observer service now owns us until shutdown.
+    gWorkerDebuggerManager = new WorkerDebuggerManager();
+    if (NS_SUCCEEDED(gWorkerDebuggerManager->Init())) {
+      ClearOnShutdown(&gWorkerDebuggerManager);
+    } else {
+      NS_WARNING("Failed to initialize worker debugger manager!");
+      gWorkerDebuggerManager = nullptr;
+    }
+  }
+
+  return gWorkerDebuggerManager;
+}
+
+WorkerDebuggerManager* WorkerDebuggerManager::Get() {
+  MOZ_ASSERT(gWorkerDebuggerManager);
+  return gWorkerDebuggerManager;
+}
+
+NS_IMPL_ISUPPORTS(WorkerDebuggerManager, nsIObserver, nsIWorkerDebuggerManager);
+
+NS_IMETHODIMP
+WorkerDebuggerManager::Observe(nsISupports* aSubject, const char* aTopic,
+                               const char16_t* aData) {
+  if (!strcmp(aTopic, NS_XPCOM_SHUTDOWN_OBSERVER_ID)) {
+    Shutdown();
+    return NS_OK;
+  }
+
+  MOZ_ASSERT_UNREACHABLE("Unknown observer topic!");
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WorkerDebuggerManager::GetWorkerDebuggerEnumerator(
+    nsISimpleEnumerator** aResult) {
+  AssertIsOnMainThread();
+
+  RefPtr<WorkerDebuggerEnumerator> enumerator =
+      new WorkerDebuggerEnumerator(mDebuggers);
+  enumerator.forget(aResult);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WorkerDebuggerManager::AddListener(
+    nsIWorkerDebuggerManagerListener* aListener) {
+  AssertIsOnMainThread();
+
+  MutexAutoLock lock(mMutex);
+
+  if (mListeners.Contains(aListener)) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
+  mListeners.AppendElement(aListener);
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WorkerDebuggerManager::RemoveListener(
+    nsIWorkerDebuggerManagerListener* aListener) {
+  AssertIsOnMainThread();
+
+  MutexAutoLock lock(mMutex);
+
+  if (!mListeners.Contains(aListener)) {
+    return NS_OK;
+  }
+
+  mListeners.RemoveElement(aListener);
+  return NS_OK;
+}
+
+nsresult WorkerDebuggerManager::Init() {
+  nsCOMPtr<nsIObserverService> obs = services::GetObserverService();
+  NS_ENSURE_TRUE(obs, NS_ERROR_FAILURE);
+
+  nsresult rv = obs->AddObserver(this, NS_XPCOM_SHUTDOWN_OBSERVER_ID, false);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  return NS_OK;
+}
+
+void WorkerDebuggerManager::Shutdown() {
+  AssertIsOnMainThread();
+
+  MutexAutoLock lock(mMutex);
+
+  mListeners.Clear();
+}
+
+void WorkerDebuggerManager::RegisterDebugger(WorkerPrivate* aWorkerPrivate) {
+  aWorkerPrivate->AssertIsOnParentThread();
+
+  if (NS_IsMainThread()) {
+    // When the parent thread is the main thread, it will always block until all
+    // register liseners have been called, since it cannot continue until the
+    // call to RegisterDebuggerMainThread returns.
+    //
+    // In this case, it is always safe to notify all listeners on the main
+    // thread, even if there were no listeners at the time this method was
+    // called, so we can always pass true for the value of aNotifyListeners.
+    // This avoids having to lock mMutex to check whether mListeners is empty.
+    RegisterDebuggerMainThread(aWorkerPrivate, true);
+  } else {
+    // We guarantee that if any register listeners are called, the worker does
+    // not start running until all register listeners have been called. To
+    // guarantee this, the parent thread should block until all register
+    // listeners have been called.
+    //
+    // However, to avoid overhead when the debugger is not being used, the
+    // parent thread will only block if there were any listeners at the time
+    // this method was called. As a result, we should not notify any listeners
+    // on the main thread if there were no listeners at the time this method was
+    // called, because the parent will not be blocking in that case.
+    bool hasListeners = false;
+    {
+      MutexAutoLock lock(mMutex);
+
+      hasListeners = !mListeners.IsEmpty();
+    }
+
+    nsCOMPtr<nsIRunnable> runnable =
+        new RegisterDebuggerMainThreadRunnable(aWorkerPrivate, hasListeners);
+    MOZ_ALWAYS_SUCCEEDS(NS_DispatchToMainThread(runnable, NS_DISPATCH_NORMAL));
+
+    if (hasListeners) {
+      aWorkerPrivate->WaitForIsDebuggerRegistered(true);
+    }
+  }
+}
+
+void WorkerDebuggerManager::UnregisterDebugger(WorkerPrivate* aWorkerPrivate) {
+  aWorkerPrivate->AssertIsOnParentThread();
+
+  if (NS_IsMainThread()) {
+    UnregisterDebuggerMainThread(aWorkerPrivate);
+  } else {
+    nsCOMPtr<nsIRunnable> runnable =
+        new UnregisterDebuggerMainThreadRunnable(aWorkerPrivate);
+    MOZ_ALWAYS_SUCCEEDS(NS_DispatchToMainThread(runnable, NS_DISPATCH_NORMAL));
+
+    aWorkerPrivate->WaitForIsDebuggerRegistered(false);
+  }
+}
+
+void WorkerDebuggerManager::RegisterDebuggerMainThread(
+    WorkerPrivate* aWorkerPrivate, bool aNotifyListeners) {
+  AssertIsOnMainThread();
+
+  RefPtr<WorkerDebugger> debugger = new WorkerDebugger(aWorkerPrivate);
+  mDebuggers.AppendElement(debugger);
+
+  aWorkerPrivate->SetDebugger(debugger);
+
+  if (aNotifyListeners) {
+    for (const auto& listener : CloneListeners()) {
+      listener->OnRegister(debugger);
+    }
+  }
+
+  aWorkerPrivate->SetIsDebuggerRegistered(true);
+}
+
+void WorkerDebuggerManager::UnregisterDebuggerMainThread(
+    WorkerPrivate* aWorkerPrivate) {
+  AssertIsOnMainThread();
+
+  // There is nothing to do here if the debugger was never succesfully
+  // registered. We need to check this on the main thread because the worker
+  // does not wait for the registration to complete if there were no listeners
+  // installed when it started.
+  if (!aWorkerPrivate->IsDebuggerRegistered()) {
+    return;
+  }
+
+  RefPtr<WorkerDebugger> debugger = aWorkerPrivate->Debugger();
+  mDebuggers.RemoveElement(debugger);
+
+  aWorkerPrivate->SetDebugger(nullptr);
+
+  for (const auto& listener : CloneListeners()) {
+    listener->OnUnregister(debugger);
+  }
+
+  debugger->Close();
+  aWorkerPrivate->SetIsDebuggerRegistered(false);
+}
+
+uint32_t WorkerDebuggerManager::GetDebuggersLength() const {
+  return mDebuggers.Length();
+}
+
+WorkerDebugger* WorkerDebuggerManager::GetDebuggerAt(uint32_t aIndex) const {
+  return mDebuggers.SafeElementAt(aIndex, nullptr);
+}
+
+nsTArray<nsCOMPtr<nsIWorkerDebuggerManagerListener>>
+WorkerDebuggerManager::CloneListeners() {
+  MutexAutoLock lock(mMutex);
+
+  return mListeners.Clone();
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/workers/WorkerDebuggerManager.h b/dom/workers/WorkerDebuggerManager.h
new file mode 100644
index 0000000000..7c22a6b62c
--- /dev/null
+++ b/dom/workers/WorkerDebuggerManager.h
@@ -0,0 +1,116 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_workers_workerdebuggermanager_h
+#define mozilla_dom_workers_workerdebuggermanager_h
+
+#include "MainThreadUtils.h"
+#include "mozilla/AlreadyAddRefed.h"
+#include "mozilla/Mutex.h"
+#include "nsCOMPtr.h"
+#include "nsDebug.h"
+#include "nsIObserver.h"
+#include "nsISupports.h"
+#include "nsIWorkerDebuggerManager.h"
+#include "nsTArray.h"
+
+#define WORKERDEBUGGERMANAGER_CID                    \
+  {                                                  \
+    0x62ec8731, 0x55ad, 0x4246, {                    \
+      0xb2, 0xea, 0xf2, 0x6c, 0x1f, 0xe1, 0x9d, 0x2d \
+    }                                                \
+  }
+#define WORKERDEBUGGERMANAGER_CONTRACTID \
+  "@mozilla.org/dom/workers/workerdebuggermanager;1"
+
+namespace mozilla::dom {
+
+class WorkerDebugger;
+class WorkerPrivate;
+
+class WorkerDebuggerManager final : public nsIObserver,
+                                    public nsIWorkerDebuggerManager {
+  Mutex mMutex MOZ_UNANNOTATED;
+
+  // Protected by mMutex.
+  nsTArray<nsCOMPtr<nsIWorkerDebuggerManagerListener>> mListeners;
+
+  // Only touched on the main thread.
+  nsTArray<RefPtr<WorkerDebugger>> mDebuggers;
+
+ public:
+  static already_AddRefed<WorkerDebuggerManager> GetInstance();
+
+  static WorkerDebuggerManager* GetOrCreate();
+
+  static WorkerDebuggerManager* Get();
+
+  WorkerDebuggerManager();
+
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSIOBSERVER
+  NS_DECL_NSIWORKERDEBUGGERMANAGER
+
+  nsresult Init();
+
+  void Shutdown();
+
+  void RegisterDebugger(WorkerPrivate* aWorkerPrivate);
+
+  void RegisterDebuggerMainThread(WorkerPrivate* aWorkerPrivate,
+                                  bool aNotifyListeners);
+
+  void UnregisterDebugger(WorkerPrivate* aWorkerPrivate);
+
+  void UnregisterDebuggerMainThread(WorkerPrivate* aWorkerPrivate);
+
+  uint32_t GetDebuggersLength() const;
+
+  WorkerDebugger* GetDebuggerAt(uint32_t aIndex) const;
+
+ private:
+  nsTArray<nsCOMPtr<nsIWorkerDebuggerManagerListener>> CloneListeners();
+
+  virtual ~WorkerDebuggerManager();
+};
+
+inline nsresult RegisterWorkerDebugger(WorkerPrivate* aWorkerPrivate) {
+  WorkerDebuggerManager* manager;
+
+  if (NS_IsMainThread()) {
+    manager = WorkerDebuggerManager::GetOrCreate();
+    if (!manager) {
+      NS_WARNING("Failed to create worker debugger manager!");
+      return NS_ERROR_FAILURE;
+    }
+  } else {
+    manager = WorkerDebuggerManager::Get();
+  }
+
+  manager->RegisterDebugger(aWorkerPrivate);
+  return NS_OK;
+}
+
+inline nsresult UnregisterWorkerDebugger(WorkerPrivate* aWorkerPrivate) {
+  WorkerDebuggerManager* manager;
+
+  if (NS_IsMainThread()) {
+    manager = WorkerDebuggerManager::GetOrCreate();
+    if (!manager) {
+      NS_WARNING("Failed to create worker debugger manager!");
+      return NS_ERROR_FAILURE;
+    }
+  } else {
+    manager = WorkerDebuggerManager::Get();
+  }
+
+  manager->UnregisterDebugger(aWorkerPrivate);
+  return NS_OK;
+}
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_workers_workerdebuggermanager_h
diff --git a/dom/workers/WorkerDocumentListener.cpp b/dom/workers/WorkerDocumentListener.cpp
new file mode 100644
index 0000000000..cdbe30e072
--- /dev/null
+++ b/dom/workers/WorkerDocumentListener.cpp
@@ -0,0 +1,111 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "WorkerDocumentListener.h"
+#include "mozilla/dom/Document.h"
+#include "mozilla/dom/WorkerPrivate.h"
+#include "mozilla/dom/WorkerRef.h"
+#include "mozilla/dom/WorkerRunnable.h"
+#include "mozilla/dom/WorkerScope.h"
+#include "nsGlobalWindowInner.h"
+
+namespace mozilla::dom {
+
+WorkerDocumentListener::WorkerDocumentListener()
+    : mMutex("mozilla::dom::WorkerDocumentListener::mMutex") {}
+
+WorkerDocumentListener::~WorkerDocumentListener() = default;
+
+RefPtr<WorkerDocumentListener> WorkerDocumentListener::Create(
+    WorkerPrivate* aWorkerPrivate) {
+  MOZ_ASSERT(aWorkerPrivate);
+  aWorkerPrivate->AssertIsOnWorkerThread();
+
+  auto listener = MakeRefPtr<WorkerDocumentListener>();
+
+  RefPtr<StrongWorkerRef> strongWorkerRef =
+      StrongWorkerRef::Create(aWorkerPrivate, "WorkerDocumentListener",
+                              [listener]() { listener->Destroy(); });
+  if (NS_WARN_IF(!strongWorkerRef)) {
+    return nullptr;
+  }
+
+  listener->mWorkerRef = new ThreadSafeWorkerRef(strongWorkerRef);
+  uint64_t windowID = aWorkerPrivate->WindowID();
+
+  aWorkerPrivate->DispatchToMainThread(NS_NewRunnableFunction(
+      "WorkerDocumentListener::Create",
+      [listener, windowID] { listener->SetListening(windowID, true); }));
+
+  return listener;
+}
+
+void WorkerDocumentListener::OnVisible(bool aVisible) {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  MutexAutoLock lock(mMutex);
+  if (!mWorkerRef) {
+    // We haven't handled the runnable to release this yet.
+    return;
+  }
+
+  class VisibleRunnable final : public WorkerRunnable {
+   public:
+    VisibleRunnable(WorkerPrivate* aWorkerPrivate, bool aVisible)
+        : WorkerRunnable(aWorkerPrivate, "VisibleRunnable"),
+          mVisible(aVisible) {}
+
+    bool WorkerRun(JSContext* aCx, WorkerPrivate* aWorkerPrivate) {
+      WorkerGlobalScope* scope = aWorkerPrivate->GlobalScope();
+      MOZ_ASSERT(scope);
+      scope->OnDocumentVisible(mVisible);
+      return true;
+    }
+
+   private:
+    const bool mVisible;
+  };
+
+  auto runnable = MakeRefPtr<VisibleRunnable>(mWorkerRef->Private(), aVisible);
+  runnable->Dispatch();
+}
+
+void WorkerDocumentListener::SetListening(uint64_t aWindowID, bool aListen) {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  auto* window = nsGlobalWindowInner::GetInnerWindowWithId(aWindowID);
+  Document* doc = window->GetExtantDoc();
+  if (NS_WARN_IF(!doc)) {
+    // This would typically happen during shutdown if there is an active worker
+    // listening for document events. The Document may already be freed when we
+    // try to deregister for notifications.
+    return;
+  }
+
+  if (aListen) {
+    doc->AddWorkerDocumentListener(this);
+  } else {
+    doc->RemoveWorkerDocumentListener(this);
+  }
+}
+
+void WorkerDocumentListener::Destroy() {
+  MutexAutoLock lock(mMutex);
+
+  MOZ_ASSERT(mWorkerRef);
+  WorkerPrivate* workerPrivate = mWorkerRef->Private();
+  MOZ_ASSERT(workerPrivate);
+  workerPrivate->AssertIsOnWorkerThread();
+
+  uint64_t windowID = workerPrivate->WindowID();
+  workerPrivate->DispatchToMainThread(NS_NewRunnableFunction(
+      "WorkerDocumentListener::Destroy", [self = RefPtr{this}, windowID] {
+        self->SetListening(windowID, false);
+      }));
+  mWorkerRef = nullptr;
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/workers/WorkerDocumentListener.h b/dom/workers/WorkerDocumentListener.h
new file mode 100644
index 0000000000..4bb46cadf2
--- /dev/null
+++ b/dom/workers/WorkerDocumentListener.h
@@ -0,0 +1,40 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_WorkerDocumentListener_h__
+#define mozilla_dom_WorkerDocumentListener_h__
+
+#include "mozilla/Mutex.h"
+#include "mozilla/RefPtr.h"
+#include "nsISupportsImpl.h"
+
+namespace mozilla::dom {
+class ThreadSafeWorkerRef;
+class WorkerPrivate;
+class WeakWorkerRef;
+
+class WorkerDocumentListener final {
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(WorkerDocumentListener)
+
+ public:
+  WorkerDocumentListener();
+
+  void OnVisible(bool aVisible);
+  void SetListening(uint64_t aWindowID, bool aListen);
+  void Destroy();
+
+  static RefPtr<WorkerDocumentListener> Create(WorkerPrivate* aWorkerPrivate);
+
+ private:
+  ~WorkerDocumentListener();
+
+  Mutex mMutex MOZ_UNANNOTATED;  // protects mWorkerRef
+  RefPtr<ThreadSafeWorkerRef> mWorkerRef;
+};
+
+}  // namespace mozilla::dom
+
+#endif /* mozilla_dom_WorkerDocumentListener_h__ */
diff --git a/dom/workers/WorkerError.cpp b/dom/workers/WorkerError.cpp
new file mode 100644
index 0000000000..1b75599211
--- /dev/null
+++ b/dom/workers/WorkerError.cpp
@@ -0,0 +1,452 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "WorkerError.h"
+
+#include <stdio.h>
+#include <algorithm>
+#include <utility>
+#include "MainThreadUtils.h"
+#include "WorkerPrivate.h"
+#include "WorkerRunnable.h"
+#include "WorkerScope.h"
+#include "js/ComparisonOperators.h"
+#include "js/UniquePtr.h"
+#include "js/friend/ErrorMessages.h"
+#include "jsapi.h"
+#include "mozilla/ArrayAlgorithm.h"
+#include "mozilla/ArrayIterator.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/BasicEvents.h"
+#include "mozilla/DOMEventTargetHelper.h"
+#include "mozilla/ErrorResult.h"
+#include "mozilla/EventDispatcher.h"
+#include "mozilla/RefPtr.h"
+#include "mozilla/Span.h"
+#include "mozilla/ThreadSafeWeakPtr.h"
+#include "mozilla/Unused.h"
+#include "mozilla/dom/BindingDeclarations.h"
+#include "mozilla/dom/BindingUtils.h"
+#include "mozilla/dom/ErrorEvent.h"
+#include "mozilla/dom/ErrorEventBinding.h"
+#include "mozilla/dom/Event.h"
+#include "mozilla/dom/EventBinding.h"
+#include "mozilla/dom/EventTarget.h"
+#include "mozilla/dom/RemoteWorkerChild.h"
+#include "mozilla/dom/RemoteWorkerTypes.h"
+#include "mozilla/dom/RootedDictionary.h"
+#include "mozilla/dom/ServiceWorkerManager.h"
+#include "mozilla/dom/ServiceWorkerUtils.h"
+#include "mozilla/dom/SimpleGlobalObject.h"
+#include "mozilla/dom/Worker.h"
+#include "mozilla/dom/WorkerCommon.h"
+#include "mozilla/dom/WorkerDebuggerGlobalScopeBinding.h"
+#include "mozilla/dom/WorkerGlobalScopeBinding.h"
+#include "mozilla/fallible.h"
+#include "nsCOMPtr.h"
+#include "nsDebug.h"
+#include "nsGlobalWindowInner.h"
+#include "nsIConsoleService.h"
+#include "nsIScriptError.h"
+#include "nsScriptError.h"
+#include "nsServiceManagerUtils.h"
+#include "nsString.h"
+#include "nsWrapperCacheInlines.h"
+#include "nscore.h"
+#include "xpcpublic.h"
+
+namespace mozilla::dom {
+
+namespace {
+
+class ReportErrorRunnable final : public WorkerDebuggeeRunnable {
+  UniquePtr<WorkerErrorReport> mReport;
+
+ public:
+  ReportErrorRunnable(WorkerPrivate* aWorkerPrivate,
+                      UniquePtr<WorkerErrorReport> aReport)
+      : WorkerDebuggeeRunnable(aWorkerPrivate, "ReportErrorRunnable"),
+        mReport(std::move(aReport)) {}
+
+ private:
+  virtual void PostDispatch(WorkerPrivate* aWorkerPrivate,
+                            bool aDispatchResult) override {
+    aWorkerPrivate->AssertIsOnWorkerThread();
+
+    // Dispatch may fail if the worker was canceled, no need to report that as
+    // an error, so don't call base class PostDispatch.
+  }
+
+  virtual bool WorkerRun(JSContext* aCx,
+                         WorkerPrivate* aWorkerPrivate) override {
+    uint64_t innerWindowId;
+    bool fireAtScope = true;
+
+    bool workerIsAcceptingEvents = aWorkerPrivate->IsAcceptingEvents();
+
+    WorkerPrivate* parent = aWorkerPrivate->GetParent();
+    if (parent) {
+      innerWindowId = 0;
+    } else {
+      AssertIsOnMainThread();
+
+      if (aWorkerPrivate->IsSharedWorker()) {
+        aWorkerPrivate->GetRemoteWorkerController()
+            ->ErrorPropagationOnMainThread(mReport.get(),
+                                           /* isErrorEvent */ true);
+        return true;
+      }
+
+      // Service workers do not have a main thread parent global, so normal
+      // worker error reporting will crash.  Instead, pass the error to
+      // the ServiceWorkerManager to report on any controlled documents.
+      if (aWorkerPrivate->IsServiceWorker()) {
+        RefPtr<RemoteWorkerChild> actor(
+            aWorkerPrivate->GetRemoteWorkerController());
+
+        Unused << NS_WARN_IF(!actor);
+
+        if (actor) {
+          actor->ErrorPropagationOnMainThread(nullptr, false);
+        }
+
+        return true;
+      }
+
+      // The innerWindowId is only required if we are going to ReportError
+      // below, which is gated on this condition. The inner window correctness
+      // check is only going to succeed when the worker is accepting events.
+      if (workerIsAcceptingEvents) {
+        aWorkerPrivate->AssertInnerWindowIsCorrect();
+        innerWindowId = aWorkerPrivate->WindowID();
+      }
+    }
+
+    // Don't fire this event if the JS object has been disconnected from the
+    // private object.
+    if (!workerIsAcceptingEvents) {
+      return true;
+    }
+
+    WorkerErrorReport::ReportError(aCx, parent, fireAtScope,
+                                   aWorkerPrivate->ParentEventTargetRef(),
+                                   std::move(mReport), innerWindowId);
+    return true;
+  }
+};
+
+class ReportGenericErrorRunnable final : public WorkerDebuggeeRunnable {
+ public:
+  static void CreateAndDispatch(WorkerPrivate* aWorkerPrivate) {
+    MOZ_ASSERT(aWorkerPrivate);
+    aWorkerPrivate->AssertIsOnWorkerThread();
+
+    RefPtr<ReportGenericErrorRunnable> runnable =
+        new ReportGenericErrorRunnable(aWorkerPrivate);
+    runnable->Dispatch();
+  }
+
+ private:
+  explicit ReportGenericErrorRunnable(WorkerPrivate* aWorkerPrivate)
+      : WorkerDebuggeeRunnable(aWorkerPrivate, "ReportGenericErrorRunnable") {
+    aWorkerPrivate->AssertIsOnWorkerThread();
+  }
+
+  void PostDispatch(WorkerPrivate* aWorkerPrivate,
+                    bool aDispatchResult) override {
+    aWorkerPrivate->AssertIsOnWorkerThread();
+
+    // Dispatch may fail if the worker was canceled, no need to report that as
+    // an error, so don't call base class PostDispatch.
+  }
+
+  bool WorkerRun(JSContext* aCx, WorkerPrivate* aWorkerPrivate) override {
+    if (!aWorkerPrivate->IsAcceptingEvents()) {
+      return true;
+    }
+
+    if (aWorkerPrivate->IsSharedWorker()) {
+      aWorkerPrivate->GetRemoteWorkerController()->ErrorPropagationOnMainThread(
+          nullptr, false);
+      return true;
+    }
+
+    if (aWorkerPrivate->IsServiceWorker()) {
+      RefPtr<RemoteWorkerChild> actor(
+          aWorkerPrivate->GetRemoteWorkerController());
+
+      Unused << NS_WARN_IF(!actor);
+
+      if (actor) {
+        actor->ErrorPropagationOnMainThread(nullptr, false);
+      }
+
+      return true;
+    }
+
+    RefPtr<mozilla::dom::EventTarget> parentEventTarget =
+        aWorkerPrivate->ParentEventTargetRef();
+    RefPtr<Event> event =
+        Event::Constructor(parentEventTarget, u"error"_ns, EventInit());
+    event->SetTrusted(true);
+
+    parentEventTarget->DispatchEvent(*event);
+    return true;
+  }
+};
+
+}  // namespace
+
+void WorkerErrorBase::AssignErrorBase(JSErrorBase* aReport) {
+  CopyUTF8toUTF16(MakeStringSpan(aReport->filename.c_str()), mFilename);
+  mLineNumber = aReport->lineno;
+  mColumnNumber = aReport->column.oneOriginValue();
+  mErrorNumber = aReport->errorNumber;
+}
+
+void WorkerErrorNote::AssignErrorNote(JSErrorNotes::Note* aNote) {
+  WorkerErrorBase::AssignErrorBase(aNote);
+  xpc::ErrorNote::ErrorNoteToMessageString(aNote, mMessage);
+}
+
+WorkerErrorReport::WorkerErrorReport()
+    : mIsWarning(false), mExnType(JSEXN_ERR), mMutedError(false) {}
+
+void WorkerErrorReport::AssignErrorReport(JSErrorReport* aReport) {
+  WorkerErrorBase::AssignErrorBase(aReport);
+  xpc::ErrorReport::ErrorReportToMessageString(aReport, mMessage);
+
+  mLine.Assign(aReport->linebuf(), aReport->linebufLength());
+  mIsWarning = aReport->isWarning();
+  MOZ_ASSERT(aReport->exnType >= JSEXN_FIRST && aReport->exnType < JSEXN_LIMIT);
+  mExnType = JSExnType(aReport->exnType);
+  mMutedError = aReport->isMuted;
+
+  if (aReport->notes) {
+    if (!mNotes.SetLength(aReport->notes->length(), fallible)) {
+      return;
+    }
+
+    size_t i = 0;
+    for (auto&& note : *aReport->notes) {
+      mNotes.ElementAt(i).AssignErrorNote(note.get());
+      i++;
+    }
+  }
+}
+
+// aWorkerPrivate is the worker thread we're on (or the main thread, if null)
+// aTarget is the worker object that we are going to fire an error at
+// (if any).
+/* static */
+void WorkerErrorReport::ReportError(
+    JSContext* aCx, WorkerPrivate* aWorkerPrivate, bool aFireAtScope,
+    DOMEventTargetHelper* aTarget, UniquePtr<WorkerErrorReport> aReport,
+    uint64_t aInnerWindowId, JS::Handle<JS::Value> aException) {
+  if (aWorkerPrivate) {
+    aWorkerPrivate->AssertIsOnWorkerThread();
+  } else {
+    AssertIsOnMainThread();
+  }
+
+  // We should not fire error events for warnings but instead make sure that
+  // they show up in the error console.
+  if (!aReport->mIsWarning) {
+    // First fire an ErrorEvent at the worker.
+    RootedDictionary<ErrorEventInit> init(aCx);
+
+    if (aReport->mMutedError) {
+      init.mMessage.AssignLiteral("Script error.");
+    } else {
+      init.mMessage = aReport->mMessage;
+      init.mFilename = aReport->mFilename;
+      init.mLineno = aReport->mLineNumber;
+      init.mColno = aReport->mColumnNumber;
+      init.mError = aException;
+    }
+
+    init.mCancelable = true;
+    init.mBubbles = false;
+
+    if (aTarget) {
+      RefPtr<ErrorEvent> event =
+          ErrorEvent::Constructor(aTarget, u"error"_ns, init);
+      event->SetTrusted(true);
+
+      bool defaultActionEnabled =
+          aTarget->DispatchEvent(*event, CallerType::System, IgnoreErrors());
+      if (!defaultActionEnabled) {
+        return;
+      }
+    }
+
+    // Now fire an event at the global object, but don't do that if the error
+    // code is too much recursion and this is the same script threw the error.
+    // XXXbz the interaction of this with worker errors seems kinda broken.
+    // An overrecursion in the debugger or debugger sandbox will get turned
+    // into an error event on our parent worker!
+    // https://bugzilla.mozilla.org/show_bug.cgi?id=1271441 tracks making this
+    // better.
+    if (aFireAtScope &&
+        (aTarget || aReport->mErrorNumber != JSMSG_OVER_RECURSED)) {
+      JS::Rooted<JSObject*> global(aCx, JS::CurrentGlobalOrNull(aCx));
+      NS_ASSERTION(global, "This should never be null!");
+
+      nsEventStatus status = nsEventStatus_eIgnore;
+
+      if (aWorkerPrivate) {
+        RefPtr<WorkerGlobalScope> globalScope;
+        UNWRAP_OBJECT(WorkerGlobalScope, &global, globalScope);
+
+        if (!globalScope) {
+          WorkerDebuggerGlobalScope* globalScope = nullptr;
+          UNWRAP_OBJECT(WorkerDebuggerGlobalScope, &global, globalScope);
+
+          MOZ_ASSERT_IF(globalScope,
+                        globalScope->GetWrapperPreserveColor() == global);
+          if (globalScope || IsWorkerDebuggerSandbox(global)) {
+            aWorkerPrivate->ReportErrorToDebugger(
+                aReport->mFilename, aReport->mLineNumber, aReport->mMessage);
+            return;
+          }
+
+          MOZ_ASSERT(SimpleGlobalObject::SimpleGlobalType(global) ==
+                     SimpleGlobalObject::GlobalType::BindingDetail);
+          // XXXbz We should really log this to console, but unwinding out of
+          // this stuff without ending up firing any events is ... hard.  Just
+          // return for now.
+          // https://bugzilla.mozilla.org/show_bug.cgi?id=1271441 tracks
+          // making this better.
+          return;
+        }
+
+        MOZ_ASSERT(globalScope->GetWrapperPreserveColor() == global);
+
+        RefPtr<ErrorEvent> event =
+            ErrorEvent::Constructor(aTarget, u"error"_ns, init);
+        event->SetTrusted(true);
+
+        if (NS_FAILED(EventDispatcher::DispatchDOMEvent(
+                globalScope, nullptr, event, nullptr, &status))) {
+          NS_WARNING("Failed to dispatch worker thread error event!");
+          status = nsEventStatus_eIgnore;
+        }
+      } else if (nsGlobalWindowInner* win = xpc::WindowOrNull(global)) {
+        MOZ_ASSERT(NS_IsMainThread());
+
+        if (!win->HandleScriptError(init, &status)) {
+          NS_WARNING("Failed to dispatch main thread error event!");
+          status = nsEventStatus_eIgnore;
+        }
+      }
+
+      // Was preventDefault() called?
+      if (status == nsEventStatus_eConsumeNoDefault) {
+        return;
+      }
+    }
+  }
+
+  // Now fire a runnable to do the same on the parent's thread if we can.
+  if (aWorkerPrivate) {
+    RefPtr<ReportErrorRunnable> runnable =
+        new ReportErrorRunnable(aWorkerPrivate, std::move(aReport));
+    runnable->Dispatch();
+    return;
+  }
+
+  // Otherwise log an error to the error console.
+  WorkerErrorReport::LogErrorToConsole(aCx, *aReport, aInnerWindowId);
+}
+
+/* static */
+void WorkerErrorReport::LogErrorToConsole(JSContext* aCx,
+                                          WorkerErrorReport& aReport,
+                                          uint64_t aInnerWindowId) {
+  JS::Rooted<JSObject*> stack(aCx, aReport.ReadStack(aCx));
+  JS::Rooted<JSObject*> stackGlobal(aCx, JS::CurrentGlobalOrNull(aCx));
+
+  ErrorData errorData(
+      aReport.mIsWarning, aReport.mLineNumber, aReport.mColumnNumber,
+      aReport.mMessage, aReport.mFilename, aReport.mLine,
+      TransformIntoNewArray(aReport.mNotes, [](const WorkerErrorNote& note) {
+        return ErrorDataNote(note.mLineNumber, note.mColumnNumber,
+                             note.mMessage, note.mFilename);
+      }));
+  LogErrorToConsole(errorData, aInnerWindowId, stack, stackGlobal);
+}
+
+/* static */
+void WorkerErrorReport::LogErrorToConsole(const ErrorData& aReport,
+                                          uint64_t aInnerWindowId,
+                                          JS::Handle<JSObject*> aStack,
+                                          JS::Handle<JSObject*> aStackGlobal) {
+  AssertIsOnMainThread();
+
+  RefPtr<nsScriptErrorBase> scriptError =
+      CreateScriptError(nullptr, JS::NothingHandleValue, aStack, aStackGlobal);
+
+  NS_WARNING_ASSERTION(scriptError, "Failed to create script error!");
+
+  if (scriptError) {
+    nsAutoCString category("Web Worker");
+    uint32_t flags = aReport.isWarning() ? nsIScriptError::warningFlag
+                                         : nsIScriptError::errorFlag;
+    if (NS_FAILED(scriptError->nsIScriptError::InitWithWindowID(
+            aReport.message(), aReport.filename(), aReport.line(),
+            aReport.lineNumber(), aReport.columnNumber(), flags, category,
+            aInnerWindowId))) {
+      NS_WARNING("Failed to init script error!");
+      scriptError = nullptr;
+    }
+
+    for (const ErrorDataNote& note : aReport.notes()) {
+      nsScriptErrorNote* noteObject = new nsScriptErrorNote();
+      noteObject->Init(note.message(), note.filename(), 0, note.lineNumber(),
+                       note.columnNumber());
+      scriptError->AddNote(noteObject);
+    }
+  }
+
+  nsCOMPtr<nsIConsoleService> consoleService =
+      do_GetService(NS_CONSOLESERVICE_CONTRACTID);
+  NS_WARNING_ASSERTION(consoleService, "Failed to get console service!");
+
+  if (consoleService) {
+    if (scriptError) {
+      if (NS_SUCCEEDED(consoleService->LogMessage(scriptError))) {
+        return;
+      }
+      NS_WARNING("LogMessage failed!");
+    } else if (NS_SUCCEEDED(consoleService->LogStringMessage(
+                   aReport.message().BeginReading()))) {
+      return;
+    }
+    NS_WARNING("LogStringMessage failed!");
+  }
+
+  NS_ConvertUTF16toUTF8 msg(aReport.message());
+  NS_ConvertUTF16toUTF8 filename(aReport.filename());
+
+  static const char kErrorString[] = "JS error in Web Worker: %s [%s:%u]";
+
+#ifdef ANDROID
+  __android_log_print(ANDROID_LOG_INFO, "Gecko", kErrorString, msg.get(),
+                      filename.get(), aReport.lineNumber());
+#endif
+
+  fprintf(stderr, kErrorString, msg.get(), filename.get(),
+          aReport.lineNumber());
+  fflush(stderr);
+}
+
+/* static */
+void WorkerErrorReport::CreateAndDispatchGenericErrorRunnableToParent(
+    WorkerPrivate* aWorkerPrivate) {
+  ReportGenericErrorRunnable::CreateAndDispatch(aWorkerPrivate);
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/workers/WorkerError.h b/dom/workers/WorkerError.h
new file mode 100644
index 0000000000..43600fbf1a
--- /dev/null
+++ b/dom/workers/WorkerError.h
@@ -0,0 +1,80 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_workers_WorkerError_h
+#define mozilla_dom_workers_WorkerError_h
+
+#include "mozilla/dom/SerializedStackHolder.h"
+#include "mozilla/dom/WorkerCommon.h"
+#include "jsapi.h"
+
+namespace mozilla {
+
+class DOMEventTargetHelper;
+
+namespace dom {
+
+class ErrorData;
+class WorkerErrorBase {
+ public:
+  nsString mMessage;
+  nsString mFilename;
+  // Line number (1-origin).
+  uint32_t mLineNumber;
+  // Column number in UTF-16 code units (1-origin).
+  uint32_t mColumnNumber;
+  uint32_t mErrorNumber;
+
+  WorkerErrorBase() : mLineNumber(0), mColumnNumber(0), mErrorNumber(0) {}
+
+  void AssignErrorBase(JSErrorBase* aReport);
+};
+
+class WorkerErrorNote : public WorkerErrorBase {
+ public:
+  void AssignErrorNote(JSErrorNotes::Note* aNote);
+};
+
+class WorkerPrivate;
+
+class WorkerErrorReport : public WorkerErrorBase, public SerializedStackHolder {
+ public:
+  nsString mLine;
+  bool mIsWarning;
+  JSExnType mExnType;
+  bool mMutedError;
+  nsTArray<WorkerErrorNote> mNotes;
+
+  WorkerErrorReport();
+
+  void AssignErrorReport(JSErrorReport* aReport);
+
+  // aWorkerPrivate is the worker thread we're on (or the main thread, if null)
+  // aTarget is the worker object that we are going to fire an error at
+  // (if any).
+  // TODO: Convert this to MOZ_CAN_RUN_SCRIPT (bug 1743443)
+  MOZ_CAN_RUN_SCRIPT_BOUNDARY static void ReportError(
+      JSContext* aCx, WorkerPrivate* aWorkerPrivate, bool aFireAtScope,
+      DOMEventTargetHelper* aTarget, UniquePtr<WorkerErrorReport> aReport,
+      uint64_t aInnerWindowId,
+      JS::Handle<JS::Value> aException = JS::NullHandleValue);
+
+  static void LogErrorToConsole(JSContext* aCx, WorkerErrorReport& aReport,
+                                uint64_t aInnerWindowId);
+
+  static void LogErrorToConsole(const mozilla::dom::ErrorData& aReport,
+                                uint64_t aInnerWindowId,
+                                JS::Handle<JSObject*> aStack = nullptr,
+                                JS::Handle<JSObject*> aStackGlobal = nullptr);
+
+  static void CreateAndDispatchGenericErrorRunnableToParent(
+      WorkerPrivate* aWorkerPrivate);
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_workers_WorkerError_h
diff --git a/dom/workers/WorkerEventTarget.cpp b/dom/workers/WorkerEventTarget.cpp
new file mode 100644
index 0000000000..cb58b4f8ed
--- /dev/null
+++ b/dom/workers/WorkerEventTarget.cpp
@@ -0,0 +1,199 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "WorkerEventTarget.h"
+#include "WorkerPrivate.h"
+#include "WorkerRunnable.h"
+
+#include "mozilla/Logging.h"
+#include "mozilla/dom/ReferrerInfo.h"
+
+namespace mozilla::dom {
+
+static mozilla::LazyLogModule sWorkerEventTargetLog("WorkerEventTarget");
+
+#ifdef LOG
+#  undef LOG
+#endif
+#ifdef LOGV
+#  undef LOGV
+#endif
+#define LOG(args) MOZ_LOG(sWorkerEventTargetLog, LogLevel::Debug, args);
+#define LOGV(args) MOZ_LOG(sWorkerEventTargetLog, LogLevel::Verbose, args);
+
+namespace {
+
+class WrappedControlRunnable final : public WorkerControlRunnable {
+  nsCOMPtr<nsIRunnable> mInner;
+
+  ~WrappedControlRunnable() = default;
+
+ public:
+  WrappedControlRunnable(WorkerPrivate* aWorkerPrivate,
+                         nsCOMPtr<nsIRunnable>&& aInner)
+      : WorkerControlRunnable(aWorkerPrivate, "WrappedControlRunnable",
+                              WorkerThread),
+        mInner(std::move(aInner)) {}
+
+  virtual bool PreDispatch(WorkerPrivate* aWorkerPrivate) override {
+    // Silence bad assertions, this can be dispatched from any thread.
+    return true;
+  }
+
+  virtual void PostDispatch(WorkerPrivate* aWorkerPrivate,
+                            bool aDispatchResult) override {
+    // Silence bad assertions, this can be dispatched from any thread.
+  }
+
+  bool WorkerRun(JSContext* aCx, WorkerPrivate* aWorkerPrivate) override {
+    mInner->Run();
+    return true;
+  }
+
+  nsresult Cancel() override {
+    nsCOMPtr<nsICancelableRunnable> cr = do_QueryInterface(mInner);
+
+    // If the inner runnable is not cancellable, then just do the normal
+    // WorkerControlRunnable thing.  This will end up calling Run().
+    if (!cr) {
+      return Run();
+    }
+
+    // Otherwise call the inner runnable's Cancel() and treat this like
+    // a WorkerRunnable cancel.  We can't call WorkerControlRunnable::Cancel()
+    // in this case since that would result in both Run() and the inner
+    // Cancel() being called.
+    return cr->Cancel();
+  }
+};
+
+}  // anonymous namespace
+
+NS_IMPL_ISUPPORTS(WorkerEventTarget, nsIEventTarget, nsISerialEventTarget)
+
+WorkerEventTarget::WorkerEventTarget(WorkerPrivate* aWorkerPrivate,
+                                     Behavior aBehavior)
+    : mMutex("WorkerEventTarget"),
+      mWorkerPrivate(aWorkerPrivate),
+      mBehavior(aBehavior) {
+  LOG(("WorkerEventTarget::WorkerEventTarget [%p] aBehavior: %u", this,
+       (uint8_t)aBehavior));
+  MOZ_DIAGNOSTIC_ASSERT(mWorkerPrivate);
+}
+
+void WorkerEventTarget::ForgetWorkerPrivate(WorkerPrivate* aWorkerPrivate) {
+  LOG(("WorkerEventTarget::ForgetWorkerPrivate [%p] aWorkerPrivate: %p", this,
+       aWorkerPrivate));
+  MutexAutoLock lock(mMutex);
+  MOZ_DIAGNOSTIC_ASSERT(!mWorkerPrivate || mWorkerPrivate == aWorkerPrivate);
+  mWorkerPrivate = nullptr;
+}
+
+NS_IMETHODIMP
+WorkerEventTarget::DispatchFromScript(nsIRunnable* aRunnable, uint32_t aFlags) {
+  LOGV(("WorkerEventTarget::DispatchFromScript [%p] aRunnable: %p", this,
+        aRunnable));
+  nsCOMPtr<nsIRunnable> runnable(aRunnable);
+  return Dispatch(runnable.forget(), aFlags);
+}
+
+NS_IMETHODIMP
+WorkerEventTarget::Dispatch(already_AddRefed<nsIRunnable> aRunnable,
+                            uint32_t aFlags) {
+  nsCOMPtr<nsIRunnable> runnable(aRunnable);
+  LOGV(
+      ("WorkerEventTarget::Dispatch [%p] aRunnable: %p", this, runnable.get()));
+
+  MutexAutoLock lock(mMutex);
+
+  if (!mWorkerPrivate) {
+    return NS_ERROR_FAILURE;
+  }
+
+  if (mBehavior == Behavior::Hybrid) {
+    LOGV(("WorkerEventTarget::Dispatch [%p] Dispatch as normal runnable(%p)",
+          this, runnable.get()));
+
+    RefPtr<WorkerRunnable> r =
+        mWorkerPrivate->MaybeWrapAsWorkerRunnable(runnable.forget());
+    if (r->Dispatch()) {
+      return NS_OK;
+    }
+    runnable = std::move(r);
+    LOGV((
+        "WorkerEventTarget::Dispatch [%p] Dispatch as normal runnable(%p) fail",
+        this, runnable.get()));
+  }
+
+  RefPtr<WorkerControlRunnable> r =
+      new WrappedControlRunnable(mWorkerPrivate, std::move(runnable));
+  LOGV(
+      ("WorkerEventTarget::Dispatch [%p] Wrapped runnable as control "
+       "runnable(%p)",
+       this, r.get()));
+  if (!r->Dispatch()) {
+    LOGV(
+        ("WorkerEventTarget::Dispatch [%p] Dispatch as control runnable(%p) "
+         "fail",
+         this, r.get()));
+    return NS_ERROR_FAILURE;
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WorkerEventTarget::DelayedDispatch(already_AddRefed<nsIRunnable>, uint32_t) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+WorkerEventTarget::RegisterShutdownTask(nsITargetShutdownTask* aTask) {
+  NS_ENSURE_ARG(aTask);
+
+  MutexAutoLock lock(mMutex);
+
+  // If mWorkerPrivate is gone, the event target is already late during
+  // shutdown, return NS_ERROR_UNEXPECTED as documented in `nsIEventTarget.idl`.
+  if (!mWorkerPrivate) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  return mWorkerPrivate->RegisterShutdownTask(aTask);
+}
+
+NS_IMETHODIMP
+WorkerEventTarget::UnregisterShutdownTask(nsITargetShutdownTask* aTask) {
+  NS_ENSURE_ARG(aTask);
+
+  MutexAutoLock lock(mMutex);
+
+  if (!mWorkerPrivate) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  return mWorkerPrivate->UnregisterShutdownTask(aTask);
+}
+
+NS_IMETHODIMP_(bool)
+WorkerEventTarget::IsOnCurrentThreadInfallible() {
+  MutexAutoLock lock(mMutex);
+
+  if (!mWorkerPrivate) {
+    return false;
+  }
+
+  return mWorkerPrivate->IsOnCurrentThread();
+}
+
+NS_IMETHODIMP
+WorkerEventTarget::IsOnCurrentThread(bool* aIsOnCurrentThread) {
+  MOZ_ASSERT(aIsOnCurrentThread);
+  *aIsOnCurrentThread = IsOnCurrentThreadInfallible();
+  return NS_OK;
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/workers/WorkerEventTarget.h b/dom/workers/WorkerEventTarget.h
new file mode 100644
index 0000000000..dd9cb61748
--- /dev/null
+++ b/dom/workers/WorkerEventTarget.h
@@ -0,0 +1,48 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_WorkerEventTarget_h
+#define mozilla_dom_WorkerEventTarget_h
+
+#include "nsISerialEventTarget.h"
+#include "mozilla/Mutex.h"
+#include "mozilla/dom/WorkerPrivate.h"
+
+namespace mozilla::dom {
+
+class WorkerEventTarget final : public nsISerialEventTarget {
+ public:
+  // The WorkerEventTarget supports different dispatch behaviors:
+  //
+  // * Hybrid targets will attempt to dispatch as a normal runnable,
+  //   but fallback to a control runnable if that fails.  This is
+  //   often necessary for code that wants normal dispatch order, but
+  //   also needs to execute while the worker is shutting down (possibly
+  //   with a holder in place.)
+  //
+  // * ControlOnly targets will simply dispatch a control runnable.
+  enum class Behavior : uint8_t { Hybrid, ControlOnly };
+
+ private:
+  mozilla::Mutex mMutex;
+  CheckedUnsafePtr<WorkerPrivate> mWorkerPrivate MOZ_GUARDED_BY(mMutex);
+  const Behavior mBehavior MOZ_GUARDED_BY(mMutex);
+
+  ~WorkerEventTarget() = default;
+
+ public:
+  WorkerEventTarget(WorkerPrivate* aWorkerPrivate, Behavior aBehavior);
+
+  void ForgetWorkerPrivate(WorkerPrivate* aWorkerPrivate);
+
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSIEVENTTARGET
+  NS_DECL_NSISERIALEVENTTARGET
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_WorkerEventTarget_h
diff --git a/dom/workers/WorkerIPCUtils.h b/dom/workers/WorkerIPCUtils.h
new file mode 100644
index 0000000000..0be45b307f
--- /dev/null
+++ b/dom/workers/WorkerIPCUtils.h
@@ -0,0 +1,26 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+#ifndef _mozilla_dom_WorkerIPCUtils_h
+#define _mozilla_dom_WorkerIPCUtils_h
+
+#include "ipc/EnumSerializer.h"
+
+// Undo X11/X.h's definition of None
+#undef None
+
+#include "mozilla/dom/WorkerBinding.h"
+
+namespace IPC {
+
+template <>
+struct ParamTraits<mozilla::dom::WorkerType>
+    : public ContiguousEnumSerializer<mozilla::dom::WorkerType,
+                                      mozilla::dom::WorkerType::Classic,
+                                      mozilla::dom::WorkerType::EndGuard_> {};
+
+}  // namespace IPC
+
+#endif  // _mozilla_dom_WorkerIPCUtils_h
diff --git a/dom/workers/WorkerLoadInfo.cpp b/dom/workers/WorkerLoadInfo.cpp
new file mode 100644
index 0000000000..0dec07a675
--- /dev/null
+++ b/dom/workers/WorkerLoadInfo.cpp
@@ -0,0 +1,508 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "WorkerLoadInfo.h"
+#include "WorkerPrivate.h"
+
+#include "mozilla/BasePrincipal.h"
+#include "mozilla/dom/nsCSPUtils.h"
+#include "mozilla/dom/BrowserChild.h"
+#include "mozilla/dom/ReferrerInfo.h"
+#include "mozilla/ipc/BackgroundUtils.h"
+#include "mozilla/ipc/PBackgroundSharedTypes.h"
+#include "mozilla/LoadContext.h"
+#include "mozilla/StorageAccess.h"
+#include "mozilla/StoragePrincipalHelper.h"
+#include "nsContentUtils.h"
+#include "nsIContentSecurityPolicy.h"
+#include "nsICookieJarSettings.h"
+#include "nsINetworkInterceptController.h"
+#include "nsIProtocolHandler.h"
+#include "nsIReferrerInfo.h"
+#include "nsIBrowserChild.h"
+#include "nsScriptSecurityManager.h"
+#include "nsNetUtil.h"
+
+namespace mozilla {
+
+using namespace ipc;
+
+namespace dom {
+
+namespace {
+
+class MainThreadReleaseRunnable final : public Runnable {
+  nsTArray<nsCOMPtr<nsISupports>> mDoomed;
+  nsCOMPtr<nsILoadGroup> mLoadGroupToCancel;
+
+ public:
+  MainThreadReleaseRunnable(nsTArray<nsCOMPtr<nsISupports>>&& aDoomed,
+                            nsCOMPtr<nsILoadGroup>&& aLoadGroupToCancel)
+      : mozilla::Runnable("MainThreadReleaseRunnable"),
+        mDoomed(std::move(aDoomed)),
+        mLoadGroupToCancel(std::move(aLoadGroupToCancel)) {}
+
+  NS_INLINE_DECL_REFCOUNTING_INHERITED(MainThreadReleaseRunnable, Runnable)
+
+  NS_IMETHOD
+  Run() override {
+    if (mLoadGroupToCancel) {
+      mLoadGroupToCancel->CancelWithReason(
+          NS_BINDING_ABORTED, "WorkerLoadInfo::MainThreadReleaseRunnable"_ns);
+      mLoadGroupToCancel = nullptr;
+    }
+
+    mDoomed.Clear();
+    return NS_OK;
+  }
+
+ private:
+  ~MainThreadReleaseRunnable() = default;
+};
+
+// Specialize this if there's some class that has multiple nsISupports bases.
+template <class T>
+struct ISupportsBaseInfo {
+  using ISupportsBase = T;
+};
+
+template <template <class> class SmartPtr, class T>
+inline void SwapToISupportsArray(SmartPtr<T>& aSrc,
+                                 nsTArray<nsCOMPtr<nsISupports>>& aDest) {
+  nsCOMPtr<nsISupports>* dest = aDest.AppendElement();
+
+  T* raw = nullptr;
+  aSrc.swap(raw);
+
+  nsISupports* rawSupports =
+      static_cast<typename ISupportsBaseInfo<T>::ISupportsBase*>(raw);
+  dest->swap(rawSupports);
+}
+
+}  // namespace
+
+WorkerLoadInfoData::WorkerLoadInfoData()
+    : mLoadFlags(nsIRequest::LOAD_NORMAL),
+      mWindowID(UINT64_MAX),
+      mAssociatedBrowsingContextID(0),
+      mReferrerInfo(new ReferrerInfo(nullptr)),
+      mFromWindow(false),
+      mEvalAllowed(false),
+      mReportEvalCSPViolations(false),
+      mWasmEvalAllowed(false),
+      mReportWasmEvalCSPViolations(false),
+      mXHRParamsAllowed(false),
+      mWatchedByDevTools(false),
+      mStorageAccess(StorageAccess::eDeny),
+      mUseRegularPrincipal(false),
+      mUsingStorageAccess(false),
+      mServiceWorkersTestingInWindow(false),
+      mShouldResistFingerprinting(false),
+      mIsThirdPartyContextToTopWindow(true),
+      mSecureContext(eNotSet) {}
+
+nsresult WorkerLoadInfo::SetPrincipalsAndCSPOnMainThread(
+    nsIPrincipal* aPrincipal, nsIPrincipal* aPartitionedPrincipal,
+    nsILoadGroup* aLoadGroup, nsIContentSecurityPolicy* aCsp) {
+  AssertIsOnMainThread();
+  MOZ_ASSERT(NS_LoadGroupMatchesPrincipal(aLoadGroup, aPrincipal));
+
+  mPrincipal = aPrincipal;
+  mPartitionedPrincipal = aPartitionedPrincipal;
+
+  mCSP = aCsp;
+
+  if (mCSP) {
+    mCSP->GetAllowsEval(&mReportEvalCSPViolations, &mEvalAllowed);
+    mCSP->GetAllowsWasmEval(&mReportWasmEvalCSPViolations, &mWasmEvalAllowed);
+    mCSPInfo = MakeUnique<CSPInfo>();
+    nsresult rv = CSPToCSPInfo(aCsp, mCSPInfo.get());
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+  } else {
+    mEvalAllowed = true;
+    mReportEvalCSPViolations = false;
+    mWasmEvalAllowed = true;
+    mReportWasmEvalCSPViolations = false;
+  }
+
+  mLoadGroup = aLoadGroup;
+
+  mPrincipalInfo = MakeUnique<PrincipalInfo>();
+  mPartitionedPrincipalInfo = MakeUnique<PrincipalInfo>();
+  StoragePrincipalHelper::GetRegularPrincipalOriginAttributes(
+      aLoadGroup, mOriginAttributes);
+
+  nsresult rv = PrincipalToPrincipalInfo(aPrincipal, mPrincipalInfo.get());
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  if (aPrincipal->Equals(aPartitionedPrincipal)) {
+    *mPartitionedPrincipalInfo = *mPrincipalInfo;
+  } else {
+    mPartitionedPrincipalInfo = MakeUnique<PrincipalInfo>();
+    rv = PrincipalToPrincipalInfo(aPartitionedPrincipal,
+                                  mPartitionedPrincipalInfo.get());
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+  return NS_OK;
+}
+
+nsresult WorkerLoadInfo::GetPrincipalsAndLoadGroupFromChannel(
+    nsIChannel* aChannel, nsIPrincipal** aPrincipalOut,
+    nsIPrincipal** aPartitionedPrincipalOut, nsILoadGroup** aLoadGroupOut) {
+  AssertIsOnMainThread();
+  MOZ_DIAGNOSTIC_ASSERT(aChannel);
+  MOZ_DIAGNOSTIC_ASSERT(aPrincipalOut);
+  MOZ_DIAGNOSTIC_ASSERT(aPartitionedPrincipalOut);
+  MOZ_DIAGNOSTIC_ASSERT(aLoadGroupOut);
+
+  // Initial triggering principal should be set
+  NS_ENSURE_TRUE(mLoadingPrincipal, NS_ERROR_DOM_INVALID_STATE_ERR);
+
+  nsIScriptSecurityManager* ssm = nsContentUtils::GetSecurityManager();
+  MOZ_DIAGNOSTIC_ASSERT(ssm);
+
+  nsCOMPtr<nsIPrincipal> channelPrincipal;
+  nsCOMPtr<nsIPrincipal> channelPartitionedPrincipal;
+  nsresult rv = ssm->GetChannelResultPrincipals(
+      aChannel, getter_AddRefs(channelPrincipal),
+      getter_AddRefs(channelPartitionedPrincipal));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  // Every time we call GetChannelResultPrincipal() it will return a different
+  // null principal for a data URL.  We don't want to change the worker's
+  // principal again, though.  Instead just keep the original null principal we
+  // first got from the channel.
+  //
+  // Note, we don't do this by setting principalToInherit on the channel's
+  // load info because we don't yet have the first null principal when we
+  // create the channel.
+  if (mPrincipal && mPrincipal->GetIsNullPrincipal() &&
+      channelPrincipal->GetIsNullPrincipal()) {
+    channelPrincipal = mPrincipal;
+    channelPartitionedPrincipal = mPrincipal;
+  }
+
+  nsCOMPtr<nsILoadGroup> channelLoadGroup;
+  rv = aChannel->GetLoadGroup(getter_AddRefs(channelLoadGroup));
+  NS_ENSURE_SUCCESS(rv, rv);
+  MOZ_ASSERT(channelLoadGroup);
+
+  // If the loading principal is the system principal then the channel
+  // principal must also be the system principal (we do not allow chrome
+  // code to create workers with non-chrome scripts, and if we ever decide
+  // to change this we need to make sure we don't always set
+  // mPrincipalIsSystem to true in WorkerPrivate::GetLoadInfo()). Otherwise
+  // this channel principal must be same origin with the load principal (we
+  // check again here in case redirects changed the location of the script).
+  if (mLoadingPrincipal->IsSystemPrincipal()) {
+    if (!channelPrincipal->IsSystemPrincipal()) {
+      nsCOMPtr<nsIURI> finalURI;
+      rv = NS_GetFinalChannelURI(aChannel, getter_AddRefs(finalURI));
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      // See if this is a resource URI. Since JSMs usually come from
+      // resource:// URIs we're currently considering all URIs with the
+      // URI_IS_UI_RESOURCE flag as valid for creating privileged workers.
+      bool isResource;
+      rv = NS_URIChainHasFlags(finalURI, nsIProtocolHandler::URI_IS_UI_RESOURCE,
+                               &isResource);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      if (isResource) {
+        // Assign the system principal to the resource:// worker only if it
+        // was loaded from code using the system principal.
+        channelPrincipal = mLoadingPrincipal;
+        channelPartitionedPrincipal = mLoadingPrincipal;
+      } else {
+        return NS_ERROR_DOM_BAD_URI;
+      }
+    }
+  }
+
+  // The principal can change, but it should still match the original
+  // load group's browser element flag.
+  MOZ_ASSERT(NS_LoadGroupMatchesPrincipal(channelLoadGroup, channelPrincipal));
+
+  channelPrincipal.forget(aPrincipalOut);
+  channelPartitionedPrincipal.forget(aPartitionedPrincipalOut);
+  channelLoadGroup.forget(aLoadGroupOut);
+
+  return NS_OK;
+}
+
+nsresult WorkerLoadInfo::SetPrincipalsAndCSPFromChannel(nsIChannel* aChannel) {
+  AssertIsOnMainThread();
+
+  nsCOMPtr<nsIPrincipal> principal;
+  nsCOMPtr<nsIPrincipal> partitionedPrincipal;
+  nsCOMPtr<nsILoadGroup> loadGroup;
+  nsresult rv = GetPrincipalsAndLoadGroupFromChannel(
+      aChannel, getter_AddRefs(principal), getter_AddRefs(partitionedPrincipal),
+      getter_AddRefs(loadGroup));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  // Workers themselves can have their own CSP - Workers of an opaque origin
+  // however inherit the CSP of the document that spawned the worker.
+  nsCOMPtr<nsIContentSecurityPolicy> csp;
+  if (CSP_ShouldResponseInheritCSP(aChannel)) {
+    nsCOMPtr<nsILoadInfo> loadinfo = aChannel->LoadInfo();
+    csp = loadinfo->GetCsp();
+  }
+  return SetPrincipalsAndCSPOnMainThread(principal, partitionedPrincipal,
+                                         loadGroup, csp);
+}
+
+bool WorkerLoadInfo::FinalChannelPrincipalIsValid(nsIChannel* aChannel) {
+  AssertIsOnMainThread();
+
+  nsCOMPtr<nsIPrincipal> principal;
+  nsCOMPtr<nsIPrincipal> partitionedPrincipal;
+  nsCOMPtr<nsILoadGroup> loadGroup;
+  nsresult rv = GetPrincipalsAndLoadGroupFromChannel(
+      aChannel, getter_AddRefs(principal), getter_AddRefs(partitionedPrincipal),
+      getter_AddRefs(loadGroup));
+  NS_ENSURE_SUCCESS(rv, false);
+
+  // Verify that the channel is still a null principal.  We don't care
+  // if these are the exact same null principal object, though.  From
+  // the worker's perspective its the same effect.
+  if (principal->GetIsNullPrincipal() && mPrincipal->GetIsNullPrincipal()) {
+    return true;
+  }
+
+  // Otherwise we require exact equality.  Redirects can happen, but they
+  // are not allowed to change our principal.
+  if (principal->Equals(mPrincipal)) {
+    return true;
+  }
+
+  return false;
+}
+
+#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
+bool WorkerLoadInfo::PrincipalIsValid() const {
+  return mPrincipal && mPrincipalInfo &&
+         mPrincipalInfo->type() != PrincipalInfo::T__None &&
+         mPrincipalInfo->type() <= PrincipalInfo::T__Last &&
+         mPartitionedPrincipal && mPartitionedPrincipalInfo &&
+         mPartitionedPrincipalInfo->type() != PrincipalInfo::T__None &&
+         mPartitionedPrincipalInfo->type() <= PrincipalInfo::T__Last;
+}
+
+bool WorkerLoadInfo::PrincipalURIMatchesScriptURL() {
+  AssertIsOnMainThread();
+
+  nsAutoCString scheme;
+  nsresult rv = mBaseURI->GetScheme(scheme);
+  NS_ENSURE_SUCCESS(rv, false);
+
+  // A system principal must either be a blob URL or a resource JSM.
+  if (mPrincipal->IsSystemPrincipal()) {
+    if (scheme == "blob"_ns) {
+      return true;
+    }
+
+    bool isResource = false;
+    nsresult rv = NS_URIChainHasFlags(
+        mBaseURI, nsIProtocolHandler::URI_IS_UI_RESOURCE, &isResource);
+    NS_ENSURE_SUCCESS(rv, false);
+
+    return isResource;
+  }
+
+  // A null principal can occur for a data URL worker script or a blob URL
+  // worker script from a sandboxed iframe.
+  if (mPrincipal->GetIsNullPrincipal()) {
+    return scheme == "data"_ns || scheme == "blob"_ns;
+  }
+
+  // The principal for a blob: URL worker script does not have a matching URL.
+  // This is likely a bug in our referer setting logic, but exempt it for now.
+  // This is another reason we should fix bug 1340694 so that referer does not
+  // depend on the principal URI.
+  if (scheme == "blob"_ns) {
+    return true;
+  }
+
+  if (mPrincipal->IsSameOrigin(mBaseURI)) {
+    return true;
+  }
+
+  // If strict file origin policy is in effect, local files will always fail
+  // IsSameOrigin unless they are identical. Explicitly check file origin
+  // policy, in that case.
+
+  bool allowsRelaxedOriginPolicy = false;
+  rv = mPrincipal->AllowsRelaxStrictFileOriginPolicy(
+      mBaseURI, &allowsRelaxedOriginPolicy);
+
+  if (nsScriptSecurityManager::GetStrictFileOriginPolicy() &&
+      NS_URIIsLocalFile(mBaseURI) &&
+      (NS_SUCCEEDED(rv) && allowsRelaxedOriginPolicy)) {
+    return true;
+  }
+
+  return false;
+}
+#endif  // MOZ_DIAGNOSTIC_ASSERT_ENABLED
+
+bool WorkerLoadInfo::ProxyReleaseMainThreadObjects(
+    WorkerPrivate* aWorkerPrivate) {
+  nsCOMPtr<nsILoadGroup> nullLoadGroup;
+  return ProxyReleaseMainThreadObjects(aWorkerPrivate,
+                                       std::move(nullLoadGroup));
+}
+
+bool WorkerLoadInfo::ProxyReleaseMainThreadObjects(
+    WorkerPrivate* aWorkerPrivate,
+    nsCOMPtr<nsILoadGroup>&& aLoadGroupToCancel) {
+  static const uint32_t kDoomedCount = 11;
+  nsTArray<nsCOMPtr<nsISupports>> doomed(kDoomedCount);
+
+  SwapToISupportsArray(mWindow, doomed);
+  SwapToISupportsArray(mScriptContext, doomed);
+  SwapToISupportsArray(mBaseURI, doomed);
+  SwapToISupportsArray(mResolvedScriptURI, doomed);
+  SwapToISupportsArray(mPrincipal, doomed);
+  SwapToISupportsArray(mPartitionedPrincipal, doomed);
+  SwapToISupportsArray(mLoadingPrincipal, doomed);
+  SwapToISupportsArray(mChannel, doomed);
+  SwapToISupportsArray(mCSP, doomed);
+  SwapToISupportsArray(mLoadGroup, doomed);
+  SwapToISupportsArray(mInterfaceRequestor, doomed);
+  // Before adding anything here update kDoomedCount above!
+
+  MOZ_ASSERT(doomed.Length() == kDoomedCount);
+
+  RefPtr<MainThreadReleaseRunnable> runnable = new MainThreadReleaseRunnable(
+      std::move(doomed), std::move(aLoadGroupToCancel));
+  return NS_SUCCEEDED(aWorkerPrivate->DispatchToMainThread(runnable.forget()));
+}
+
+WorkerLoadInfo::InterfaceRequestor::InterfaceRequestor(
+    nsIPrincipal* aPrincipal, nsILoadGroup* aLoadGroup) {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(aPrincipal);
+
+  // Look for an existing LoadContext.  This is optional and it's ok if
+  // we don't find one.
+  nsCOMPtr<nsILoadContext> baseContext;
+  if (aLoadGroup) {
+    nsCOMPtr<nsIInterfaceRequestor> callbacks;
+    aLoadGroup->GetNotificationCallbacks(getter_AddRefs(callbacks));
+    if (callbacks) {
+      callbacks->GetInterface(NS_GET_IID(nsILoadContext),
+                              getter_AddRefs(baseContext));
+    }
+    mOuterRequestor = callbacks;
+  }
+
+  mLoadContext = new LoadContext(aPrincipal, baseContext);
+}
+
+void WorkerLoadInfo::InterfaceRequestor::MaybeAddBrowserChild(
+    nsILoadGroup* aLoadGroup) {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  if (!aLoadGroup) {
+    return;
+  }
+
+  nsCOMPtr<nsIInterfaceRequestor> callbacks;
+  aLoadGroup->GetNotificationCallbacks(getter_AddRefs(callbacks));
+  if (!callbacks) {
+    return;
+  }
+
+  nsCOMPtr<nsIBrowserChild> browserChild;
+  callbacks->GetInterface(NS_GET_IID(nsIBrowserChild),
+                          getter_AddRefs(browserChild));
+  if (!browserChild) {
+    return;
+  }
+
+  // Use weak references to the tab child.  Holding a strong reference will
+  // not prevent an ActorDestroy() from being called on the BrowserChild.
+  // Therefore, we should let the BrowserChild destroy itself as soon as
+  // possible.
+  mBrowserChildList.AppendElement(do_GetWeakReference(browserChild));
+}
+
+NS_IMETHODIMP
+WorkerLoadInfo::InterfaceRequestor::GetInterface(const nsIID& aIID,
+                                                 void** aSink) {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(mLoadContext);
+
+  if (aIID.Equals(NS_GET_IID(nsILoadContext))) {
+    nsCOMPtr<nsILoadContext> ref = mLoadContext;
+    ref.forget(aSink);
+    return NS_OK;
+  }
+
+  // If we still have an active nsIBrowserChild, then return it.  Its possible,
+  // though, that all of the BrowserChild objects have been destroyed.  In that
+  // case we return NS_NOINTERFACE.
+  if (aIID.Equals(NS_GET_IID(nsIBrowserChild))) {
+    nsCOMPtr<nsIBrowserChild> browserChild = GetAnyLiveBrowserChild();
+    if (!browserChild) {
+      return NS_NOINTERFACE;
+    }
+    browserChild.forget(aSink);
+    return NS_OK;
+  }
+
+  if (aIID.Equals(NS_GET_IID(nsINetworkInterceptController)) &&
+      mOuterRequestor) {
+    // If asked for the network intercept controller, ask the outer requestor,
+    // which could be the docshell.
+    return mOuterRequestor->GetInterface(aIID, aSink);
+  }
+
+  return NS_NOINTERFACE;
+}
+
+already_AddRefed<nsIBrowserChild>
+WorkerLoadInfo::InterfaceRequestor::GetAnyLiveBrowserChild() {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  // Search our list of known BrowserChild objects for one that still exists.
+  while (!mBrowserChildList.IsEmpty()) {
+    nsCOMPtr<nsIBrowserChild> browserChild =
+        do_QueryReferent(mBrowserChildList.LastElement());
+
+    // Does this tab child still exist?  If so, return it.  We are done.  If the
+    // PBrowser actor is no longer useful, don't bother returning this tab.
+    if (browserChild &&
+        !static_cast<BrowserChild*>(browserChild.get())->IsDestroyed()) {
+      return browserChild.forget();
+    }
+
+    // Otherwise remove the stale weak reference and check the next one
+    mBrowserChildList.RemoveLastElement();
+  }
+
+  return nullptr;
+}
+
+NS_IMPL_ADDREF(WorkerLoadInfo::InterfaceRequestor)
+NS_IMPL_RELEASE(WorkerLoadInfo::InterfaceRequestor)
+NS_IMPL_QUERY_INTERFACE(WorkerLoadInfo::InterfaceRequestor,
+                        nsIInterfaceRequestor)
+
+WorkerLoadInfo::WorkerLoadInfo() { MOZ_COUNT_CTOR(WorkerLoadInfo); }
+
+WorkerLoadInfo::WorkerLoadInfo(WorkerLoadInfo&& aOther) noexcept
+    : WorkerLoadInfoData(std::move(aOther)) {
+  MOZ_COUNT_CTOR(WorkerLoadInfo);
+}
+
+WorkerLoadInfo::~WorkerLoadInfo() { MOZ_COUNT_DTOR(WorkerLoadInfo); }
+
+}  // namespace dom
+}  // namespace mozilla
diff --git a/dom/workers/WorkerLoadInfo.h b/dom/workers/WorkerLoadInfo.h
new file mode 100644
index 0000000000..722e71d6f3
--- /dev/null
+++ b/dom/workers/WorkerLoadInfo.h
@@ -0,0 +1,200 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_workers_WorkerLoadInfo_h
+#define mozilla_dom_workers_WorkerLoadInfo_h
+
+#include "mozilla/OriginAttributes.h"
+#include "mozilla/StorageAccess.h"
+#include "mozilla/OriginTrials.h"
+#include "mozilla/UniquePtr.h"
+#include "mozilla/dom/ChannelInfo.h"
+#include "mozilla/net/NeckoChannelParams.h"
+#include "mozilla/dom/ServiceWorkerRegistrationDescriptor.h"
+#include "mozilla/dom/WorkerCommon.h"
+
+#include "nsIInterfaceRequestor.h"
+#include "nsILoadContext.h"
+#include "nsIRequest.h"
+#include "nsISupportsImpl.h"
+#include "nsIWeakReferenceUtils.h"
+#include "nsRFPService.h"
+#include "nsTArray.h"
+
+class nsIChannel;
+class nsIContentSecurityPolicy;
+class nsICookieJarSettings;
+class nsILoadGroup;
+class nsIPrincipal;
+class nsIReferrerInfo;
+class nsIRunnable;
+class nsIScriptContext;
+class nsIBrowserChild;
+class nsIURI;
+class nsPIDOMWindowInner;
+
+namespace mozilla {
+
+namespace ipc {
+class PrincipalInfo;
+class CSPInfo;
+}  // namespace ipc
+
+namespace dom {
+
+class WorkerPrivate;
+
+struct WorkerLoadInfoData {
+  // All of these should be released in
+  // WorkerPrivateParent::ForgetMainThreadObjects.
+  nsCOMPtr<nsIURI> mBaseURI;
+  nsCOMPtr<nsIURI> mResolvedScriptURI;
+
+  // This is the principal of the global (parent worker or a window) loading
+  // the worker. It can be null if we are executing a ServiceWorker, otherwise,
+  // except for data: URL, it must subsumes the worker principal.
+  // If we load a data: URL, mPrincipal will be a null principal.
+  nsCOMPtr<nsIPrincipal> mLoadingPrincipal;
+  nsCOMPtr<nsIPrincipal> mPrincipal;
+  nsCOMPtr<nsIPrincipal> mPartitionedPrincipal;
+
+  // Taken from the parent context.
+  nsCOMPtr<nsICookieJarSettings> mCookieJarSettings;
+
+  // The CookieJarSettingsArgs of mCookieJarSettings.
+  // This is specific for accessing on worker thread.
+  net::CookieJarSettingsArgs mCookieJarSettingsArgs;
+
+  nsCOMPtr<nsIScriptContext> mScriptContext;
+  nsCOMPtr<nsPIDOMWindowInner> mWindow;
+  nsCOMPtr<nsIContentSecurityPolicy> mCSP;
+  // Thread boundaries require us to not only store a CSP object, but also a
+  // serialized version of the CSP. Reason being: Serializing a CSP to a CSPInfo
+  // needs to happen on the main thread, but storing the CSPInfo needs to happen
+  // on the worker thread. We move the CSPInfo into the Client within
+  // ScriptLoader::PreRun().
+  UniquePtr<mozilla::ipc::CSPInfo> mCSPInfo;
+
+  nsCOMPtr<nsIChannel> mChannel;
+  nsCOMPtr<nsILoadGroup> mLoadGroup;
+
+  class InterfaceRequestor final : public nsIInterfaceRequestor {
+    NS_DECL_ISUPPORTS
+
+   public:
+    InterfaceRequestor(nsIPrincipal* aPrincipal, nsILoadGroup* aLoadGroup);
+    void MaybeAddBrowserChild(nsILoadGroup* aLoadGroup);
+    NS_IMETHOD GetInterface(const nsIID& aIID, void** aSink) override;
+
+    void SetOuterRequestor(nsIInterfaceRequestor* aOuterRequestor) {
+      MOZ_ASSERT(!mOuterRequestor);
+      MOZ_ASSERT(aOuterRequestor);
+      mOuterRequestor = aOuterRequestor;
+    }
+
+   private:
+    ~InterfaceRequestor() = default;
+
+    already_AddRefed<nsIBrowserChild> GetAnyLiveBrowserChild();
+
+    nsCOMPtr<nsILoadContext> mLoadContext;
+    nsCOMPtr<nsIInterfaceRequestor> mOuterRequestor;
+
+    // Array of weak references to nsIBrowserChild.  We do not want to keep
+    // BrowserChild actors alive for long after their ActorDestroy() methods are
+    // called.
+    nsTArray<nsWeakPtr> mBrowserChildList;
+  };
+
+  // Only set if we have a custom overriden load group
+  RefPtr<InterfaceRequestor> mInterfaceRequestor;
+
+  UniquePtr<mozilla::ipc::PrincipalInfo> mPrincipalInfo;
+  UniquePtr<mozilla::ipc::PrincipalInfo> mPartitionedPrincipalInfo;
+  nsCString mDomain;
+
+  nsString mServiceWorkerCacheName;
+  Maybe<ServiceWorkerDescriptor> mServiceWorkerDescriptor;
+  Maybe<ServiceWorkerRegistrationDescriptor>
+      mServiceWorkerRegistrationDescriptor;
+
+  Maybe<ServiceWorkerDescriptor> mParentController;
+
+  nsID mAgentClusterId;
+
+  ChannelInfo mChannelInfo;
+  nsLoadFlags mLoadFlags;
+
+  uint64_t mWindowID;
+  uint64_t mAssociatedBrowsingContextID;
+
+  nsCOMPtr<nsIReferrerInfo> mReferrerInfo;
+  OriginTrials mTrials;
+  bool mFromWindow;
+  bool mEvalAllowed;
+  bool mReportEvalCSPViolations;
+  bool mWasmEvalAllowed;
+  bool mReportWasmEvalCSPViolations;
+  bool mXHRParamsAllowed;
+  bool mWatchedByDevTools;
+  StorageAccess mStorageAccess;
+  bool mUseRegularPrincipal;
+  bool mUsingStorageAccess;
+  bool mServiceWorkersTestingInWindow;
+  bool mShouldResistFingerprinting;
+  Maybe<RFPTarget> mOverriddenFingerprintingSettings;
+  OriginAttributes mOriginAttributes;
+  bool mIsThirdPartyContextToTopWindow;
+
+  enum {
+    eNotSet,
+    eInsecureContext,
+    eSecureContext,
+  } mSecureContext;
+
+  WorkerLoadInfoData();
+  WorkerLoadInfoData(WorkerLoadInfoData&& aOther) = default;
+
+  WorkerLoadInfoData& operator=(WorkerLoadInfoData&& aOther) = default;
+};
+
+struct WorkerLoadInfo : WorkerLoadInfoData {
+  WorkerLoadInfo();
+  WorkerLoadInfo(WorkerLoadInfo&& aOther) noexcept;
+  ~WorkerLoadInfo();
+
+  WorkerLoadInfo& operator=(WorkerLoadInfo&& aOther) = default;
+
+  nsresult SetPrincipalsAndCSPOnMainThread(nsIPrincipal* aPrincipal,
+                                           nsIPrincipal* aPartitionedPrincipal,
+                                           nsILoadGroup* aLoadGroup,
+                                           nsIContentSecurityPolicy* aCSP);
+
+  nsresult GetPrincipalsAndLoadGroupFromChannel(
+      nsIChannel* aChannel, nsIPrincipal** aPrincipalOut,
+      nsIPrincipal** aPartitionedPrincipalOut, nsILoadGroup** aLoadGroupOut);
+
+  nsresult SetPrincipalsAndCSPFromChannel(nsIChannel* aChannel);
+
+  bool FinalChannelPrincipalIsValid(nsIChannel* aChannel);
+
+#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
+  bool PrincipalIsValid() const;
+
+  bool PrincipalURIMatchesScriptURL();
+#endif
+
+  bool ProxyReleaseMainThreadObjects(WorkerPrivate* aWorkerPrivate);
+
+  bool ProxyReleaseMainThreadObjects(
+      WorkerPrivate* aWorkerPrivate,
+      nsCOMPtr<nsILoadGroup>&& aLoadGroupToCancel);
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_workers_WorkerLoadInfo_h
diff --git a/dom/workers/WorkerLocation.cpp b/dom/workers/WorkerLocation.cpp
new file mode 100644
index 0000000000..94b662efb1
--- /dev/null
+++ b/dom/workers/WorkerLocation.cpp
@@ -0,0 +1,36 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/WorkerLocation.h"
+
+#include "mozilla/dom/WorkerLocationBinding.h"
+
+namespace mozilla::dom {
+
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_0(WorkerLocation)
+
+/* static */
+already_AddRefed<WorkerLocation> WorkerLocation::Create(
+    WorkerPrivate::LocationInfo& aInfo) {
+  RefPtr<WorkerLocation> location =
+      new WorkerLocation(NS_ConvertUTF8toUTF16(aInfo.mHref),
+                         NS_ConvertUTF8toUTF16(aInfo.mProtocol),
+                         NS_ConvertUTF8toUTF16(aInfo.mHost),
+                         NS_ConvertUTF8toUTF16(aInfo.mHostname),
+                         NS_ConvertUTF8toUTF16(aInfo.mPort),
+                         NS_ConvertUTF8toUTF16(aInfo.mPathname),
+                         NS_ConvertUTF8toUTF16(aInfo.mSearch),
+                         NS_ConvertUTF8toUTF16(aInfo.mHash), aInfo.mOrigin);
+
+  return location.forget();
+}
+
+JSObject* WorkerLocation::WrapObject(JSContext* aCx,
+                                     JS::Handle<JSObject*> aGivenProto) {
+  return WorkerLocation_Binding::Wrap(aCx, this, aGivenProto);
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/workers/WorkerLocation.h b/dom/workers/WorkerLocation.h
new file mode 100644
index 0000000000..d51e73cde5
--- /dev/null
+++ b/dom/workers/WorkerLocation.h
@@ -0,0 +1,72 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_location_h__
+#define mozilla_dom_location_h__
+
+#include "WorkerCommon.h"
+#include "WorkerPrivate.h"
+#include "nsWrapperCache.h"
+
+namespace mozilla::dom {
+
+class WorkerLocation final : public nsWrapperCache {
+  nsString mHref;
+  nsString mProtocol;
+  nsString mHost;
+  nsString mHostname;
+  nsString mPort;
+  nsString mPathname;
+  nsString mSearch;
+  nsString mHash;
+  nsString mOrigin;
+
+  WorkerLocation(const nsAString& aHref, const nsAString& aProtocol,
+                 const nsAString& aHost, const nsAString& aHostname,
+                 const nsAString& aPort, const nsAString& aPathname,
+                 const nsAString& aSearch, const nsAString& aHash,
+                 const nsAString& aOrigin)
+      : mHref(aHref),
+        mProtocol(aProtocol),
+        mHost(aHost),
+        mHostname(aHostname),
+        mPort(aPort),
+        mPathname(aPathname),
+        mSearch(aSearch),
+        mHash(aHash),
+        mOrigin(aOrigin) {
+    MOZ_COUNT_CTOR(WorkerLocation);
+  }
+
+  MOZ_COUNTED_DTOR(WorkerLocation)
+
+ public:
+  NS_INLINE_DECL_CYCLE_COLLECTING_NATIVE_REFCOUNTING(WorkerLocation)
+  NS_DECL_CYCLE_COLLECTION_NATIVE_WRAPPERCACHE_CLASS(WorkerLocation)
+
+  static already_AddRefed<WorkerLocation> Create(
+      WorkerPrivate::LocationInfo& aInfo);
+
+  virtual JSObject* WrapObject(JSContext* aCx,
+                               JS::Handle<JSObject*> aGivenProto) override;
+
+  nsISupports* GetParentObject() const { return nullptr; }
+
+  void Stringify(nsString& aHref) const { aHref = mHref; }
+  void GetHref(nsString& aHref) const { aHref = mHref; }
+  void GetProtocol(nsString& aProtocol) const { aProtocol = mProtocol; }
+  void GetHost(nsString& aHost) const { aHost = mHost; }
+  void GetHostname(nsString& aHostname) const { aHostname = mHostname; }
+  void GetPort(nsString& aPort) const { aPort = mPort; }
+  void GetPathname(nsString& aPathname) const { aPathname = mPathname; }
+  void GetSearch(nsString& aSearch) const { aSearch = mSearch; }
+  void GetHash(nsString& aHash) const { aHash = mHash; }
+  void GetOrigin(nsString& aOrigin) const { aOrigin = mOrigin; }
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_location_h__
diff --git a/dom/workers/WorkerNavigator.cpp b/dom/workers/WorkerNavigator.cpp
new file mode 100644
index 0000000000..1be36bc7d4
--- /dev/null
+++ b/dom/workers/WorkerNavigator.cpp
@@ -0,0 +1,285 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/WorkerNavigator.h"
+
+#include <utility>
+
+#include "ErrorList.h"
+#include "MainThreadUtils.h"
+#include "RuntimeService.h"
+#include "WorkerRunnable.h"
+#include "WorkerScope.h"
+#include "mozilla/dom/LockManager.h"
+#include "mozilla/dom/MediaCapabilities.h"
+#include "mozilla/dom/Navigator.h"
+#include "mozilla/dom/StorageManager.h"
+#include "mozilla/dom/WorkerCommon.h"
+#include "mozilla/dom/WorkerNavigatorBinding.h"
+#include "mozilla/dom/WorkerStatus.h"
+#include "mozilla/dom/network/Connection.h"
+#include "mozilla/webgpu/Instance.h"
+#include "nsCOMPtr.h"
+#include "nsDebug.h"
+#include "nsError.h"
+#include "nsIGlobalObject.h"
+#include "nsLiteralString.h"
+#include "nsPIDOMWindow.h"
+#include "nsRFPService.h"
+#include "nsString.h"
+
+class JSObject;
+struct JSContext;
+
+namespace mozilla::dom {
+
+using namespace workerinternals;
+
+NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(WorkerNavigator)
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(WorkerNavigator)
+  tmp->Invalidate();
+  NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(WorkerNavigator)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mStorageManager)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mConnection)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mMediaCapabilities)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mWebGpu)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mLocks)
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+WorkerNavigator::WorkerNavigator(const NavigatorProperties& aProperties,
+                                 bool aOnline)
+    : mProperties(aProperties), mOnline(aOnline) {}
+
+WorkerNavigator::~WorkerNavigator() { Invalidate(); }
+
+/* static */
+already_AddRefed<WorkerNavigator> WorkerNavigator::Create(bool aOnLine) {
+  RuntimeService* rts = RuntimeService::GetService();
+  MOZ_ASSERT(rts);
+
+  const RuntimeService::NavigatorProperties& properties =
+      rts->GetNavigatorProperties();
+
+  RefPtr<WorkerNavigator> navigator = new WorkerNavigator(properties, aOnLine);
+
+  return navigator.forget();
+}
+
+void WorkerNavigator::Invalidate() {
+  if (mStorageManager) {
+    mStorageManager->Shutdown();
+    mStorageManager = nullptr;
+  }
+
+  mConnection = nullptr;
+
+  mMediaCapabilities = nullptr;
+
+  mWebGpu = nullptr;
+
+  mLocks = nullptr;
+}
+
+JSObject* WorkerNavigator::WrapObject(JSContext* aCx,
+                                      JS::Handle<JSObject*> aGivenProto) {
+  return WorkerNavigator_Binding::Wrap(aCx, this, aGivenProto);
+}
+
+bool WorkerNavigator::GlobalPrivacyControl() const {
+  bool gpcStatus = StaticPrefs::privacy_globalprivacycontrol_enabled();
+  if (!gpcStatus) {
+    JSObject* jso = GetWrapper();
+    if (const nsCOMPtr<nsIGlobalObject> global = xpc::NativeGlobal(jso)) {
+      if (const nsCOMPtr<nsIPrincipal> principal = global->PrincipalOrNull()) {
+        gpcStatus = principal->GetPrivateBrowsingId() > 0 &&
+                    StaticPrefs::privacy_globalprivacycontrol_pbmode_enabled();
+      }
+    }
+  }
+  return StaticPrefs::privacy_globalprivacycontrol_functionality_enabled() &&
+         gpcStatus;
+}
+
+void WorkerNavigator::SetLanguages(const nsTArray<nsString>& aLanguages) {
+  WorkerNavigator_Binding::ClearCachedLanguagesValue(this);
+  mProperties.mLanguages = aLanguages.Clone();
+}
+
+void WorkerNavigator::GetAppVersion(nsString& aAppVersion,
+                                    CallerType aCallerType,
+                                    ErrorResult& aRv) const {
+  WorkerPrivate* workerPrivate = GetCurrentThreadWorkerPrivate();
+  MOZ_ASSERT(workerPrivate);
+
+  if (aCallerType != CallerType::System) {
+    if (workerPrivate->ShouldResistFingerprinting(
+            RFPTarget::NavigatorAppVersion)) {
+      // See nsRFPService.h for spoofed value.
+      aAppVersion.AssignLiteral(SPOOFED_APPVERSION);
+      return;
+    }
+
+    if (!mProperties.mAppVersionOverridden.IsEmpty()) {
+      aAppVersion = mProperties.mAppVersionOverridden;
+      return;
+    }
+  }
+
+  aAppVersion = mProperties.mAppVersion;
+}
+
+void WorkerNavigator::GetPlatform(nsString& aPlatform, CallerType aCallerType,
+                                  ErrorResult& aRv) const {
+  WorkerPrivate* workerPrivate = GetCurrentThreadWorkerPrivate();
+  MOZ_ASSERT(workerPrivate);
+
+  if (aCallerType != CallerType::System) {
+    if (workerPrivate->ShouldResistFingerprinting(
+            RFPTarget::NavigatorPlatform)) {
+      // See nsRFPService.h for spoofed value.
+      aPlatform.AssignLiteral(SPOOFED_PLATFORM);
+      return;
+    }
+
+    if (!mProperties.mPlatformOverridden.IsEmpty()) {
+      aPlatform = mProperties.mPlatformOverridden;
+      return;
+    }
+  }
+
+  aPlatform = mProperties.mPlatform;
+}
+
+namespace {
+
+/*
+ * This Worker Runnable needs to check RFP; but our standard way of doing so
+ * relies on accessing GlobalScope() - which can only be accessed on the worker
+ * thread. So we need to pass it in.
+ */
+class GetUserAgentRunnable final : public WorkerMainThreadRunnable {
+  nsString& mUA;
+  bool mShouldResistFingerprinting;
+
+ public:
+  GetUserAgentRunnable(WorkerPrivate* aWorkerPrivate, nsString& aUA,
+                       bool aShouldResistFingerprinting)
+      : WorkerMainThreadRunnable(aWorkerPrivate, "UserAgent getter"_ns),
+        mUA(aUA),
+        mShouldResistFingerprinting(aShouldResistFingerprinting) {
+    MOZ_ASSERT(aWorkerPrivate);
+    aWorkerPrivate->AssertIsOnWorkerThread();
+  }
+
+  virtual bool MainThreadRun() override {
+    AssertIsOnMainThread();
+
+    nsCOMPtr<nsPIDOMWindowInner> window = mWorkerPrivate->GetWindow();
+
+    nsresult rv =
+        dom::Navigator::GetUserAgent(window, mWorkerPrivate->GetDocument(),
+                                     Some(mShouldResistFingerprinting), mUA);
+    if (NS_FAILED(rv)) {
+      NS_WARNING("Failed to retrieve user-agent from the worker thread.");
+    }
+
+    return true;
+  }
+};
+
+}  // namespace
+
+void WorkerNavigator::GetUserAgent(nsString& aUserAgent, CallerType aCallerType,
+                                   ErrorResult& aRv) const {
+  WorkerPrivate* workerPrivate = GetCurrentThreadWorkerPrivate();
+  MOZ_ASSERT(workerPrivate);
+
+  RefPtr<GetUserAgentRunnable> runnable = new GetUserAgentRunnable(
+      workerPrivate, aUserAgent,
+      workerPrivate->ShouldResistFingerprinting(RFPTarget::NavigatorUserAgent));
+
+  runnable->Dispatch(Canceling, aRv);
+}
+
+uint64_t WorkerNavigator::HardwareConcurrency() const {
+  RuntimeService* rts = RuntimeService::GetService();
+  MOZ_ASSERT(rts);
+
+  WorkerPrivate* aWorkerPrivate = GetCurrentThreadWorkerPrivate();
+  bool rfp = aWorkerPrivate->ShouldResistFingerprinting(
+      RFPTarget::NavigatorHWConcurrency);
+
+  return rts->ClampedHardwareConcurrency(rfp);
+}
+
+StorageManager* WorkerNavigator::Storage() {
+  if (!mStorageManager) {
+    WorkerPrivate* workerPrivate = GetCurrentThreadWorkerPrivate();
+    MOZ_ASSERT(workerPrivate);
+
+    RefPtr<nsIGlobalObject> global = workerPrivate->GlobalScope();
+    MOZ_ASSERT(global);
+
+    mStorageManager = new StorageManager(global);
+  }
+
+  return mStorageManager;
+}
+
+network::Connection* WorkerNavigator::GetConnection(ErrorResult& aRv) {
+  if (!mConnection) {
+    WorkerPrivate* workerPrivate = GetCurrentThreadWorkerPrivate();
+    MOZ_ASSERT(workerPrivate);
+
+    mConnection = network::Connection::CreateForWorker(workerPrivate, aRv);
+  }
+
+  return mConnection;
+}
+
+dom::MediaCapabilities* WorkerNavigator::MediaCapabilities() {
+  if (!mMediaCapabilities) {
+    WorkerPrivate* workerPrivate = GetCurrentThreadWorkerPrivate();
+    MOZ_ASSERT(workerPrivate);
+
+    nsIGlobalObject* global = workerPrivate->GlobalScope();
+    MOZ_ASSERT(global);
+
+    mMediaCapabilities = new dom::MediaCapabilities(global);
+  }
+  return mMediaCapabilities;
+}
+
+webgpu::Instance* WorkerNavigator::Gpu() {
+  if (!mWebGpu) {
+    WorkerPrivate* workerPrivate = GetCurrentThreadWorkerPrivate();
+    MOZ_ASSERT(workerPrivate);
+
+    nsIGlobalObject* global = workerPrivate->GlobalScope();
+    MOZ_ASSERT(global);
+
+    mWebGpu = webgpu::Instance::Create(global);
+  }
+  return mWebGpu;
+}
+
+dom::LockManager* WorkerNavigator::Locks() {
+  if (!mLocks) {
+    WorkerPrivate* workerPrivate = GetCurrentThreadWorkerPrivate();
+    MOZ_ASSERT(workerPrivate);
+
+    nsIGlobalObject* global = workerPrivate->GlobalScope();
+    MOZ_ASSERT(global);
+
+    mLocks = dom::LockManager::Create(*global);
+  }
+  return mLocks;
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/workers/WorkerNavigator.h b/dom/workers/WorkerNavigator.h
new file mode 100644
index 0000000000..0db9292d78
--- /dev/null
+++ b/dom/workers/WorkerNavigator.h
@@ -0,0 +1,121 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_workernavigator_h__
+#define mozilla_dom_workernavigator_h__
+
+#include <stdint.h>
+#include "js/RootingAPI.h"
+#include "mozilla/AlreadyAddRefed.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/RefPtr.h"
+#include "mozilla/dom/BindingDeclarations.h"
+#include "mozilla/dom/workerinternals/RuntimeService.h"
+#include "mozilla/StaticPrefs_privacy.h"
+#include "nsCycleCollectionParticipant.h"
+#include "nsISupports.h"
+#include "nsStringFwd.h"
+#include "nsTArray.h"
+#include "nsWrapperCache.h"
+
+namespace mozilla {
+class ErrorResult;
+
+namespace webgpu {
+class Instance;
+}  // namespace webgpu
+namespace dom {
+class StorageManager;
+class MediaCapabilities;
+class LockManager;
+
+namespace network {
+class Connection;
+}  // namespace network
+
+class WorkerNavigator final : public nsWrapperCache {
+  using NavigatorProperties =
+      workerinternals::RuntimeService::NavigatorProperties;
+
+  NavigatorProperties mProperties;
+  RefPtr<StorageManager> mStorageManager;
+  RefPtr<network::Connection> mConnection;
+  RefPtr<dom::MediaCapabilities> mMediaCapabilities;
+  RefPtr<webgpu::Instance> mWebGpu;
+  RefPtr<dom::LockManager> mLocks;
+  bool mOnline;
+
+  WorkerNavigator(const NavigatorProperties& aProperties, bool aOnline);
+  ~WorkerNavigator();
+
+ public:
+  NS_INLINE_DECL_CYCLE_COLLECTING_NATIVE_REFCOUNTING(WorkerNavigator)
+  NS_DECL_CYCLE_COLLECTION_NATIVE_WRAPPERCACHE_CLASS(WorkerNavigator)
+
+  static already_AddRefed<WorkerNavigator> Create(bool aOnLine);
+
+  void Invalidate();
+
+  virtual JSObject* WrapObject(JSContext* aCx,
+                               JS::Handle<JSObject*> aGivenProto) override;
+
+  nsISupports* GetParentObject() const { return nullptr; }
+
+  void GetAppCodeName(nsString& aAppCodeName, ErrorResult& /* unused */) const {
+    aAppCodeName.AssignLiteral("Mozilla");
+  }
+  void GetAppName(nsString& aAppName) const {
+    aAppName.AssignLiteral("Netscape");
+  }
+
+  void GetAppVersion(nsString& aAppVersion, CallerType aCallerType,
+                     ErrorResult& aRv) const;
+
+  void GetPlatform(nsString& aPlatform, CallerType aCallerType,
+                   ErrorResult& aRv) const;
+
+  void GetProduct(nsString& aProduct) const { aProduct.AssignLiteral("Gecko"); }
+
+  bool TaintEnabled() const { return false; }
+
+  void GetLanguage(nsString& aLanguage) const {
+    MOZ_ASSERT(mProperties.mLanguages.Length() >= 1);
+    aLanguage.Assign(mProperties.mLanguages[0]);
+  }
+
+  void GetLanguages(nsTArray<nsString>& aLanguages) const {
+    aLanguages = mProperties.mLanguages.Clone();
+  }
+
+  void GetUserAgent(nsString& aUserAgent, CallerType aCallerType,
+                    ErrorResult& aRv) const;
+
+  bool OnLine() const { return mOnline; }
+
+  // Worker thread only!
+  void SetOnLine(bool aOnline) { mOnline = aOnline; }
+
+  bool GlobalPrivacyControl() const;
+
+  void SetLanguages(const nsTArray<nsString>& aLanguages);
+
+  uint64_t HardwareConcurrency() const;
+
+  StorageManager* Storage();
+
+  network::Connection* GetConnection(ErrorResult& aRv);
+
+  dom::MediaCapabilities* MediaCapabilities();
+
+  webgpu::Instance* Gpu();
+
+  dom::LockManager* Locks();
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_workernavigator_h__
diff --git a/dom/workers/WorkerPrivate.cpp b/dom/workers/WorkerPrivate.cpp
new file mode 100644
index 0000000000..78de4adc3a
--- /dev/null
+++ b/dom/workers/WorkerPrivate.cpp
@@ -0,0 +1,6208 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "WorkerPrivate.h"
+
+#include <utility>
+
+#include "js/CallAndConstruct.h"  // JS_CallFunctionValue
+#include "js/CompilationAndEvaluation.h"
+#include "js/ContextOptions.h"
+#include "js/Exception.h"
+#include "js/friend/ErrorMessages.h"  // JSMSG_OUT_OF_MEMORY
+#include "js/LocaleSensitive.h"
+#include "js/MemoryMetrics.h"
+#include "js/SourceText.h"
+#include "MessageEventRunnable.h"
+#include "mozilla/AntiTrackingUtils.h"
+#include "mozilla/BasePrincipal.h"
+#include "mozilla/CycleCollectedJSContext.h"
+#include "mozilla/ExtensionPolicyService.h"
+#include "mozilla/Mutex.h"
+#include "mozilla/ProfilerLabels.h"
+#include "mozilla/Result.h"
+#include "mozilla/ScopeExit.h"
+#include "mozilla/StaticPrefs_browser.h"
+#include "mozilla/StaticPrefs_dom.h"
+#include "mozilla/dom/BrowsingContextGroup.h"
+#include "mozilla/dom/CallbackDebuggerNotification.h"
+#include "mozilla/dom/ClientManager.h"
+#include "mozilla/dom/ClientState.h"
+#include "mozilla/dom/Console.h"
+#include "mozilla/dom/DocGroup.h"
+#include "mozilla/dom/Document.h"
+#include "mozilla/dom/DOMTypes.h"
+#include "mozilla/dom/Event.h"
+#include "mozilla/dom/Exceptions.h"
+#include "mozilla/dom/FunctionBinding.h"
+#include "mozilla/dom/IndexedDatabaseManager.h"
+#include "mozilla/dom/MessageEvent.h"
+#include "mozilla/dom/MessageEventBinding.h"
+#include "mozilla/dom/MessagePort.h"
+#include "mozilla/dom/MessagePortBinding.h"
+#include "mozilla/dom/nsCSPContext.h"
+#include "mozilla/dom/nsCSPUtils.h"
+#include "mozilla/dom/Performance.h"
+#include "mozilla/dom/PerformanceStorageWorker.h"
+#include "mozilla/dom/PromiseDebugging.h"
+#include "mozilla/dom/ReferrerInfo.h"
+#include "mozilla/dom/RemoteWorkerChild.h"
+#include "mozilla/dom/RemoteWorkerService.h"
+#include "mozilla/dom/RootedDictionary.h"
+#include "mozilla/dom/TimeoutHandler.h"
+#include "mozilla/dom/UseCounterMetrics.h"
+#include "mozilla/dom/WorkerBinding.h"
+#include "mozilla/dom/WorkerScope.h"
+#include "mozilla/dom/WorkerStatus.h"
+#include "mozilla/dom/WebTaskScheduler.h"
+#include "mozilla/dom/JSExecutionManager.h"
+#include "mozilla/dom/WindowContext.h"
+#include "mozilla/extensions/ExtensionBrowser.h"  // extensions::Create{AndDispatchInitWorkerContext,WorkerLoaded,WorkerDestroyed}Runnable
+#include "mozilla/extensions/WebExtensionPolicy.h"
+#include "mozilla/glean/GleanMetrics.h"
+#include "mozilla/ipc/BackgroundChild.h"
+#include "mozilla/ipc/PBackgroundChild.h"
+#include "mozilla/StorageAccess.h"
+#include "mozilla/StoragePrincipalHelper.h"
+#include "mozilla/Telemetry.h"
+#include "mozilla/ThreadEventQueue.h"
+#include "mozilla/ThreadSafety.h"
+#include "mozilla/ThrottledEventQueue.h"
+#include "nsCycleCollector.h"
+#include "nsGlobalWindowInner.h"
+#include "nsIDUtils.h"
+#include "nsNetUtil.h"
+#include "nsIFile.h"
+#include "nsIMemoryReporter.h"
+#include "nsIPermissionManager.h"
+#include "nsIProtocolHandler.h"
+#include "nsIScriptError.h"
+#include "nsIURI.h"
+#include "nsIURL.h"
+#include "nsIUUIDGenerator.h"
+#include "nsPrintfCString.h"
+#include "nsProxyRelease.h"
+#include "nsQueryObject.h"
+#include "nsRFPService.h"
+#include "nsSandboxFlags.h"
+#include "nsThreadUtils.h"
+#include "nsUTF8Utils.h"
+
+#include "RuntimeService.h"
+#include "ScriptLoader.h"
+#include "mozilla/dom/ServiceWorkerEvents.h"
+#include "mozilla/dom/ServiceWorkerManager.h"
+#include "mozilla/net/CookieJarSettings.h"
+#include "WorkerCSPEventListener.h"
+#include "WorkerDebugger.h"
+#include "WorkerDebuggerManager.h"
+#include "WorkerError.h"
+#include "WorkerEventTarget.h"
+#include "WorkerNavigator.h"
+#include "WorkerRef.h"
+#include "WorkerRunnable.h"
+#include "WorkerThread.h"
+#include "nsContentSecurityManager.h"
+
+#include "nsThreadManager.h"
+
+#ifdef XP_WIN
+#  undef PostMessage
+#endif
+
+// JS_MaybeGC will run once every second during normal execution.
+#define PERIODIC_GC_TIMER_DELAY_SEC 1
+
+// A shrinking GC will run five seconds after the last event is processed.
+#define IDLE_GC_TIMER_DELAY_SEC 5
+
+static mozilla::LazyLogModule sWorkerPrivateLog("WorkerPrivate");
+static mozilla::LazyLogModule sWorkerTimeoutsLog("WorkerTimeouts");
+
+mozilla::LogModule* WorkerLog() { return sWorkerPrivateLog; }
+
+mozilla::LogModule* TimeoutsLog() { return sWorkerTimeoutsLog; }
+
+#ifdef LOG
+#  undef LOG
+#endif
+#ifdef LOGV
+#  undef LOGV
+#endif
+#define LOG(log, _args) MOZ_LOG(log, LogLevel::Debug, _args);
+#define LOGV(args) MOZ_LOG(sWorkerPrivateLog, LogLevel::Verbose, args);
+
+namespace mozilla {
+
+using namespace ipc;
+
+namespace dom {
+
+using namespace workerinternals;
+
+MOZ_DEFINE_MALLOC_SIZE_OF(JsWorkerMallocSizeOf)
+
+namespace {
+
+#ifdef DEBUG
+
+const nsIID kDEBUGWorkerEventTargetIID = {
+    0xccaba3fa,
+    0x5be2,
+    0x4de2,
+    {0xba, 0x87, 0x3b, 0x3b, 0x5b, 0x1d, 0x5, 0xfb}};
+
+#endif
+
+template <class T>
+class UniquePtrComparator {
+  using A = UniquePtr<T>;
+  using B = T*;
+
+ public:
+  bool Equals(const A& a, const A& b) const {
+    return (a && b) ? (*a == *b) : (!a && !b);
+  }
+  bool LessThan(const A& a, const A& b) const {
+    return (a && b) ? (*a < *b) : !!b;
+  }
+};
+
+template <class T>
+inline UniquePtrComparator<T> GetUniquePtrComparator(
+    const nsTArray<UniquePtr<T>>&) {
+  return UniquePtrComparator<T>();
+}
+
+// This class is used to wrap any runnables that the worker receives via the
+// nsIEventTarget::Dispatch() method (either from NS_DispatchToCurrentThread or
+// from the worker's EventTarget).
+class ExternalRunnableWrapper final : public WorkerRunnable {
+  nsCOMPtr<nsIRunnable> mWrappedRunnable;
+
+ public:
+  ExternalRunnableWrapper(WorkerPrivate* aWorkerPrivate,
+                          nsIRunnable* aWrappedRunnable)
+      : WorkerRunnable(aWorkerPrivate, "ExternalRunnableWrapper", WorkerThread),
+        mWrappedRunnable(aWrappedRunnable) {
+    MOZ_ASSERT(aWorkerPrivate);
+    MOZ_ASSERT(aWrappedRunnable);
+  }
+
+  NS_INLINE_DECL_REFCOUNTING_INHERITED(ExternalRunnableWrapper, WorkerRunnable)
+
+ private:
+  ~ExternalRunnableWrapper() = default;
+
+  virtual bool PreDispatch(WorkerPrivate* aWorkerPrivate) override {
+    // Silence bad assertions.
+    return true;
+  }
+
+  virtual void PostDispatch(WorkerPrivate* aWorkerPrivate,
+                            bool aDispatchResult) override {
+    // Silence bad assertions.
+  }
+
+  virtual bool WorkerRun(JSContext* aCx,
+                         WorkerPrivate* aWorkerPrivate) override {
+    nsresult rv = mWrappedRunnable->Run();
+    mWrappedRunnable = nullptr;
+    if (NS_FAILED(rv)) {
+      if (!JS_IsExceptionPending(aCx)) {
+        Throw(aCx, rv);
+      }
+      return false;
+    }
+    return true;
+  }
+
+  nsresult Cancel() override {
+    nsCOMPtr<nsIDiscardableRunnable> doomed =
+        do_QueryInterface(mWrappedRunnable);
+    if (doomed) {
+      doomed->OnDiscard();
+    }
+    mWrappedRunnable = nullptr;
+    return NS_OK;
+  }
+};
+
+struct WindowAction {
+  nsPIDOMWindowInner* mWindow;
+  bool mDefaultAction;
+
+  MOZ_IMPLICIT WindowAction(nsPIDOMWindowInner* aWindow)
+      : mWindow(aWindow), mDefaultAction(true) {}
+
+  bool operator==(const WindowAction& aOther) const {
+    return mWindow == aOther.mWindow;
+  }
+};
+
+class WorkerFinishedRunnable final : public WorkerControlRunnable {
+  WorkerPrivate* mFinishedWorker;
+
+ public:
+  WorkerFinishedRunnable(WorkerPrivate* aWorkerPrivate,
+                         WorkerPrivate* aFinishedWorker)
+      : WorkerControlRunnable(aWorkerPrivate, "WorkerFinishedRunnable",
+                              WorkerThread),
+        mFinishedWorker(aFinishedWorker) {
+    aFinishedWorker->IncreaseWorkerFinishedRunnableCount();
+  }
+
+ private:
+  virtual bool PreDispatch(WorkerPrivate* aWorkerPrivate) override {
+    // Silence bad assertions.
+    return true;
+  }
+
+  virtual void PostDispatch(WorkerPrivate* aWorkerPrivate,
+                            bool aDispatchResult) override {
+    // Silence bad assertions.
+  }
+
+  virtual bool WorkerRun(JSContext* aCx,
+                         WorkerPrivate* aWorkerPrivate) override {
+    // This may block on the main thread.
+    AutoYieldJSThreadExecution yield;
+
+    mFinishedWorker->DecreaseWorkerFinishedRunnableCount();
+
+    if (!mFinishedWorker->ProxyReleaseMainThreadObjects()) {
+      NS_WARNING("Failed to dispatch, going to leak!");
+    }
+
+    RuntimeService* runtime = RuntimeService::GetService();
+    NS_ASSERTION(runtime, "This should never be null!");
+
+    mFinishedWorker->DisableDebugger();
+
+    runtime->UnregisterWorker(*mFinishedWorker);
+
+    mFinishedWorker->ClearSelfAndParentEventTargetRef();
+    return true;
+  }
+};
+
+class TopLevelWorkerFinishedRunnable final : public Runnable {
+  WorkerPrivate* mFinishedWorker;
+
+ public:
+  explicit TopLevelWorkerFinishedRunnable(WorkerPrivate* aFinishedWorker)
+      : mozilla::Runnable("TopLevelWorkerFinishedRunnable"),
+        mFinishedWorker(aFinishedWorker) {
+    aFinishedWorker->AssertIsOnWorkerThread();
+    aFinishedWorker->IncreaseTopLevelWorkerFinishedRunnableCount();
+  }
+
+  NS_INLINE_DECL_REFCOUNTING_INHERITED(TopLevelWorkerFinishedRunnable, Runnable)
+
+ private:
+  ~TopLevelWorkerFinishedRunnable() = default;
+
+  NS_IMETHOD
+  Run() override {
+    AssertIsOnMainThread();
+
+    mFinishedWorker->DecreaseTopLevelWorkerFinishedRunnableCount();
+
+    RuntimeService* runtime = RuntimeService::GetService();
+    MOZ_ASSERT(runtime);
+
+    mFinishedWorker->DisableDebugger();
+
+    runtime->UnregisterWorker(*mFinishedWorker);
+
+    if (!mFinishedWorker->ProxyReleaseMainThreadObjects()) {
+      NS_WARNING("Failed to dispatch, going to leak!");
+    }
+
+    mFinishedWorker->ClearSelfAndParentEventTargetRef();
+    return NS_OK;
+  }
+};
+
+class CompileScriptRunnable final : public WorkerDebuggeeRunnable {
+  nsString mScriptURL;
+  const mozilla::Encoding* mDocumentEncoding;
+  UniquePtr<SerializedStackHolder> mOriginStack;
+
+ public:
+  explicit CompileScriptRunnable(WorkerPrivate* aWorkerPrivate,
+                                 UniquePtr<SerializedStackHolder> aOriginStack,
+                                 const nsAString& aScriptURL,
+                                 const mozilla::Encoding* aDocumentEncoding)
+      : WorkerDebuggeeRunnable(aWorkerPrivate, "CompileScriptRunnable",
+                               WorkerThread),
+        mScriptURL(aScriptURL),
+        mDocumentEncoding(aDocumentEncoding),
+        mOriginStack(aOriginStack.release()) {}
+
+ private:
+  // We can't implement PreRun effectively, because at the point when that would
+  // run we have not yet done our load so don't know things like our final
+  // principal and whatnot.
+
+  virtual bool WorkerRun(JSContext* aCx,
+                         WorkerPrivate* aWorkerPrivate) override {
+    aWorkerPrivate->AssertIsOnWorkerThread();
+
+    WorkerGlobalScope* globalScope =
+        aWorkerPrivate->GetOrCreateGlobalScope(aCx);
+    if (NS_WARN_IF(!globalScope)) {
+      return false;
+    }
+
+    if (NS_WARN_IF(!aWorkerPrivate->EnsureCSPEventListener())) {
+      return false;
+    }
+
+    ErrorResult rv;
+    workerinternals::LoadMainScript(aWorkerPrivate, std::move(mOriginStack),
+                                    mScriptURL, WorkerScript, rv,
+                                    mDocumentEncoding);
+
+    if (aWorkerPrivate->ExtensionAPIAllowed()) {
+      MOZ_ASSERT(aWorkerPrivate->IsServiceWorker());
+      RefPtr<Runnable> extWorkerRunnable =
+          extensions::CreateWorkerLoadedRunnable(
+              aWorkerPrivate->ServiceWorkerID(), aWorkerPrivate->GetBaseURI());
+      // Dispatch as a low priority runnable.
+      if (NS_FAILED(aWorkerPrivate->DispatchToMainThreadForMessaging(
+              extWorkerRunnable.forget()))) {
+        NS_WARNING(
+            "Failed to dispatch runnable to notify extensions worker loaded");
+      }
+    }
+
+    rv.WouldReportJSException();
+    // Explicitly ignore NS_BINDING_ABORTED on rv.  Or more precisely, still
+    // return false and don't SetWorkerScriptExecutedSuccessfully() in that
+    // case, but don't throw anything on aCx.  The idea is to not dispatch error
+    // events if our load is canceled with that error code.
+    if (rv.ErrorCodeIs(NS_BINDING_ABORTED)) {
+      rv.SuppressException();
+      return false;
+    }
+
+    // Make sure to propagate exceptions from rv onto aCx, so that they will get
+    // reported after we return.  We want to propagate just JS exceptions,
+    // because all the other errors are handled when the script is loaded.
+    // See: https://dom.spec.whatwg.org/#concept-event-fire
+    if (rv.Failed() && !rv.IsJSException()) {
+      WorkerErrorReport::CreateAndDispatchGenericErrorRunnableToParent(
+          aWorkerPrivate);
+      rv.SuppressException();
+      return false;
+    }
+
+    // This is a little dumb, but aCx is in the null realm here because we
+    // set it up that way in our Run(), since we had not created the global at
+    // that point yet.  So we need to enter the realm of our global,
+    // because setting a pending exception on aCx involves wrapping into its
+    // current compartment.  Luckily we have a global now.
+    JSAutoRealm ar(aCx, globalScope->GetGlobalJSObject());
+    if (rv.MaybeSetPendingException(aCx)) {
+      // In the event of an uncaught exception, the worker should still keep
+      // running (return true) but should not be marked as having executed
+      // successfully (which will cause ServiceWorker installation to fail).
+      // In previous error handling cases in this method, we return false (to
+      // trigger CloseInternal) because the global is not in an operable
+      // state at all.
+      //
+      // For ServiceWorkers, this would correspond to the "Run Service Worker"
+      // algorithm returning an "abrupt completion" and _not_ failure.
+      //
+      // For DedicatedWorkers and SharedWorkers, this would correspond to the
+      // "run a worker" algorithm disregarding the return value of "run the
+      // classic script"/"run the module script" in step 24:
+      //
+      // "If script is a classic script, then run the classic script script.
+      // Otherwise, it is a module script; run the module script script."
+      return true;
+    }
+
+    aWorkerPrivate->SetWorkerScriptExecutedSuccessfully();
+    return true;
+  }
+
+  void PostRun(JSContext* aCx, WorkerPrivate* aWorkerPrivate,
+               bool aRunResult) override {
+    if (!aRunResult) {
+      aWorkerPrivate->CloseInternal();
+    }
+    WorkerRunnable::PostRun(aCx, aWorkerPrivate, aRunResult);
+  }
+};
+
+class NotifyRunnable final : public WorkerControlRunnable {
+  WorkerStatus mStatus;
+
+ public:
+  NotifyRunnable(WorkerPrivate* aWorkerPrivate, WorkerStatus aStatus)
+      : WorkerControlRunnable(aWorkerPrivate, "NotifyRunnable", WorkerThread),
+        mStatus(aStatus) {
+    MOZ_ASSERT(aStatus == Closing || aStatus == Canceling ||
+               aStatus == Killing);
+  }
+
+ private:
+  virtual bool PreDispatch(WorkerPrivate* aWorkerPrivate) override {
+    aWorkerPrivate->AssertIsOnParentThread();
+    return true;
+  }
+
+  virtual void PostDispatch(WorkerPrivate* aWorkerPrivate,
+                            bool aDispatchResult) override {
+    aWorkerPrivate->AssertIsOnParentThread();
+  }
+
+  virtual bool WorkerRun(JSContext* aCx,
+                         WorkerPrivate* aWorkerPrivate) override {
+    return aWorkerPrivate->NotifyInternal(mStatus);
+  }
+
+  virtual void PostRun(JSContext* aCx, WorkerPrivate* aWorkerPrivate,
+                       bool aRunResult) override {}
+};
+
+class FreezeRunnable final : public WorkerControlRunnable {
+ public:
+  explicit FreezeRunnable(WorkerPrivate* aWorkerPrivate)
+      : WorkerControlRunnable(aWorkerPrivate, "FreezeRunnable", WorkerThread) {}
+
+ private:
+  virtual bool WorkerRun(JSContext* aCx,
+                         WorkerPrivate* aWorkerPrivate) override {
+    return aWorkerPrivate->FreezeInternal();
+  }
+};
+
+class ThawRunnable final : public WorkerControlRunnable {
+ public:
+  explicit ThawRunnable(WorkerPrivate* aWorkerPrivate)
+      : WorkerControlRunnable(aWorkerPrivate, "ThawRunnable", WorkerThread) {}
+
+ private:
+  virtual bool WorkerRun(JSContext* aCx,
+                         WorkerPrivate* aWorkerPrivate) override {
+    return aWorkerPrivate->ThawInternal();
+  }
+};
+
+class PropagateStorageAccessPermissionGrantedRunnable final
+    : public WorkerControlRunnable {
+ public:
+  explicit PropagateStorageAccessPermissionGrantedRunnable(
+      WorkerPrivate* aWorkerPrivate)
+      : WorkerControlRunnable(aWorkerPrivate,
+                              "PropagateStorageAccessPermissionGrantedRunnable",
+                              WorkerThread) {}
+
+ private:
+  bool WorkerRun(JSContext* aCx, WorkerPrivate* aWorkerPrivate) override {
+    aWorkerPrivate->PropagateStorageAccessPermissionGrantedInternal();
+    return true;
+  }
+};
+
+class ReportErrorToConsoleRunnable final : public WorkerRunnable {
+  const char* mMessage;
+  const nsTArray<nsString> mParams;
+
+ public:
+  // aWorkerPrivate is the worker thread we're on (or the main thread, if null)
+  static void Report(WorkerPrivate* aWorkerPrivate, const char* aMessage,
+                     const nsTArray<nsString>& aParams) {
+    if (aWorkerPrivate) {
+      aWorkerPrivate->AssertIsOnWorkerThread();
+    } else {
+      AssertIsOnMainThread();
+    }
+
+    // Now fire a runnable to do the same on the parent's thread if we can.
+    if (aWorkerPrivate) {
+      RefPtr<ReportErrorToConsoleRunnable> runnable =
+          new ReportErrorToConsoleRunnable(aWorkerPrivate, aMessage, aParams);
+      runnable->Dispatch();
+      return;
+    }
+
+    // Log a warning to the console.
+    nsContentUtils::ReportToConsole(nsIScriptError::warningFlag, "DOM"_ns,
+                                    nullptr, nsContentUtils::eDOM_PROPERTIES,
+                                    aMessage, aParams);
+  }
+
+ private:
+  ReportErrorToConsoleRunnable(WorkerPrivate* aWorkerPrivate,
+                               const char* aMessage,
+                               const nsTArray<nsString>& aParams)
+      : WorkerRunnable(aWorkerPrivate, "ReportErrorToConsoleRunnable",
+                       ParentThread),
+        mMessage(aMessage),
+        mParams(aParams.Clone()) {}
+
+  virtual void PostDispatch(WorkerPrivate* aWorkerPrivate,
+                            bool aDispatchResult) override {
+    aWorkerPrivate->AssertIsOnWorkerThread();
+
+    // Dispatch may fail if the worker was canceled, no need to report that as
+    // an error, so don't call base class PostDispatch.
+  }
+
+  virtual bool WorkerRun(JSContext* aCx,
+                         WorkerPrivate* aWorkerPrivate) override {
+    WorkerPrivate* parent = aWorkerPrivate->GetParent();
+    MOZ_ASSERT_IF(!parent, NS_IsMainThread());
+    Report(parent, mMessage, mParams);
+    return true;
+  }
+};
+
+class RunExpiredTimoutsRunnable final : public WorkerRunnable,
+                                        public nsITimerCallback {
+ public:
+  NS_DECL_ISUPPORTS_INHERITED
+
+  explicit RunExpiredTimoutsRunnable(WorkerPrivate* aWorkerPrivate)
+      : WorkerRunnable(aWorkerPrivate, "RunExpiredTimoutsRunnable",
+                       WorkerThread) {}
+
+ private:
+  ~RunExpiredTimoutsRunnable() = default;
+
+  virtual bool PreDispatch(WorkerPrivate* aWorkerPrivate) override {
+    // Silence bad assertions.
+    return true;
+  }
+
+  virtual void PostDispatch(WorkerPrivate* aWorkerPrivate,
+                            bool aDispatchResult) override {
+    // Silence bad assertions.
+  }
+
+  // MOZ_CAN_RUN_SCRIPT_BOUNDARY until worker runnables are generally
+  // MOZ_CAN_RUN_SCRIPT.
+  MOZ_CAN_RUN_SCRIPT_BOUNDARY
+  virtual bool WorkerRun(JSContext* aCx,
+                         WorkerPrivate* aWorkerPrivate) override {
+    return aWorkerPrivate->RunExpiredTimeouts(aCx);
+  }
+
+  NS_IMETHOD
+  Notify(nsITimer* aTimer) override { return Run(); }
+};
+
+NS_IMPL_ISUPPORTS_INHERITED(RunExpiredTimoutsRunnable, WorkerRunnable,
+                            nsITimerCallback)
+
+class DebuggerImmediateRunnable final : public WorkerRunnable {
+  RefPtr<dom::Function> mHandler;
+
+ public:
+  explicit DebuggerImmediateRunnable(WorkerPrivate* aWorkerPrivate,
+                                     dom::Function& aHandler)
+      : WorkerRunnable(aWorkerPrivate, "DebuggerImmediateRunnable",
+                       WorkerThread),
+        mHandler(&aHandler) {}
+
+ private:
+  virtual bool IsDebuggerRunnable() const override { return true; }
+
+  virtual bool PreDispatch(WorkerPrivate* aWorkerPrivate) override {
+    // Silence bad assertions.
+    return true;
+  }
+
+  virtual void PostDispatch(WorkerPrivate* aWorkerPrivate,
+                            bool aDispatchResult) override {
+    // Silence bad assertions.
+  }
+
+  virtual bool WorkerRun(JSContext* aCx,
+                         WorkerPrivate* aWorkerPrivate) override {
+    JS::Rooted<JSObject*> global(aCx, JS::CurrentGlobalOrNull(aCx));
+    JS::Rooted<JS::Value> callable(
+        aCx, JS::ObjectOrNullValue(mHandler->CallableOrNull()));
+    JS::HandleValueArray args = JS::HandleValueArray::empty();
+    JS::Rooted<JS::Value> rval(aCx);
+
+    // WorkerRunnable::Run will report the exception if it happens.
+    return JS_CallFunctionValue(aCx, global, callable, args, &rval);
+  }
+};
+
+// GetJSContext() is safe on the worker thread
+void PeriodicGCTimerCallback(nsITimer* aTimer,
+                             void* aClosure) MOZ_NO_THREAD_SAFETY_ANALYSIS {
+  auto* workerPrivate = static_cast<WorkerPrivate*>(aClosure);
+  MOZ_DIAGNOSTIC_ASSERT(workerPrivate);
+  workerPrivate->AssertIsOnWorkerThread();
+  workerPrivate->GarbageCollectInternal(workerPrivate->GetJSContext(),
+                                        false /* shrinking */,
+                                        false /* collect children */);
+  LOG(WorkerLog(), ("Worker %p run periodic GC\n", workerPrivate));
+}
+
+void IdleGCTimerCallback(nsITimer* aTimer,
+                         void* aClosure) MOZ_NO_THREAD_SAFETY_ANALYSIS {
+  auto* workerPrivate = static_cast<WorkerPrivate*>(aClosure);
+  MOZ_DIAGNOSTIC_ASSERT(workerPrivate);
+  workerPrivate->AssertIsOnWorkerThread();
+  workerPrivate->GarbageCollectInternal(workerPrivate->GetJSContext(),
+                                        true /* shrinking */,
+                                        false /* collect children */);
+  LOG(WorkerLog(), ("Worker %p run idle GC\n", workerPrivate));
+
+  // After running idle GC we can cancel the current timers.
+  workerPrivate->CancelGCTimers();
+}
+
+class UpdateContextOptionsRunnable final : public WorkerControlRunnable {
+  JS::ContextOptions mContextOptions;
+
+ public:
+  UpdateContextOptionsRunnable(WorkerPrivate* aWorkerPrivate,
+                               const JS::ContextOptions& aContextOptions)
+      : WorkerControlRunnable(aWorkerPrivate, "UpdateContextOptionsRunnable",
+                              WorkerThread),
+        mContextOptions(aContextOptions) {}
+
+ private:
+  virtual bool WorkerRun(JSContext* aCx,
+                         WorkerPrivate* aWorkerPrivate) override {
+    aWorkerPrivate->UpdateContextOptionsInternal(aCx, mContextOptions);
+    return true;
+  }
+};
+
+class UpdateLanguagesRunnable final : public WorkerRunnable {
+  nsTArray<nsString> mLanguages;
+
+ public:
+  UpdateLanguagesRunnable(WorkerPrivate* aWorkerPrivate,
+                          const nsTArray<nsString>& aLanguages)
+      : WorkerRunnable(aWorkerPrivate, "UpdateLanguagesRunnable"),
+        mLanguages(aLanguages.Clone()) {}
+
+  virtual bool WorkerRun(JSContext* aCx,
+                         WorkerPrivate* aWorkerPrivate) override {
+    aWorkerPrivate->UpdateLanguagesInternal(mLanguages);
+    return true;
+  }
+};
+
+class UpdateJSWorkerMemoryParameterRunnable final
+    : public WorkerControlRunnable {
+  Maybe<uint32_t> mValue;
+  JSGCParamKey mKey;
+
+ public:
+  UpdateJSWorkerMemoryParameterRunnable(WorkerPrivate* aWorkerPrivate,
+                                        JSGCParamKey aKey,
+                                        Maybe<uint32_t> aValue)
+      : WorkerControlRunnable(aWorkerPrivate,
+                              "UpdateJSWorkerMemoryParameterRunnable",
+                              WorkerThread),
+        mValue(aValue),
+        mKey(aKey) {}
+
+ private:
+  virtual bool WorkerRun(JSContext* aCx,
+                         WorkerPrivate* aWorkerPrivate) override {
+    aWorkerPrivate->UpdateJSWorkerMemoryParameterInternal(aCx, mKey, mValue);
+    return true;
+  }
+};
+
+#ifdef JS_GC_ZEAL
+class UpdateGCZealRunnable final : public WorkerControlRunnable {
+  uint8_t mGCZeal;
+  uint32_t mFrequency;
+
+ public:
+  UpdateGCZealRunnable(WorkerPrivate* aWorkerPrivate, uint8_t aGCZeal,
+                       uint32_t aFrequency)
+      : WorkerControlRunnable(aWorkerPrivate, "UpdateGCZealRunnable",
+                              WorkerThread),
+        mGCZeal(aGCZeal),
+        mFrequency(aFrequency) {}
+
+ private:
+  virtual bool WorkerRun(JSContext* aCx,
+                         WorkerPrivate* aWorkerPrivate) override {
+    aWorkerPrivate->UpdateGCZealInternal(aCx, mGCZeal, mFrequency);
+    return true;
+  }
+};
+#endif
+
+class SetLowMemoryStateRunnable final : public WorkerControlRunnable {
+  bool mState;
+
+ public:
+  SetLowMemoryStateRunnable(WorkerPrivate* aWorkerPrivate, bool aState)
+      : WorkerControlRunnable(aWorkerPrivate, "SetLowMemoryStateRunnable",
+                              WorkerThread),
+        mState(aState) {}
+
+ private:
+  virtual bool WorkerRun(JSContext* aCx,
+                         WorkerPrivate* aWorkerPrivate) override {
+    aWorkerPrivate->SetLowMemoryStateInternal(aCx, mState);
+    return true;
+  }
+};
+
+class GarbageCollectRunnable final : public WorkerControlRunnable {
+  bool mShrinking;
+  bool mCollectChildren;
+
+ public:
+  GarbageCollectRunnable(WorkerPrivate* aWorkerPrivate, bool aShrinking,
+                         bool aCollectChildren)
+      : WorkerControlRunnable(aWorkerPrivate, "GarbageCollectRunnable",
+                              WorkerThread),
+        mShrinking(aShrinking),
+        mCollectChildren(aCollectChildren) {}
+
+ private:
+  virtual bool PreDispatch(WorkerPrivate* aWorkerPrivate) override {
+    // Silence bad assertions, this can be dispatched from either the main
+    // thread or the timer thread..
+    return true;
+  }
+
+  virtual void PostDispatch(WorkerPrivate* aWorkerPrivate,
+                            bool aDispatchResult) override {
+    // Silence bad assertions, this can be dispatched from either the main
+    // thread or the timer thread..
+  }
+
+  virtual bool WorkerRun(JSContext* aCx,
+                         WorkerPrivate* aWorkerPrivate) override {
+    aWorkerPrivate->GarbageCollectInternal(aCx, mShrinking, mCollectChildren);
+    if (mShrinking) {
+      // Either we've run the idle GC or explicit GC call from the parent,
+      // we can cancel the current timers.
+      aWorkerPrivate->CancelGCTimers();
+    }
+    return true;
+  }
+};
+
+class CycleCollectRunnable final : public WorkerControlRunnable {
+  bool mCollectChildren;
+
+ public:
+  CycleCollectRunnable(WorkerPrivate* aWorkerPrivate, bool aCollectChildren)
+      : WorkerControlRunnable(aWorkerPrivate, "CycleCollectRunnable",
+                              WorkerThread),
+        mCollectChildren(aCollectChildren) {}
+
+  bool WorkerRun(JSContext* aCx, WorkerPrivate* aWorkerPrivate) override {
+    aWorkerPrivate->CycleCollectInternal(mCollectChildren);
+    return true;
+  }
+};
+
+class OfflineStatusChangeRunnable final : public WorkerRunnable {
+ public:
+  OfflineStatusChangeRunnable(WorkerPrivate* aWorkerPrivate, bool aIsOffline)
+      : WorkerRunnable(aWorkerPrivate, "OfflineStatusChangeRunnable"),
+        mIsOffline(aIsOffline) {}
+
+  bool WorkerRun(JSContext* aCx, WorkerPrivate* aWorkerPrivate) override {
+    aWorkerPrivate->OfflineStatusChangeEventInternal(mIsOffline);
+    return true;
+  }
+
+ private:
+  bool mIsOffline;
+};
+
+class MemoryPressureRunnable final : public WorkerControlRunnable {
+ public:
+  explicit MemoryPressureRunnable(WorkerPrivate* aWorkerPrivate)
+      : WorkerControlRunnable(aWorkerPrivate, "MemoryPressureRunnable",
+                              WorkerThread) {}
+
+  bool WorkerRun(JSContext* aCx, WorkerPrivate* aWorkerPrivate) override {
+    aWorkerPrivate->MemoryPressureInternal();
+    return true;
+  }
+};
+
+#ifdef DEBUG
+static bool StartsWithExplicit(nsACString& s) {
+  return StringBeginsWith(s, "explicit/"_ns);
+}
+#endif
+
+PRThread* PRThreadFromThread(nsIThread* aThread) {
+  MOZ_ASSERT(aThread);
+
+  PRThread* result;
+  MOZ_ALWAYS_SUCCEEDS(aThread->GetPRThread(&result));
+  MOZ_ASSERT(result);
+
+  return result;
+}
+
+// A runnable to cancel the worker from the parent thread when self.close() is
+// called. This runnable is executed on the parent process in order to cancel
+// the current runnable. It uses a normal WorkerDebuggeeRunnable in order to be
+// sure that all the pending WorkerDebuggeeRunnables are executed before this.
+class CancelingOnParentRunnable final : public WorkerDebuggeeRunnable {
+ public:
+  explicit CancelingOnParentRunnable(WorkerPrivate* aWorkerPrivate)
+      : WorkerDebuggeeRunnable(aWorkerPrivate, "CancelingOnParentRunnable",
+                               ParentThread) {}
+
+  bool WorkerRun(JSContext* aCx, WorkerPrivate* aWorkerPrivate) override {
+    aWorkerPrivate->Cancel();
+    return true;
+  }
+};
+
+// A runnable to cancel the worker from the parent process.
+class CancelingWithTimeoutOnParentRunnable final
+    : public WorkerControlRunnable {
+ public:
+  explicit CancelingWithTimeoutOnParentRunnable(WorkerPrivate* aWorkerPrivate)
+      : WorkerControlRunnable(aWorkerPrivate,
+                              "CancelingWithTimeoutOnParentRunnable",
+                              ParentThread) {}
+
+  bool WorkerRun(JSContext* aCx, WorkerPrivate* aWorkerPrivate) override {
+    aWorkerPrivate->AssertIsOnParentThread();
+    aWorkerPrivate->StartCancelingTimer();
+    return true;
+  }
+};
+
+class CancelingTimerCallback final : public nsITimerCallback {
+ public:
+  NS_DECL_ISUPPORTS
+
+  explicit CancelingTimerCallback(WorkerPrivate* aWorkerPrivate)
+      : mWorkerPrivate(aWorkerPrivate) {}
+
+  NS_IMETHOD
+  Notify(nsITimer* aTimer) override {
+    mWorkerPrivate->AssertIsOnParentThread();
+    mWorkerPrivate->Cancel();
+    return NS_OK;
+  }
+
+ private:
+  ~CancelingTimerCallback() = default;
+
+  // Raw pointer here is OK because the timer is canceled during the shutdown
+  // steps.
+  WorkerPrivate* mWorkerPrivate;
+};
+
+NS_IMPL_ISUPPORTS(CancelingTimerCallback, nsITimerCallback)
+
+// This runnable starts the canceling of a worker after a self.close().
+class CancelingRunnable final : public Runnable {
+ public:
+  CancelingRunnable() : Runnable("CancelingRunnable") {}
+
+  NS_IMETHOD
+  Run() override {
+    LOG(WorkerLog(), ("CancelingRunnable::Run [%p]", this));
+    WorkerPrivate* workerPrivate = GetCurrentThreadWorkerPrivate();
+    MOZ_ASSERT(workerPrivate);
+    workerPrivate->AssertIsOnWorkerThread();
+
+    // Now we can cancel the this worker from the parent process.
+    RefPtr<CancelingOnParentRunnable> r =
+        new CancelingOnParentRunnable(workerPrivate);
+    r->Dispatch();
+
+    return NS_OK;
+  }
+};
+
+} /* anonymous namespace */
+
+nsString ComputeWorkerPrivateId() {
+  nsID uuid = nsID::GenerateUUID();
+  return NSID_TrimBracketsUTF16(uuid);
+}
+
+class WorkerPrivate::EventTarget final : public nsISerialEventTarget {
+  // This mutex protects mWorkerPrivate and must be acquired *before* the
+  // WorkerPrivate's mutex whenever they must both be held.
+  mozilla::Mutex mMutex;
+  WorkerPrivate* mWorkerPrivate MOZ_GUARDED_BY(mMutex);
+  nsCOMPtr<nsIEventTarget> mNestedEventTarget MOZ_GUARDED_BY(mMutex);
+  bool mDisabled MOZ_GUARDED_BY(mMutex);
+  bool mShutdown MOZ_GUARDED_BY(mMutex);
+
+ public:
+  EventTarget(WorkerPrivate* aWorkerPrivate, nsIEventTarget* aNestedEventTarget)
+      : mMutex("WorkerPrivate::EventTarget::mMutex"),
+        mWorkerPrivate(aWorkerPrivate),
+        mNestedEventTarget(aNestedEventTarget),
+        mDisabled(false),
+        mShutdown(false) {
+    MOZ_ASSERT(aWorkerPrivate);
+    MOZ_ASSERT(aNestedEventTarget);
+  }
+
+  void Disable() {
+    {
+      MutexAutoLock lock(mMutex);
+
+      // Note, Disable() can be called more than once safely.
+      mDisabled = true;
+    }
+  }
+
+  void Shutdown() {
+    nsCOMPtr<nsIEventTarget> nestedEventTarget;
+    {
+      MutexAutoLock lock(mMutex);
+
+      mWorkerPrivate = nullptr;
+      mNestedEventTarget.swap(nestedEventTarget);
+      MOZ_ASSERT(mDisabled);
+      mShutdown = true;
+    }
+  }
+
+  RefPtr<nsIEventTarget> GetNestedEventTarget() {
+    RefPtr<nsIEventTarget> nestedEventTarget = nullptr;
+    {
+      MutexAutoLock lock(mMutex);
+      if (mWorkerPrivate) {
+        mWorkerPrivate->AssertIsOnWorkerThread();
+        nestedEventTarget = mNestedEventTarget.get();
+      }
+    }
+    return nestedEventTarget;
+  }
+
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSIEVENTTARGET_FULL
+
+ private:
+  ~EventTarget() = default;
+};
+
+struct WorkerPrivate::TimeoutInfo {
+  TimeoutInfo()
+      : mId(0),
+        mNestingLevel(0),
+        mReason(Timeout::Reason::eTimeoutOrInterval),
+        mIsInterval(false),
+        mCanceled(false),
+        mOnChromeWorker(false) {
+    MOZ_COUNT_CTOR(mozilla::dom::WorkerPrivate::TimeoutInfo);
+  }
+
+  ~TimeoutInfo() { MOZ_COUNT_DTOR(mozilla::dom::WorkerPrivate::TimeoutInfo); }
+
+  bool operator==(const TimeoutInfo& aOther) const {
+    return mTargetTime == aOther.mTargetTime;
+  }
+
+  bool operator<(const TimeoutInfo& aOther) const {
+    return mTargetTime < aOther.mTargetTime;
+  }
+
+  void AccumulateNestingLevel(const uint32_t& aBaseLevel) {
+    if (aBaseLevel < StaticPrefs::dom_clamp_timeout_nesting_level_AtStartup()) {
+      mNestingLevel = aBaseLevel + 1;
+      return;
+    }
+    mNestingLevel = StaticPrefs::dom_clamp_timeout_nesting_level_AtStartup();
+  }
+
+  void CalculateTargetTime() {
+    auto target = mInterval;
+    // Don't clamp timeout for chrome workers
+    if (mNestingLevel >=
+            StaticPrefs::dom_clamp_timeout_nesting_level_AtStartup() &&
+        !mOnChromeWorker) {
+      target = TimeDuration::Max(
+          mInterval,
+          TimeDuration::FromMilliseconds(StaticPrefs::dom_min_timeout_value()));
+    }
+    mTargetTime = TimeStamp::Now() + target;
+  }
+
+  RefPtr<TimeoutHandler> mHandler;
+  mozilla::TimeStamp mTargetTime;
+  mozilla::TimeDuration mInterval;
+  int32_t mId;
+  uint32_t mNestingLevel;
+  Timeout::Reason mReason;
+  bool mIsInterval;
+  bool mCanceled;
+  bool mOnChromeWorker;
+};
+
+class WorkerJSContextStats final : public JS::RuntimeStats {
+  const nsCString mRtPath;
+
+ public:
+  explicit WorkerJSContextStats(const nsACString& aRtPath)
+      : JS::RuntimeStats(JsWorkerMallocSizeOf), mRtPath(aRtPath) {}
+
+  ~WorkerJSContextStats() {
+    for (JS::ZoneStats& stats : zoneStatsVector) {
+      delete static_cast<xpc::ZoneStatsExtras*>(stats.extra);
+    }
+
+    for (JS::RealmStats& stats : realmStatsVector) {
+      delete static_cast<xpc::RealmStatsExtras*>(stats.extra);
+    }
+  }
+
+  const nsCString& Path() const { return mRtPath; }
+
+  virtual void initExtraZoneStats(JS::Zone* aZone, JS::ZoneStats* aZoneStats,
+                                  const JS::AutoRequireNoGC& nogc) override {
+    MOZ_ASSERT(!aZoneStats->extra);
+
+    // ReportJSRuntimeExplicitTreeStats expects that
+    // aZoneStats->extra is a xpc::ZoneStatsExtras pointer.
+    xpc::ZoneStatsExtras* extras = new xpc::ZoneStatsExtras;
+    extras->pathPrefix = mRtPath;
+    extras->pathPrefix += nsPrintfCString("zone(0x%p)/", (void*)aZone);
+
+    MOZ_ASSERT(StartsWithExplicit(extras->pathPrefix));
+
+    aZoneStats->extra = extras;
+  }
+
+  virtual void initExtraRealmStats(JS::Realm* aRealm,
+                                   JS::RealmStats* aRealmStats,
+                                   const JS::AutoRequireNoGC& nogc) override {
+    MOZ_ASSERT(!aRealmStats->extra);
+
+    // ReportJSRuntimeExplicitTreeStats expects that
+    // aRealmStats->extra is a xpc::RealmStatsExtras pointer.
+    xpc::RealmStatsExtras* extras = new xpc::RealmStatsExtras;
+
+    // This is the |jsPathPrefix|.  Each worker has exactly one realm.
+    extras->jsPathPrefix.Assign(mRtPath);
+    extras->jsPathPrefix +=
+        nsPrintfCString("zone(0x%p)/", (void*)js::GetRealmZone(aRealm));
+    extras->jsPathPrefix += "realm(web-worker)/"_ns;
+
+    // This should never be used when reporting with workers (hence the "?!").
+    extras->domPathPrefix.AssignLiteral("explicit/workers/?!/");
+
+    MOZ_ASSERT(StartsWithExplicit(extras->jsPathPrefix));
+    MOZ_ASSERT(StartsWithExplicit(extras->domPathPrefix));
+
+    extras->location = nullptr;
+
+    aRealmStats->extra = extras;
+  }
+};
+
+class WorkerPrivate::MemoryReporter final : public nsIMemoryReporter {
+  NS_DECL_THREADSAFE_ISUPPORTS
+
+  friend class WorkerPrivate;
+
+  SharedMutex mMutex;
+  WorkerPrivate* mWorkerPrivate;
+
+ public:
+  explicit MemoryReporter(WorkerPrivate* aWorkerPrivate)
+      : mMutex(aWorkerPrivate->mMutex), mWorkerPrivate(aWorkerPrivate) {
+    aWorkerPrivate->AssertIsOnWorkerThread();
+  }
+
+  NS_IMETHOD
+  CollectReports(nsIHandleReportCallback* aHandleReport, nsISupports* aData,
+                 bool aAnonymize) override;
+
+ private:
+  class FinishCollectRunnable;
+
+  class CollectReportsRunnable final : public MainThreadWorkerControlRunnable {
+    RefPtr<FinishCollectRunnable> mFinishCollectRunnable;
+    const bool mAnonymize;
+
+   public:
+    CollectReportsRunnable(WorkerPrivate* aWorkerPrivate,
+                           nsIHandleReportCallback* aHandleReport,
+                           nsISupports* aHandlerData, bool aAnonymize,
+                           const nsACString& aPath);
+
+   private:
+    bool WorkerRun(JSContext* aCx, WorkerPrivate* aWorkerPrivate) override;
+
+    ~CollectReportsRunnable() {
+      if (NS_IsMainThread()) {
+        mFinishCollectRunnable->Run();
+        return;
+      }
+
+      WorkerPrivate* workerPrivate = GetCurrentThreadWorkerPrivate();
+      MOZ_ASSERT(workerPrivate);
+      MOZ_ALWAYS_SUCCEEDS(workerPrivate->DispatchToMainThreadForMessaging(
+          mFinishCollectRunnable.forget()));
+    }
+  };
+
+  class FinishCollectRunnable final : public Runnable {
+    nsCOMPtr<nsIHandleReportCallback> mHandleReport;
+    nsCOMPtr<nsISupports> mHandlerData;
+    size_t mPerformanceUserEntries;
+    size_t mPerformanceResourceEntries;
+    const bool mAnonymize;
+    bool mSuccess;
+
+   public:
+    WorkerJSContextStats mCxStats;
+
+    explicit FinishCollectRunnable(nsIHandleReportCallback* aHandleReport,
+                                   nsISupports* aHandlerData, bool aAnonymize,
+                                   const nsACString& aPath);
+
+    NS_IMETHOD Run() override;
+
+    void SetPerformanceSizes(size_t userEntries, size_t resourceEntries) {
+      mPerformanceUserEntries = userEntries;
+      mPerformanceResourceEntries = resourceEntries;
+    }
+
+    void SetSuccess(bool success) { mSuccess = success; }
+
+    FinishCollectRunnable(const FinishCollectRunnable&) = delete;
+    FinishCollectRunnable& operator=(const FinishCollectRunnable&) = delete;
+    FinishCollectRunnable& operator=(const FinishCollectRunnable&&) = delete;
+
+   private:
+    ~FinishCollectRunnable() {
+      // mHandleReport and mHandlerData are released on the main thread.
+      AssertIsOnMainThread();
+    }
+  };
+
+  ~MemoryReporter() = default;
+
+  void Disable() {
+    // Called from WorkerPrivate::DisableMemoryReporter.
+    mMutex.AssertCurrentThreadOwns();
+
+    NS_ASSERTION(mWorkerPrivate, "Disabled more than once!");
+    mWorkerPrivate = nullptr;
+  }
+};
+
+NS_IMPL_ISUPPORTS(WorkerPrivate::MemoryReporter, nsIMemoryReporter)
+
+NS_IMETHODIMP
+WorkerPrivate::MemoryReporter::CollectReports(
+    nsIHandleReportCallback* aHandleReport, nsISupports* aData,
+    bool aAnonymize) {
+  AssertIsOnMainThread();
+
+  RefPtr<CollectReportsRunnable> runnable;
+
+  {
+    MutexAutoLock lock(mMutex);
+
+    if (!mWorkerPrivate) {
+      // This will effectively report 0 memory.
+      nsCOMPtr<nsIMemoryReporterManager> manager =
+          do_GetService("@mozilla.org/memory-reporter-manager;1");
+      if (manager) {
+        manager->EndReport();
+      }
+      return NS_OK;
+    }
+
+    nsAutoCString path;
+    path.AppendLiteral("explicit/workers/workers(");
+    if (aAnonymize && !mWorkerPrivate->Domain().IsEmpty()) {
+      path.AppendLiteral("<anonymized-domain>)/worker(<anonymized-url>");
+    } else {
+      nsAutoCString escapedDomain(mWorkerPrivate->Domain());
+      if (escapedDomain.IsEmpty()) {
+        escapedDomain += "chrome";
+      } else {
+        escapedDomain.ReplaceChar('/', '\\');
+      }
+      path.Append(escapedDomain);
+      path.AppendLiteral(")/worker(");
+      NS_ConvertUTF16toUTF8 escapedURL(mWorkerPrivate->ScriptURL());
+      escapedURL.ReplaceChar('/', '\\');
+      path.Append(escapedURL);
+    }
+    path.AppendPrintf(", 0x%p)/", static_cast<void*>(mWorkerPrivate));
+
+    runnable = new CollectReportsRunnable(mWorkerPrivate, aHandleReport, aData,
+                                          aAnonymize, path);
+  }
+
+  if (!runnable->Dispatch()) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  return NS_OK;
+}
+
+WorkerPrivate::MemoryReporter::CollectReportsRunnable::CollectReportsRunnable(
+    WorkerPrivate* aWorkerPrivate, nsIHandleReportCallback* aHandleReport,
+    nsISupports* aHandlerData, bool aAnonymize, const nsACString& aPath)
+    : MainThreadWorkerControlRunnable(aWorkerPrivate),
+      mFinishCollectRunnable(new FinishCollectRunnable(
+          aHandleReport, aHandlerData, aAnonymize, aPath)),
+      mAnonymize(aAnonymize) {}
+
+bool WorkerPrivate::MemoryReporter::CollectReportsRunnable::WorkerRun(
+    JSContext* aCx, WorkerPrivate* aWorkerPrivate) {
+  aWorkerPrivate->AssertIsOnWorkerThread();
+
+  RefPtr<WorkerGlobalScope> scope = aWorkerPrivate->GlobalScope();
+  RefPtr<Performance> performance =
+      scope ? scope->GetPerformanceIfExists() : nullptr;
+  if (performance) {
+    size_t userEntries = performance->SizeOfUserEntries(JsWorkerMallocSizeOf);
+    size_t resourceEntries =
+        performance->SizeOfResourceEntries(JsWorkerMallocSizeOf);
+    mFinishCollectRunnable->SetPerformanceSizes(userEntries, resourceEntries);
+  }
+
+  mFinishCollectRunnable->SetSuccess(aWorkerPrivate->CollectRuntimeStats(
+      &mFinishCollectRunnable->mCxStats, mAnonymize));
+
+  return true;
+}
+
+WorkerPrivate::MemoryReporter::FinishCollectRunnable::FinishCollectRunnable(
+    nsIHandleReportCallback* aHandleReport, nsISupports* aHandlerData,
+    bool aAnonymize, const nsACString& aPath)
+    : mozilla::Runnable(
+          "dom::WorkerPrivate::MemoryReporter::FinishCollectRunnable"),
+      mHandleReport(aHandleReport),
+      mHandlerData(aHandlerData),
+      mPerformanceUserEntries(0),
+      mPerformanceResourceEntries(0),
+      mAnonymize(aAnonymize),
+      mSuccess(false),
+      mCxStats(aPath) {}
+
+NS_IMETHODIMP
+WorkerPrivate::MemoryReporter::FinishCollectRunnable::Run() {
+  AssertIsOnMainThread();
+
+  nsCOMPtr<nsIMemoryReporterManager> manager =
+      do_GetService("@mozilla.org/memory-reporter-manager;1");
+
+  if (!manager) return NS_OK;
+
+  if (mSuccess) {
+    xpc::ReportJSRuntimeExplicitTreeStats(
+        mCxStats, mCxStats.Path(), mHandleReport, mHandlerData, mAnonymize);
+
+    if (mPerformanceUserEntries) {
+      nsCString path = mCxStats.Path();
+      path.AppendLiteral("dom/performance/user-entries");
+      mHandleReport->Callback(""_ns, path, nsIMemoryReporter::KIND_HEAP,
+                              nsIMemoryReporter::UNITS_BYTES,
+                              static_cast<int64_t>(mPerformanceUserEntries),
+                              "Memory used for performance user entries."_ns,
+                              mHandlerData);
+    }
+
+    if (mPerformanceResourceEntries) {
+      nsCString path = mCxStats.Path();
+      path.AppendLiteral("dom/performance/resource-entries");
+      mHandleReport->Callback(
+          ""_ns, path, nsIMemoryReporter::KIND_HEAP,
+          nsIMemoryReporter::UNITS_BYTES,
+          static_cast<int64_t>(mPerformanceResourceEntries),
+          "Memory used for performance resource entries."_ns, mHandlerData);
+    }
+  }
+
+  manager->EndReport();
+
+  return NS_OK;
+}
+
+WorkerPrivate::SyncLoopInfo::SyncLoopInfo(EventTarget* aEventTarget)
+    : mEventTarget(aEventTarget),
+      mResult(NS_ERROR_FAILURE),
+      mCompleted(false)
+#ifdef DEBUG
+      ,
+      mHasRun(false)
+#endif
+{
+}
+
+Document* WorkerPrivate::GetDocument() const {
+  AssertIsOnMainThread();
+  if (nsPIDOMWindowInner* window = GetAncestorWindow()) {
+    return window->GetExtantDoc();
+  }
+  // couldn't query a document, give up and return nullptr
+  return nullptr;
+}
+
+nsPIDOMWindowInner* WorkerPrivate::GetAncestorWindow() const {
+  AssertIsOnMainThread();
+  if (mLoadInfo.mWindow) {
+    return mLoadInfo.mWindow;
+  }
+  // if we don't have a document, we should query the document
+  // from the parent in case of a nested worker
+  WorkerPrivate* parent = mParent;
+  while (parent) {
+    if (parent->mLoadInfo.mWindow) {
+      return parent->mLoadInfo.mWindow;
+    }
+    parent = parent->GetParent();
+  }
+  // couldn't query a window, give up and return nullptr
+  return nullptr;
+}
+
+class EvictFromBFCacheRunnable final : public WorkerProxyToMainThreadRunnable {
+ public:
+  void RunOnMainThread(WorkerPrivate* aWorkerPrivate) override {
+    MOZ_ASSERT(aWorkerPrivate);
+    AssertIsOnMainThread();
+    if (nsCOMPtr<nsPIDOMWindowInner> win =
+            aWorkerPrivate->GetAncestorWindow()) {
+      win->RemoveFromBFCacheSync();
+    }
+  }
+
+  void RunBackOnWorkerThreadForCleanup(WorkerPrivate* aWorkerPrivate) override {
+    MOZ_ASSERT(aWorkerPrivate);
+    aWorkerPrivate->AssertIsOnWorkerThread();
+  }
+};
+
+void WorkerPrivate::EvictFromBFCache() {
+  AssertIsOnWorkerThread();
+  RefPtr<EvictFromBFCacheRunnable> runnable = new EvictFromBFCacheRunnable();
+  runnable->Dispatch(this);
+}
+
+void WorkerPrivate::SetCsp(nsIContentSecurityPolicy* aCSP) {
+  AssertIsOnMainThread();
+  if (!aCSP) {
+    return;
+  }
+  aCSP->EnsureEventTarget(mMainThreadEventTarget);
+
+  mLoadInfo.mCSP = aCSP;
+  mLoadInfo.mCSPInfo = MakeUnique<CSPInfo>();
+  nsresult rv = CSPToCSPInfo(mLoadInfo.mCSP, mLoadInfo.mCSPInfo.get());
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return;
+  }
+}
+
+nsresult WorkerPrivate::SetCSPFromHeaderValues(
+    const nsACString& aCSPHeaderValue,
+    const nsACString& aCSPReportOnlyHeaderValue) {
+  AssertIsOnMainThread();
+  MOZ_DIAGNOSTIC_ASSERT(!mLoadInfo.mCSP);
+
+  NS_ConvertASCIItoUTF16 cspHeaderValue(aCSPHeaderValue);
+  NS_ConvertASCIItoUTF16 cspROHeaderValue(aCSPReportOnlyHeaderValue);
+
+  nsresult rv;
+  nsCOMPtr<nsIContentSecurityPolicy> csp = new nsCSPContext();
+
+  // First, we try to query the URI from the Principal, but
+  // in case selfURI remains empty (e.g in case the Principal
+  // is a SystemPrincipal) then we fall back and use the
+  // base URI as selfURI for CSP.
+  nsCOMPtr<nsIURI> selfURI;
+  // Its not recommended to use the BasePrincipal to get the URI
+  // but in this case we need to make an exception
+  auto* basePrin = BasePrincipal::Cast(mLoadInfo.mPrincipal);
+  if (basePrin) {
+    basePrin->GetURI(getter_AddRefs(selfURI));
+  }
+  if (!selfURI) {
+    selfURI = mLoadInfo.mBaseURI;
+  }
+  MOZ_ASSERT(selfURI, "need a self URI for CSP");
+
+  rv = csp->SetRequestContextWithPrincipal(mLoadInfo.mPrincipal, selfURI,
+                                           u""_ns, 0);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  csp->EnsureEventTarget(mMainThreadEventTarget);
+
+  // If there's a CSP header, apply it.
+  if (!cspHeaderValue.IsEmpty()) {
+    rv = CSP_AppendCSPFromHeader(csp, cspHeaderValue, false);
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+  // If there's a report-only CSP header, apply it.
+  if (!cspROHeaderValue.IsEmpty()) {
+    rv = CSP_AppendCSPFromHeader(csp, cspROHeaderValue, true);
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+
+  RefPtr<extensions::WebExtensionPolicy> addonPolicy;
+
+  if (basePrin) {
+    addonPolicy = basePrin->AddonPolicy();
+  }
+
+  // For extension workers there aren't any csp header values,
+  // instead it will inherit the Extension CSP.
+  if (addonPolicy) {
+    csp->AppendPolicy(addonPolicy->BaseCSP(), false, false);
+    csp->AppendPolicy(addonPolicy->ExtensionPageCSP(), false, false);
+  }
+
+  mLoadInfo.mCSP = csp;
+
+  // Set evalAllowed, default value is set in GetAllowsEval
+  bool evalAllowed = false;
+  bool reportEvalViolations = false;
+  rv = csp->GetAllowsEval(&reportEvalViolations, &evalAllowed);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  mLoadInfo.mEvalAllowed = evalAllowed;
+  mLoadInfo.mReportEvalCSPViolations = reportEvalViolations;
+
+  // Set wasmEvalAllowed
+  bool wasmEvalAllowed = false;
+  bool reportWasmEvalViolations = false;
+  rv = csp->GetAllowsWasmEval(&reportWasmEvalViolations, &wasmEvalAllowed);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  // As for nsScriptSecurityManager::ContentSecurityPolicyPermitsJSAction,
+  // for MV2 extensions we have to allow wasm by default and report violations
+  // for historical reasons.
+  // TODO bug 1770909: remove this exception.
+  if (!wasmEvalAllowed && addonPolicy && addonPolicy->ManifestVersion() == 2) {
+    wasmEvalAllowed = true;
+    reportWasmEvalViolations = true;
+  }
+
+  mLoadInfo.mWasmEvalAllowed = wasmEvalAllowed;
+  mLoadInfo.mReportWasmEvalCSPViolations = reportWasmEvalViolations;
+
+  mLoadInfo.mCSPInfo = MakeUnique<CSPInfo>();
+  rv = CSPToCSPInfo(csp, mLoadInfo.mCSPInfo.get());
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+  return NS_OK;
+}
+
+void WorkerPrivate::StoreCSPOnClient() {
+  auto data = mWorkerThreadAccessible.Access();
+  MOZ_ASSERT(data->mScope);
+  if (mLoadInfo.mCSPInfo) {
+    data->mScope->MutableClientSourceRef().SetCspInfo(*mLoadInfo.mCSPInfo);
+  }
+}
+
+void WorkerPrivate::UpdateReferrerInfoFromHeader(
+    const nsACString& aReferrerPolicyHeaderValue) {
+  NS_ConvertUTF8toUTF16 headerValue(aReferrerPolicyHeaderValue);
+
+  if (headerValue.IsEmpty()) {
+    return;
+  }
+
+  ReferrerPolicy policy =
+      ReferrerInfo::ReferrerPolicyFromHeaderString(headerValue);
+  if (policy == ReferrerPolicy::_empty) {
+    return;
+  }
+
+  nsCOMPtr<nsIReferrerInfo> referrerInfo =
+      static_cast<ReferrerInfo*>(GetReferrerInfo())->CloneWithNewPolicy(policy);
+  SetReferrerInfo(referrerInfo);
+}
+
+void WorkerPrivate::Traverse(nsCycleCollectionTraversalCallback& aCb) {
+  AssertIsOnParentThread();
+
+  // The WorkerPrivate::mParentEventTargetRef has a reference to the exposed
+  // Worker object, which is really held by the worker thread.  We traverse this
+  // reference if and only if all main thread event queues are empty, no
+  // shutdown tasks, no StrongWorkerRefs, no child workers, no timeouts, no
+  // blocking background actors, and we have not released the main thread
+  // reference.  We do not unlink it. This allows the CC to break cycles
+  // involving the Worker and begin shutting it down (which does happen in
+  // unlink) but ensures that the WorkerPrivate won't be deleted before we're
+  // done shutting down the thread.
+  if (IsEligibleForCC() && !mMainThreadObjectsForgotten) {
+    nsCycleCollectionTraversalCallback& cb = aCb;
+    WorkerPrivate* tmp = this;
+    NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mParentEventTargetRef);
+  }
+}
+
+nsresult WorkerPrivate::Dispatch(already_AddRefed<WorkerRunnable> aRunnable,
+                                 nsIEventTarget* aSyncLoopTarget) {
+  // May be called on any thread!
+  MutexAutoLock lock(mMutex);
+  return DispatchLockHeld(std::move(aRunnable), aSyncLoopTarget, lock);
+}
+
+nsresult WorkerPrivate::DispatchLockHeld(
+    already_AddRefed<WorkerRunnable> aRunnable, nsIEventTarget* aSyncLoopTarget,
+    const MutexAutoLock& aProofOfLock) {
+  // May be called on any thread!
+  RefPtr<WorkerRunnable> runnable(aRunnable);
+  LOGV(("WorkerPrivate::DispatchLockHeld [%p] runnable: %p", this,
+        runnable.get()));
+
+  MOZ_ASSERT_IF(aSyncLoopTarget, mThread);
+
+  if (mStatus == Dead || (!aSyncLoopTarget && ParentStatus() > Canceling)) {
+    LOGV(("WorkerPrivate::DispatchLockHeld [%p] runnable %p, parent status: %u",
+          this, runnable.get(), (uint8_t)(ParentStatus())));
+    NS_WARNING(
+        "A runnable was posted to a worker that is already shutting "
+        "down!");
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  if (runnable->IsDebuggeeRunnable() && !mDebuggerReady) {
+    MOZ_RELEASE_ASSERT(!aSyncLoopTarget);
+    mDelayedDebuggeeRunnables.AppendElement(runnable);
+    return NS_OK;
+  }
+
+  if (!mThread) {
+    if (ParentStatus() == Pending || mStatus == Pending) {
+      LOGV(
+          ("WorkerPrivate::DispatchLockHeld [%p] runnable %p is queued in "
+           "mPreStartRunnables",
+           this, runnable.get()));
+      mPreStartRunnables.AppendElement(runnable);
+      return NS_OK;
+    }
+
+    NS_WARNING(
+        "Using a worker event target after the thread has already"
+        "been released!");
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  nsresult rv;
+  if (aSyncLoopTarget) {
+    LOGV(
+        ("WorkerPrivate::DispatchLockHeld [%p] runnable %p dispatch to a "
+         "SyncLoop(%p)",
+         this, runnable.get(), aSyncLoopTarget));
+    rv = aSyncLoopTarget->Dispatch(runnable.forget(), NS_DISPATCH_NORMAL);
+  } else {
+    // WorkerDebuggeeRunnables don't need any special treatment here. True,
+    // they should not be delivered to a frozen worker. But frozen workers
+    // aren't drawing from the thread's main event queue anyway, only from
+    // mControlQueue.
+    LOGV(
+        ("WorkerPrivate::DispatchLockHeld [%p] runnable %p dispatch to the "
+         "main event queue",
+         this, runnable.get()));
+    rv = mThread->DispatchAnyThread(WorkerThreadFriendKey(), runnable.forget());
+  }
+
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  mCondVar.Notify();
+  return NS_OK;
+}
+
+void WorkerPrivate::EnableDebugger() {
+  AssertIsOnParentThread();
+
+  if (NS_FAILED(RegisterWorkerDebugger(this))) {
+    NS_WARNING("Failed to register worker debugger!");
+    return;
+  }
+}
+
+void WorkerPrivate::DisableDebugger() {
+  AssertIsOnParentThread();
+
+  // RegisterDebuggerMainThreadRunnable might be dispatched but not executed.
+  // Wait for its execution before unregistraion.
+  if (!NS_IsMainThread()) {
+    WaitForIsDebuggerRegistered(true);
+  }
+
+  if (NS_FAILED(UnregisterWorkerDebugger(this))) {
+    NS_WARNING("Failed to unregister worker debugger!");
+  }
+}
+
+nsresult WorkerPrivate::DispatchControlRunnable(
+    already_AddRefed<WorkerControlRunnable> aWorkerControlRunnable) {
+  // May be called on any thread!
+  RefPtr<WorkerControlRunnable> runnable(aWorkerControlRunnable);
+  MOZ_ASSERT(runnable);
+
+  LOG(WorkerLog(), ("WorkerPrivate::DispatchControlRunnable [%p] runnable %p",
+                    this, runnable.get()));
+
+  {
+    MutexAutoLock lock(mMutex);
+
+    if (mStatus == Dead) {
+      return NS_ERROR_UNEXPECTED;
+    }
+
+    // Transfer ownership to the control queue.
+    mControlQueue.Push(runnable.forget().take());
+
+    if (JSContext* cx = mJSContext) {
+      MOZ_ASSERT(mThread);
+      JS_RequestInterruptCallback(cx);
+    }
+
+    mCondVar.Notify();
+  }
+
+  return NS_OK;
+}
+
+nsresult WorkerPrivate::DispatchDebuggerRunnable(
+    already_AddRefed<WorkerRunnable> aDebuggerRunnable) {
+  // May be called on any thread!
+
+  RefPtr<WorkerRunnable> runnable(aDebuggerRunnable);
+
+  MOZ_ASSERT(runnable);
+
+  {
+    MutexAutoLock lock(mMutex);
+
+    if (mStatus == Dead) {
+      NS_WARNING(
+          "A debugger runnable was posted to a worker that is already "
+          "shutting down!");
+      return NS_ERROR_UNEXPECTED;
+    }
+
+    // Transfer ownership to the debugger queue.
+    mDebuggerQueue.Push(runnable.forget().take());
+
+    mCondVar.Notify();
+  }
+
+  return NS_OK;
+}
+
+already_AddRefed<WorkerRunnable> WorkerPrivate::MaybeWrapAsWorkerRunnable(
+    already_AddRefed<nsIRunnable> aRunnable) {
+  // May be called on any thread!
+
+  nsCOMPtr<nsIRunnable> runnable(aRunnable);
+  MOZ_ASSERT(runnable);
+
+  LOGV(("WorkerPrivate::MaybeWrapAsWorkerRunnable [%p] runnable: %p", this,
+        runnable.get()));
+
+  RefPtr<WorkerRunnable> workerRunnable =
+      WorkerRunnable::FromRunnable(runnable);
+  if (workerRunnable) {
+    return workerRunnable.forget();
+  }
+
+  workerRunnable = new ExternalRunnableWrapper(this, runnable);
+  return workerRunnable.forget();
+}
+
+bool WorkerPrivate::Start() {
+  // May be called on any thread!
+  LOG(WorkerLog(), ("WorkerPrivate::Start [%p]", this));
+  {
+    MutexAutoLock lock(mMutex);
+    NS_ASSERTION(mParentStatus != Running, "How can this be?!");
+
+    if (mParentStatus == Pending) {
+      mParentStatus = Running;
+      return true;
+    }
+  }
+
+  return false;
+}
+
+// aCx is null when called from the finalizer
+bool WorkerPrivate::Notify(WorkerStatus aStatus) {
+  AssertIsOnParentThread();
+  // This method is only called for Canceling or later.
+  MOZ_DIAGNOSTIC_ASSERT(aStatus >= Canceling);
+
+  bool pending;
+  {
+    MutexAutoLock lock(mMutex);
+
+    if (mParentStatus >= aStatus) {
+      return true;
+    }
+
+    pending = mParentStatus == Pending;
+    mParentStatus = aStatus;
+  }
+
+  if (mCancellationCallback) {
+    mCancellationCallback(!pending);
+    mCancellationCallback = nullptr;
+  }
+
+  if (pending) {
+#ifdef DEBUG
+    {
+      // Fake a thread here just so that our assertions don't go off for no
+      // reason.
+      nsIThread* currentThread = NS_GetCurrentThread();
+      MOZ_ASSERT(currentThread);
+
+      MOZ_ASSERT(!mPRThread);
+      mPRThread = PRThreadFromThread(currentThread);
+      MOZ_ASSERT(mPRThread);
+    }
+#endif
+
+    // Worker never got a chance to run, go ahead and delete it.
+    ScheduleDeletion(WorkerPrivate::WorkerNeverRan);
+    return true;
+  }
+
+  // No Canceling timeout is needed.
+  if (mCancelingTimer) {
+    mCancelingTimer->Cancel();
+    mCancelingTimer = nullptr;
+  }
+
+  // The NotifyRunnable kicks off a series of events that need the
+  // CancelingOnParentRunnable to be executed always.
+  // Note that we already advanced mParentStatus above and we check that
+  // status in all other (asynchronous) call sites of SetIsPaused.
+  if (!mParent) {
+    MOZ_ALWAYS_SUCCEEDS(mMainThreadDebuggeeEventTarget->SetIsPaused(false));
+  }
+
+  RefPtr<NotifyRunnable> runnable = new NotifyRunnable(this, aStatus);
+  return runnable->Dispatch();
+}
+
+bool WorkerPrivate::Freeze(const nsPIDOMWindowInner* aWindow) {
+  AssertIsOnParentThread();
+
+  mParentFrozen = true;
+
+  bool isCanceling = false;
+  {
+    MutexAutoLock lock(mMutex);
+
+    isCanceling = mParentStatus >= Canceling;
+  }
+
+  // WorkerDebuggeeRunnables sent from a worker to content must not be
+  // delivered while the worker is frozen.
+  //
+  // Since a top-level worker and all its children share the same
+  // mMainThreadDebuggeeEventTarget, it's sufficient to do this only in the
+  // top-level worker.
+  if (aWindow) {
+    // This is called from WorkerPrivate construction, and We may not have
+    // allocated mMainThreadDebuggeeEventTarget yet.
+    if (mMainThreadDebuggeeEventTarget) {
+      // Pausing a ThrottledEventQueue is infallible.
+      MOZ_ALWAYS_SUCCEEDS(
+          mMainThreadDebuggeeEventTarget->SetIsPaused(!isCanceling));
+    }
+  }
+
+  if (isCanceling) {
+    return true;
+  }
+
+  DisableDebugger();
+
+  RefPtr<FreezeRunnable> runnable = new FreezeRunnable(this);
+  return runnable->Dispatch();
+}
+
+bool WorkerPrivate::Thaw(const nsPIDOMWindowInner* aWindow) {
+  AssertIsOnParentThread();
+  MOZ_ASSERT(mParentFrozen);
+
+  mParentFrozen = false;
+
+  {
+    bool isCanceling = false;
+
+    {
+      MutexAutoLock lock(mMutex);
+
+      isCanceling = mParentStatus >= Canceling;
+    }
+
+    // Delivery of WorkerDebuggeeRunnables to the window may resume.
+    //
+    // Since a top-level worker and all its children share the same
+    // mMainThreadDebuggeeEventTarget, it's sufficient to do this only in the
+    // top-level worker.
+    if (aWindow) {
+      // Since the worker is no longer frozen, only a paused parent window
+      // should require the queue to remain paused.
+      //
+      // This can only fail if the ThrottledEventQueue cannot dispatch its
+      // executor to the main thread, in which case the main thread was never
+      // going to draw runnables from it anyway, so the failure doesn't matter.
+      Unused << mMainThreadDebuggeeEventTarget->SetIsPaused(
+          IsParentWindowPaused() && !isCanceling);
+    }
+
+    if (isCanceling) {
+      return true;
+    }
+  }
+
+  EnableDebugger();
+
+  RefPtr<ThawRunnable> runnable = new ThawRunnable(this);
+  return runnable->Dispatch();
+}
+
+void WorkerPrivate::ParentWindowPaused() {
+  AssertIsOnMainThread();
+  MOZ_ASSERT(!mParentWindowPaused);
+  mParentWindowPaused = true;
+
+  // This is called from WorkerPrivate construction, and we may not have
+  // allocated mMainThreadDebuggeeEventTarget yet.
+  if (mMainThreadDebuggeeEventTarget) {
+    bool isCanceling = false;
+
+    {
+      MutexAutoLock lock(mMutex);
+
+      isCanceling = mParentStatus >= Canceling;
+    }
+
+    // If we are already canceling we might wait for CancelingOnParentRunnable
+    // to be executed, so do not pause.
+    MOZ_ALWAYS_SUCCEEDS(
+        mMainThreadDebuggeeEventTarget->SetIsPaused(!isCanceling));
+  }
+}
+
+void WorkerPrivate::ParentWindowResumed() {
+  AssertIsOnMainThread();
+
+  MOZ_ASSERT(mParentWindowPaused);
+  mParentWindowPaused = false;
+
+  bool isCanceling = false;
+  {
+    MutexAutoLock lock(mMutex);
+
+    isCanceling = mParentStatus >= Canceling;
+  }
+
+  // Since the window is no longer paused, the queue should only remain paused
+  // if the worker is frozen.
+  //
+  // This can only fail if the ThrottledEventQueue cannot dispatch its executor
+  // to the main thread, in which case the main thread was never going to draw
+  // runnables from it anyway, so the failure doesn't matter.
+  Unused << mMainThreadDebuggeeEventTarget->SetIsPaused(IsFrozen() &&
+                                                        !isCanceling);
+}
+
+void WorkerPrivate::PropagateStorageAccessPermissionGranted() {
+  AssertIsOnParentThread();
+
+  {
+    MutexAutoLock lock(mMutex);
+
+    if (mParentStatus >= Canceling) {
+      return;
+    }
+  }
+
+  RefPtr<PropagateStorageAccessPermissionGrantedRunnable> runnable =
+      new PropagateStorageAccessPermissionGrantedRunnable(this);
+  Unused << NS_WARN_IF(!runnable->Dispatch());
+}
+
+bool WorkerPrivate::Close() {
+  mMutex.AssertCurrentThreadOwns();
+  if (mParentStatus < Closing) {
+    mParentStatus = Closing;
+  }
+
+  return true;
+}
+
+bool WorkerPrivate::ProxyReleaseMainThreadObjects() {
+  AssertIsOnParentThread();
+  MOZ_ASSERT(!mMainThreadObjectsForgotten);
+
+  nsCOMPtr<nsILoadGroup> loadGroupToCancel;
+  // If we're not overriden, then do nothing here.  Let the load group get
+  // handled in ForgetMainThreadObjects().
+  if (mLoadInfo.mInterfaceRequestor) {
+    mLoadInfo.mLoadGroup.swap(loadGroupToCancel);
+  }
+
+  bool result = mLoadInfo.ProxyReleaseMainThreadObjects(
+      this, std::move(loadGroupToCancel));
+
+  mMainThreadObjectsForgotten = true;
+
+  return result;
+}
+
+void WorkerPrivate::UpdateContextOptions(
+    const JS::ContextOptions& aContextOptions) {
+  AssertIsOnParentThread();
+
+  {
+    MutexAutoLock lock(mMutex);
+    mJSSettings.contextOptions = aContextOptions;
+  }
+
+  RefPtr<UpdateContextOptionsRunnable> runnable =
+      new UpdateContextOptionsRunnable(this, aContextOptions);
+  if (!runnable->Dispatch()) {
+    NS_WARNING("Failed to update worker context options!");
+  }
+}
+
+void WorkerPrivate::UpdateLanguages(const nsTArray<nsString>& aLanguages) {
+  AssertIsOnParentThread();
+
+  RefPtr<UpdateLanguagesRunnable> runnable =
+      new UpdateLanguagesRunnable(this, aLanguages);
+  if (!runnable->Dispatch()) {
+    NS_WARNING("Failed to update worker languages!");
+  }
+}
+
+void WorkerPrivate::UpdateJSWorkerMemoryParameter(JSGCParamKey aKey,
+                                                  Maybe<uint32_t> aValue) {
+  AssertIsOnParentThread();
+
+  bool changed = false;
+
+  {
+    MutexAutoLock lock(mMutex);
+    changed = mJSSettings.ApplyGCSetting(aKey, aValue);
+  }
+
+  if (changed) {
+    RefPtr<UpdateJSWorkerMemoryParameterRunnable> runnable =
+        new UpdateJSWorkerMemoryParameterRunnable(this, aKey, aValue);
+    if (!runnable->Dispatch()) {
+      NS_WARNING("Failed to update memory parameter!");
+    }
+  }
+}
+
+#ifdef JS_GC_ZEAL
+void WorkerPrivate::UpdateGCZeal(uint8_t aGCZeal, uint32_t aFrequency) {
+  AssertIsOnParentThread();
+
+  {
+    MutexAutoLock lock(mMutex);
+    mJSSettings.gcZeal = aGCZeal;
+    mJSSettings.gcZealFrequency = aFrequency;
+  }
+
+  RefPtr<UpdateGCZealRunnable> runnable =
+      new UpdateGCZealRunnable(this, aGCZeal, aFrequency);
+  if (!runnable->Dispatch()) {
+    NS_WARNING("Failed to update worker gczeal!");
+  }
+}
+#endif
+
+void WorkerPrivate::SetLowMemoryState(bool aState) {
+  AssertIsOnParentThread();
+
+  RefPtr<SetLowMemoryStateRunnable> runnable =
+      new SetLowMemoryStateRunnable(this, aState);
+  if (!runnable->Dispatch()) {
+    NS_WARNING("Failed to set low memory state!");
+  }
+}
+
+void WorkerPrivate::GarbageCollect(bool aShrinking) {
+  AssertIsOnParentThread();
+
+  RefPtr<GarbageCollectRunnable> runnable = new GarbageCollectRunnable(
+      this, aShrinking, /* aCollectChildren = */ true);
+  if (!runnable->Dispatch()) {
+    NS_WARNING("Failed to GC worker!");
+  }
+}
+
+void WorkerPrivate::CycleCollect() {
+  AssertIsOnParentThread();
+
+  RefPtr<CycleCollectRunnable> runnable =
+      new CycleCollectRunnable(this, /* aCollectChildren = */ true);
+  if (!runnable->Dispatch()) {
+    NS_WARNING("Failed to CC worker!");
+  }
+}
+
+void WorkerPrivate::OfflineStatusChangeEvent(bool aIsOffline) {
+  AssertIsOnParentThread();
+
+  RefPtr<OfflineStatusChangeRunnable> runnable =
+      new OfflineStatusChangeRunnable(this, aIsOffline);
+  if (!runnable->Dispatch()) {
+    NS_WARNING("Failed to dispatch offline status change event!");
+  }
+}
+
+void WorkerPrivate::OfflineStatusChangeEventInternal(bool aIsOffline) {
+  auto data = mWorkerThreadAccessible.Access();
+
+  // The worker is already in this state. No need to dispatch an event.
+  if (data->mOnLine == !aIsOffline) {
+    return;
+  }
+
+  for (uint32_t index = 0; index < data->mChildWorkers.Length(); ++index) {
+    data->mChildWorkers[index]->OfflineStatusChangeEvent(aIsOffline);
+  }
+
+  data->mOnLine = !aIsOffline;
+  WorkerGlobalScope* globalScope = GlobalScope();
+  RefPtr<WorkerNavigator> nav = globalScope->GetExistingNavigator();
+  if (nav) {
+    nav->SetOnLine(data->mOnLine);
+  }
+
+  nsString eventType;
+  if (aIsOffline) {
+    eventType.AssignLiteral("offline");
+  } else {
+    eventType.AssignLiteral("online");
+  }
+
+  RefPtr<Event> event = NS_NewDOMEvent(globalScope, nullptr, nullptr);
+
+  event->InitEvent(eventType, false, false);
+  event->SetTrusted(true);
+
+  globalScope->DispatchEvent(*event);
+}
+
+void WorkerPrivate::MemoryPressure() {
+  AssertIsOnParentThread();
+
+  RefPtr<MemoryPressureRunnable> runnable = new MemoryPressureRunnable(this);
+  Unused << NS_WARN_IF(!runnable->Dispatch());
+}
+
+RefPtr<WorkerPrivate::JSMemoryUsagePromise> WorkerPrivate::GetJSMemoryUsage() {
+  AssertIsOnMainThread();
+
+  {
+    MutexAutoLock lock(mMutex);
+    // If we have started shutting down the worker, do not dispatch a runnable
+    // to measure its memory.
+    if (ParentStatus() > Running) {
+      return nullptr;
+    }
+  }
+
+  return InvokeAsync(ControlEventTarget(), __func__, []() {
+    WorkerPrivate* wp = GetCurrentThreadWorkerPrivate();
+    MOZ_ASSERT(wp);
+    wp->AssertIsOnWorkerThread();
+    MutexAutoLock lock(wp->mMutex);
+    return JSMemoryUsagePromise::CreateAndResolve(
+        js::GetGCHeapUsage(wp->mJSContext), __func__);
+  });
+}
+
+void WorkerPrivate::WorkerScriptLoaded() {
+  AssertIsOnMainThread();
+
+  if (IsSharedWorker() || IsServiceWorker()) {
+    // No longer need to hold references to the window or document we came from.
+    mLoadInfo.mWindow = nullptr;
+    mLoadInfo.mScriptContext = nullptr;
+  }
+}
+
+void WorkerPrivate::SetBaseURI(nsIURI* aBaseURI) {
+  AssertIsOnMainThread();
+
+  if (!mLoadInfo.mBaseURI) {
+    NS_ASSERTION(GetParent(), "Shouldn't happen without a parent!");
+    mLoadInfo.mResolvedScriptURI = aBaseURI;
+  }
+
+  mLoadInfo.mBaseURI = aBaseURI;
+
+  if (NS_FAILED(aBaseURI->GetSpec(mLocationInfo.mHref))) {
+    mLocationInfo.mHref.Truncate();
+  }
+
+  mLocationInfo.mHostname.Truncate();
+  nsContentUtils::GetHostOrIPv6WithBrackets(aBaseURI, mLocationInfo.mHostname);
+
+  nsCOMPtr<nsIURL> url(do_QueryInterface(aBaseURI));
+  if (!url || NS_FAILED(url->GetFilePath(mLocationInfo.mPathname))) {
+    mLocationInfo.mPathname.Truncate();
+  }
+
+  nsCString temp;
+
+  if (url && NS_SUCCEEDED(url->GetQuery(temp)) && !temp.IsEmpty()) {
+    mLocationInfo.mSearch.Assign('?');
+    mLocationInfo.mSearch.Append(temp);
+  }
+
+  if (NS_SUCCEEDED(aBaseURI->GetRef(temp)) && !temp.IsEmpty()) {
+    if (mLocationInfo.mHash.IsEmpty()) {
+      mLocationInfo.mHash.Assign('#');
+      mLocationInfo.mHash.Append(temp);
+    }
+  }
+
+  if (NS_SUCCEEDED(aBaseURI->GetScheme(mLocationInfo.mProtocol))) {
+    mLocationInfo.mProtocol.Append(':');
+  } else {
+    mLocationInfo.mProtocol.Truncate();
+  }
+
+  int32_t port;
+  if (NS_SUCCEEDED(aBaseURI->GetPort(&port)) && port != -1) {
+    mLocationInfo.mPort.AppendInt(port);
+
+    nsAutoCString host(mLocationInfo.mHostname);
+    host.Append(':');
+    host.Append(mLocationInfo.mPort);
+
+    mLocationInfo.mHost.Assign(host);
+  } else {
+    mLocationInfo.mHost.Assign(mLocationInfo.mHostname);
+  }
+
+  nsContentUtils::GetWebExposedOriginSerialization(aBaseURI,
+                                                   mLocationInfo.mOrigin);
+}
+
+nsresult WorkerPrivate::SetPrincipalsAndCSPOnMainThread(
+    nsIPrincipal* aPrincipal, nsIPrincipal* aPartitionedPrincipal,
+    nsILoadGroup* aLoadGroup, nsIContentSecurityPolicy* aCsp) {
+  return mLoadInfo.SetPrincipalsAndCSPOnMainThread(
+      aPrincipal, aPartitionedPrincipal, aLoadGroup, aCsp);
+}
+
+nsresult WorkerPrivate::SetPrincipalsAndCSPFromChannel(nsIChannel* aChannel) {
+  return mLoadInfo.SetPrincipalsAndCSPFromChannel(aChannel);
+}
+
+bool WorkerPrivate::FinalChannelPrincipalIsValid(nsIChannel* aChannel) {
+  return mLoadInfo.FinalChannelPrincipalIsValid(aChannel);
+}
+
+#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
+bool WorkerPrivate::PrincipalURIMatchesScriptURL() {
+  return mLoadInfo.PrincipalURIMatchesScriptURL();
+}
+#endif
+
+void WorkerPrivate::UpdateOverridenLoadGroup(nsILoadGroup* aBaseLoadGroup) {
+  AssertIsOnMainThread();
+
+  // The load group should have been overriden at init time.
+  mLoadInfo.mInterfaceRequestor->MaybeAddBrowserChild(aBaseLoadGroup);
+}
+
+bool WorkerPrivate::IsOnParentThread() const {
+  if (GetParent()) {
+    return GetParent()->IsOnWorkerThread();
+  }
+  return NS_IsMainThread();
+}
+
+#ifdef DEBUG
+
+void WorkerPrivate::AssertIsOnParentThread() const {
+  if (GetParent()) {
+    GetParent()->AssertIsOnWorkerThread();
+  } else {
+    AssertIsOnMainThread();
+  }
+}
+
+void WorkerPrivate::AssertInnerWindowIsCorrect() const {
+  AssertIsOnParentThread();
+
+  // Only care about top level workers from windows.
+  if (mParent || !mLoadInfo.mWindow) {
+    return;
+  }
+
+  AssertIsOnMainThread();
+
+  nsPIDOMWindowOuter* outer = mLoadInfo.mWindow->GetOuterWindow();
+  NS_ASSERTION(outer && outer->GetCurrentInnerWindow() == mLoadInfo.mWindow,
+               "Inner window no longer correct!");
+}
+
+#endif
+
+#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
+bool WorkerPrivate::PrincipalIsValid() const {
+  return mLoadInfo.PrincipalIsValid();
+}
+#endif
+
+WorkerPrivate::WorkerThreadAccessible::WorkerThreadAccessible(
+    WorkerPrivate* const aParent)
+    : mNumWorkerRefsPreventingShutdownStart(0),
+      mDebuggerEventLoopLevel(0),
+      mNonblockingCCBackgroundActorCount(0),
+      mErrorHandlerRecursionCount(0),
+      mNextTimeoutId(1),
+      mCurrentTimerNestingLevel(0),
+      mFrozen(false),
+      mTimerRunning(false),
+      mRunningExpiredTimeouts(false),
+      mPeriodicGCTimerRunning(false),
+      mIdleGCTimerRunning(false),
+      mOnLine(aParent ? aParent->OnLine() : !NS_IsOffline()),
+      mJSThreadExecutionGranted(false),
+      mCCCollectedAnything(false) {}
+
+namespace {
+
+bool IsNewWorkerSecureContext(const WorkerPrivate* const aParent,
+                              const WorkerKind aWorkerKind,
+                              const WorkerLoadInfo& aLoadInfo) {
+  if (aParent) {
+    return aParent->IsSecureContext();
+  }
+
+  // Our secure context state depends on the kind of worker we have.
+
+  if (aLoadInfo.mPrincipal && aLoadInfo.mPrincipal->IsSystemPrincipal()) {
+    return true;
+  }
+
+  if (aWorkerKind == WorkerKindService) {
+    return true;
+  }
+
+  if (aLoadInfo.mSecureContext != WorkerLoadInfo::eNotSet) {
+    return aLoadInfo.mSecureContext == WorkerLoadInfo::eSecureContext;
+  }
+
+  MOZ_ASSERT_UNREACHABLE(
+      "non-chrome worker that is not a service worker "
+      "that has no parent and no associated window");
+
+  return false;
+}
+
+}  // namespace
+
+WorkerPrivate::WorkerPrivate(
+    WorkerPrivate* aParent, const nsAString& aScriptURL, bool aIsChromeWorker,
+    WorkerKind aWorkerKind, RequestCredentials aRequestCredentials,
+    enum WorkerType aWorkerType, const nsAString& aWorkerName,
+    const nsACString& aServiceWorkerScope, WorkerLoadInfo& aLoadInfo,
+    nsString&& aId, const nsID& aAgentClusterId,
+    const nsILoadInfo::CrossOriginOpenerPolicy aAgentClusterOpenerPolicy,
+    CancellationCallback&& aCancellationCallback,
+    TerminationCallback&& aTerminationCallback)
+    : mMutex("WorkerPrivate Mutex"),
+      mCondVar(mMutex, "WorkerPrivate CondVar"),
+      mParent(aParent),
+      mScriptURL(aScriptURL),
+      mWorkerName(aWorkerName),
+      mCredentialsMode(aRequestCredentials),
+      mWorkerType(aWorkerType),  // If the worker runs as a script or a module
+      mWorkerKind(aWorkerKind),
+      mCancellationCallback(std::move(aCancellationCallback)),
+      mTerminationCallback(std::move(aTerminationCallback)),
+      mLoadInfo(std::move(aLoadInfo)),
+      mDebugger(nullptr),
+      mJSContext(nullptr),
+      mPRThread(nullptr),
+      mWorkerControlEventTarget(new WorkerEventTarget(
+          this, WorkerEventTarget::Behavior::ControlOnly)),
+      mWorkerHybridEventTarget(
+          new WorkerEventTarget(this, WorkerEventTarget::Behavior::Hybrid)),
+      mParentStatus(Pending),
+      mStatus(Pending),
+      mCreationTimeStamp(TimeStamp::Now()),
+      mCreationTimeHighRes((double)PR_Now() / PR_USEC_PER_MSEC),
+      mReportedUseCounters(false),
+      mAgentClusterId(aAgentClusterId),
+      mWorkerThreadAccessible(aParent),
+      mPostSyncLoopOperations(0),
+      mParentWindowPaused(false),
+      mWorkerScriptExecutedSuccessfully(false),
+      mFetchHandlerWasAdded(false),
+      mMainThreadObjectsForgotten(false),
+      mIsChromeWorker(aIsChromeWorker),
+      mParentFrozen(false),
+      mIsSecureContext(
+          IsNewWorkerSecureContext(mParent, mWorkerKind, mLoadInfo)),
+      mDebuggerRegistered(false),
+      mDebuggerReady(true),
+      mExtensionAPIAllowed(false),
+      mIsInAutomation(false),
+      mId(std::move(aId)),
+      mAgentClusterOpenerPolicy(aAgentClusterOpenerPolicy),
+      mIsPrivilegedAddonGlobal(false),
+      mTopLevelWorkerFinishedRunnableCount(0),
+      mWorkerFinishedRunnableCount(0) {
+  LOG(WorkerLog(), ("WorkerPrivate::WorkerPrivate [%p]", this));
+  MOZ_ASSERT_IF(!IsDedicatedWorker(), NS_IsMainThread());
+
+  if (aParent) {
+    aParent->AssertIsOnWorkerThread();
+
+    // Note that this copies our parent's secure context state into mJSSettings.
+    aParent->CopyJSSettings(mJSSettings);
+
+    MOZ_ASSERT_IF(mIsChromeWorker, mIsSecureContext);
+
+    mIsInAutomation = aParent->IsInAutomation();
+
+    MOZ_ASSERT(IsDedicatedWorker());
+
+    if (aParent->mParentFrozen) {
+      Freeze(nullptr);
+    }
+
+    mIsPrivilegedAddonGlobal = aParent->mIsPrivilegedAddonGlobal;
+  } else {
+    AssertIsOnMainThread();
+
+    RuntimeService::GetDefaultJSSettings(mJSSettings);
+
+    {
+      JS::RealmOptions& chromeRealmOptions = mJSSettings.chromeRealmOptions;
+      JS::RealmOptions& contentRealmOptions = mJSSettings.contentRealmOptions;
+
+      xpc::InitGlobalObjectOptions(
+          chromeRealmOptions, UsesSystemPrincipal(), mIsSecureContext,
+          ShouldResistFingerprinting(RFPTarget::JSDateTimeUTC),
+          ShouldResistFingerprinting(RFPTarget::JSMathFdlibm),
+          ShouldResistFingerprinting(RFPTarget::JSLocale));
+      xpc::InitGlobalObjectOptions(
+          contentRealmOptions, UsesSystemPrincipal(), mIsSecureContext,
+          ShouldResistFingerprinting(RFPTarget::JSDateTimeUTC),
+          ShouldResistFingerprinting(RFPTarget::JSMathFdlibm),
+          ShouldResistFingerprinting(RFPTarget::JSLocale));
+
+      // Check if it's a privileged addon executing in order to allow access
+      // to SharedArrayBuffer
+      if (mLoadInfo.mPrincipal) {
+        if (auto* policy =
+                BasePrincipal::Cast(mLoadInfo.mPrincipal)->AddonPolicy()) {
+          if (policy->IsPrivileged() &&
+              ExtensionPolicyService::GetSingleton().IsExtensionProcess()) {
+            // Privileged extensions are allowed to use SharedArrayBuffer in
+            // their extension process, but never in content scripts in
+            // content processes.
+            mIsPrivilegedAddonGlobal = true;
+          }
+
+          if (StaticPrefs::
+                  extensions_backgroundServiceWorker_enabled_AtStartup() &&
+              mWorkerKind == WorkerKindService &&
+              policy->IsManifestBackgroundWorker(mScriptURL)) {
+            // Only allows ExtensionAPI for extension service workers
+            // that are declared in the extension manifest json as
+            // the background service worker.
+            mExtensionAPIAllowed = true;
+          }
+        }
+      }
+
+      // The SharedArrayBuffer global constructor property should not be present
+      // in a fresh global object when shared memory objects aren't allowed
+      // (because COOP/COEP support isn't enabled, or because COOP/COEP don't
+      // act to isolate this worker to a separate process).
+      const bool defineSharedArrayBufferConstructor = IsSharedMemoryAllowed();
+      chromeRealmOptions.creationOptions()
+          .setDefineSharedArrayBufferConstructor(
+              defineSharedArrayBufferConstructor);
+      contentRealmOptions.creationOptions()
+          .setDefineSharedArrayBufferConstructor(
+              defineSharedArrayBufferConstructor);
+    }
+
+    mIsInAutomation = xpc::IsInAutomation();
+
+    // Our parent can get suspended after it initiates the async creation
+    // of a new worker thread.  In this case suspend the new worker as well.
+    if (mLoadInfo.mWindow && mLoadInfo.mWindow->IsSuspended()) {
+      ParentWindowPaused();
+    }
+
+    if (mLoadInfo.mWindow && mLoadInfo.mWindow->IsFrozen()) {
+      Freeze(mLoadInfo.mWindow);
+    }
+  }
+
+  nsCOMPtr<nsISerialEventTarget> target;
+
+  // A child worker just inherits the parent workers ThrottledEventQueue
+  // and main thread target for now.  This is mainly due to the restriction
+  // that ThrottledEventQueue can only be created on the main thread at the
+  // moment.
+  if (aParent) {
+    mMainThreadEventTargetForMessaging =
+        aParent->mMainThreadEventTargetForMessaging;
+    mMainThreadEventTarget = aParent->mMainThreadEventTarget;
+    mMainThreadDebuggeeEventTarget = aParent->mMainThreadDebuggeeEventTarget;
+    return;
+  }
+
+  MOZ_ASSERT(NS_IsMainThread());
+  target = GetWindow()
+               ? GetWindow()->GetBrowsingContextGroup()->GetWorkerEventQueue()
+               : nullptr;
+
+  if (!target) {
+    target = GetMainThreadSerialEventTarget();
+    MOZ_DIAGNOSTIC_ASSERT(target);
+  }
+
+  // Throttle events to the main thread using a ThrottledEventQueue specific to
+  // this tree of worker threads.
+  mMainThreadEventTargetForMessaging =
+      ThrottledEventQueue::Create(target, "Worker queue for messaging");
+  if (StaticPrefs::dom_worker_use_medium_high_event_queue()) {
+    mMainThreadEventTarget = ThrottledEventQueue::Create(
+        GetMainThreadSerialEventTarget(), "Worker queue",
+        nsIRunnablePriority::PRIORITY_MEDIUMHIGH);
+  } else {
+    mMainThreadEventTarget = mMainThreadEventTargetForMessaging;
+  }
+  mMainThreadDebuggeeEventTarget =
+      ThrottledEventQueue::Create(target, "Worker debuggee queue");
+  if (IsParentWindowPaused() || IsFrozen()) {
+    MOZ_ALWAYS_SUCCEEDS(mMainThreadDebuggeeEventTarget->SetIsPaused(true));
+  }
+}
+
+WorkerPrivate::~WorkerPrivate() {
+  MOZ_DIAGNOSTIC_ASSERT(mTopLevelWorkerFinishedRunnableCount == 0);
+  MOZ_DIAGNOSTIC_ASSERT(mWorkerFinishedRunnableCount == 0);
+
+  mWorkerControlEventTarget->ForgetWorkerPrivate(this);
+
+  // We force the hybrid event target to forget the thread when we
+  // enter the Killing state, but we do it again here to be safe.
+  // Its possible that we may be created and destroyed without progressing
+  // to Killing via some obscure code path.
+  mWorkerHybridEventTarget->ForgetWorkerPrivate(this);
+}
+
+WorkerPrivate::AgentClusterIdAndCoop
+WorkerPrivate::ComputeAgentClusterIdAndCoop(WorkerPrivate* aParent,
+                                            WorkerKind aWorkerKind,
+                                            WorkerLoadInfo* aLoadInfo) {
+  nsILoadInfo::CrossOriginOpenerPolicy agentClusterCoop =
+      nsILoadInfo::OPENER_POLICY_UNSAFE_NONE;
+
+  if (aParent) {
+    MOZ_ASSERT(aWorkerKind == WorkerKind::WorkerKindDedicated);
+
+    return {aParent->AgentClusterId(), aParent->mAgentClusterOpenerPolicy};
+  }
+
+  AssertIsOnMainThread();
+
+  if (aWorkerKind == WorkerKind::WorkerKindService ||
+      aWorkerKind == WorkerKind::WorkerKindShared) {
+    return {aLoadInfo->mAgentClusterId, agentClusterCoop};
+  }
+
+  if (aLoadInfo->mWindow) {
+    Document* doc = aLoadInfo->mWindow->GetExtantDoc();
+    MOZ_DIAGNOSTIC_ASSERT(doc);
+    RefPtr<DocGroup> docGroup = doc->GetDocGroup();
+
+    nsID agentClusterId =
+        docGroup ? docGroup->AgentClusterId() : nsID::GenerateUUID();
+
+    BrowsingContext* bc = aLoadInfo->mWindow->GetBrowsingContext();
+    MOZ_DIAGNOSTIC_ASSERT(bc);
+    return {agentClusterId, bc->Top()->GetOpenerPolicy()};
+  }
+
+  // If the window object was failed to be set into the WorkerLoadInfo, we
+  // make the worker into another agent cluster group instead of failures.
+  return {nsID::GenerateUUID(), agentClusterCoop};
+}
+
+// static
+already_AddRefed<WorkerPrivate> WorkerPrivate::Constructor(
+    JSContext* aCx, const nsAString& aScriptURL, bool aIsChromeWorker,
+    WorkerKind aWorkerKind, RequestCredentials aRequestCredentials,
+    enum WorkerType aWorkerType, const nsAString& aWorkerName,
+    const nsACString& aServiceWorkerScope, WorkerLoadInfo* aLoadInfo,
+    ErrorResult& aRv, nsString aId,
+    CancellationCallback&& aCancellationCallback,
+    TerminationCallback&& aTerminationCallback) {
+  WorkerPrivate* parent =
+      NS_IsMainThread() ? nullptr : GetCurrentThreadWorkerPrivate();
+
+  // If this is a sub-worker, we need to keep the parent worker alive until this
+  // one is registered.
+  RefPtr<StrongWorkerRef> workerRef;
+  if (parent) {
+    parent->AssertIsOnWorkerThread();
+
+    workerRef = StrongWorkerRef::Create(parent, "WorkerPrivate::Constructor");
+    if (NS_WARN_IF(!workerRef)) {
+      aRv.Throw(NS_ERROR_DOM_INVALID_STATE_ERR);
+      return nullptr;
+    }
+  } else {
+    AssertIsOnMainThread();
+  }
+
+  Maybe<WorkerLoadInfo> stackLoadInfo;
+  if (!aLoadInfo) {
+    stackLoadInfo.emplace();
+
+    nsresult rv = GetLoadInfo(
+        aCx, nullptr, parent, aScriptURL, aWorkerType, aRequestCredentials,
+        aIsChromeWorker, InheritLoadGroup, aWorkerKind, stackLoadInfo.ptr());
+    aRv.MightThrowJSException();
+    if (NS_FAILED(rv)) {
+      workerinternals::ReportLoadError(aRv, rv, aScriptURL);
+      return nullptr;
+    }
+
+    aLoadInfo = stackLoadInfo.ptr();
+  }
+
+  // NB: This has to be done before creating the WorkerPrivate, because it will
+  // attempt to use static variables that are initialized in the RuntimeService
+  // constructor.
+  RuntimeService* runtimeService;
+
+  if (!parent) {
+    runtimeService = RuntimeService::GetOrCreateService();
+    if (!runtimeService) {
+      aRv.Throw(NS_ERROR_FAILURE);
+      return nullptr;
+    }
+  } else {
+    runtimeService = RuntimeService::GetService();
+  }
+
+  MOZ_ASSERT(runtimeService);
+
+  // Don't create a worker with the shutting down RuntimeService.
+  if (runtimeService->IsShuttingDown()) {
+    aRv.Throw(NS_ERROR_UNEXPECTED);
+    return nullptr;
+  }
+
+  AgentClusterIdAndCoop idAndCoop =
+      ComputeAgentClusterIdAndCoop(parent, aWorkerKind, aLoadInfo);
+
+  RefPtr<WorkerPrivate> worker = new WorkerPrivate(
+      parent, aScriptURL, aIsChromeWorker, aWorkerKind, aRequestCredentials,
+      aWorkerType, aWorkerName, aServiceWorkerScope, *aLoadInfo, std::move(aId),
+      idAndCoop.mId, idAndCoop.mCoop, std::move(aCancellationCallback),
+      std::move(aTerminationCallback));
+
+  // Gecko contexts always have an explicitly-set default locale (set by
+  // XPJSRuntime::Initialize for the main thread, set by
+  // WorkerThreadPrimaryRunnable::Run for workers just before running worker
+  // code), so this is never SpiderMonkey's builtin default locale.
+  JS::UniqueChars defaultLocale = JS_GetDefaultLocale(aCx);
+  if (NS_WARN_IF(!defaultLocale)) {
+    aRv.Throw(NS_ERROR_UNEXPECTED);
+    return nullptr;
+  }
+
+  worker->mDefaultLocale = std::move(defaultLocale);
+
+  if (!runtimeService->RegisterWorker(*worker)) {
+    aRv.Throw(NS_ERROR_UNEXPECTED);
+    return nullptr;
+  }
+
+  // From this point on (worker thread has been started) we
+  // must keep ourself alive. We can now only be cleared by
+  // ClearSelfAndParentEventTargetRef().
+  worker->mSelfRef = worker;
+
+  worker->EnableDebugger();
+
+  MOZ_DIAGNOSTIC_ASSERT(worker->PrincipalIsValid());
+
+  UniquePtr<SerializedStackHolder> stack;
+  if (worker->IsWatchedByDevTools()) {
+    stack = GetCurrentStackForNetMonitor(aCx);
+  }
+
+  // This should be non-null for dedicated workers and null for Shared and
+  // Service workers. All Encoding values are static and will live as long
+  // as the process and the convention is to therefore use raw pointers.
+  const mozilla::Encoding* aDocumentEncoding =
+      NS_IsMainThread() && !worker->GetParent() && worker->GetDocument()
+          ? worker->GetDocument()->GetDocumentCharacterSet().get()
+          : nullptr;
+
+  RefPtr<CompileScriptRunnable> compiler = new CompileScriptRunnable(
+      worker, std::move(stack), aScriptURL, aDocumentEncoding);
+  if (!compiler->Dispatch()) {
+    aRv.Throw(NS_ERROR_UNEXPECTED);
+    return nullptr;
+  }
+
+  return worker.forget();
+}
+
+nsresult WorkerPrivate::SetIsDebuggerReady(bool aReady) {
+  AssertIsOnMainThread();
+  MutexAutoLock lock(mMutex);
+
+  if (mDebuggerReady == aReady) {
+    return NS_OK;
+  }
+
+  if (!aReady && mDebuggerRegistered) {
+    // The debugger can only be marked as not ready during registration.
+    return NS_ERROR_FAILURE;
+  }
+
+  mDebuggerReady = aReady;
+
+  if (aReady && mDebuggerRegistered) {
+    // Dispatch all the delayed runnables without releasing the lock, to ensure
+    // that the order in which debuggee runnables execute is the same as the
+    // order in which they were originally dispatched.
+    auto pending = std::move(mDelayedDebuggeeRunnables);
+    for (uint32_t i = 0; i < pending.Length(); i++) {
+      RefPtr<WorkerRunnable> runnable = std::move(pending[i]);
+      nsresult rv = DispatchLockHeld(runnable.forget(), nullptr, lock);
+      NS_ENSURE_SUCCESS(rv, rv);
+    }
+    MOZ_RELEASE_ASSERT(mDelayedDebuggeeRunnables.IsEmpty());
+  }
+
+  return NS_OK;
+}
+
+// static
+nsresult WorkerPrivate::GetLoadInfo(
+    JSContext* aCx, nsPIDOMWindowInner* aWindow, WorkerPrivate* aParent,
+    const nsAString& aScriptURL, const enum WorkerType& aWorkerType,
+    const RequestCredentials& aCredentials, bool aIsChromeWorker,
+    LoadGroupBehavior aLoadGroupBehavior, WorkerKind aWorkerKind,
+    WorkerLoadInfo* aLoadInfo) {
+  using namespace mozilla::dom::workerinternals;
+
+  MOZ_ASSERT(aCx);
+  MOZ_ASSERT_IF(NS_IsMainThread(),
+                aCx == nsContentUtils::GetCurrentJSContext());
+
+  if (aWindow) {
+    AssertIsOnMainThread();
+  }
+
+  WorkerLoadInfo loadInfo;
+  nsresult rv;
+
+  if (aParent) {
+    aParent->AssertIsOnWorkerThread();
+
+    // If the parent is going away give up now.
+    WorkerStatus parentStatus;
+    {
+      MutexAutoLock lock(aParent->mMutex);
+      parentStatus = aParent->mStatus;
+    }
+
+    if (parentStatus > Running) {
+      return NS_ERROR_FAILURE;
+    }
+
+    // Passing a pointer to our stack loadInfo is safe here because this
+    // method uses a sync runnable to get the channel from the main thread.
+    rv = ChannelFromScriptURLWorkerThread(aCx, aParent, aScriptURL, aWorkerType,
+                                          aCredentials, loadInfo);
+    if (NS_FAILED(rv)) {
+      MOZ_ALWAYS_TRUE(loadInfo.ProxyReleaseMainThreadObjects(aParent));
+      return rv;
+    }
+
+    // Now that we've spun the loop there's no guarantee that our parent is
+    // still alive.  We may have received control messages initiating shutdown.
+    {
+      MutexAutoLock lock(aParent->mMutex);
+      parentStatus = aParent->mStatus;
+    }
+
+    if (parentStatus > Running) {
+      MOZ_ALWAYS_TRUE(loadInfo.ProxyReleaseMainThreadObjects(aParent));
+      return NS_ERROR_FAILURE;
+    }
+
+    loadInfo.mTrials = aParent->Trials();
+    loadInfo.mDomain = aParent->Domain();
+    loadInfo.mFromWindow = aParent->IsFromWindow();
+    loadInfo.mWindowID = aParent->WindowID();
+    loadInfo.mAssociatedBrowsingContextID =
+        aParent->AssociatedBrowsingContextID();
+    loadInfo.mStorageAccess = aParent->StorageAccess();
+    loadInfo.mUseRegularPrincipal = aParent->UseRegularPrincipal();
+    loadInfo.mUsingStorageAccess = aParent->UsingStorageAccess();
+    loadInfo.mCookieJarSettings = aParent->CookieJarSettings();
+    if (loadInfo.mCookieJarSettings) {
+      loadInfo.mCookieJarSettingsArgs = aParent->CookieJarSettingsArgs();
+    }
+    loadInfo.mOriginAttributes = aParent->GetOriginAttributes();
+    loadInfo.mServiceWorkersTestingInWindow =
+        aParent->ServiceWorkersTestingInWindow();
+    loadInfo.mIsThirdPartyContextToTopWindow =
+        aParent->IsThirdPartyContextToTopWindow();
+    loadInfo.mShouldResistFingerprinting = aParent->ShouldResistFingerprinting(
+        RFPTarget::IsAlwaysEnabledForPrecompute);
+    loadInfo.mOverriddenFingerprintingSettings =
+        aParent->GetOverriddenFingerprintingSettings();
+    loadInfo.mParentController = aParent->GlobalScope()->GetController();
+    loadInfo.mWatchedByDevTools = aParent->IsWatchedByDevTools();
+  } else {
+    AssertIsOnMainThread();
+
+    // Make sure that the IndexedDatabaseManager is set up
+    Unused << NS_WARN_IF(!IndexedDatabaseManager::GetOrCreate());
+
+    nsIScriptSecurityManager* ssm = nsContentUtils::GetSecurityManager();
+    MOZ_ASSERT(ssm);
+
+    bool isChrome = nsContentUtils::IsSystemCaller(aCx);
+
+    // First check to make sure the caller has permission to make a privileged
+    // worker if they called the ChromeWorker/ChromeSharedWorker constructor.
+    if (aIsChromeWorker && !isChrome) {
+      return NS_ERROR_DOM_SECURITY_ERR;
+    }
+
+    // Chrome callers (whether creating a ChromeWorker or Worker) always get the
+    // system principal here as they're allowed to load anything. The script
+    // loader will refuse to run any script that does not also have the system
+    // principal.
+    if (isChrome) {
+      rv = ssm->GetSystemPrincipal(getter_AddRefs(loadInfo.mLoadingPrincipal));
+      NS_ENSURE_SUCCESS(rv, rv);
+    }
+
+    // See if we're being called from a window.
+    nsCOMPtr<nsPIDOMWindowInner> globalWindow = aWindow;
+    if (!globalWindow) {
+      globalWindow = xpc::CurrentWindowOrNull(aCx);
+    }
+
+    nsCOMPtr<Document> document;
+    Maybe<ClientInfo> clientInfo;
+
+    if (globalWindow) {
+      // Only use the current inner window, and only use it if the caller can
+      // access it.
+      if (nsPIDOMWindowOuter* outerWindow = globalWindow->GetOuterWindow()) {
+        loadInfo.mWindow = outerWindow->GetCurrentInnerWindow();
+      }
+
+      loadInfo.mTrials =
+          OriginTrials::FromWindow(nsGlobalWindowInner::Cast(loadInfo.mWindow));
+
+      BrowsingContext* browsingContext = globalWindow->GetBrowsingContext();
+
+      // TODO: fix this for SharedWorkers with multiple documents (bug
+      // 1177935)
+      loadInfo.mServiceWorkersTestingInWindow =
+          browsingContext &&
+          browsingContext->Top()->ServiceWorkersTestingEnabled();
+
+      if (!loadInfo.mWindow ||
+          (globalWindow != loadInfo.mWindow &&
+           !nsContentUtils::CanCallerAccess(loadInfo.mWindow))) {
+        return NS_ERROR_DOM_SECURITY_ERR;
+      }
+
+      nsCOMPtr<nsIScriptGlobalObject> sgo = do_QueryInterface(loadInfo.mWindow);
+      MOZ_ASSERT(sgo);
+
+      loadInfo.mScriptContext = sgo->GetContext();
+      NS_ENSURE_TRUE(loadInfo.mScriptContext, NS_ERROR_FAILURE);
+
+      // If we're called from a window then we can dig out the principal and URI
+      // from the document.
+      document = loadInfo.mWindow->GetExtantDoc();
+      NS_ENSURE_TRUE(document, NS_ERROR_FAILURE);
+
+      loadInfo.mBaseURI = document->GetDocBaseURI();
+      loadInfo.mLoadGroup = document->GetDocumentLoadGroup();
+      NS_ENSURE_TRUE(loadInfo.mLoadGroup, NS_ERROR_FAILURE);
+
+      clientInfo = globalWindow->GetClientInfo();
+
+      // Use the document's NodePrincipal as loading principal if we're not
+      // being called from chrome.
+      if (!loadInfo.mLoadingPrincipal) {
+        loadInfo.mLoadingPrincipal = document->NodePrincipal();
+        NS_ENSURE_TRUE(loadInfo.mLoadingPrincipal, NS_ERROR_FAILURE);
+
+        // We use the document's base domain to limit the number of workers
+        // each domain can create. For sandboxed documents, we use the domain
+        // of their first non-sandboxed document, walking up until we find
+        // one. If we can't find one, we fall back to using the GUID of the
+        // null principal as the base domain.
+        if (document->GetSandboxFlags() & SANDBOXED_ORIGIN) {
+          nsCOMPtr<Document> tmpDoc = document;
+          do {
+            tmpDoc = tmpDoc->GetInProcessParentDocument();
+          } while (tmpDoc && tmpDoc->GetSandboxFlags() & SANDBOXED_ORIGIN);
+
+          if (tmpDoc) {
+            // There was an unsandboxed ancestor, yay!
+            nsCOMPtr<nsIPrincipal> tmpPrincipal = tmpDoc->NodePrincipal();
+            rv = tmpPrincipal->GetBaseDomain(loadInfo.mDomain);
+            NS_ENSURE_SUCCESS(rv, rv);
+          } else {
+            // No unsandboxed ancestor, use our GUID.
+            rv = loadInfo.mLoadingPrincipal->GetBaseDomain(loadInfo.mDomain);
+            NS_ENSURE_SUCCESS(rv, rv);
+          }
+        } else {
+          // Document creating the worker is not sandboxed.
+          rv = loadInfo.mLoadingPrincipal->GetBaseDomain(loadInfo.mDomain);
+          NS_ENSURE_SUCCESS(rv, rv);
+        }
+      }
+
+      NS_ENSURE_TRUE(NS_LoadGroupMatchesPrincipal(loadInfo.mLoadGroup,
+                                                  loadInfo.mLoadingPrincipal),
+                     NS_ERROR_FAILURE);
+
+      nsCOMPtr<nsIPermissionManager> permMgr =
+          do_GetService(NS_PERMISSIONMANAGER_CONTRACTID, &rv);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      uint32_t perm;
+      rv = permMgr->TestPermissionFromPrincipal(loadInfo.mLoadingPrincipal,
+                                                "systemXHR"_ns, &perm);
+      NS_ENSURE_SUCCESS(rv, rv);
+
+      loadInfo.mXHRParamsAllowed = perm == nsIPermissionManager::ALLOW_ACTION;
+
+      loadInfo.mWatchedByDevTools =
+          browsingContext && browsingContext->WatchedByDevTools();
+
+      loadInfo.mReferrerInfo =
+          ReferrerInfo::CreateForFetch(loadInfo.mLoadingPrincipal, document);
+      loadInfo.mFromWindow = true;
+      loadInfo.mWindowID = globalWindow->WindowID();
+      loadInfo.mAssociatedBrowsingContextID =
+          globalWindow->GetBrowsingContext()->Id();
+      loadInfo.mStorageAccess = StorageAllowedForWindow(globalWindow);
+      loadInfo.mUseRegularPrincipal = document->UseRegularPrincipal();
+      loadInfo.mUsingStorageAccess = document->UsingStorageAccess();
+      loadInfo.mShouldResistFingerprinting =
+          document->ShouldResistFingerprinting(
+              RFPTarget::IsAlwaysEnabledForPrecompute);
+      loadInfo.mOverriddenFingerprintingSettings =
+          document->GetOverriddenFingerprintingSettings();
+
+      // This is an hack to deny the storage-access-permission for workers of
+      // sub-iframes.
+      if (loadInfo.mUsingStorageAccess &&
+          StorageAllowedForDocument(document) != StorageAccess::eAllow) {
+        loadInfo.mUsingStorageAccess = false;
+      }
+      loadInfo.mIsThirdPartyContextToTopWindow =
+          AntiTrackingUtils::IsThirdPartyWindow(globalWindow, nullptr);
+      loadInfo.mCookieJarSettings = document->CookieJarSettings();
+      if (loadInfo.mCookieJarSettings) {
+        auto* cookieJarSettings =
+            net::CookieJarSettings::Cast(loadInfo.mCookieJarSettings);
+        cookieJarSettings->Serialize(loadInfo.mCookieJarSettingsArgs);
+      }
+      StoragePrincipalHelper::GetRegularPrincipalOriginAttributes(
+          document, loadInfo.mOriginAttributes);
+      loadInfo.mParentController = globalWindow->GetController();
+      loadInfo.mSecureContext = loadInfo.mWindow->IsSecureContext()
+                                    ? WorkerLoadInfo::eSecureContext
+                                    : WorkerLoadInfo::eInsecureContext;
+    } else {
+      // Not a window
+      MOZ_ASSERT(isChrome);
+
+      // We're being created outside of a window. Need to figure out the script
+      // that is creating us in order for us to use relative URIs later on.
+      JS::AutoFilename fileName;
+      if (JS::DescribeScriptedCaller(aCx, &fileName)) {
+        // In most cases, fileName is URI. In a few other cases
+        // (e.g. xpcshell), fileName is a file path. Ideally, we would
+        // prefer testing whether fileName parses as an URI and fallback
+        // to file path in case of error, but Windows file paths have
+        // the interesting property that they can be parsed as bogus
+        // URIs (e.g. C:/Windows/Tmp is interpreted as scheme "C",
+        // hostname "Windows", path "Tmp"), which defeats this algorithm.
+        // Therefore, we adopt the opposite convention.
+        nsCOMPtr<nsIFile> scriptFile =
+            do_CreateInstance("@mozilla.org/file/local;1", &rv);
+        if (NS_FAILED(rv)) {
+          return rv;
+        }
+
+        rv = scriptFile->InitWithPath(NS_ConvertUTF8toUTF16(fileName.get()));
+        if (NS_SUCCEEDED(rv)) {
+          rv = NS_NewFileURI(getter_AddRefs(loadInfo.mBaseURI), scriptFile);
+        }
+        if (NS_FAILED(rv)) {
+          // As expected, fileName is not a path, so proceed with
+          // a uri.
+          rv = NS_NewURI(getter_AddRefs(loadInfo.mBaseURI), fileName.get());
+        }
+        if (NS_FAILED(rv)) {
+          return rv;
+        }
+      }
+      loadInfo.mXHRParamsAllowed = true;
+      loadInfo.mFromWindow = false;
+      loadInfo.mWindowID = UINT64_MAX;
+      loadInfo.mStorageAccess = StorageAccess::eAllow;
+      loadInfo.mUseRegularPrincipal = true;
+      loadInfo.mUsingStorageAccess = false;
+      loadInfo.mCookieJarSettings =
+          mozilla::net::CookieJarSettings::Create(loadInfo.mLoadingPrincipal);
+      loadInfo.mShouldResistFingerprinting =
+          nsContentUtils::ShouldResistFingerprinting_dangerous(
+              loadInfo.mLoadingPrincipal,
+              "Unusual situation - we have no document or CookieJarSettings",
+              RFPTarget::IsAlwaysEnabledForPrecompute);
+      MOZ_ASSERT(loadInfo.mCookieJarSettings);
+      auto* cookieJarSettings =
+          net::CookieJarSettings::Cast(loadInfo.mCookieJarSettings);
+      cookieJarSettings->Serialize(loadInfo.mCookieJarSettingsArgs);
+
+      loadInfo.mOriginAttributes = OriginAttributes();
+      loadInfo.mIsThirdPartyContextToTopWindow = false;
+    }
+
+    MOZ_ASSERT(loadInfo.mLoadingPrincipal);
+    MOZ_ASSERT(isChrome || !loadInfo.mDomain.IsEmpty());
+
+    if (!loadInfo.mLoadGroup || aLoadGroupBehavior == OverrideLoadGroup) {
+      OverrideLoadInfoLoadGroup(loadInfo, loadInfo.mLoadingPrincipal);
+    }
+    MOZ_ASSERT(NS_LoadGroupMatchesPrincipal(loadInfo.mLoadGroup,
+                                            loadInfo.mLoadingPrincipal));
+
+    // Top level workers' main script use the document charset for the script
+    // uri encoding.
+    nsCOMPtr<nsIURI> url;
+    rv = nsContentUtils::NewURIWithDocumentCharset(
+        getter_AddRefs(url), aScriptURL, document, loadInfo.mBaseURI);
+    NS_ENSURE_SUCCESS(rv, NS_ERROR_DOM_SYNTAX_ERR);
+
+    rv = ChannelFromScriptURLMainThread(
+        loadInfo.mLoadingPrincipal, document, loadInfo.mLoadGroup, url,
+        aWorkerType, aCredentials, clientInfo, ContentPolicyType(aWorkerKind),
+        loadInfo.mCookieJarSettings, loadInfo.mReferrerInfo,
+        getter_AddRefs(loadInfo.mChannel));
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    rv = NS_GetFinalChannelURI(loadInfo.mChannel,
+                               getter_AddRefs(loadInfo.mResolvedScriptURI));
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    // We need the correct hasStoragePermission flag for the channel here since
+    // we will do a content blocking check later when we set the storage
+    // principal for the worker. The channel here won't be opened when we do the
+    // check later, so the hasStoragePermission flag is incorrect. To address
+    // this, We copy the hasStoragePermission flag from the document if there is
+    // a window. The worker is created as the same origin of the window. So, the
+    // worker is supposed to have the same storage permission as the window as
+    // well as the hasStoragePermission flag.
+    nsCOMPtr<nsILoadInfo> channelLoadInfo = loadInfo.mChannel->LoadInfo();
+    rv = channelLoadInfo->SetStoragePermission(
+        loadInfo.mUsingStorageAccess ? nsILoadInfo::HasStoragePermission
+                                     : nsILoadInfo::NoStoragePermission);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    rv = loadInfo.SetPrincipalsAndCSPFromChannel(loadInfo.mChannel);
+    NS_ENSURE_SUCCESS(rv, rv);
+  }
+
+  MOZ_DIAGNOSTIC_ASSERT(loadInfo.mLoadingPrincipal);
+  MOZ_DIAGNOSTIC_ASSERT(loadInfo.PrincipalIsValid());
+
+  *aLoadInfo = std::move(loadInfo);
+  return NS_OK;
+}
+
+// static
+void WorkerPrivate::OverrideLoadInfoLoadGroup(WorkerLoadInfo& aLoadInfo,
+                                              nsIPrincipal* aPrincipal) {
+  MOZ_ASSERT(!aLoadInfo.mInterfaceRequestor);
+  MOZ_ASSERT(aLoadInfo.mLoadingPrincipal == aPrincipal);
+
+  aLoadInfo.mInterfaceRequestor =
+      new WorkerLoadInfo::InterfaceRequestor(aPrincipal, aLoadInfo.mLoadGroup);
+  aLoadInfo.mInterfaceRequestor->MaybeAddBrowserChild(aLoadInfo.mLoadGroup);
+
+  // NOTE: this defaults the load context to:
+  //  - private browsing = false
+  //  - content = true
+  //  - use remote tabs = false
+  nsCOMPtr<nsILoadGroup> loadGroup = do_CreateInstance(NS_LOADGROUP_CONTRACTID);
+
+  nsresult rv =
+      loadGroup->SetNotificationCallbacks(aLoadInfo.mInterfaceRequestor);
+  MOZ_ALWAYS_SUCCEEDS(rv);
+
+  aLoadInfo.mLoadGroup = std::move(loadGroup);
+
+  MOZ_ASSERT(NS_LoadGroupMatchesPrincipal(aLoadInfo.mLoadGroup, aPrincipal));
+}
+
+void WorkerPrivate::RunLoopNeverRan() {
+  LOG(WorkerLog(), ("WorkerPrivate::RunLoopNeverRan [%p]", this));
+  {
+    MutexAutoLock lock(mMutex);
+
+    mStatus = Dead;
+  }
+
+  // After mStatus is set to Dead there can be no more
+  // WorkerControlRunnables so no need to lock here.
+  if (!mControlQueue.IsEmpty()) {
+    WorkerControlRunnable* runnable = nullptr;
+    while (mControlQueue.Pop(runnable)) {
+      runnable->Cancel();
+      runnable->Release();
+    }
+  }
+
+  // There should be no StrongWorkerRefs, child Workers, and Timeouts, but
+  // WeakWorkerRefs could. WorkerThreadPrimaryRunnable could have created a
+  // PerformanceStorageWorker which holds a WeakWorkerRef.
+  // Notify WeakWorkerRefs with Dead status.
+  NotifyWorkerRefs(Dead);
+
+  ScheduleDeletion(WorkerPrivate::WorkerRan);
+}
+
+void WorkerPrivate::UnrootGlobalScopes() {
+  LOG(WorkerLog(), ("WorkerPrivate::UnrootGlobalScopes [%p]", this));
+  auto data = mWorkerThreadAccessible.Access();
+
+  RefPtr<WorkerDebuggerGlobalScope> debugScope = data->mDebuggerScope.forget();
+  if (debugScope) {
+    MOZ_ASSERT(debugScope->mWorkerPrivate == this);
+  }
+  RefPtr<WorkerGlobalScope> scope = data->mScope.forget();
+  if (scope) {
+    MOZ_ASSERT(scope->mWorkerPrivate == this);
+  }
+}
+
+void WorkerPrivate::DoRunLoop(JSContext* aCx) {
+  LOG(WorkerLog(), ("WorkerPrivate::DoRunLoop [%p]", this));
+  auto data = mWorkerThreadAccessible.Access();
+  MOZ_RELEASE_ASSERT(!GetExecutionManager());
+
+  RefPtr<WorkerThread> thread;
+  {
+    MutexAutoLock lock(mMutex);
+    mJSContext = aCx;
+    // mThread is set before we enter, and is never changed during DoRunLoop.
+    // copy to local so we don't trigger mutex analysis
+    MOZ_ASSERT(mThread);
+    thread = mThread;
+
+    MOZ_ASSERT(mStatus == Pending);
+    mStatus = Running;
+  }
+
+  // Now that we've done that, we can go ahead and set up our AutoJSAPI.  We
+  // can't before this point, because it can't find the right JSContext before
+  // then, since it gets it from our mJSContext.
+  AutoJSAPI jsapi;
+  jsapi.Init();
+  MOZ_ASSERT(jsapi.cx() == aCx);
+
+  EnableMemoryReporter();
+
+  InitializeGCTimers();
+
+  bool checkFinalGCCC =
+      StaticPrefs::dom_workers_GCCC_on_potentially_last_event();
+
+  bool debuggerRunnablesPending = false;
+  bool normalRunnablesPending = false;
+  auto noRunnablesPendingAndKeepAlive =
+      [&debuggerRunnablesPending, &normalRunnablesPending, &thread, this]()
+          MOZ_REQUIRES(mMutex) {
+            // We want to keep both pending flags always updated while looping.
+            debuggerRunnablesPending = !mDebuggerQueue.IsEmpty();
+            normalRunnablesPending = NS_HasPendingEvents(thread);
+
+            bool anyRunnablesPending = !mControlQueue.IsEmpty() ||
+                                       debuggerRunnablesPending ||
+                                       normalRunnablesPending;
+            bool keepWorkerAlive = mStatus == Running || HasActiveWorkerRefs();
+
+            return (!anyRunnablesPending && keepWorkerAlive);
+          };
+
+  for (;;) {
+    WorkerStatus currentStatus;
+
+    if (checkFinalGCCC) {
+      // If we get here after the last event ran but someone holds a WorkerRef
+      // and there is no other logic to release that WorkerRef than lazily
+      // through GC/CC, we might block forever on the next WaitForWorkerEvents.
+      // Every object holding a WorkerRef should really have a straight,
+      // deterministic line from the WorkerRef's callback being invoked to the
+      // WorkerRef being released which is supported by strong-references that
+      // can't form a cycle.
+      bool mayNeedFinalGCCC = false;
+      {
+        MutexAutoLock lock(mMutex);
+
+        currentStatus = mStatus;
+        mayNeedFinalGCCC =
+            (mStatus >= Canceling && HasActiveWorkerRefs() &&
+             !debuggerRunnablesPending && !normalRunnablesPending &&
+             data->mPerformedShutdownAfterLastContentTaskExecuted);
+      }
+      if (mayNeedFinalGCCC) {
+#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
+        // WorkerRef::ReleaseWorker will check this flag via
+        // AssertIsNotPotentiallyLastGCCCRunning
+        data->mIsPotentiallyLastGCCCRunning = true;
+#endif
+        // GarbageCollectInternal will trigger both GC and CC
+        GarbageCollectInternal(aCx, true /* aShrinking */,
+                               true /* aCollectChildren */);
+#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
+        data->mIsPotentiallyLastGCCCRunning = false;
+#endif
+      }
+    }
+
+    {
+      MutexAutoLock lock(mMutex);
+
+      LOGV(
+          ("WorkerPrivate::DoRunLoop [%p] mStatus %u before getting events"
+           " to run",
+           this, (uint8_t)mStatus));
+      if (checkFinalGCCC && currentStatus != mStatus) {
+        // Something moved our status while we were supposed to check for a
+        // potentially needed GC/CC. Just check again.
+        continue;
+      }
+
+      // Wait for a runnable to arrive that we can execute, or for it to be okay
+      // to shutdown this worker once all holders have been removed.
+      // Holders may be removed from inside normal runnables,  but we don't
+      // check for that after processing normal runnables, so we need to let
+      // control flow to the shutdown logic without blocking.
+      while (noRunnablesPendingAndKeepAlive()) {
+        // We pop out to this loop when there are no pending events.
+        // If we don't reset these, we may not re-enter ProcessNextEvent()
+        // until we have events to process, and it may seem like we have
+        // an event running for a very long time.
+        thread->SetRunningEventDelay(TimeDuration(), TimeStamp());
+
+        mWorkerLoopIsIdle = true;
+
+        WaitForWorkerEvents();
+
+        mWorkerLoopIsIdle = false;
+      }
+
+      auto result = ProcessAllControlRunnablesLocked();
+      if (result != ProcessAllControlRunnablesResult::Nothing) {
+        // Update all saved runnable flags for side effect for the
+        // loop check about transitioning to Killing below.
+        (void)noRunnablesPendingAndKeepAlive();
+      }
+
+      currentStatus = mStatus;
+    }
+
+    // Transition from Canceling to Killing and exit this loop when:
+    //  * All (non-weak) WorkerRefs have been released.
+    //  * There are no runnables pending. This is intended to let same-thread
+    //    dispatches as part of cleanup be able to run to completion, but any
+    //    logic that still wants async things to happen should be holding a
+    //    StrongWorkerRef.
+    if (currentStatus != Running && !HasActiveWorkerRefs() &&
+        !normalRunnablesPending && !debuggerRunnablesPending) {
+      // Now we are ready to kill the worker thread.
+      if (currentStatus == Canceling) {
+        NotifyInternal(Killing);
+
+#ifdef DEBUG
+        {
+          MutexAutoLock lock(mMutex);
+          currentStatus = mStatus;
+        }
+        MOZ_ASSERT(currentStatus == Killing);
+#else
+        currentStatus = Killing;
+#endif
+      }
+
+      // If we're supposed to die then we should exit the loop.
+      if (currentStatus == Killing) {
+        // We are about to destroy worker, report all use counters.
+        ReportUseCounters();
+
+        // Flush uncaught rejections immediately, without
+        // waiting for a next tick.
+        PromiseDebugging::FlushUncaughtRejections();
+
+        ShutdownGCTimers();
+
+        DisableMemoryReporter();
+
+        {
+          MutexAutoLock lock(mMutex);
+
+          mStatus = Dead;
+          mJSContext = nullptr;
+        }
+
+        // After mStatus is set to Dead there can be no more
+        // WorkerControlRunnables so no need to lock here.
+        if (!mControlQueue.IsEmpty()) {
+          LOG(WorkerLog(),
+              ("WorkerPrivate::DoRunLoop [%p] dropping control runnables in "
+               "Dead status",
+               this));
+          WorkerControlRunnable* runnable = nullptr;
+          while (mControlQueue.Pop(runnable)) {
+            runnable->Cancel();
+            runnable->Release();
+          }
+        }
+
+        // We do not need the timeouts any more, they have been canceled
+        // by NotifyInternal(Killing) above if they were active.
+        UnlinkTimeouts();
+
+        return;
+      }
+    }
+
+    // Status transitions to Closing/Canceling and there are no SyncLoops,
+    // set global start dying, disconnect EventTargetObjects and
+    // WebTaskScheduler.
+    if (currentStatus >= Closing &&
+        !data->mPerformedShutdownAfterLastContentTaskExecuted) {
+      data->mPerformedShutdownAfterLastContentTaskExecuted.Flip();
+      if (data->mScope) {
+        data->mScope->NoteTerminating();
+        data->mScope->DisconnectGlobalTeardownObservers();
+        if (data->mScope->GetExistingScheduler()) {
+          data->mScope->GetExistingScheduler()->Disconnect();
+        }
+      }
+    }
+
+    if (debuggerRunnablesPending || normalRunnablesPending) {
+      // Start the periodic GC timer if it is not already running.
+      SetGCTimerMode(PeriodicTimer);
+    }
+
+    if (debuggerRunnablesPending) {
+      WorkerRunnable* runnable = nullptr;
+
+      {
+        MutexAutoLock lock(mMutex);
+
+        mDebuggerQueue.Pop(runnable);
+        debuggerRunnablesPending = !mDebuggerQueue.IsEmpty();
+      }
+
+      {
+        MOZ_ASSERT(runnable);
+        AUTO_PROFILE_FOLLOWING_RUNNABLE(runnable);
+        static_cast<nsIRunnable*>(runnable)->Run();
+      }
+      runnable->Release();
+
+      CycleCollectedJSContext* ccjs = CycleCollectedJSContext::Get();
+      ccjs->PerformDebuggerMicroTaskCheckpoint();
+
+      if (debuggerRunnablesPending) {
+        WorkerDebuggerGlobalScope* globalScope = DebuggerGlobalScope();
+        // If the worker was canceled before ever creating its content global
+        // then mCancelBeforeWorkerScopeConstructed could have been flipped and
+        // all of the WorkerDebuggerRunnables canceled, so the debugger global
+        // would never have been created.
+        if (globalScope) {
+          // Now *might* be a good time to GC. Let the JS engine make the
+          // decision.
+          JSAutoRealm ar(aCx, globalScope->GetGlobalJSObject());
+          JS_MaybeGC(aCx);
+        }
+      }
+    } else if (normalRunnablesPending) {
+      // Process a single runnable from the main queue.
+      NS_ProcessNextEvent(thread, false);
+
+      normalRunnablesPending = NS_HasPendingEvents(thread);
+      if (normalRunnablesPending && GlobalScope()) {
+        // Now *might* be a good time to GC. Let the JS engine make the
+        // decision.
+        JSAutoRealm ar(aCx, GlobalScope()->GetGlobalJSObject());
+        JS_MaybeGC(aCx);
+      }
+    }
+
+    // Checking the background actors if needed, any runnable execution could
+    // release background actors which blocks GC/CC on
+    // WorkerPrivate::mParentEventTargetRef.
+    if (currentStatus < Canceling) {
+      UpdateCCFlag(CCFlag::CheckBackgroundActors);
+    }
+
+    if (!debuggerRunnablesPending && !normalRunnablesPending) {
+      // Both the debugger event queue and the normal event queue has been
+      // exhausted, cancel the periodic GC timer and schedule the idle GC timer.
+      SetGCTimerMode(IdleTimer);
+    }
+
+    // If the worker thread is spamming the main thread faster than it can
+    // process the work, then pause the worker thread until the main thread
+    // catches up.
+    size_t queuedEvents = mMainThreadEventTargetForMessaging->Length() +
+                          mMainThreadDebuggeeEventTarget->Length();
+    if (queuedEvents > 5000) {
+      // Note, postMessage uses mMainThreadDebuggeeEventTarget!
+      mMainThreadDebuggeeEventTarget->AwaitIdle();
+    }
+  }
+
+  MOZ_CRASH("Shouldn't get here!");
+}
+
+namespace {
+/**
+ * If there is a current CycleCollectedJSContext, return its recursion depth,
+ * otherwise return 1.
+ *
+ * In the edge case where a worker is starting up so late that PBackground is
+ * already shutting down, the cycle collected context will never be created,
+ * but we will need to drain the event loop in ClearMainEventQueue.  This will
+ * result in a normal NS_ProcessPendingEvents invocation which will call
+ * WorkerPrivate::OnProcessNextEvent and WorkerPrivate::AfterProcessNextEvent
+ * which want to handle the need to process control runnables and perform a
+ * sanity check assertion, respectively.
+ *
+ * We claim a depth of 1 when there's no CCJS because this most corresponds to
+ * reality, but this doesn't meant that other code might want to drain various
+ * runnable queues as part of this cleanup.
+ */
+uint32_t GetEffectiveEventLoopRecursionDepth() {
+  auto* ccjs = CycleCollectedJSContext::Get();
+  if (ccjs) {
+    return ccjs->RecursionDepth();
+  }
+
+  return 1;
+}
+
+}  // namespace
+
+void WorkerPrivate::OnProcessNextEvent() {
+  AssertIsOnWorkerThread();
+
+  uint32_t recursionDepth = GetEffectiveEventLoopRecursionDepth();
+  MOZ_ASSERT(recursionDepth);
+
+  // Normally we process control runnables in DoRunLoop or RunCurrentSyncLoop.
+  // However, it's possible that non-worker C++ could spin its own nested event
+  // loop, and in that case we must ensure that we continue to process control
+  // runnables here.
+  if (recursionDepth > 1 && mSyncLoopStack.Length() < recursionDepth - 1) {
+    Unused << ProcessAllControlRunnables();
+    // There's no running JS, and no state to revalidate, so we can ignore the
+    // return value.
+  }
+}
+
+void WorkerPrivate::AfterProcessNextEvent() {
+  AssertIsOnWorkerThread();
+  MOZ_ASSERT(GetEffectiveEventLoopRecursionDepth());
+}
+
+nsISerialEventTarget* WorkerPrivate::MainThreadEventTargetForMessaging() {
+  return mMainThreadEventTargetForMessaging;
+}
+
+nsresult WorkerPrivate::DispatchToMainThreadForMessaging(nsIRunnable* aRunnable,
+                                                         uint32_t aFlags) {
+  nsCOMPtr<nsIRunnable> r = aRunnable;
+  return DispatchToMainThreadForMessaging(r.forget(), aFlags);
+}
+
+nsresult WorkerPrivate::DispatchToMainThreadForMessaging(
+    already_AddRefed<nsIRunnable> aRunnable, uint32_t aFlags) {
+  return mMainThreadEventTargetForMessaging->Dispatch(std::move(aRunnable),
+                                                      aFlags);
+}
+
+nsISerialEventTarget* WorkerPrivate::MainThreadEventTarget() {
+  return mMainThreadEventTarget;
+}
+
+nsresult WorkerPrivate::DispatchToMainThread(nsIRunnable* aRunnable,
+                                             uint32_t aFlags) {
+  nsCOMPtr<nsIRunnable> r = aRunnable;
+  return DispatchToMainThread(r.forget(), aFlags);
+}
+
+nsresult WorkerPrivate::DispatchToMainThread(
+    already_AddRefed<nsIRunnable> aRunnable, uint32_t aFlags) {
+  return mMainThreadEventTarget->Dispatch(std::move(aRunnable), aFlags);
+}
+
+nsresult WorkerPrivate::DispatchDebuggeeToMainThread(
+    already_AddRefed<WorkerDebuggeeRunnable> aRunnable, uint32_t aFlags) {
+  return mMainThreadDebuggeeEventTarget->Dispatch(std::move(aRunnable), aFlags);
+}
+
+nsISerialEventTarget* WorkerPrivate::ControlEventTarget() {
+  return mWorkerControlEventTarget;
+}
+
+nsISerialEventTarget* WorkerPrivate::HybridEventTarget() {
+  return mWorkerHybridEventTarget;
+}
+
+ClientType WorkerPrivate::GetClientType() const {
+  switch (Kind()) {
+    case WorkerKindDedicated:
+      return ClientType::Worker;
+    case WorkerKindShared:
+      return ClientType::Sharedworker;
+    case WorkerKindService:
+      return ClientType::Serviceworker;
+    default:
+      MOZ_CRASH("unknown worker type!");
+  }
+}
+
+UniquePtr<ClientSource> WorkerPrivate::CreateClientSource() {
+  auto data = mWorkerThreadAccessible.Access();
+  MOZ_ASSERT(!data->mScope, "Client should be created before the global");
+
+  auto clientSource = ClientManager::CreateSource(
+      GetClientType(), mWorkerHybridEventTarget,
+      StoragePrincipalHelper::ShouldUsePartitionPrincipalForServiceWorker(this)
+          ? GetPartitionedPrincipalInfo()
+          : GetPrincipalInfo());
+  MOZ_DIAGNOSTIC_ASSERT(clientSource);
+
+  clientSource->SetAgentClusterId(mAgentClusterId);
+
+  if (data->mFrozen) {
+    clientSource->Freeze();
+  }
+
+  // Shortly after the client is reserved we will try loading the main script
+  // for the worker.  This may get intercepted by the ServiceWorkerManager
+  // which will then try to create a ClientHandle.  Its actually possible for
+  // the main thread to create this ClientHandle before our IPC message creating
+  // the ClientSource completes.  To avoid this race we synchronously ping our
+  // parent Client actor here.  This ensure the worker ClientSource is created
+  // in the parent before the main thread might try reaching it with a
+  // ClientHandle.
+  //
+  // An alternative solution would have been to handle the out-of-order
+  // operations on the parent side.  We could have created a small window where
+  // we allow ClientHandle objects to exist without a ClientSource.  We would
+  // then time out these handles if they stayed orphaned for too long.  This
+  // approach would be much more complex, but also avoid this extra bit of
+  // latency when starting workers.
+  //
+  // Note, we only have to do this for workers that can be controlled by a
+  // service worker.  So avoid the sync overhead here if we are starting a
+  // service worker or a chrome worker.
+  if (Kind() != WorkerKindService && !IsChromeWorker()) {
+    clientSource->WorkerSyncPing(this);
+  }
+
+  return clientSource;
+}
+
+bool WorkerPrivate::EnsureCSPEventListener() {
+  if (!mCSPEventListener) {
+    mCSPEventListener = WorkerCSPEventListener::Create(this);
+    if (NS_WARN_IF(!mCSPEventListener)) {
+      return false;
+    }
+  }
+  return true;
+}
+
+nsICSPEventListener* WorkerPrivate::CSPEventListener() const {
+  MOZ_ASSERT(mCSPEventListener);
+  return mCSPEventListener;
+}
+
+void WorkerPrivate::EnsurePerformanceStorage() {
+  AssertIsOnWorkerThread();
+
+  if (!mPerformanceStorage) {
+    mPerformanceStorage = PerformanceStorageWorker::Create(this);
+  }
+}
+
+bool WorkerPrivate::GetExecutionGranted() const {
+  auto data = mWorkerThreadAccessible.Access();
+  return data->mJSThreadExecutionGranted;
+}
+
+void WorkerPrivate::SetExecutionGranted(bool aGranted) {
+  auto data = mWorkerThreadAccessible.Access();
+  data->mJSThreadExecutionGranted = aGranted;
+}
+
+void WorkerPrivate::ScheduleTimeSliceExpiration(uint32_t aDelay) {
+  auto data = mWorkerThreadAccessible.Access();
+
+  if (!data->mTSTimer) {
+    data->mTSTimer = NS_NewTimer();
+    MOZ_ALWAYS_SUCCEEDS(data->mTSTimer->SetTarget(mWorkerControlEventTarget));
+  }
+
+  // Whenever an event is scheduled on the WorkerControlEventTarget an
+  // interrupt is automatically requested which causes us to yield JS execution
+  // and the next JS execution in the queue to execute.
+  // This allows for simple code reuse of the existing interrupt callback code
+  // used for control events.
+  MOZ_ALWAYS_SUCCEEDS(data->mTSTimer->InitWithNamedFuncCallback(
+      [](nsITimer* Timer, void* aClosure) { return; }, nullptr, aDelay,
+      nsITimer::TYPE_ONE_SHOT, "TimeSliceExpirationTimer"));
+}
+
+void WorkerPrivate::CancelTimeSliceExpiration() {
+  auto data = mWorkerThreadAccessible.Access();
+  MOZ_ALWAYS_SUCCEEDS(data->mTSTimer->Cancel());
+}
+
+JSExecutionManager* WorkerPrivate::GetExecutionManager() const {
+  auto data = mWorkerThreadAccessible.Access();
+  return data->mExecutionManager.get();
+}
+
+void WorkerPrivate::SetExecutionManager(JSExecutionManager* aManager) {
+  auto data = mWorkerThreadAccessible.Access();
+  data->mExecutionManager = aManager;
+}
+
+void WorkerPrivate::ExecutionReady() {
+  auto data = mWorkerThreadAccessible.Access();
+  {
+    MutexAutoLock lock(mMutex);
+    if (mStatus >= Canceling) {
+      return;
+    }
+  }
+
+  data->mScope->MutableClientSourceRef().WorkerExecutionReady(this);
+
+  if (ExtensionAPIAllowed()) {
+    extensions::CreateAndDispatchInitWorkerContextRunnable();
+  }
+}
+
+void WorkerPrivate::InitializeGCTimers() {
+  auto data = mWorkerThreadAccessible.Access();
+
+  // We need timers for GC. The basic plan is to run a non-shrinking GC
+  // periodically (PERIODIC_GC_TIMER_DELAY_SEC) while the worker is running.
+  // Once the worker goes idle we set a short (IDLE_GC_TIMER_DELAY_SEC) timer to
+  // run a shrinking GC.
+  data->mPeriodicGCTimer = NS_NewTimer();
+  data->mIdleGCTimer = NS_NewTimer();
+
+  data->mPeriodicGCTimerRunning = false;
+  data->mIdleGCTimerRunning = false;
+}
+
+void WorkerPrivate::SetGCTimerMode(GCTimerMode aMode) {
+  auto data = mWorkerThreadAccessible.Access();
+
+  if (!data->mPeriodicGCTimer || !data->mIdleGCTimer) {
+    // GC timers have been cleared already.
+    return;
+  }
+
+  if (aMode == NoTimer) {
+    MOZ_ALWAYS_SUCCEEDS(data->mPeriodicGCTimer->Cancel());
+    data->mPeriodicGCTimerRunning = false;
+    MOZ_ALWAYS_SUCCEEDS(data->mIdleGCTimer->Cancel());
+    data->mIdleGCTimerRunning = false;
+    return;
+  }
+
+  WorkerStatus status;
+  {
+    MutexAutoLock lock(mMutex);
+    status = mStatus;
+  }
+
+  if (status >= Killing) {
+    ShutdownGCTimers();
+    return;
+  }
+
+  // If the idle timer is running, don't cancel it when the periodic timer
+  // is scheduled since we do want shrinking GC to be called occasionally.
+  if (aMode == PeriodicTimer && data->mPeriodicGCTimerRunning) {
+    return;
+  }
+
+  if (aMode == IdleTimer) {
+    if (!data->mPeriodicGCTimerRunning) {
+      // Since running idle GC cancels both GC timers, after that we want
+      // first at least periodic GC timer getting activated, since that tells
+      // us that there have been some non-control tasks to process. Otherwise
+      // idle GC timer would keep running all the time.
+      return;
+    }
+
+    // Cancel the periodic timer now, since the event loop is (in the common
+    // case) empty now.
+    MOZ_ALWAYS_SUCCEEDS(data->mPeriodicGCTimer->Cancel());
+    data->mPeriodicGCTimerRunning = false;
+
+    if (data->mIdleGCTimerRunning) {
+      return;
+    }
+  }
+
+  MOZ_ASSERT(aMode == PeriodicTimer || aMode == IdleTimer);
+
+  uint32_t delay = 0;
+  int16_t type = nsITimer::TYPE_ONE_SHOT;
+  nsTimerCallbackFunc callback = nullptr;
+  const char* name = nullptr;
+  nsITimer* timer = nullptr;
+
+  if (aMode == PeriodicTimer) {
+    delay = PERIODIC_GC_TIMER_DELAY_SEC * 1000;
+    type = nsITimer::TYPE_REPEATING_SLACK;
+    callback = PeriodicGCTimerCallback;
+    name = "dom::PeriodicGCTimerCallback";
+    timer = data->mPeriodicGCTimer;
+    data->mPeriodicGCTimerRunning = true;
+    LOG(WorkerLog(), ("Worker %p scheduled periodic GC timer\n", this));
+  } else {
+    delay = IDLE_GC_TIMER_DELAY_SEC * 1000;
+    type = nsITimer::TYPE_ONE_SHOT;
+    callback = IdleGCTimerCallback;
+    name = "dom::IdleGCTimerCallback";
+    timer = data->mIdleGCTimer;
+    data->mIdleGCTimerRunning = true;
+    LOG(WorkerLog(), ("Worker %p scheduled idle GC timer\n", this));
+  }
+
+  MOZ_ALWAYS_SUCCEEDS(timer->SetTarget(mWorkerControlEventTarget));
+  MOZ_ALWAYS_SUCCEEDS(
+      timer->InitWithNamedFuncCallback(callback, this, delay, type, name));
+}
+
+void WorkerPrivate::ShutdownGCTimers() {
+  auto data = mWorkerThreadAccessible.Access();
+
+  MOZ_ASSERT(!data->mPeriodicGCTimer == !data->mIdleGCTimer);
+
+  if (!data->mPeriodicGCTimer && !data->mIdleGCTimer) {
+    return;
+  }
+
+  // Always make sure the timers are canceled.
+  MOZ_ALWAYS_SUCCEEDS(data->mPeriodicGCTimer->Cancel());
+  MOZ_ALWAYS_SUCCEEDS(data->mIdleGCTimer->Cancel());
+
+  LOG(WorkerLog(), ("Worker %p killed the GC timers\n", this));
+
+  data->mPeriodicGCTimer = nullptr;
+  data->mIdleGCTimer = nullptr;
+  data->mPeriodicGCTimerRunning = false;
+  data->mIdleGCTimerRunning = false;
+}
+
+bool WorkerPrivate::InterruptCallback(JSContext* aCx) {
+  auto data = mWorkerThreadAccessible.Access();
+
+  AutoYieldJSThreadExecution yield;
+
+  // If we are here it's because a WorkerControlRunnable has been dispatched.
+  // The runnable could be processed here or it could have already been
+  // processed by a sync event loop.
+  // The most important thing this method must do, is to decide if the JS
+  // execution should continue or not. If the runnable returns an error or if
+  // the worker status is >= Canceling, we should stop the JS execution.
+
+  MOZ_ASSERT(!JS_IsExceptionPending(aCx));
+
+  bool mayContinue = true;
+  bool scheduledIdleGC = false;
+
+  for (;;) {
+    // Run all control events now.
+    auto result = ProcessAllControlRunnables();
+    if (result == ProcessAllControlRunnablesResult::Abort) {
+      mayContinue = false;
+    }
+
+    bool mayFreeze = data->mFrozen;
+
+    {
+      MutexAutoLock lock(mMutex);
+
+      if (mayFreeze) {
+        mayFreeze = mStatus <= Running;
+      }
+
+      if (mStatus >= Canceling) {
+        mayContinue = false;
+      }
+    }
+
+    if (!mayContinue || !mayFreeze) {
+      break;
+    }
+
+    // Cancel the periodic GC timer here before freezing. The idle GC timer
+    // will clean everything up once it runs.
+    if (!scheduledIdleGC) {
+      SetGCTimerMode(IdleTimer);
+      scheduledIdleGC = true;
+    }
+
+    while ((mayContinue = MayContinueRunning())) {
+      MutexAutoLock lock(mMutex);
+      if (!mControlQueue.IsEmpty()) {
+        break;
+      }
+
+      WaitForWorkerEvents();
+    }
+  }
+
+  if (!mayContinue) {
+    // We want only uncatchable exceptions here.
+    NS_ASSERTION(!JS_IsExceptionPending(aCx),
+                 "Should not have an exception set here!");
+    return false;
+  }
+
+  // Make sure the periodic timer gets turned back on here.
+  SetGCTimerMode(PeriodicTimer);
+
+  return true;
+}
+
+void WorkerPrivate::CloseInternal() {
+  AssertIsOnWorkerThread();
+  NotifyInternal(Closing);
+}
+
+bool WorkerPrivate::IsOnCurrentThread() {
+  // May be called on any thread!
+
+  MOZ_ASSERT(mPRThread);
+  return PR_GetCurrentThread() == mPRThread;
+}
+
+void WorkerPrivate::ScheduleDeletion(WorkerRanOrNot aRanOrNot) {
+  AssertIsOnWorkerThread();
+  {
+    // mWorkerThreadAccessible's accessor must be destructed before
+    // the scheduled Runnable gets to run.
+    auto data = mWorkerThreadAccessible.Access();
+    MOZ_ASSERT(data->mChildWorkers.IsEmpty());
+
+    MOZ_RELEASE_ASSERT(!data->mDeletionScheduled);
+    data->mDeletionScheduled.Flip();
+  }
+  MOZ_ASSERT(mSyncLoopStack.IsEmpty());
+  MOZ_ASSERT(mPostSyncLoopOperations == 0);
+
+  // If Worker is never ran, clear the mPreStartRunnables. To let the resource
+  // hold by the pre-submmited runnables.
+  if (WorkerNeverRan == aRanOrNot) {
+    ClearPreStartRunnables();
+  }
+
+#ifdef DEBUG
+  if (WorkerRan == aRanOrNot) {
+    nsIThread* currentThread = NS_GetCurrentThread();
+    MOZ_ASSERT(currentThread);
+    // On the worker thread WorkerRunnable will refuse to run if not nested
+    // on top of a WorkerThreadPrimaryRunnable.
+    Unused << NS_WARN_IF(NS_HasPendingEvents(currentThread));
+  }
+#endif
+
+  if (WorkerPrivate* parent = GetParent()) {
+    RefPtr<WorkerFinishedRunnable> runnable =
+        new WorkerFinishedRunnable(parent, this);
+    if (!runnable->Dispatch()) {
+      NS_WARNING("Failed to dispatch runnable!");
+    }
+  } else {
+    if (ExtensionAPIAllowed()) {
+      MOZ_ASSERT(IsServiceWorker());
+      RefPtr<Runnable> extWorkerRunnable =
+          extensions::CreateWorkerDestroyedRunnable(ServiceWorkerID(),
+                                                    GetBaseURI());
+      // Dispatch as a low priority runnable.
+      if (NS_FAILED(
+              DispatchToMainThreadForMessaging(extWorkerRunnable.forget()))) {
+        NS_WARNING(
+            "Failed to dispatch runnable to notify extensions worker "
+            "destroyed");
+      }
+    }
+
+    // Note, this uses the lower priority DispatchToMainThreadForMessaging for
+    // dispatching TopLevelWorkerFinishedRunnable to the main thread so that
+    // other relevant runnables are guaranteed to run before it.
+    RefPtr<TopLevelWorkerFinishedRunnable> runnable =
+        new TopLevelWorkerFinishedRunnable(this);
+    if (NS_FAILED(DispatchToMainThreadForMessaging(runnable.forget()))) {
+      NS_WARNING("Failed to dispatch runnable!");
+    }
+
+    // NOTE: Calling any WorkerPrivate methods (or accessing member data) after
+    // this point is unsafe (the TopLevelWorkerFinishedRunnable just dispatched
+    // may be able to call ClearSelfAndParentEventTargetRef on this
+    // WorkerPrivate instance and by the time we get here the WorkerPrivate
+    // instance destructor may have been already called).
+  }
+}
+
+bool WorkerPrivate::CollectRuntimeStats(
+    JS::RuntimeStats* aRtStats, bool aAnonymize) MOZ_NO_THREAD_SAFETY_ANALYSIS {
+  // We don't have a lock to access mJSContext, but it's safe to access on this
+  // thread.
+  AssertIsOnWorkerThread();
+  NS_ASSERTION(aRtStats, "Null RuntimeStats!");
+  // We don't really own it, but it's safe to access on this thread
+  NS_ASSERTION(mJSContext, "This must never be null!");
+
+  return JS::CollectRuntimeStats(mJSContext, aRtStats, nullptr, aAnonymize);
+}
+
+void WorkerPrivate::EnableMemoryReporter() {
+  auto data = mWorkerThreadAccessible.Access();
+  MOZ_ASSERT(!data->mMemoryReporter);
+
+  // No need to lock here since the main thread can't race until we've
+  // successfully registered the reporter.
+  data->mMemoryReporter = new MemoryReporter(this);
+
+  if (NS_FAILED(RegisterWeakAsyncMemoryReporter(data->mMemoryReporter))) {
+    NS_WARNING("Failed to register memory reporter!");
+    // No need to lock here since a failed registration means our memory
+    // reporter can't start running. Just clean up.
+    data->mMemoryReporter = nullptr;
+  }
+}
+
+void WorkerPrivate::DisableMemoryReporter() {
+  auto data = mWorkerThreadAccessible.Access();
+
+  RefPtr<MemoryReporter> memoryReporter;
+  {
+    // Mutex protectes MemoryReporter::mWorkerPrivate which is cleared by
+    // MemoryReporter::Disable() below.
+    MutexAutoLock lock(mMutex);
+
+    // There is nothing to do here if the memory reporter was never successfully
+    // registered.
+    if (!data->mMemoryReporter) {
+      return;
+    }
+
+    // We don't need this set any longer. Swap it out so that we can unregister
+    // below.
+    data->mMemoryReporter.swap(memoryReporter);
+
+    // Next disable the memory reporter so that the main thread stops trying to
+    // signal us.
+    memoryReporter->Disable();
+  }
+
+  // Finally unregister the memory reporter.
+  if (NS_FAILED(UnregisterWeakMemoryReporter(memoryReporter))) {
+    NS_WARNING("Failed to unregister memory reporter!");
+  }
+}
+
+void WorkerPrivate::WaitForWorkerEvents() {
+  AUTO_PROFILER_LABEL("WorkerPrivate::WaitForWorkerEvents", IDLE);
+
+  AssertIsOnWorkerThread();
+  mMutex.AssertCurrentThreadOwns();
+
+  // Wait for a worker event.
+  mCondVar.Wait();
+}
+
+WorkerPrivate::ProcessAllControlRunnablesResult
+WorkerPrivate::ProcessAllControlRunnablesLocked() {
+  AssertIsOnWorkerThread();
+  mMutex.AssertCurrentThreadOwns();
+
+  AutoYieldJSThreadExecution yield;
+
+  auto result = ProcessAllControlRunnablesResult::Nothing;
+
+  for (;;) {
+    WorkerControlRunnable* event;
+    if (!mControlQueue.Pop(event)) {
+      break;
+    }
+
+    MutexAutoUnlock unlock(mMutex);
+
+    {
+      MOZ_ASSERT(event);
+      AUTO_PROFILE_FOLLOWING_RUNNABLE(event);
+      if (NS_FAILED(static_cast<nsIRunnable*>(event)->Run())) {
+        result = ProcessAllControlRunnablesResult::Abort;
+      }
+    }
+
+    if (result == ProcessAllControlRunnablesResult::Nothing) {
+      // We ran at least one thing.
+      result = ProcessAllControlRunnablesResult::MayContinue;
+    }
+    event->Release();
+  }
+
+  return result;
+}
+
+void WorkerPrivate::ShutdownModuleLoader() {
+  AssertIsOnWorkerThread();
+
+  WorkerGlobalScope* globalScope = GlobalScope();
+  if (globalScope) {
+    if (globalScope->GetModuleLoader(nullptr)) {
+      globalScope->GetModuleLoader(nullptr)->Shutdown();
+    }
+  }
+  WorkerDebuggerGlobalScope* debugGlobalScope = DebuggerGlobalScope();
+  if (debugGlobalScope) {
+    if (debugGlobalScope->GetModuleLoader(nullptr)) {
+      debugGlobalScope->GetModuleLoader(nullptr)->Shutdown();
+    }
+  }
+}
+
+void WorkerPrivate::ClearPreStartRunnables() {
+  nsTArray<RefPtr<WorkerRunnable>> prestart;
+  {
+    MutexAutoLock lock(mMutex);
+    mPreStartRunnables.SwapElements(prestart);
+  }
+  for (uint32_t count = prestart.Length(), index = 0; index < count; index++) {
+    LOG(WorkerLog(), ("WorkerPrivate::ClearPreStartRunnable [%p]", this));
+    RefPtr<WorkerRunnable> runnable = std::move(prestart[index]);
+    runnable->Cancel();
+  }
+}
+
+void WorkerPrivate::ClearDebuggerEventQueue() {
+  while (!mDebuggerQueue.IsEmpty()) {
+    WorkerRunnable* runnable = nullptr;
+    mDebuggerQueue.Pop(runnable);
+    // It should be ok to simply release the runnable, without running it.
+    runnable->Release();
+  }
+}
+
+bool WorkerPrivate::FreezeInternal() {
+  auto data = mWorkerThreadAccessible.Access();
+  NS_ASSERTION(!data->mFrozen, "Already frozen!");
+
+  AutoYieldJSThreadExecution yield;
+
+  // The worker can freeze even if it failed to run (and doesn't have a global).
+  if (data->mScope) {
+    data->mScope->MutableClientSourceRef().Freeze();
+  }
+
+  data->mFrozen = true;
+
+  for (uint32_t index = 0; index < data->mChildWorkers.Length(); index++) {
+    data->mChildWorkers[index]->Freeze(nullptr);
+  }
+
+  return true;
+}
+
+bool WorkerPrivate::ThawInternal() {
+  auto data = mWorkerThreadAccessible.Access();
+  NS_ASSERTION(data->mFrozen, "Not yet frozen!");
+
+  for (uint32_t index = 0; index < data->mChildWorkers.Length(); index++) {
+    data->mChildWorkers[index]->Thaw(nullptr);
+  }
+
+  data->mFrozen = false;
+
+  // The worker can thaw even if it failed to run (and doesn't have a global).
+  if (data->mScope) {
+    data->mScope->MutableClientSourceRef().Thaw();
+  }
+
+  return true;
+}
+
+void WorkerPrivate::PropagateStorageAccessPermissionGrantedInternal() {
+  auto data = mWorkerThreadAccessible.Access();
+
+  mLoadInfo.mUseRegularPrincipal = true;
+  mLoadInfo.mUsingStorageAccess = true;
+
+  WorkerGlobalScope* globalScope = GlobalScope();
+  if (globalScope) {
+    globalScope->StorageAccessPermissionGranted();
+  }
+
+  for (uint32_t index = 0; index < data->mChildWorkers.Length(); index++) {
+    data->mChildWorkers[index]->PropagateStorageAccessPermissionGranted();
+  }
+}
+
+void WorkerPrivate::TraverseTimeouts(nsCycleCollectionTraversalCallback& cb) {
+  auto data = mWorkerThreadAccessible.Access();
+  for (uint32_t i = 0; i < data->mTimeouts.Length(); ++i) {
+    // TODO(erahm): No idea what's going on here.
+    TimeoutInfo* tmp = data->mTimeouts[i].get();
+    NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mHandler)
+  }
+}
+
+void WorkerPrivate::UnlinkTimeouts() {
+  auto data = mWorkerThreadAccessible.Access();
+  data->mTimeouts.Clear();
+}
+
+bool WorkerPrivate::AddChildWorker(WorkerPrivate& aChildWorker) {
+  auto data = mWorkerThreadAccessible.Access();
+
+#ifdef DEBUG
+  {
+    WorkerStatus currentStatus;
+    {
+      MutexAutoLock lock(mMutex);
+      currentStatus = mStatus;
+    }
+
+    MOZ_ASSERT(currentStatus == Running);
+  }
+#endif
+
+  NS_ASSERTION(!data->mChildWorkers.Contains(&aChildWorker),
+               "Already know about this one!");
+  data->mChildWorkers.AppendElement(&aChildWorker);
+
+  if (data->mChildWorkers.Length() == 1) {
+    UpdateCCFlag(CCFlag::IneligibleForChildWorker);
+  }
+
+  return true;
+}
+
+void WorkerPrivate::RemoveChildWorker(WorkerPrivate& aChildWorker) {
+  auto data = mWorkerThreadAccessible.Access();
+
+  NS_ASSERTION(data->mChildWorkers.Contains(&aChildWorker),
+               "Didn't know about this one!");
+  data->mChildWorkers.RemoveElement(&aChildWorker);
+
+  if (data->mChildWorkers.IsEmpty()) {
+    UpdateCCFlag(CCFlag::EligibleForChildWorker);
+  }
+}
+
+bool WorkerPrivate::AddWorkerRef(WorkerRef* aWorkerRef,
+                                 WorkerStatus aFailStatus) {
+  MOZ_ASSERT(aWorkerRef);
+  auto data = mWorkerThreadAccessible.Access();
+
+  {
+    MutexAutoLock lock(mMutex);
+
+    LOG(WorkerLog(),
+        ("WorkerPrivate::AddWorkerRef [%p] mStatus: %u, aFailStatus: (%u)",
+         this, static_cast<uint8_t>(mStatus),
+         static_cast<uint8_t>(aFailStatus)));
+
+    if (mStatus >= aFailStatus) {
+      return false;
+    }
+
+    // We shouldn't create strong references to workers before their main loop
+    // begins running. Strong references must be disposed of on the worker
+    // thread, so strong references from other threads use a control runnable
+    // for that purpose. If the worker fails to reach the main loop stage then
+    // no control runnables get run and it would be impossible to get rid of the
+    // reference properly.
+    MOZ_DIAGNOSTIC_ASSERT_IF(aWorkerRef->IsPreventingShutdown(),
+                             mStatus >= WorkerStatus::Running);
+  }
+
+  MOZ_ASSERT(!data->mWorkerRefs.Contains(aWorkerRef),
+             "Already know about this one!");
+
+  if (aWorkerRef->IsPreventingShutdown()) {
+    data->mNumWorkerRefsPreventingShutdownStart += 1;
+    if (data->mNumWorkerRefsPreventingShutdownStart == 1) {
+      UpdateCCFlag(CCFlag::IneligibleForWorkerRef);
+    }
+  }
+
+  data->mWorkerRefs.AppendElement(aWorkerRef);
+  return true;
+}
+
+void WorkerPrivate::RemoveWorkerRef(WorkerRef* aWorkerRef) {
+  MOZ_ASSERT(aWorkerRef);
+  LOG(WorkerLog(),
+      ("WorkerPrivate::RemoveWorkerRef [%p] aWorkerRef: %p", this, aWorkerRef));
+  auto data = mWorkerThreadAccessible.Access();
+
+  MOZ_ASSERT(data->mWorkerRefs.Contains(aWorkerRef),
+             "Didn't know about this one!");
+  data->mWorkerRefs.RemoveElement(aWorkerRef);
+
+  if (aWorkerRef->IsPreventingShutdown()) {
+    data->mNumWorkerRefsPreventingShutdownStart -= 1;
+    if (!data->mNumWorkerRefsPreventingShutdownStart) {
+      UpdateCCFlag(CCFlag::EligibleForWorkerRef);
+    }
+  }
+}
+
+void WorkerPrivate::NotifyWorkerRefs(WorkerStatus aStatus) {
+  auto data = mWorkerThreadAccessible.Access();
+
+  NS_ASSERTION(aStatus > Closing, "Bad status!");
+
+  LOG(WorkerLog(), ("WorkerPrivate::NotifyWorkerRefs [%p] aStatus: %u", this,
+                    static_cast<uint8_t>(aStatus)));
+
+  for (auto* workerRef : data->mWorkerRefs.ForwardRange()) {
+    LOG(WorkerLog(), ("WorkerPrivate::NotifyWorkerRefs [%p] WorkerRefs(%s %p)",
+                      this, workerRef->mName, workerRef));
+    workerRef->Notify();
+  }
+
+  AutoTArray<CheckedUnsafePtr<WorkerPrivate>, 10> children;
+  children.AppendElements(data->mChildWorkers);
+
+  for (uint32_t index = 0; index < children.Length(); index++) {
+    if (!children[index]->Notify(aStatus)) {
+      NS_WARNING("Failed to notify child worker!");
+    }
+  }
+}
+
+nsresult WorkerPrivate::RegisterShutdownTask(nsITargetShutdownTask* aTask) {
+  NS_ENSURE_ARG(aTask);
+
+  MutexAutoLock lock(mMutex);
+
+  // If we've already started running shutdown tasks, don't allow registering
+  // new ones.
+  if (mShutdownTasksRun) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  MOZ_ASSERT(!mShutdownTasks.Contains(aTask));
+  mShutdownTasks.AppendElement(aTask);
+  return NS_OK;
+}
+
+nsresult WorkerPrivate::UnregisterShutdownTask(nsITargetShutdownTask* aTask) {
+  NS_ENSURE_ARG(aTask);
+
+  MutexAutoLock lock(mMutex);
+
+  // We've already started running shutdown tasks, so can't unregister them
+  // anymore.
+  if (mShutdownTasksRun) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  return mShutdownTasks.RemoveElement(aTask) ? NS_OK : NS_ERROR_UNEXPECTED;
+}
+
+void WorkerPrivate::RunShutdownTasks() {
+  nsTArray<nsCOMPtr<nsITargetShutdownTask>> shutdownTasks;
+
+  {
+    MutexAutoLock lock(mMutex);
+    shutdownTasks = std::move(mShutdownTasks);
+    mShutdownTasks.Clear();
+    mShutdownTasksRun = true;
+  }
+
+  for (auto& task : shutdownTasks) {
+    task->TargetShutdown();
+  }
+  mWorkerHybridEventTarget->ForgetWorkerPrivate(this);
+}
+
+void WorkerPrivate::AdjustNonblockingCCBackgroundActorCount(int32_t aCount) {
+  AssertIsOnWorkerThread();
+  auto data = mWorkerThreadAccessible.Access();
+  LOGV(("WorkerPrivate::AdjustNonblockingCCBackgroundActors [%p] (%d/%u)", this,
+        aCount, data->mNonblockingCCBackgroundActorCount));
+
+#ifdef DEBUG
+  if (aCount < 0) {
+    MOZ_ASSERT(data->mNonblockingCCBackgroundActorCount >=
+               (uint32_t)abs(aCount));
+  }
+#endif
+
+  data->mNonblockingCCBackgroundActorCount += aCount;
+}
+
+void WorkerPrivate::UpdateCCFlag(const CCFlag aFlag) {
+  LOGV(("WorkerPrivate::UpdateCCFlag [%p]", this));
+  AssertIsOnWorkerThread();
+
+  auto data = mWorkerThreadAccessible.Access();
+
+#ifdef DEBUG
+  switch (aFlag) {
+    case CCFlag::EligibleForWorkerRef: {
+      MOZ_ASSERT(!data->mNumWorkerRefsPreventingShutdownStart);
+      break;
+    }
+    case CCFlag::IneligibleForWorkerRef: {
+      MOZ_ASSERT(data->mNumWorkerRefsPreventingShutdownStart);
+      break;
+    }
+    case CCFlag::EligibleForChildWorker: {
+      MOZ_ASSERT(data->mChildWorkers.IsEmpty());
+      break;
+    }
+    case CCFlag::IneligibleForChildWorker: {
+      MOZ_ASSERT(!data->mChildWorkers.IsEmpty());
+      break;
+    }
+    case CCFlag::EligibleForTimeout: {
+      MOZ_ASSERT(data->mTimeouts.IsEmpty());
+      break;
+    }
+    case CCFlag::IneligibleForTimeout: {
+      MOZ_ASSERT(!data->mTimeouts.IsEmpty());
+      break;
+    }
+    case CCFlag::CheckBackgroundActors: {
+      break;
+    }
+  }
+#endif
+
+  {
+    MutexAutoLock lock(mMutex);
+    if (mStatus > Canceling) {
+      mCCFlagSaysEligible = true;
+      return;
+    }
+  }
+  auto HasBackgroundActors = [nonblockingActorCount =
+                                  data->mNonblockingCCBackgroundActorCount]() {
+    RefPtr<PBackgroundChild> backgroundChild =
+        BackgroundChild::GetForCurrentThread();
+    MOZ_ASSERT(backgroundChild);
+    auto totalCount = backgroundChild->AllManagedActorsCount();
+    LOGV(("WorkerPrivate::UpdateCCFlag HasBackgroundActors: %s(%u/%u)",
+          totalCount > nonblockingActorCount ? "true" : "false", totalCount,
+          nonblockingActorCount));
+
+    return totalCount > nonblockingActorCount;
+  };
+
+  bool eligibleForCC = data->mChildWorkers.IsEmpty() &&
+                       data->mTimeouts.IsEmpty() &&
+                       !data->mNumWorkerRefsPreventingShutdownStart;
+
+  // Only checking BackgroundActors when no strong WorkerRef, ChildWorker, and
+  // Timeout since the checking is expensive.
+  if (eligibleForCC) {
+    eligibleForCC = !HasBackgroundActors();
+  }
+
+  {
+    MutexAutoLock lock(mMutex);
+    mCCFlagSaysEligible = eligibleForCC;
+  }
+}
+
+bool WorkerPrivate::IsEligibleForCC() {
+  LOGV(("WorkerPrivate::IsEligibleForCC [%p]", this));
+  MutexAutoLock lock(mMutex);
+  if (mStatus > Canceling) {
+    return true;
+  }
+
+  bool hasShutdownTasks = !mShutdownTasks.IsEmpty();
+  bool hasPendingEvents = false;
+  if (mThread) {
+    hasPendingEvents =
+        NS_SUCCEEDED(mThread->HasPendingEvents(&hasPendingEvents)) &&
+        hasPendingEvents;
+  }
+
+  LOGV(("mMainThreadEventTarget: %s",
+        mMainThreadEventTarget->IsEmpty() ? "empty" : "non-empty"));
+  LOGV(("mMainThreadEventTargetForMessaging: %s",
+        mMainThreadEventTargetForMessaging->IsEmpty() ? "empty" : "non-empty"));
+  LOGV(("mMainThreadDebuggerEventTarget: %s",
+        mMainThreadDebuggeeEventTarget->IsEmpty() ? "empty" : "non-empty"));
+  LOGV(("mCCFlagSaysEligible: %s", mCCFlagSaysEligible ? "true" : "false"));
+  LOGV(("hasShutdownTasks: %s", hasShutdownTasks ? "true" : "false"));
+  LOGV(("hasPendingEvents: %s", hasPendingEvents ? "true" : "false"));
+
+  return mMainThreadEventTarget->IsEmpty() &&
+         mMainThreadEventTargetForMessaging->IsEmpty() &&
+         mMainThreadDebuggeeEventTarget->IsEmpty() && mCCFlagSaysEligible &&
+         !hasShutdownTasks && !hasPendingEvents && mWorkerLoopIsIdle;
+}
+
+void WorkerPrivate::CancelAllTimeouts() {
+  auto data = mWorkerThreadAccessible.Access();
+
+  LOG(TimeoutsLog(), ("Worker %p CancelAllTimeouts.\n", this));
+
+  if (data->mTimerRunning) {
+    NS_ASSERTION(data->mTimer && data->mTimerRunnable, "Huh?!");
+    NS_ASSERTION(!data->mTimeouts.IsEmpty(), "Huh?!");
+
+    if (NS_FAILED(data->mTimer->Cancel())) {
+      NS_WARNING("Failed to cancel timer!");
+    }
+
+    for (uint32_t index = 0; index < data->mTimeouts.Length(); index++) {
+      data->mTimeouts[index]->mCanceled = true;
+    }
+
+    // If mRunningExpiredTimeouts, then the fact that they are all canceled now
+    // means that the currently executing RunExpiredTimeouts will deal with
+    // them.  Otherwise, we need to clean them up ourselves.
+    if (!data->mRunningExpiredTimeouts) {
+      data->mTimeouts.Clear();
+      UpdateCCFlag(CCFlag::EligibleForTimeout);
+    }
+
+    // Set mTimerRunning false even if mRunningExpiredTimeouts is true, so that
+    // if we get reentered under this same RunExpiredTimeouts call we don't
+    // assert above that !mTimeouts().IsEmpty(), because that's clearly false
+    // now.
+    data->mTimerRunning = false;
+  }
+#ifdef DEBUG
+  else if (!data->mRunningExpiredTimeouts) {
+    NS_ASSERTION(data->mTimeouts.IsEmpty(), "Huh?!");
+  }
+#endif
+
+  data->mTimer = nullptr;
+  data->mTimerRunnable = nullptr;
+}
+
+already_AddRefed<nsISerialEventTarget> WorkerPrivate::CreateNewSyncLoop(
+    WorkerStatus aFailStatus) {
+  AssertIsOnWorkerThread();
+  MOZ_ASSERT(
+      aFailStatus >= Canceling,
+      "Sync loops can be created when the worker is in Running/Closing state!");
+
+  LOG(WorkerLog(), ("WorkerPrivate::CreateNewSyncLoop [%p] failstatus: %u",
+                    this, static_cast<uint8_t>(aFailStatus)));
+
+  ThreadEventQueue* queue = nullptr;
+  {
+    MutexAutoLock lock(mMutex);
+
+    if (mStatus >= aFailStatus) {
+      return nullptr;
+    }
+    queue = static_cast<ThreadEventQueue*>(mThread->EventQueue());
+  }
+
+  nsCOMPtr<nsISerialEventTarget> nestedEventTarget = queue->PushEventQueue();
+  MOZ_ASSERT(nestedEventTarget);
+
+  RefPtr<EventTarget> workerEventTarget =
+      new EventTarget(this, nestedEventTarget);
+
+  {
+    // Modifications must be protected by mMutex in DEBUG builds, see comment
+    // about mSyncLoopStack in WorkerPrivate.h.
+#ifdef DEBUG
+    MutexAutoLock lock(mMutex);
+#endif
+
+    mSyncLoopStack.AppendElement(new SyncLoopInfo(workerEventTarget));
+  }
+
+  return workerEventTarget.forget();
+}
+
+nsresult WorkerPrivate::RunCurrentSyncLoop() {
+  AssertIsOnWorkerThread();
+  LOG(WorkerLog(), ("WorkerPrivate::RunCurrentSyncLoop [%p]", this));
+  RefPtr<WorkerThread> thread;
+  JSContext* cx = GetJSContext();
+  MOZ_ASSERT(cx);
+  // mThread is set before we enter, and is never changed during
+  // RunCurrentSyncLoop.
+  {
+    MutexAutoLock lock(mMutex);
+    // Copy to local so we don't trigger mutex analysis lower down
+    // mThread is set before we enter, and is never changed during
+    // RunCurrentSyncLoop copy to local so we don't trigger mutex analysis
+    thread = mThread;
+  }
+
+  AutoPushEventLoopGlobal eventLoopGlobal(this, cx);
+
+  // This should not change between now and the time we finish running this sync
+  // loop.
+  uint32_t currentLoopIndex = mSyncLoopStack.Length() - 1;
+
+  SyncLoopInfo* loopInfo = mSyncLoopStack[currentLoopIndex].get();
+
+  AutoYieldJSThreadExecution yield;
+
+  MOZ_ASSERT(loopInfo);
+  MOZ_ASSERT(!loopInfo->mHasRun);
+  MOZ_ASSERT(!loopInfo->mCompleted);
+
+#ifdef DEBUG
+  loopInfo->mHasRun = true;
+#endif
+
+  {
+    while (!loopInfo->mCompleted) {
+      bool normalRunnablesPending = false;
+
+      // Don't block with the periodic GC timer running.
+      if (!NS_HasPendingEvents(thread)) {
+        SetGCTimerMode(IdleTimer);
+      }
+
+      // Wait for something to do.
+      {
+        MutexAutoLock lock(mMutex);
+
+        for (;;) {
+          while (mControlQueue.IsEmpty() && !normalRunnablesPending &&
+                 !(normalRunnablesPending = NS_HasPendingEvents(thread))) {
+            WaitForWorkerEvents();
+          }
+
+          auto result = ProcessAllControlRunnablesLocked();
+          if (result != ProcessAllControlRunnablesResult::Nothing) {
+            // The state of the world may have changed. Recheck it if we need to
+            // continue.
+            normalRunnablesPending =
+                result == ProcessAllControlRunnablesResult::MayContinue &&
+                NS_HasPendingEvents(thread);
+
+            // NB: If we processed a NotifyRunnable, we might have run
+            // non-control runnables, one of which may have shut down the
+            // sync loop.
+            if (loopInfo->mCompleted) {
+              break;
+            }
+          }
+
+          // If we *didn't* run any control runnables, this should be unchanged.
+          MOZ_ASSERT(!loopInfo->mCompleted);
+
+          if (normalRunnablesPending) {
+            break;
+          }
+        }
+      }
+
+      if (normalRunnablesPending) {
+        // Make sure the periodic timer is running before we continue.
+        SetGCTimerMode(PeriodicTimer);
+
+        MOZ_ALWAYS_TRUE(NS_ProcessNextEvent(thread, false));
+
+        // Now *might* be a good time to GC. Let the JS engine make the
+        // decision.
+        if (GetCurrentEventLoopGlobal()) {
+          // If GetCurrentEventLoopGlobal() is non-null, our JSContext is in a
+          // Realm, so it's safe to try to GC.
+          MOZ_ASSERT(JS::CurrentGlobalOrNull(cx));
+          JS_MaybeGC(cx);
+        }
+      }
+    }
+  }
+
+  // Make sure that the stack didn't change underneath us.
+  MOZ_ASSERT(mSyncLoopStack[currentLoopIndex].get() == loopInfo);
+
+  return DestroySyncLoop(currentLoopIndex);
+}
+
+nsresult WorkerPrivate::DestroySyncLoop(uint32_t aLoopIndex) {
+  MOZ_ASSERT(!mSyncLoopStack.IsEmpty());
+  MOZ_ASSERT(mSyncLoopStack.Length() - 1 == aLoopIndex);
+
+  LOG(WorkerLog(),
+      ("WorkerPrivate::DestroySyncLoop [%p] aLoopIndex: %u", this, aLoopIndex));
+
+  AutoYieldJSThreadExecution yield;
+
+  // We're about to delete the loop, stash its event target and result.
+  const auto& loopInfo = mSyncLoopStack[aLoopIndex];
+
+  nsresult result = loopInfo->mResult;
+
+  {
+    RefPtr<nsIEventTarget> nestedEventTarget(
+        loopInfo->mEventTarget->GetNestedEventTarget());
+    MOZ_ASSERT(nestedEventTarget);
+
+    loopInfo->mEventTarget->Shutdown();
+
+    {
+      MutexAutoLock lock(mMutex);
+      static_cast<ThreadEventQueue*>(mThread->EventQueue())
+          ->PopEventQueue(nestedEventTarget);
+    }
+  }
+
+  // Are we making a 1 -> 0 transition here?
+  if (mSyncLoopStack.Length() == 1) {
+    if ((mPostSyncLoopOperations & eDispatchCancelingRunnable)) {
+      LOG(WorkerLog(),
+          ("WorkerPrivate::DestroySyncLoop [%p] Dispatching CancelingRunnables",
+           this));
+      DispatchCancelingRunnable();
+    }
+
+    mPostSyncLoopOperations = 0;
+  }
+
+  {
+    // Modifications must be protected by mMutex in DEBUG builds, see comment
+    // about mSyncLoopStack in WorkerPrivate.h.
+#ifdef DEBUG
+    MutexAutoLock lock(mMutex);
+#endif
+
+    // This will delete |loopInfo|!
+    mSyncLoopStack.RemoveElementAt(aLoopIndex);
+  }
+
+  return result;
+}
+
+void WorkerPrivate::DispatchCancelingRunnable() {
+  // Here we use a normal runnable to know when the current JS chunk of code
+  // is finished. We cannot use a WorkerRunnable because they are not
+  // accepted any more by the worker, and we do not want to use a
+  // WorkerControlRunnable because they are immediately executed.
+
+  LOG(WorkerLog(), ("WorkerPrivate::DispatchCancelingRunnable [%p]", this));
+  RefPtr<CancelingRunnable> r = new CancelingRunnable();
+  {
+    MutexAutoLock lock(mMutex);
+    mThread->nsThread::Dispatch(r.forget(), NS_DISPATCH_NORMAL);
+  }
+
+  // At the same time, we want to be sure that we interrupt infinite loops.
+  // The following runnable starts a timer that cancel the worker, from the
+  // parent thread, after CANCELING_TIMEOUT millseconds.
+  LOG(WorkerLog(), ("WorkerPrivate::DispatchCancelingRunnable [%p] Setup a "
+                    "timeout canceling",
+                    this));
+  RefPtr<CancelingWithTimeoutOnParentRunnable> rr =
+      new CancelingWithTimeoutOnParentRunnable(this);
+  rr->Dispatch();
+}
+
+void WorkerPrivate::ReportUseCounters() {
+  AssertIsOnWorkerThread();
+
+  if (mReportedUseCounters) {
+    return;
+  }
+  mReportedUseCounters = true;
+
+  if (IsChromeWorker()) {
+    return;
+  }
+
+  const size_t kind = Kind();
+  switch (kind) {
+    case WorkerKindDedicated:
+      glean::use_counter::dedicated_workers_destroyed.Add();
+      break;
+    case WorkerKindShared:
+      glean::use_counter::shared_workers_destroyed.Add();
+      break;
+    case WorkerKindService:
+      glean::use_counter::service_workers_destroyed.Add();
+      break;
+    default:
+      MOZ_ASSERT(false, "Unknown worker kind");
+      return;
+  }
+
+  Maybe<nsCString> workerPathForLogging;
+  const bool dumpCounters = StaticPrefs::dom_use_counters_dump_worker();
+  if (dumpCounters) {
+    nsAutoCString path(Domain());
+    path.AppendLiteral("(");
+    NS_ConvertUTF16toUTF8 script(ScriptURL());
+    path.Append(script);
+    path.AppendPrintf(", 0x%p)", this);
+    workerPathForLogging.emplace(std::move(path));
+  }
+
+  const size_t count = static_cast<size_t>(UseCounterWorker::Count);
+
+  const auto workerKind = Kind();
+  for (size_t c = 0; c < count; ++c) {
+    if (!GetUseCounter(static_cast<UseCounterWorker>(c))) {
+      continue;
+    }
+    const char* metricName =
+        IncrementWorkerUseCounter(static_cast<UseCounterWorker>(c), workerKind);
+    if (dumpCounters) {
+      printf_stderr("USE_COUNTER_WORKER: %s - %s\n", metricName,
+                    workerPathForLogging->get());
+    }
+  }
+}
+
+void WorkerPrivate::StopSyncLoop(nsIEventTarget* aSyncLoopTarget,
+                                 nsresult aResult) {
+  AssertValidSyncLoop(aSyncLoopTarget);
+
+  if (!MaybeStopSyncLoop(aSyncLoopTarget, aResult)) {
+    // TODO: I wonder if we should really ever crash here given the assert.
+    MOZ_CRASH("Unknown sync loop!");
+  }
+}
+
+bool WorkerPrivate::MaybeStopSyncLoop(nsIEventTarget* aSyncLoopTarget,
+                                      nsresult aResult) {
+  AssertIsOnWorkerThread();
+
+  for (uint32_t index = mSyncLoopStack.Length(); index > 0; index--) {
+    const auto& loopInfo = mSyncLoopStack[index - 1];
+    MOZ_ASSERT(loopInfo);
+    MOZ_ASSERT(loopInfo->mEventTarget);
+
+    if (loopInfo->mEventTarget == aSyncLoopTarget) {
+      // Can't assert |loop->mHasRun| here because dispatch failures can cause
+      // us to bail out early.
+      MOZ_ASSERT(!loopInfo->mCompleted);
+
+      loopInfo->mResult = aResult;
+      loopInfo->mCompleted = true;
+
+      loopInfo->mEventTarget->Disable();
+
+      return true;
+    }
+
+    MOZ_ASSERT(!SameCOMIdentity(loopInfo->mEventTarget, aSyncLoopTarget));
+  }
+
+  return false;
+}
+
+#ifdef DEBUG
+void WorkerPrivate::AssertValidSyncLoop(nsIEventTarget* aSyncLoopTarget) {
+  MOZ_ASSERT(aSyncLoopTarget);
+
+  EventTarget* workerTarget;
+  nsresult rv = aSyncLoopTarget->QueryInterface(
+      kDEBUGWorkerEventTargetIID, reinterpret_cast<void**>(&workerTarget));
+  MOZ_ASSERT(NS_SUCCEEDED(rv));
+  MOZ_ASSERT(workerTarget);
+
+  bool valid = false;
+
+  {
+    MutexAutoLock lock(mMutex);
+
+    for (uint32_t index = 0; index < mSyncLoopStack.Length(); index++) {
+      const auto& loopInfo = mSyncLoopStack[index];
+      MOZ_ASSERT(loopInfo);
+      MOZ_ASSERT(loopInfo->mEventTarget);
+
+      if (loopInfo->mEventTarget == aSyncLoopTarget) {
+        valid = true;
+        break;
+      }
+
+      MOZ_ASSERT(!SameCOMIdentity(loopInfo->mEventTarget, aSyncLoopTarget));
+    }
+  }
+
+  MOZ_ASSERT(valid);
+}
+#endif
+
+void WorkerPrivate::PostMessageToParent(
+    JSContext* aCx, JS::Handle<JS::Value> aMessage,
+    const Sequence<JSObject*>& aTransferable, ErrorResult& aRv) {
+  LOG(WorkerLog(), ("WorkerPrivate::PostMessageToParent [%p]", this));
+  AssertIsOnWorkerThread();
+  MOZ_DIAGNOSTIC_ASSERT(IsDedicatedWorker());
+
+  JS::Rooted<JS::Value> transferable(aCx, JS::UndefinedValue());
+
+  aRv = nsContentUtils::CreateJSValueFromSequenceOfObject(aCx, aTransferable,
+                                                          &transferable);
+  if (NS_WARN_IF(aRv.Failed())) {
+    return;
+  }
+
+  RefPtr<MessageEventRunnable> runnable =
+      new MessageEventRunnable(this, WorkerRunnable::ParentThread);
+
+  JS::CloneDataPolicy clonePolicy;
+
+  // Parent and dedicated workers are always part of the same cluster.
+  clonePolicy.allowIntraClusterClonableSharedObjects();
+
+  if (IsSharedMemoryAllowed()) {
+    clonePolicy.allowSharedMemoryObjects();
+  }
+
+  runnable->Write(aCx, aMessage, transferable, clonePolicy, aRv);
+
+  if (NS_WARN_IF(aRv.Failed())) {
+    return;
+  }
+
+  if (!runnable->Dispatch()) {
+    aRv = NS_ERROR_FAILURE;
+  }
+}
+
+void WorkerPrivate::EnterDebuggerEventLoop() {
+  auto data = mWorkerThreadAccessible.Access();
+
+  JSContext* cx = GetJSContext();
+  MOZ_ASSERT(cx);
+
+  AutoPushEventLoopGlobal eventLoopGlobal(this, cx);
+  AutoYieldJSThreadExecution yield;
+
+  CycleCollectedJSContext* ccjscx = CycleCollectedJSContext::Get();
+
+  uint32_t currentEventLoopLevel = ++data->mDebuggerEventLoopLevel;
+
+  while (currentEventLoopLevel <= data->mDebuggerEventLoopLevel) {
+    bool debuggerRunnablesPending = false;
+
+    {
+      MutexAutoLock lock(mMutex);
+
+      debuggerRunnablesPending = !mDebuggerQueue.IsEmpty();
+    }
+
+    // Don't block with the periodic GC timer running.
+    if (!debuggerRunnablesPending) {
+      SetGCTimerMode(IdleTimer);
+    }
+
+    // Wait for something to do
+    {
+      MutexAutoLock lock(mMutex);
+
+      std::deque<RefPtr<MicroTaskRunnable>>& debuggerMtQueue =
+          ccjscx->GetDebuggerMicroTaskQueue();
+      while (mControlQueue.IsEmpty() &&
+             !(debuggerRunnablesPending = !mDebuggerQueue.IsEmpty()) &&
+             debuggerMtQueue.empty()) {
+        WaitForWorkerEvents();
+      }
+
+      ProcessAllControlRunnablesLocked();
+
+      // XXXkhuey should we abort JS on the stack here if we got Abort above?
+    }
+    ccjscx->PerformDebuggerMicroTaskCheckpoint();
+    if (debuggerRunnablesPending) {
+      // Start the periodic GC timer if it is not already running.
+      SetGCTimerMode(PeriodicTimer);
+
+      WorkerRunnable* runnable = nullptr;
+
+      {
+        MutexAutoLock lock(mMutex);
+
+        mDebuggerQueue.Pop(runnable);
+      }
+
+      MOZ_ASSERT(runnable);
+      static_cast<nsIRunnable*>(runnable)->Run();
+      runnable->Release();
+
+      ccjscx->PerformDebuggerMicroTaskCheckpoint();
+
+      // Now *might* be a good time to GC. Let the JS engine make the decision.
+      if (GetCurrentEventLoopGlobal()) {
+        // If GetCurrentEventLoopGlobal() is non-null, our JSContext is in a
+        // Realm, so it's safe to try to GC.
+        MOZ_ASSERT(JS::CurrentGlobalOrNull(cx));
+        JS_MaybeGC(cx);
+      }
+    }
+  }
+}
+
+void WorkerPrivate::LeaveDebuggerEventLoop() {
+  auto data = mWorkerThreadAccessible.Access();
+
+  // TODO: Why lock the mutex if we're accessing data accessible to one thread
+  // only?
+  MutexAutoLock lock(mMutex);
+
+  if (data->mDebuggerEventLoopLevel > 0) {
+    --data->mDebuggerEventLoopLevel;
+  }
+}
+
+void WorkerPrivate::PostMessageToDebugger(const nsAString& aMessage) {
+  mDebugger->PostMessageToDebugger(aMessage);
+}
+
+void WorkerPrivate::SetDebuggerImmediate(dom::Function& aHandler,
+                                         ErrorResult& aRv) {
+  AssertIsOnWorkerThread();
+
+  RefPtr<DebuggerImmediateRunnable> runnable =
+      new DebuggerImmediateRunnable(this, aHandler);
+  if (!runnable->Dispatch()) {
+    aRv.Throw(NS_ERROR_FAILURE);
+  }
+}
+
+void WorkerPrivate::ReportErrorToDebugger(const nsAString& aFilename,
+                                          uint32_t aLineno,
+                                          const nsAString& aMessage) {
+  mDebugger->ReportErrorToDebugger(aFilename, aLineno, aMessage);
+}
+
+bool WorkerPrivate::NotifyInternal(WorkerStatus aStatus) {
+  auto data = mWorkerThreadAccessible.Access();
+
+  // Yield execution while notifying out-of-module WorkerRefs and cancelling
+  // runnables.
+  AutoYieldJSThreadExecution yield;
+
+  NS_ASSERTION(aStatus > Running && aStatus < Dead, "Bad status!");
+
+  RefPtr<EventTarget> eventTarget;
+
+  // Save the old status and set the new status.
+  {
+    MutexAutoLock lock(mMutex);
+
+    LOG(WorkerLog(),
+        ("WorkerPrivate::NotifyInternal [%p] mStatus: %u, aStatus: %u", this,
+         static_cast<uint8_t>(mStatus), static_cast<uint8_t>(aStatus)));
+
+    if (mStatus >= aStatus) {
+      return true;
+    }
+
+    MOZ_ASSERT_IF(aStatus == Killing,
+                  mStatus == Canceling && mParentStatus == Canceling);
+
+    if (aStatus >= Canceling) {
+      MutexAutoUnlock unlock(mMutex);
+      if (data->mScope) {
+        if (aStatus == Canceling) {
+          data->mScope->NoteTerminating();
+        } else {
+          data->mScope->NoteShuttingDown();
+        }
+      }
+    }
+
+    mStatus = aStatus;
+
+    // Mark parent status as closing immediately to avoid new events being
+    // dispatched after we clear the queue below.
+    if (aStatus == Closing) {
+      Close();
+    }
+
+    // Synchronize the mParentStatus with mStatus, such that event dispatching
+    // will fail in proper after WorkerPrivate gets into Killing status.
+    if (aStatus == Killing) {
+      mParentStatus = Killing;
+    }
+  }
+
+  if (aStatus >= Closing) {
+    CancelAllTimeouts();
+  }
+
+  if (aStatus == Closing && GlobalScope()) {
+    GlobalScope()->SetIsNotEligibleForMessaging();
+  }
+
+  // Let all our holders know the new status.
+  if (aStatus == Canceling) {
+    NotifyWorkerRefs(aStatus);
+  }
+
+  // If the worker script never ran, or failed to compile, we don't need to do
+  // anything else.
+  WorkerGlobalScope* global = GlobalScope();
+  if (!global) {
+    if (aStatus == Canceling) {
+      MOZ_ASSERT(!data->mCancelBeforeWorkerScopeConstructed);
+      data->mCancelBeforeWorkerScopeConstructed.Flip();
+    }
+    return true;
+  }
+
+  // Don't abort the script now, but we dispatch a runnable to do it when the
+  // current JS frame is executed.
+  if (aStatus == Closing) {
+    if (!mSyncLoopStack.IsEmpty()) {
+      LOG(WorkerLog(), ("WorkerPrivate::NotifyInternal [%p] request to "
+                        "dispatch canceling runnables...",
+                        this));
+      mPostSyncLoopOperations |= eDispatchCancelingRunnable;
+    } else {
+      DispatchCancelingRunnable();
+    }
+    return true;
+  }
+
+  MOZ_ASSERT(aStatus == Canceling || aStatus == Killing);
+
+  LOG(WorkerLog(), ("WorkerPrivate::NotifyInternal [%p] abort script", this));
+
+  // Always abort the script.
+  return false;
+}
+
+void WorkerPrivate::ReportError(JSContext* aCx,
+                                JS::ConstUTF8CharsZ aToStringResult,
+                                JSErrorReport* aReport) {
+  auto data = mWorkerThreadAccessible.Access();
+
+  if (!MayContinueRunning() || data->mErrorHandlerRecursionCount == 2) {
+    return;
+  }
+
+  NS_ASSERTION(data->mErrorHandlerRecursionCount == 0 ||
+                   data->mErrorHandlerRecursionCount == 1,
+               "Bad recursion logic!");
+
+  UniquePtr<WorkerErrorReport> report = MakeUnique<WorkerErrorReport>();
+  if (aReport) {
+    report->AssignErrorReport(aReport);
+  }
+
+  JS::ExceptionStack exnStack(aCx);
+  if (JS_IsExceptionPending(aCx)) {
+    if (!JS::StealPendingExceptionStack(aCx, &exnStack)) {
+      JS_ClearPendingException(aCx);
+      return;
+    }
+
+    JS::Rooted<JSObject*> stack(aCx), stackGlobal(aCx);
+    xpc::FindExceptionStackForConsoleReport(
+        nullptr, exnStack.exception(), exnStack.stack(), &stack, &stackGlobal);
+
+    if (stack) {
+      JSAutoRealm ar(aCx, stackGlobal);
+      report->SerializeWorkerStack(aCx, this, stack);
+    }
+  } else {
+    // ReportError is also used for reporting warnings,
+    // so there won't be a pending exception.
+    MOZ_ASSERT(aReport && aReport->isWarning());
+  }
+
+  if (report->mMessage.IsEmpty() && aToStringResult) {
+    nsDependentCString toStringResult(aToStringResult.c_str());
+    if (!AppendUTF8toUTF16(toStringResult, report->mMessage,
+                           mozilla::fallible)) {
+      // Try again, with only a 1 KB string. Do this infallibly this time.
+      // If the user doesn't have 1 KB to spare we're done anyways.
+      size_t index = std::min<size_t>(1024, toStringResult.Length());
+
+      // Drop the last code point that may be cropped.
+      index = RewindToPriorUTF8Codepoint(toStringResult.BeginReading(), index);
+
+      nsDependentCString truncatedToStringResult(aToStringResult.c_str(),
+                                                 index);
+      AppendUTF8toUTF16(truncatedToStringResult, report->mMessage);
+    }
+  }
+
+  data->mErrorHandlerRecursionCount++;
+
+  // Don't want to run the scope's error handler if this is a recursive error or
+  // if we ran out of memory.
+  bool fireAtScope = data->mErrorHandlerRecursionCount == 1 &&
+                     report->mErrorNumber != JSMSG_OUT_OF_MEMORY &&
+                     JS::CurrentGlobalOrNull(aCx);
+
+  WorkerErrorReport::ReportError(aCx, this, fireAtScope, nullptr,
+                                 std::move(report), 0, exnStack.exception());
+
+  data->mErrorHandlerRecursionCount--;
+}
+
+// static
+void WorkerPrivate::ReportErrorToConsole(const char* aMessage) {
+  nsTArray<nsString> emptyParams;
+  WorkerPrivate::ReportErrorToConsole(aMessage, emptyParams);
+}
+
+// static
+void WorkerPrivate::ReportErrorToConsole(const char* aMessage,
+                                         const nsTArray<nsString>& aParams) {
+  WorkerPrivate* wp = nullptr;
+  if (!NS_IsMainThread()) {
+    wp = GetCurrentThreadWorkerPrivate();
+  }
+
+  ReportErrorToConsoleRunnable::Report(wp, aMessage, aParams);
+}
+
+int32_t WorkerPrivate::SetTimeout(JSContext* aCx, TimeoutHandler* aHandler,
+                                  int32_t aTimeout, bool aIsInterval,
+                                  Timeout::Reason aReason, ErrorResult& aRv) {
+  auto data = mWorkerThreadAccessible.Access();
+  MOZ_ASSERT(aHandler);
+
+  // Reasons that doesn't support cancellation will get -1 as their ids.
+  int32_t timerId = -1;
+  if (aReason == Timeout::Reason::eTimeoutOrInterval) {
+    timerId = data->mNextTimeoutId;
+    data->mNextTimeoutId += 1;
+  }
+
+  WorkerStatus currentStatus;
+  {
+    MutexAutoLock lock(mMutex);
+    currentStatus = mStatus;
+  }
+
+  // If the worker is trying to call setTimeout/setInterval and the parent
+  // thread has initiated the close process then just silently fail.
+  if (currentStatus >= Closing) {
+    return timerId;
+  }
+
+  auto newInfo = MakeUnique<TimeoutInfo>();
+  newInfo->mReason = aReason;
+  newInfo->mOnChromeWorker = mIsChromeWorker;
+  newInfo->mIsInterval = aIsInterval;
+  newInfo->mId = timerId;
+  if (newInfo->mReason == Timeout::Reason::eTimeoutOrInterval ||
+      newInfo->mReason == Timeout::Reason::eIdleCallbackTimeout) {
+    newInfo->AccumulateNestingLevel(data->mCurrentTimerNestingLevel);
+  }
+
+  if (MOZ_UNLIKELY(timerId == INT32_MAX)) {
+    NS_WARNING("Timeout ids overflowed!");
+    if (aReason == Timeout::Reason::eTimeoutOrInterval) {
+      data->mNextTimeoutId = 1;
+    }
+  }
+
+  newInfo->mHandler = aHandler;
+
+  // See if any of the optional arguments were passed.
+  aTimeout = std::max(0, aTimeout);
+  newInfo->mInterval = TimeDuration::FromMilliseconds(aTimeout);
+  newInfo->CalculateTargetTime();
+
+  const auto& insertedInfo = data->mTimeouts.InsertElementSorted(
+      std::move(newInfo), GetUniquePtrComparator(data->mTimeouts));
+
+  LOG(TimeoutsLog(), ("Worker %p has new timeout: delay=%d interval=%s\n", this,
+                      aTimeout, aIsInterval ? "yes" : "no"));
+
+  // If the timeout we just made is set to fire next then we need to update the
+  // timer, unless we're currently running timeouts.
+  if (insertedInfo == data->mTimeouts.Elements() &&
+      !data->mRunningExpiredTimeouts) {
+    if (!data->mTimer) {
+      data->mTimer = NS_NewTimer(GlobalScope()->SerialEventTarget());
+      if (!data->mTimer) {
+        aRv.Throw(NS_ERROR_UNEXPECTED);
+        return 0;
+      }
+
+      data->mTimerRunnable = new RunExpiredTimoutsRunnable(this);
+    }
+
+    if (!data->mTimerRunning) {
+      UpdateCCFlag(CCFlag::IneligibleForTimeout);
+      data->mTimerRunning = true;
+    }
+
+    if (!RescheduleTimeoutTimer(aCx)) {
+      aRv.Throw(NS_ERROR_FAILURE);
+      return 0;
+    }
+  }
+
+  return timerId;
+}
+
+void WorkerPrivate::ClearTimeout(int32_t aId, Timeout::Reason aReason) {
+  MOZ_ASSERT(aReason == Timeout::Reason::eTimeoutOrInterval,
+             "This timeout reason doesn't support cancellation.");
+
+  auto data = mWorkerThreadAccessible.Access();
+
+  if (!data->mTimeouts.IsEmpty()) {
+    NS_ASSERTION(data->mTimerRunning, "Huh?!");
+
+    for (uint32_t index = 0; index < data->mTimeouts.Length(); index++) {
+      const auto& info = data->mTimeouts[index];
+      if (info->mId == aId && info->mReason == aReason) {
+        info->mCanceled = true;
+        break;
+      }
+    }
+  }
+}
+
+bool WorkerPrivate::RunExpiredTimeouts(JSContext* aCx) {
+  auto data = mWorkerThreadAccessible.Access();
+
+  // We may be called recursively (e.g. close() inside a timeout) or we could
+  // have been canceled while this event was pending, bail out if there is
+  // nothing to do.
+  if (data->mRunningExpiredTimeouts || !data->mTimerRunning) {
+    return true;
+  }
+
+  NS_ASSERTION(data->mTimer && data->mTimerRunnable, "Must have a timer!");
+  NS_ASSERTION(!data->mTimeouts.IsEmpty(), "Should have some work to do!");
+
+  bool retval = true;
+
+  auto comparator = GetUniquePtrComparator(data->mTimeouts);
+  JS::Rooted<JSObject*> global(aCx, JS::CurrentGlobalOrNull(aCx));
+
+  // We want to make sure to run *something*, even if the timer fired a little
+  // early. Fudge the value of now to at least include the first timeout.
+  const TimeStamp actual_now = TimeStamp::Now();
+  const TimeStamp now = std::max(actual_now, data->mTimeouts[0]->mTargetTime);
+
+  if (now != actual_now) {
+    LOG(TimeoutsLog(), ("Worker %p fudged timeout by %f ms.\n", this,
+                        (now - actual_now).ToMilliseconds()));
+#ifdef DEBUG
+    double microseconds = (now - actual_now).ToMicroseconds();
+    uint32_t allowedEarlyFiringMicroseconds;
+    data->mTimer->GetAllowedEarlyFiringMicroseconds(
+        &allowedEarlyFiringMicroseconds);
+    MOZ_ASSERT(microseconds < allowedEarlyFiringMicroseconds);
+#endif
+  }
+
+  AutoTArray<TimeoutInfo*, 10> expiredTimeouts;
+  for (uint32_t index = 0; index < data->mTimeouts.Length(); index++) {
+    TimeoutInfo* info = data->mTimeouts[index].get();
+    if (info->mTargetTime > now) {
+      break;
+    }
+    expiredTimeouts.AppendElement(info);
+  }
+
+  // Guard against recursion.
+  data->mRunningExpiredTimeouts = true;
+
+  MOZ_DIAGNOSTIC_ASSERT(data->mCurrentTimerNestingLevel == 0);
+
+  // Run expired timeouts.
+  for (uint32_t index = 0; index < expiredTimeouts.Length(); index++) {
+    TimeoutInfo*& info = expiredTimeouts[index];
+    AutoRestore<uint32_t> nestingLevel(data->mCurrentTimerNestingLevel);
+
+    if (info->mCanceled) {
+      continue;
+    }
+
+    // Set current timer nesting level to current running timer handler's
+    // nesting level
+    data->mCurrentTimerNestingLevel = info->mNestingLevel;
+
+    LOG(TimeoutsLog(),
+        ("Worker %p executing timeout with original delay %f ms.\n", this,
+         info->mInterval.ToMilliseconds()));
+
+    // Always check JS_IsExceptionPending if something fails, and if
+    // JS_IsExceptionPending returns false (i.e. uncatchable exception) then
+    // break out of the loop.
+
+    RefPtr<TimeoutHandler> handler(info->mHandler);
+
+    const char* reason;
+    switch (info->mReason) {
+      case Timeout::Reason::eTimeoutOrInterval:
+        if (info->mIsInterval) {
+          reason = "setInterval handler";
+        } else {
+          reason = "setTimeout handler";
+        }
+        break;
+      case Timeout::Reason::eDelayedWebTaskTimeout:
+        reason = "delayedWebTask handler";
+        break;
+      default:
+        MOZ_ASSERT(info->mReason == Timeout::Reason::eAbortSignalTimeout);
+        reason = "AbortSignal Timeout";
+    }
+    if (info->mReason == Timeout::Reason::eTimeoutOrInterval ||
+        info->mReason == Timeout::Reason::eDelayedWebTaskTimeout) {
+      RefPtr<WorkerGlobalScope> scope(this->GlobalScope());
+      CallbackDebuggerNotificationGuard guard(
+          scope, info->mIsInterval
+                     ? DebuggerNotificationType::SetIntervalCallback
+                     : DebuggerNotificationType::SetTimeoutCallback);
+
+      if (!handler->Call(reason)) {
+        retval = false;
+        break;
+      }
+    } else {
+      MOZ_ASSERT(info->mReason == Timeout::Reason::eAbortSignalTimeout);
+      MOZ_ALWAYS_TRUE(handler->Call(reason));
+    }
+
+    NS_ASSERTION(data->mRunningExpiredTimeouts, "Someone changed this!");
+  }
+
+  // No longer possible to be called recursively.
+  data->mRunningExpiredTimeouts = false;
+
+  // Now remove canceled and expired timeouts from the main list.
+  // NB: The timeouts present in expiredTimeouts must have the same order
+  // with respect to each other in mTimeouts.  That is, mTimeouts is just
+  // expiredTimeouts with extra elements inserted.  There may be unexpired
+  // timeouts that have been inserted between the expired timeouts if the
+  // timeout event handler called setTimeout/setInterval.
+  for (uint32_t index = 0, expiredTimeoutIndex = 0,
+                expiredTimeoutLength = expiredTimeouts.Length();
+       index < data->mTimeouts.Length();) {
+    const auto& info = data->mTimeouts[index];
+    if ((expiredTimeoutIndex < expiredTimeoutLength &&
+         info == expiredTimeouts[expiredTimeoutIndex] &&
+         ++expiredTimeoutIndex) ||
+        info->mCanceled) {
+      if (info->mIsInterval && !info->mCanceled) {
+        // Reschedule intervals.
+        // Reschedule a timeout, if needed, increase the nesting level.
+        info->AccumulateNestingLevel(info->mNestingLevel);
+        info->CalculateTargetTime();
+        // Don't resort the list here, we'll do that at the end.
+        ++index;
+      } else {
+        data->mTimeouts.RemoveElement(info);
+      }
+    } else {
+      // If info did not match the current entry in expiredTimeouts, it
+      // shouldn't be there at all.
+      NS_ASSERTION(!expiredTimeouts.Contains(info),
+                   "Our timeouts are out of order!");
+      ++index;
+    }
+  }
+
+  data->mTimeouts.Sort(comparator);
+
+  // Either signal the parent that we're no longer using timeouts or reschedule
+  // the timer.
+  if (data->mTimeouts.IsEmpty()) {
+    UpdateCCFlag(CCFlag::EligibleForTimeout);
+    data->mTimerRunning = false;
+  } else if (retval && !RescheduleTimeoutTimer(aCx)) {
+    retval = false;
+  }
+
+  return retval;
+}
+
+bool WorkerPrivate::RescheduleTimeoutTimer(JSContext* aCx) {
+  auto data = mWorkerThreadAccessible.Access();
+  MOZ_ASSERT(!data->mRunningExpiredTimeouts);
+  NS_ASSERTION(!data->mTimeouts.IsEmpty(), "Should have some timeouts!");
+  NS_ASSERTION(data->mTimer && data->mTimerRunnable, "Should have a timer!");
+
+  // NB: This is important! The timer may have already fired, e.g. if a timeout
+  // callback itself calls setTimeout for a short duration and then takes longer
+  // than that to finish executing. If that has happened, it's very important
+  // that we don't execute the event that is now pending in our event queue, or
+  // our code in RunExpiredTimeouts to "fudge" the timeout value will unleash an
+  // early timeout when we execute the event we're about to queue.
+  data->mTimer->Cancel();
+
+  double delta =
+      (data->mTimeouts[0]->mTargetTime - TimeStamp::Now()).ToMilliseconds();
+  uint32_t delay = delta > 0 ? static_cast<uint32_t>(std::ceil(
+                                   std::min(delta, double(UINT32_MAX))))
+                             : 0;
+
+  LOG(TimeoutsLog(),
+      ("Worker %p scheduled timer for %d ms, %zu pending timeouts\n", this,
+       delay, data->mTimeouts.Length()));
+
+  nsresult rv = data->mTimer->InitWithCallback(data->mTimerRunnable, delay,
+                                               nsITimer::TYPE_ONE_SHOT);
+  if (NS_FAILED(rv)) {
+    JS_ReportErrorASCII(aCx, "Failed to start timer!");
+    return false;
+  }
+
+  return true;
+}
+
+void WorkerPrivate::StartCancelingTimer() {
+  AssertIsOnParentThread();
+
+  // return if mCancelingTimer has already existed.
+  if (mCancelingTimer) {
+    return;
+  }
+
+  auto errorCleanup = MakeScopeExit([&] { mCancelingTimer = nullptr; });
+
+  if (WorkerPrivate* parent = GetParent()) {
+    mCancelingTimer = NS_NewTimer(parent->ControlEventTarget());
+  } else {
+    mCancelingTimer = NS_NewTimer();
+  }
+
+  if (NS_WARN_IF(!mCancelingTimer)) {
+    return;
+  }
+
+  // This is not needed if we are already in an advanced shutdown state.
+  {
+    MutexAutoLock lock(mMutex);
+    if (ParentStatus() >= Canceling) {
+      return;
+    }
+  }
+
+  uint32_t cancelingTimeoutMillis =
+      StaticPrefs::dom_worker_canceling_timeoutMilliseconds();
+
+  RefPtr<CancelingTimerCallback> callback = new CancelingTimerCallback(this);
+  nsresult rv = mCancelingTimer->InitWithCallback(
+      callback, cancelingTimeoutMillis, nsITimer::TYPE_ONE_SHOT);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return;
+  }
+
+  errorCleanup.release();
+}
+
+void WorkerPrivate::UpdateContextOptionsInternal(
+    JSContext* aCx, const JS::ContextOptions& aContextOptions) {
+  auto data = mWorkerThreadAccessible.Access();
+
+  JS::ContextOptionsRef(aCx) = aContextOptions;
+
+  for (uint32_t index = 0; index < data->mChildWorkers.Length(); index++) {
+    data->mChildWorkers[index]->UpdateContextOptions(aContextOptions);
+  }
+}
+
+void WorkerPrivate::UpdateLanguagesInternal(
+    const nsTArray<nsString>& aLanguages) {
+  WorkerGlobalScope* globalScope = GlobalScope();
+  RefPtr<WorkerNavigator> nav = globalScope->GetExistingNavigator();
+  if (nav) {
+    nav->SetLanguages(aLanguages);
+  }
+
+  auto data = mWorkerThreadAccessible.Access();
+  for (uint32_t index = 0; index < data->mChildWorkers.Length(); index++) {
+    data->mChildWorkers[index]->UpdateLanguages(aLanguages);
+  }
+
+  RefPtr<Event> event = NS_NewDOMEvent(globalScope, nullptr, nullptr);
+
+  event->InitEvent(u"languagechange"_ns, false, false);
+  event->SetTrusted(true);
+
+  globalScope->DispatchEvent(*event);
+}
+
+void WorkerPrivate::UpdateJSWorkerMemoryParameterInternal(
+    JSContext* aCx, JSGCParamKey aKey, Maybe<uint32_t> aValue) {
+  auto data = mWorkerThreadAccessible.Access();
+
+  if (aValue) {
+    JS_SetGCParameter(aCx, aKey, *aValue);
+  } else {
+    JS_ResetGCParameter(aCx, aKey);
+  }
+
+  for (uint32_t index = 0; index < data->mChildWorkers.Length(); index++) {
+    data->mChildWorkers[index]->UpdateJSWorkerMemoryParameter(aKey, aValue);
+  }
+}
+
+#ifdef JS_GC_ZEAL
+void WorkerPrivate::UpdateGCZealInternal(JSContext* aCx, uint8_t aGCZeal,
+                                         uint32_t aFrequency) {
+  auto data = mWorkerThreadAccessible.Access();
+
+  JS_SetGCZeal(aCx, aGCZeal, aFrequency);
+
+  for (uint32_t index = 0; index < data->mChildWorkers.Length(); index++) {
+    data->mChildWorkers[index]->UpdateGCZeal(aGCZeal, aFrequency);
+  }
+}
+#endif
+
+void WorkerPrivate::SetLowMemoryStateInternal(JSContext* aCx, bool aState) {
+  auto data = mWorkerThreadAccessible.Access();
+
+  JS::SetLowMemoryState(aCx, aState);
+
+  for (uint32_t index = 0; index < data->mChildWorkers.Length(); index++) {
+    data->mChildWorkers[index]->SetLowMemoryState(aState);
+  }
+}
+
+void WorkerPrivate::SetCCCollectedAnything(bool collectedAnything) {
+  mWorkerThreadAccessible.Access()->mCCCollectedAnything = collectedAnything;
+}
+
+bool WorkerPrivate::isLastCCCollectedAnything() {
+  return mWorkerThreadAccessible.Access()->mCCCollectedAnything;
+}
+
+void WorkerPrivate::GarbageCollectInternal(JSContext* aCx, bool aShrinking,
+                                           bool aCollectChildren) {
+  // Perform GC followed by CC (the CC is triggered by
+  // WorkerJSRuntime::CustomGCCallback at the end of the collection).
+
+  auto data = mWorkerThreadAccessible.Access();
+
+  if (!GlobalScope()) {
+    // We haven't compiled anything yet. Just bail out.
+    return;
+  }
+
+  if (aShrinking || aCollectChildren) {
+    JS::PrepareForFullGC(aCx);
+
+    if (aShrinking && mSyncLoopStack.IsEmpty()) {
+      JS::NonIncrementalGC(aCx, JS::GCOptions::Shrink,
+                           JS::GCReason::DOM_WORKER);
+
+      // Check whether the CC collected anything and if so GC again. This is
+      // necessary to collect all garbage.
+      if (data->mCCCollectedAnything) {
+        JS::NonIncrementalGC(aCx, JS::GCOptions::Normal,
+                             JS::GCReason::DOM_WORKER);
+      }
+
+      if (!aCollectChildren) {
+        LOG(WorkerLog(), ("Worker %p collected idle garbage\n", this));
+      }
+    } else {
+      JS::NonIncrementalGC(aCx, JS::GCOptions::Normal,
+                           JS::GCReason::DOM_WORKER);
+      LOG(WorkerLog(), ("Worker %p collected garbage\n", this));
+    }
+  } else {
+    JS_MaybeGC(aCx);
+    LOG(WorkerLog(), ("Worker %p collected periodic garbage\n", this));
+  }
+
+  if (aCollectChildren) {
+    for (uint32_t index = 0; index < data->mChildWorkers.Length(); index++) {
+      data->mChildWorkers[index]->GarbageCollect(aShrinking);
+    }
+  }
+}
+
+void WorkerPrivate::CycleCollectInternal(bool aCollectChildren) {
+  auto data = mWorkerThreadAccessible.Access();
+
+  nsCycleCollector_collect(CCReason::WORKER, nullptr);
+
+  if (aCollectChildren) {
+    for (uint32_t index = 0; index < data->mChildWorkers.Length(); index++) {
+      data->mChildWorkers[index]->CycleCollect();
+    }
+  }
+}
+
+void WorkerPrivate::MemoryPressureInternal() {
+  auto data = mWorkerThreadAccessible.Access();
+
+  if (data->mScope) {
+    RefPtr<Console> console = data->mScope->GetConsoleIfExists();
+    if (console) {
+      console->ClearStorage();
+    }
+
+    RefPtr<Performance> performance = data->mScope->GetPerformanceIfExists();
+    if (performance) {
+      performance->MemoryPressure();
+    }
+
+    data->mScope->RemoveReportRecords();
+  }
+
+  if (data->mDebuggerScope) {
+    RefPtr<Console> console = data->mDebuggerScope->GetConsoleIfExists();
+    if (console) {
+      console->ClearStorage();
+    }
+  }
+
+  for (uint32_t index = 0; index < data->mChildWorkers.Length(); index++) {
+    data->mChildWorkers[index]->MemoryPressure();
+  }
+}
+
+void WorkerPrivate::SetThread(WorkerThread* aThread) {
+  if (aThread) {
+#ifdef DEBUG
+    {
+      bool isOnCurrentThread;
+      MOZ_ASSERT(NS_SUCCEEDED(aThread->IsOnCurrentThread(&isOnCurrentThread)));
+      MOZ_ASSERT(!isOnCurrentThread);
+    }
+#endif
+
+    MOZ_ASSERT(!mPRThread);
+    mPRThread = PRThreadFromThread(aThread);
+    MOZ_ASSERT(mPRThread);
+
+    mWorkerThreadAccessible.Transfer(mPRThread);
+  } else {
+    MOZ_ASSERT(mPRThread);
+  }
+}
+
+void WorkerPrivate::SetWorkerPrivateInWorkerThread(
+    WorkerThread* const aThread) {
+  LOG(WorkerLog(),
+      ("WorkerPrivate::SetWorkerPrivateInWorkerThread [%p]", this));
+  MutexAutoLock lock(mMutex);
+
+  MOZ_ASSERT(!mThread);
+  MOZ_ASSERT(mStatus == Pending);
+
+  mThread = aThread;
+  mThread->SetWorker(WorkerThreadFriendKey{}, this);
+
+  if (!mPreStartRunnables.IsEmpty()) {
+    for (uint32_t index = 0; index < mPreStartRunnables.Length(); index++) {
+      MOZ_ALWAYS_SUCCEEDS(mThread->DispatchAnyThread(
+          WorkerThreadFriendKey{}, mPreStartRunnables[index].forget()));
+    }
+    mPreStartRunnables.Clear();
+  }
+}
+
+void WorkerPrivate::ResetWorkerPrivateInWorkerThread() {
+  LOG(WorkerLog(),
+      ("WorkerPrivate::ResetWorkerPrivateInWorkerThread [%p]", this));
+  RefPtr<WorkerThread> doomedThread;
+
+  // Release the mutex before doomedThread.
+  MutexAutoLock lock(mMutex);
+
+  MOZ_ASSERT(mThread);
+
+  mThread->SetWorker(WorkerThreadFriendKey{}, nullptr);
+  mThread.swap(doomedThread);
+}
+
+void WorkerPrivate::BeginCTypesCall() {
+  AssertIsOnWorkerThread();
+  auto data = mWorkerThreadAccessible.Access();
+
+  // Don't try to GC while we're blocked in a ctypes call.
+  SetGCTimerMode(NoTimer);
+
+  data->mYieldJSThreadExecution.EmplaceBack();
+}
+
+void WorkerPrivate::EndCTypesCall() {
+  AssertIsOnWorkerThread();
+  auto data = mWorkerThreadAccessible.Access();
+
+  data->mYieldJSThreadExecution.RemoveLastElement();
+
+  // Make sure the periodic timer is running before we start running JS again.
+  SetGCTimerMode(PeriodicTimer);
+}
+
+void WorkerPrivate::BeginCTypesCallback() {
+  AssertIsOnWorkerThread();
+
+  // Make sure the periodic timer is running before we start running JS again.
+  SetGCTimerMode(PeriodicTimer);
+
+  // Re-requesting execution is not needed since the JSRuntime code calling
+  // this will do an AutoEntryScript.
+}
+
+void WorkerPrivate::EndCTypesCallback() {
+  AssertIsOnWorkerThread();
+
+  // Don't try to GC while we're blocked in a ctypes call.
+  SetGCTimerMode(NoTimer);
+}
+
+bool WorkerPrivate::ConnectMessagePort(JSContext* aCx,
+                                       UniqueMessagePortId& aIdentifier) {
+  AssertIsOnWorkerThread();
+
+  WorkerGlobalScope* globalScope = GlobalScope();
+
+  JS::Rooted<JSObject*> jsGlobal(aCx, globalScope->GetWrapper());
+  MOZ_ASSERT(jsGlobal);
+
+  // This UniqueMessagePortId is used to create a new port, still connected
+  // with the other one, but in the worker thread.
+  ErrorResult rv;
+  RefPtr<MessagePort> port = MessagePort::Create(globalScope, aIdentifier, rv);
+  if (NS_WARN_IF(rv.Failed())) {
+    rv.SuppressException();
+    return false;
+  }
+
+  GlobalObject globalObject(aCx, jsGlobal);
+  if (globalObject.Failed()) {
+    return false;
+  }
+
+  RootedDictionary<MessageEventInit> init(aCx);
+  init.mData = JS_GetEmptyStringValue(aCx);
+  init.mBubbles = false;
+  init.mCancelable = false;
+  init.mSource.SetValue().SetAsMessagePort() = port;
+  if (!init.mPorts.AppendElement(port.forget(), fallible)) {
+    return false;
+  }
+
+  RefPtr<MessageEvent> event =
+      MessageEvent::Constructor(globalObject, u"connect"_ns, init);
+
+  event->SetTrusted(true);
+
+  globalScope->DispatchEvent(*event);
+
+  return true;
+}
+
+WorkerGlobalScope* WorkerPrivate::GetOrCreateGlobalScope(JSContext* aCx) {
+  auto data = mWorkerThreadAccessible.Access();
+
+  if (data->mScope) {
+    return data->mScope;
+  }
+
+  if (IsSharedWorker()) {
+    data->mScope =
+        new SharedWorkerGlobalScope(this, CreateClientSource(), WorkerName());
+  } else if (IsServiceWorker()) {
+    data->mScope = new ServiceWorkerGlobalScope(
+        this, CreateClientSource(), GetServiceWorkerRegistrationDescriptor());
+  } else {
+    data->mScope = new DedicatedWorkerGlobalScope(this, CreateClientSource(),
+                                                  WorkerName());
+  }
+
+  JS::Rooted<JSObject*> global(aCx);
+  NS_ENSURE_TRUE(data->mScope->WrapGlobalObject(aCx, &global), nullptr);
+
+  JSAutoRealm ar(aCx, global);
+
+  if (!RegisterBindings(aCx, global)) {
+    data->mScope = nullptr;
+    return nullptr;
+  }
+
+  // Worker has already in "Canceling", let the WorkerGlobalScope start dying.
+  if (data->mCancelBeforeWorkerScopeConstructed) {
+    data->mScope->NoteTerminating();
+    data->mScope->DisconnectGlobalTeardownObservers();
+  }
+
+  JS_FireOnNewGlobalObject(aCx, global);
+
+  return data->mScope;
+}
+
+WorkerDebuggerGlobalScope* WorkerPrivate::CreateDebuggerGlobalScope(
+    JSContext* aCx) {
+  auto data = mWorkerThreadAccessible.Access();
+  MOZ_ASSERT(!data->mDebuggerScope);
+
+  // The debugger global gets a dummy client, not the "real" client used by the
+  // debugee worker.
+  auto clientSource = ClientManager::CreateSource(
+      GetClientType(), HybridEventTarget(), NullPrincipalInfo());
+
+  data->mDebuggerScope =
+      new WorkerDebuggerGlobalScope(this, std::move(clientSource));
+
+  JS::Rooted<JSObject*> global(aCx);
+  NS_ENSURE_TRUE(data->mDebuggerScope->WrapGlobalObject(aCx, &global), nullptr);
+
+  JSAutoRealm ar(aCx, global);
+
+  if (!RegisterDebuggerBindings(aCx, global)) {
+    data->mDebuggerScope = nullptr;
+    return nullptr;
+  }
+
+  JS_FireOnNewGlobalObject(aCx, global);
+
+  return data->mDebuggerScope;
+}
+
+bool WorkerPrivate::IsOnWorkerThread() const {
+  // We can't use mThread because it must be protected by mMutex and sometimes
+  // this method is called when mMutex is already locked. This method should
+  // always work.
+  MOZ_ASSERT(mPRThread,
+             "AssertIsOnWorkerThread() called before a thread was assigned!");
+
+  return mPRThread == PR_GetCurrentThread();
+}
+
+#ifdef DEBUG
+void WorkerPrivate::AssertIsOnWorkerThread() const {
+  MOZ_ASSERT(IsOnWorkerThread());
+}
+#endif  // DEBUG
+
+void WorkerPrivate::DumpCrashInformation(nsACString& aString) {
+  auto data = mWorkerThreadAccessible.Access();
+
+  aString.Append("IsChromeWorker(");
+  if (IsChromeWorker()) {
+    aString.Append(NS_ConvertUTF16toUTF8(ScriptURL()));
+  } else {
+    aString.Append("false");
+  }
+  aString.Append(")");
+  for (const auto* workerRef : data->mWorkerRefs.NonObservingRange()) {
+    if (workerRef->IsPreventingShutdown()) {
+      aString.Append("|");
+      aString.Append(workerRef->Name());
+      const nsCString status = GET_WORKERREF_DEBUG_STATUS(workerRef);
+      if (!status.IsEmpty()) {
+        aString.Append("[");
+        aString.Append(status);
+        aString.Append("]");
+      }
+    }
+  }
+}
+
+PerformanceStorage* WorkerPrivate::GetPerformanceStorage() {
+  MOZ_ASSERT(mPerformanceStorage);
+  return mPerformanceStorage;
+}
+
+bool WorkerPrivate::ShouldResistFingerprinting(RFPTarget aTarget) const {
+  return mLoadInfo.mShouldResistFingerprinting &&
+         nsRFPService::IsRFPEnabledFor(
+             mLoadInfo.mOriginAttributes.mPrivateBrowsingId >
+                 nsIScriptSecurityManager::DEFAULT_PRIVATE_BROWSING_ID,
+             aTarget, mLoadInfo.mOverriddenFingerprintingSettings);
+}
+
+void WorkerPrivate::SetRemoteWorkerController(RemoteWorkerChild* aController) {
+  AssertIsOnMainThread();
+  MOZ_ASSERT(aController);
+  MOZ_ASSERT(!mRemoteWorkerController);
+
+  mRemoteWorkerController = aController;
+}
+
+RemoteWorkerChild* WorkerPrivate::GetRemoteWorkerController() {
+  AssertIsOnMainThread();
+  MOZ_ASSERT(mRemoteWorkerController);
+  return mRemoteWorkerController;
+}
+
+RefPtr<GenericPromise> WorkerPrivate::SetServiceWorkerSkipWaitingFlag() {
+  AssertIsOnWorkerThread();
+  MOZ_ASSERT(IsServiceWorker());
+
+  RefPtr<RemoteWorkerChild> rwc = mRemoteWorkerController;
+
+  if (!rwc) {
+    return GenericPromise::CreateAndReject(NS_ERROR_DOM_ABORT_ERR, __func__);
+  }
+
+  RefPtr<GenericPromise> promise =
+      rwc->MaybeSendSetServiceWorkerSkipWaitingFlag();
+
+  return promise;
+}
+
+const nsAString& WorkerPrivate::Id() {
+  AssertIsOnMainThread();
+
+  if (mId.IsEmpty()) {
+    mId = ComputeWorkerPrivateId();
+  }
+
+  MOZ_ASSERT(!mId.IsEmpty());
+
+  return mId;
+}
+
+bool WorkerPrivate::IsSharedMemoryAllowed() const {
+  if (StaticPrefs::
+          dom_postMessage_sharedArrayBuffer_bypassCOOP_COEP_insecure_enabled()) {
+    return true;
+  }
+
+  if (mIsPrivilegedAddonGlobal) {
+    return true;
+  }
+
+  return CrossOriginIsolated();
+}
+
+bool WorkerPrivate::CrossOriginIsolated() const {
+  if (!StaticPrefs::
+          dom_postMessage_sharedArrayBuffer_withCOOP_COEP_AtStartup()) {
+    return false;
+  }
+
+  return mAgentClusterOpenerPolicy ==
+         nsILoadInfo::OPENER_POLICY_SAME_ORIGIN_EMBEDDER_POLICY_REQUIRE_CORP;
+}
+
+nsILoadInfo::CrossOriginEmbedderPolicy WorkerPrivate::GetEmbedderPolicy()
+    const {
+  if (!StaticPrefs::browser_tabs_remote_useCrossOriginEmbedderPolicy()) {
+    return nsILoadInfo::EMBEDDER_POLICY_NULL;
+  }
+
+  return mEmbedderPolicy.valueOr(nsILoadInfo::EMBEDDER_POLICY_NULL);
+}
+
+Result<Ok, nsresult> WorkerPrivate::SetEmbedderPolicy(
+    nsILoadInfo::CrossOriginEmbedderPolicy aPolicy) {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(mEmbedderPolicy.isNothing());
+
+  if (!StaticPrefs::browser_tabs_remote_useCrossOriginEmbedderPolicy()) {
+    return Ok();
+  }
+
+  // https://html.spec.whatwg.org/multipage/browsers.html#check-a-global-object's-embedder-policy
+  // If ownerPolicy's value is not compatible with cross-origin isolation or
+  // policy's value is compatible with cross-origin isolation, then return true.
+  EnsureOwnerEmbedderPolicy();
+  nsILoadInfo::CrossOriginEmbedderPolicy ownerPolicy =
+      mOwnerEmbedderPolicy.valueOr(nsILoadInfo::EMBEDDER_POLICY_NULL);
+  if (nsContentSecurityManager::IsCompatibleWithCrossOriginIsolation(
+          ownerPolicy) &&
+      !nsContentSecurityManager::IsCompatibleWithCrossOriginIsolation(
+          aPolicy)) {
+    return Err(NS_ERROR_BLOCKED_BY_POLICY);
+  }
+
+  mEmbedderPolicy.emplace(aPolicy);
+
+  return Ok();
+}
+
+void WorkerPrivate::InheritOwnerEmbedderPolicyOrNull(nsIRequest* aRequest) {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(aRequest);
+
+  EnsureOwnerEmbedderPolicy();
+
+  if (mOwnerEmbedderPolicy.isSome()) {
+    nsCOMPtr<nsIChannel> channel = do_QueryInterface(aRequest);
+    MOZ_ASSERT(channel);
+
+    nsCOMPtr<nsIURI> scriptURI;
+    MOZ_ALWAYS_SUCCEEDS(channel->GetURI(getter_AddRefs(scriptURI)));
+
+    bool isLocalScriptURI = false;
+    MOZ_ALWAYS_SUCCEEDS(NS_URIChainHasFlags(
+        scriptURI, nsIProtocolHandler::URI_IS_LOCAL_RESOURCE,
+        &isLocalScriptURI));
+
+    MOZ_RELEASE_ASSERT(isLocalScriptURI);
+  }
+
+  mEmbedderPolicy.emplace(
+      mOwnerEmbedderPolicy.valueOr(nsILoadInfo::EMBEDDER_POLICY_NULL));
+}
+
+bool WorkerPrivate::MatchEmbedderPolicy(
+    nsILoadInfo::CrossOriginEmbedderPolicy aPolicy) const {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  if (!StaticPrefs::browser_tabs_remote_useCrossOriginEmbedderPolicy()) {
+    return true;
+  }
+
+  return mEmbedderPolicy.value() == aPolicy;
+}
+
+nsILoadInfo::CrossOriginEmbedderPolicy WorkerPrivate::GetOwnerEmbedderPolicy()
+    const {
+  if (!StaticPrefs::browser_tabs_remote_useCrossOriginEmbedderPolicy()) {
+    return nsILoadInfo::EMBEDDER_POLICY_NULL;
+  }
+
+  return mOwnerEmbedderPolicy.valueOr(nsILoadInfo::EMBEDDER_POLICY_NULL);
+}
+
+void WorkerPrivate::EnsureOwnerEmbedderPolicy() {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(mOwnerEmbedderPolicy.isNothing());
+
+  if (GetParent()) {
+    mOwnerEmbedderPolicy.emplace(GetParent()->GetEmbedderPolicy());
+  } else if (GetWindow() && GetWindow()->GetWindowContext()) {
+    mOwnerEmbedderPolicy.emplace(
+        GetWindow()->GetWindowContext()->GetEmbedderPolicy());
+  }
+}
+
+nsIPrincipal* WorkerPrivate::GetEffectiveStoragePrincipal() const {
+  AssertIsOnWorkerThread();
+
+  if (mLoadInfo.mUseRegularPrincipal) {
+    return mLoadInfo.mPrincipal;
+  }
+
+  return mLoadInfo.mPartitionedPrincipal;
+}
+
+const mozilla::ipc::PrincipalInfo&
+WorkerPrivate::GetEffectiveStoragePrincipalInfo() const {
+  AssertIsOnWorkerThread();
+
+  if (mLoadInfo.mUseRegularPrincipal) {
+    return *mLoadInfo.mPrincipalInfo;
+  }
+
+  return *mLoadInfo.mPartitionedPrincipalInfo;
+}
+
+NS_IMPL_ADDREF(WorkerPrivate::EventTarget)
+NS_IMPL_RELEASE(WorkerPrivate::EventTarget)
+
+NS_INTERFACE_MAP_BEGIN(WorkerPrivate::EventTarget)
+  NS_INTERFACE_MAP_ENTRY(nsISerialEventTarget)
+  NS_INTERFACE_MAP_ENTRY(nsIEventTarget)
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+#ifdef DEBUG
+  // kDEBUGWorkerEventTargetIID is special in that it does not AddRef its
+  // result.
+  if (aIID.Equals(kDEBUGWorkerEventTargetIID)) {
+    *aInstancePtr = this;
+    return NS_OK;
+  } else
+#endif
+NS_INTERFACE_MAP_END
+
+NS_IMETHODIMP
+WorkerPrivate::EventTarget::DispatchFromScript(nsIRunnable* aRunnable,
+                                               uint32_t aFlags) {
+  nsCOMPtr<nsIRunnable> event(aRunnable);
+  return Dispatch(event.forget(), aFlags);
+}
+
+NS_IMETHODIMP
+WorkerPrivate::EventTarget::Dispatch(already_AddRefed<nsIRunnable> aRunnable,
+                                     uint32_t aFlags) {
+  // May be called on any thread!
+  nsCOMPtr<nsIRunnable> event(aRunnable);
+
+  // Workers only support asynchronous dispatch for now.
+  if (NS_WARN_IF(aFlags != NS_DISPATCH_NORMAL)) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  RefPtr<WorkerRunnable> workerRunnable;
+
+  MutexAutoLock lock(mMutex);
+
+  if (mDisabled) {
+    NS_WARNING(
+        "A runnable was posted to a worker that is already shutting "
+        "down!");
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  MOZ_ASSERT(mWorkerPrivate);
+  MOZ_ASSERT(mNestedEventTarget);
+
+  if (event) {
+    workerRunnable = mWorkerPrivate->MaybeWrapAsWorkerRunnable(event.forget());
+  }
+
+  nsresult rv =
+      mWorkerPrivate->Dispatch(workerRunnable.forget(), mNestedEventTarget);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WorkerPrivate::EventTarget::DelayedDispatch(already_AddRefed<nsIRunnable>,
+                                            uint32_t)
+
+{
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+WorkerPrivate::EventTarget::RegisterShutdownTask(nsITargetShutdownTask* aTask) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+WorkerPrivate::EventTarget::UnregisterShutdownTask(
+    nsITargetShutdownTask* aTask) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+NS_IMETHODIMP
+WorkerPrivate::EventTarget::IsOnCurrentThread(bool* aIsOnCurrentThread) {
+  // May be called on any thread!
+
+  MOZ_ASSERT(aIsOnCurrentThread);
+
+  MutexAutoLock lock(mMutex);
+
+  if (mShutdown) {
+    NS_WARNING(
+        "A worker's event target was used after the worker has shutdown!");
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  MOZ_ASSERT(mNestedEventTarget);
+
+  *aIsOnCurrentThread = mNestedEventTarget->IsOnCurrentThread();
+  return NS_OK;
+}
+
+NS_IMETHODIMP_(bool)
+WorkerPrivate::EventTarget::IsOnCurrentThreadInfallible() {
+  // May be called on any thread!
+
+  MutexAutoLock lock(mMutex);
+
+  if (mShutdown) {
+    NS_WARNING(
+        "A worker's event target was used after the worker has shutdown!");
+    return false;
+  }
+
+  MOZ_ASSERT(mNestedEventTarget);
+
+  return mNestedEventTarget->IsOnCurrentThread();
+}
+
+WorkerPrivate::AutoPushEventLoopGlobal::AutoPushEventLoopGlobal(
+    WorkerPrivate* aWorkerPrivate, JSContext* aCx)
+    : mWorkerPrivate(aWorkerPrivate) {
+  auto data = mWorkerPrivate->mWorkerThreadAccessible.Access();
+  mOldEventLoopGlobal = std::move(data->mCurrentEventLoopGlobal);
+  if (JSObject* global = JS::CurrentGlobalOrNull(aCx)) {
+    data->mCurrentEventLoopGlobal = xpc::NativeGlobal(global);
+  }
+}
+
+WorkerPrivate::AutoPushEventLoopGlobal::~AutoPushEventLoopGlobal() {
+  auto data = mWorkerPrivate->mWorkerThreadAccessible.Access();
+  data->mCurrentEventLoopGlobal = std::move(mOldEventLoopGlobal);
+}
+
+}  // namespace dom
+}  // namespace mozilla
diff --git a/dom/workers/WorkerPrivate.h b/dom/workers/WorkerPrivate.h
new file mode 100644
index 0000000000..a670d00975
--- /dev/null
+++ b/dom/workers/WorkerPrivate.h
@@ -0,0 +1,1666 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_workers_workerprivate_h__
+#define mozilla_dom_workers_workerprivate_h__
+
+#include <bitset>
+#include "MainThreadUtils.h"
+#include "ScriptLoader.h"
+#include "js/ContextOptions.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/AutoRestore.h"
+#include "mozilla/BasePrincipal.h"
+#include "mozilla/CondVar.h"
+#include "mozilla/DOMEventTargetHelper.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/MozPromise.h"
+#include "mozilla/OriginTrials.h"
+#include "mozilla/RelativeTimeline.h"
+#include "mozilla/Result.h"
+#include "mozilla/StorageAccess.h"
+#include "mozilla/ThreadBound.h"
+#include "mozilla/ThreadSafeWeakPtr.h"
+#include "mozilla/UniquePtr.h"
+#include "mozilla/UseCounter.h"
+#include "mozilla/dom/ClientSource.h"
+#include "mozilla/dom/FlippedOnce.h"
+#include "mozilla/dom/Timeout.h"
+#include "mozilla/dom/quota/CheckedUnsafePtr.h"
+#include "mozilla/dom/Worker.h"
+#include "mozilla/dom/WorkerBinding.h"
+#include "mozilla/dom/WorkerCommon.h"
+#include "mozilla/dom/WorkerLoadInfo.h"
+#include "mozilla/dom/WorkerStatus.h"
+#include "mozilla/dom/workerinternals/JSSettings.h"
+#include "mozilla/dom/workerinternals/Queue.h"
+#include "mozilla/dom/JSExecutionManager.h"
+#include "mozilla/net/NeckoChannelParams.h"
+#include "mozilla/StaticPrefs_extensions.h"
+#include "nsContentUtils.h"
+#include "nsIChannel.h"
+#include "nsIContentSecurityPolicy.h"
+#include "nsIEventTarget.h"
+#include "nsILoadInfo.h"
+#include "nsRFPService.h"
+#include "nsTObserverArray.h"
+#include "stdint.h"
+
+class nsIThreadInternal;
+
+namespace JS {
+struct RuntimeStats;
+}
+
+namespace mozilla {
+class ThrottledEventQueue;
+namespace dom {
+
+class RemoteWorkerChild;
+
+// If you change this, the corresponding list in nsIWorkerDebugger.idl needs
+// to be updated too. And histograms enum for worker use counters uses the same
+// order of worker kind. Please also update dom/base/usecounters.py.
+enum WorkerKind : uint8_t {
+  WorkerKindDedicated,
+  WorkerKindShared,
+  WorkerKindService
+};
+
+class ClientInfo;
+class ClientSource;
+class Function;
+class JSExecutionManager;
+class MessagePort;
+class UniqueMessagePortId;
+class PerformanceStorage;
+class TimeoutHandler;
+class WorkerControlRunnable;
+class WorkerCSPEventListener;
+class WorkerDebugger;
+class WorkerDebuggerGlobalScope;
+class WorkerErrorReport;
+class WorkerEventTarget;
+class WorkerGlobalScope;
+class WorkerRef;
+class WorkerRunnable;
+class WorkerDebuggeeRunnable;
+class WorkerThread;
+
+// SharedMutex is a small wrapper around an (internal) reference-counted Mutex
+// object. It exists to avoid changing a lot of code to use Mutex* instead of
+// Mutex&.
+class MOZ_CAPABILITY("mutex") SharedMutex {
+  using Mutex = mozilla::Mutex;
+
+  class MOZ_CAPABILITY("mutex") RefCountedMutex final : public Mutex {
+   public:
+    explicit RefCountedMutex(const char* aName) : Mutex(aName) {}
+
+    NS_INLINE_DECL_THREADSAFE_REFCOUNTING(RefCountedMutex)
+
+   private:
+    ~RefCountedMutex() = default;
+  };
+
+  const RefPtr<RefCountedMutex> mMutex;
+
+ public:
+  explicit SharedMutex(const char* aName)
+      : mMutex(new RefCountedMutex(aName)) {}
+
+  SharedMutex(const SharedMutex& aOther) = default;
+
+  operator Mutex&() MOZ_RETURN_CAPABILITY(this) { return *mMutex; }
+
+  operator const Mutex&() const MOZ_RETURN_CAPABILITY(this) { return *mMutex; }
+
+  // We need these to make thread-safety analysis work
+  void Lock() MOZ_CAPABILITY_ACQUIRE() { mMutex->Lock(); }
+  void Unlock() MOZ_CAPABILITY_RELEASE() { mMutex->Unlock(); }
+
+  // We can assert we own 'this', but we can't assert we hold mMutex
+  void AssertCurrentThreadOwns() const
+      MOZ_ASSERT_CAPABILITY(this) MOZ_NO_THREAD_SAFETY_ANALYSIS {
+    mMutex->AssertCurrentThreadOwns();
+  }
+};
+
+nsString ComputeWorkerPrivateId();
+
+class WorkerPrivate final
+    : public RelativeTimeline,
+      public SupportsCheckedUnsafePtr<CheckIf<DiagnosticAssertEnabled>> {
+ public:
+  // Callback invoked on the parent thread when the worker's cancellation is
+  // about to be requested.  This covers both calls to
+  // WorkerPrivate::Cancel() by the owner as well as self-initiated cancellation
+  // due to top-level script evaluation failing or close() being invoked on the
+  // global scope for Dedicated and Shared workers, but not Service Workers as
+  // they do not expose a close() method.
+  //
+  // ### Parent-Initiated Cancellation
+  //
+  // When WorkerPrivate::Cancel is invoked on the parent thread (by the binding
+  // exposed Worker::Terminate), this callback is invoked synchronously inside
+  // that call.
+  //
+  // ### Worker Self-Cancellation
+  //
+  // When a worker initiates self-cancellation, the worker's notification to the
+  // parent thread is a non-blocking, async mechanism triggered by
+  // `WorkerPrivate::DispatchCancelingRunnable`.
+  //
+  // Self-cancellation races a normally scheduled runnable against a timer that
+  // is scheduled against the parent.  The 2 paths initiated by
+  // DispatchCancelingRunnable are:
+  //
+  // 1. A CancelingRunnable is dispatched at the worker's normal event target to
+  //    wait for the event loop to be clear of runnables.  When the
+  //    CancelingRunnable runs it will dispatch a CancelingOnParentRunnable to
+  //    its parent which is a normal, non-control WorkerDebuggeeRunnable to
+  //    ensure that any postMessages to the parent or similar events get a
+  //    chance to be processed prior to cancellation.  The timer scheduled in
+  //    the next bullet will not be canceled unless
+  //
+  // 2. A CancelingWithTimeoutOnParentRunnable control runnable is dispatched
+  //    to the parent to schedule a timer which will (also) fire on the parent
+  //    thread.  This handles the case where the worker does not yield
+  //    control-flow, and so the normal runnable scheduled above does not get to
+  //    run in a timely fashion.  Because this is a control runnable, if the
+  //    parent is a worker then the runnable will be processed with urgency.
+  //    However, if the worker is top-level, then the control-like throttled
+  //    WorkerPrivate::mMainThreadEventTarget will end up getting used which is
+  //    nsIRunnablePriority::PRIORITY_MEDIUMHIGH and distinct from the
+  //    mMainThreadDebuggeeEventTarget which most runnables (like postMessage)
+  //    use.
+  //
+  //    The timer will explicitly use the control event target if the parent is
+  //    a worker and the implicit event target (via `NS_NewTimer()`) otherwise.
+  //    The callback is CancelingTimerCallback which just calls
+  //    WorkerPrivate::Cancel.
+  using CancellationCallback = std::function<void(bool aEverRan)>;
+
+  // Callback invoked on the parent just prior to dropping the worker thread's
+  // strong reference that keeps the WorkerPrivate alive while the worker thread
+  // is running.  This does not provide a guarantee that the underlying thread
+  // has fully shutdown, just that the worker logic has fully shutdown.
+  //
+  // ### Details
+  //
+  // The last thing the worker thread's WorkerThreadPrimaryRunnable does before
+  // initiating the shutdown of the underlying thread is call ScheduleDeletion.
+  // ScheduleDeletion dispatches a runnable to the parent to notify it that the
+  // worker has completed its work and will never touch the WorkerPrivate again
+  // and that the strong self-reference can be dropped.
+  //
+  // For parents that are themselves workers, this will be done by
+  // WorkerFinishedRunnable which is a WorkerControlRunnable, ensuring that this
+  // is processed in a timely fashion.  For main-thread parents,
+  // TopLevelWorkerFinishedRunnable will be used and sent via
+  // mMainThreadEventTargetForMessaging which is a weird ThrottledEventQueue
+  // which does not provide any ordering guarantees relative to
+  // mMainThreadDebuggeeEventTarget, so if you want those, you need to enhance
+  // things.
+  using TerminationCallback = std::function<void(void)>;
+
+  struct LocationInfo {
+    nsCString mHref;
+    nsCString mProtocol;
+    nsCString mHost;
+    nsCString mHostname;
+    nsCString mPort;
+    nsCString mPathname;
+    nsCString mSearch;
+    nsCString mHash;
+    nsString mOrigin;
+  };
+
+  NS_INLINE_DECL_REFCOUNTING(WorkerPrivate)
+
+  static already_AddRefed<WorkerPrivate> Constructor(
+      JSContext* aCx, const nsAString& aScriptURL, bool aIsChromeWorker,
+      WorkerKind aWorkerKind, RequestCredentials aRequestCredentials,
+      const WorkerType aWorkerType, const nsAString& aWorkerName,
+      const nsACString& aServiceWorkerScope, WorkerLoadInfo* aLoadInfo,
+      ErrorResult& aRv, nsString aId = u""_ns,
+      CancellationCallback&& aCancellationCallback = {},
+      TerminationCallback&& aTerminationCallback = {});
+
+  enum LoadGroupBehavior { InheritLoadGroup, OverrideLoadGroup };
+
+  static nsresult GetLoadInfo(
+      JSContext* aCx, nsPIDOMWindowInner* aWindow, WorkerPrivate* aParent,
+      const nsAString& aScriptURL, const enum WorkerType& aWorkerType,
+      const RequestCredentials& aCredentials, bool aIsChromeWorker,
+      LoadGroupBehavior aLoadGroupBehavior, WorkerKind aWorkerKind,
+      WorkerLoadInfo* aLoadInfo);
+
+  void Traverse(nsCycleCollectionTraversalCallback& aCb);
+
+  void ClearSelfAndParentEventTargetRef() {
+    AssertIsOnParentThread();
+    MOZ_ASSERT(mSelfRef);
+
+    if (mTerminationCallback) {
+      mTerminationCallback();
+      mTerminationCallback = nullptr;
+    }
+
+    mParentEventTargetRef = nullptr;
+    mSelfRef = nullptr;
+  }
+
+  // May be called on any thread...
+  bool Start();
+
+  // Called on the parent thread.
+  bool Notify(WorkerStatus aStatus);
+
+  bool Cancel() { return Notify(Canceling); }
+
+  bool Close() MOZ_REQUIRES(mMutex);
+
+  // The passed principal must be the Worker principal in case of a
+  // ServiceWorker and the loading principal for any other type.
+  static void OverrideLoadInfoLoadGroup(WorkerLoadInfo& aLoadInfo,
+                                        nsIPrincipal* aPrincipal);
+
+  bool IsDebuggerRegistered() MOZ_NO_THREAD_SAFETY_ANALYSIS {
+    AssertIsOnMainThread();
+
+    // No need to lock here since this is only ever modified by the same thread.
+    return mDebuggerRegistered;  // would give a thread-safety warning
+  }
+
+  bool ExtensionAPIAllowed() {
+    return (
+        StaticPrefs::extensions_backgroundServiceWorker_enabled_AtStartup() &&
+        mExtensionAPIAllowed);
+  }
+
+  void SetIsDebuggerRegistered(bool aDebuggerRegistered) {
+    AssertIsOnMainThread();
+
+    MutexAutoLock lock(mMutex);
+
+    MOZ_ASSERT(mDebuggerRegistered != aDebuggerRegistered);
+    mDebuggerRegistered = aDebuggerRegistered;
+
+    mCondVar.Notify();
+  }
+
+  void WaitForIsDebuggerRegistered(bool aDebuggerRegistered) {
+    AssertIsOnParentThread();
+
+    // Yield so that the main thread won't be blocked.
+    AutoYieldJSThreadExecution yield;
+
+    MOZ_ASSERT(!NS_IsMainThread());
+
+    MutexAutoLock lock(mMutex);
+
+    while (mDebuggerRegistered != aDebuggerRegistered) {
+      mCondVar.Wait();
+    }
+  }
+
+  nsresult SetIsDebuggerReady(bool aReady);
+
+  WorkerDebugger* Debugger() const {
+    AssertIsOnMainThread();
+
+    MOZ_ASSERT(mDebugger);
+    return mDebugger;
+  }
+
+  const OriginTrials& Trials() const { return mLoadInfo.mTrials; }
+
+  void SetDebugger(WorkerDebugger* aDebugger) {
+    AssertIsOnMainThread();
+
+    MOZ_ASSERT(mDebugger != aDebugger);
+    mDebugger = aDebugger;
+  }
+
+  JS::UniqueChars AdoptDefaultLocale() {
+    MOZ_ASSERT(mDefaultLocale,
+               "the default locale must have been successfully set for anyone "
+               "to be trying to adopt it");
+    return std::move(mDefaultLocale);
+  }
+
+  /**
+   * Invoked by WorkerThreadPrimaryRunnable::Run if it already called
+   * SetWorkerPrivateInWorkerThread but has to bail out on initialization before
+   * calling DoRunLoop because PBackground failed to initialize or something
+   * like that.  Note that there's currently no point earlier than this that
+   * failure can be reported.
+   *
+   * When this happens, the worker will need to be deleted, plus the call to
+   * SetWorkerPrivateInWorkerThread will have scheduled all the
+   * mPreStartRunnables which need to be cleaned up after, as well as any
+   * scheduled control runnables.  We're somewhat punting on debugger runnables
+   * for now, which may leak, but the intent is to moot this whole scenario via
+   * shutdown blockers, so we don't want the extra complexity right now.
+   */
+  void RunLoopNeverRan();
+
+  MOZ_CAN_RUN_SCRIPT
+  void DoRunLoop(JSContext* aCx);
+
+  void UnrootGlobalScopes();
+
+  bool InterruptCallback(JSContext* aCx);
+
+  bool IsOnCurrentThread();
+
+  void CloseInternal();
+
+  bool FreezeInternal();
+
+  bool ThawInternal();
+
+  void PropagateStorageAccessPermissionGrantedInternal();
+
+  void TraverseTimeouts(nsCycleCollectionTraversalCallback& aCallback);
+
+  void UnlinkTimeouts();
+
+  bool AddChildWorker(WorkerPrivate& aChildWorker);
+
+  void RemoveChildWorker(WorkerPrivate& aChildWorker);
+
+  void PostMessageToParent(JSContext* aCx, JS::Handle<JS::Value> aMessage,
+                           const Sequence<JSObject*>& aTransferable,
+                           ErrorResult& aRv);
+
+  void PostMessageToParentMessagePort(JSContext* aCx,
+                                      JS::Handle<JS::Value> aMessage,
+                                      const Sequence<JSObject*>& aTransferable,
+                                      ErrorResult& aRv);
+
+  MOZ_CAN_RUN_SCRIPT void EnterDebuggerEventLoop();
+
+  void LeaveDebuggerEventLoop();
+
+  void PostMessageToDebugger(const nsAString& aMessage);
+
+  void SetDebuggerImmediate(Function& aHandler, ErrorResult& aRv);
+
+  void ReportErrorToDebugger(const nsAString& aFilename, uint32_t aLineno,
+                             const nsAString& aMessage);
+
+  bool NotifyInternal(WorkerStatus aStatus);
+
+  void ReportError(JSContext* aCx, JS::ConstUTF8CharsZ aToStringResult,
+                   JSErrorReport* aReport);
+
+  static void ReportErrorToConsole(const char* aMessage);
+
+  static void ReportErrorToConsole(const char* aMessage,
+                                   const nsTArray<nsString>& aParams);
+
+  int32_t SetTimeout(JSContext* aCx, TimeoutHandler* aHandler, int32_t aTimeout,
+                     bool aIsInterval, Timeout::Reason aReason,
+                     ErrorResult& aRv);
+
+  void ClearTimeout(int32_t aId, Timeout::Reason aReason);
+
+  MOZ_CAN_RUN_SCRIPT bool RunExpiredTimeouts(JSContext* aCx);
+
+  bool RescheduleTimeoutTimer(JSContext* aCx);
+
+  void UpdateContextOptionsInternal(JSContext* aCx,
+                                    const JS::ContextOptions& aContextOptions);
+
+  void UpdateLanguagesInternal(const nsTArray<nsString>& aLanguages);
+
+  void UpdateJSWorkerMemoryParameterInternal(JSContext* aCx, JSGCParamKey key,
+                                             Maybe<uint32_t> aValue);
+
+  enum WorkerRanOrNot { WorkerNeverRan = 0, WorkerRan };
+
+  void ScheduleDeletion(WorkerRanOrNot aRanOrNot);
+
+  bool CollectRuntimeStats(JS::RuntimeStats* aRtStats, bool aAnonymize);
+
+#ifdef JS_GC_ZEAL
+  void UpdateGCZealInternal(JSContext* aCx, uint8_t aGCZeal,
+                            uint32_t aFrequency);
+#endif
+
+  void SetLowMemoryStateInternal(JSContext* aCx, bool aState);
+
+  void GarbageCollectInternal(JSContext* aCx, bool aShrinking,
+                              bool aCollectChildren);
+
+  void CycleCollectInternal(bool aCollectChildren);
+
+  void OfflineStatusChangeEventInternal(bool aIsOffline);
+
+  void MemoryPressureInternal();
+
+  typedef MozPromise<uint64_t, nsresult, true> JSMemoryUsagePromise;
+  RefPtr<JSMemoryUsagePromise> GetJSMemoryUsage();
+
+  void SetFetchHandlerWasAdded() {
+    MOZ_ASSERT(IsServiceWorker());
+    AssertIsOnWorkerThread();
+    mFetchHandlerWasAdded = true;
+  }
+
+  bool FetchHandlerWasAdded() const {
+    MOZ_ASSERT(IsServiceWorker());
+    AssertIsOnWorkerThread();
+    return mFetchHandlerWasAdded;
+  }
+
+  JSContext* GetJSContext() const MOZ_NO_THREAD_SAFETY_ANALYSIS {
+    // mJSContext is only modified on the worker thread, so workerthread code
+    // can safely read it without a lock
+    AssertIsOnWorkerThread();
+    return mJSContext;
+  }
+
+  WorkerGlobalScope* GlobalScope() const {
+    auto data = mWorkerThreadAccessible.Access();
+    return data->mScope;
+  }
+
+  WorkerDebuggerGlobalScope* DebuggerGlobalScope() const {
+    auto data = mWorkerThreadAccessible.Access();
+    return data->mDebuggerScope;
+  }
+
+  // Get the global associated with the current nested event loop.  Will return
+  // null if we're not in a nested event loop or that nested event loop does not
+  // have an associated global.
+  nsIGlobalObject* GetCurrentEventLoopGlobal() const {
+    auto data = mWorkerThreadAccessible.Access();
+    return data->mCurrentEventLoopGlobal;
+  }
+
+  nsICSPEventListener* CSPEventListener() const;
+
+  void SetThread(WorkerThread* aThread);
+
+  void SetWorkerPrivateInWorkerThread(WorkerThread* aThread);
+
+  void ResetWorkerPrivateInWorkerThread();
+
+  bool IsOnWorkerThread() const;
+
+  void AssertIsOnWorkerThread() const
+#ifdef DEBUG
+      ;
+#else
+  {
+  }
+#endif
+
+  // This may block!
+  void BeginCTypesCall();
+
+  // This may block!
+  void EndCTypesCall();
+
+  void BeginCTypesCallback();
+
+  void EndCTypesCallback();
+
+  bool ConnectMessagePort(JSContext* aCx, UniqueMessagePortId& aIdentifier);
+
+  WorkerGlobalScope* GetOrCreateGlobalScope(JSContext* aCx);
+
+  WorkerDebuggerGlobalScope* CreateDebuggerGlobalScope(JSContext* aCx);
+
+  bool RegisterBindings(JSContext* aCx, JS::Handle<JSObject*> aGlobal);
+
+  bool RegisterDebuggerBindings(JSContext* aCx, JS::Handle<JSObject*> aGlobal);
+
+  bool OnLine() const {
+    auto data = mWorkerThreadAccessible.Access();
+    return data->mOnLine;
+  }
+
+  void StopSyncLoop(nsIEventTarget* aSyncLoopTarget, nsresult aResult);
+
+  bool MaybeStopSyncLoop(nsIEventTarget* aSyncLoopTarget, nsresult aResult);
+
+  void ShutdownModuleLoader();
+
+  void ClearPreStartRunnables();
+
+  void ClearDebuggerEventQueue();
+
+  void OnProcessNextEvent();
+
+  void AfterProcessNextEvent();
+
+  void AssertValidSyncLoop(nsIEventTarget* aSyncLoopTarget)
+#ifdef DEBUG
+      ;
+#else
+  {
+  }
+#endif
+
+  void AssertIsNotPotentiallyLastGCCCRunning() {
+#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
+    auto data = mWorkerThreadAccessible.Access();
+    MOZ_DIAGNOSTIC_ASSERT(!data->mIsPotentiallyLastGCCCRunning);
+#endif
+  }
+
+  void SetWorkerScriptExecutedSuccessfully() {
+    AssertIsOnWorkerThread();
+    // Should only be called once!
+    MOZ_ASSERT(!mWorkerScriptExecutedSuccessfully);
+    mWorkerScriptExecutedSuccessfully = true;
+  }
+
+  // Only valid after CompileScriptRunnable has finished running!
+  bool WorkerScriptExecutedSuccessfully() const {
+    AssertIsOnWorkerThread();
+    return mWorkerScriptExecutedSuccessfully;
+  }
+
+  // Get the event target to use when dispatching to the main thread
+  // from this Worker thread.  This may be the main thread itself or
+  // a ThrottledEventQueue to the main thread.
+  nsISerialEventTarget* MainThreadEventTargetForMessaging();
+
+  nsresult DispatchToMainThreadForMessaging(
+      nsIRunnable* aRunnable, uint32_t aFlags = NS_DISPATCH_NORMAL);
+
+  nsresult DispatchToMainThreadForMessaging(
+      already_AddRefed<nsIRunnable> aRunnable,
+      uint32_t aFlags = NS_DISPATCH_NORMAL);
+
+  nsISerialEventTarget* MainThreadEventTarget();
+
+  nsresult DispatchToMainThread(nsIRunnable* aRunnable,
+                                uint32_t aFlags = NS_DISPATCH_NORMAL);
+
+  nsresult DispatchToMainThread(already_AddRefed<nsIRunnable> aRunnable,
+                                uint32_t aFlags = NS_DISPATCH_NORMAL);
+
+  nsresult DispatchDebuggeeToMainThread(
+      already_AddRefed<WorkerDebuggeeRunnable> aRunnable,
+      uint32_t aFlags = NS_DISPATCH_NORMAL);
+
+  // Get an event target that will dispatch runnables as control runnables on
+  // the worker thread.  Implement nsICancelableRunnable if you wish to take
+  // action on cancelation.
+  nsISerialEventTarget* ControlEventTarget();
+
+  // Get an event target that will attempt to dispatch a normal WorkerRunnable,
+  // but if that fails will then fall back to a control runnable.
+  nsISerialEventTarget* HybridEventTarget();
+
+  void DumpCrashInformation(nsACString& aString);
+
+  ClientType GetClientType() const;
+
+  bool EnsureCSPEventListener();
+
+  void EnsurePerformanceStorage();
+
+  bool GetExecutionGranted() const;
+  void SetExecutionGranted(bool aGranted);
+
+  void ScheduleTimeSliceExpiration(uint32_t aDelay);
+  void CancelTimeSliceExpiration();
+
+  JSExecutionManager* GetExecutionManager() const;
+  void SetExecutionManager(JSExecutionManager* aManager);
+
+  void ExecutionReady();
+
+  PerformanceStorage* GetPerformanceStorage();
+
+  bool IsAcceptingEvents() MOZ_EXCLUDES(mMutex) {
+    AssertIsOnParentThread();
+
+    MutexAutoLock lock(mMutex);
+    return mParentStatus < Canceling;
+  }
+
+  WorkerStatus ParentStatusProtected() {
+    AssertIsOnParentThread();
+    MutexAutoLock lock(mMutex);
+    return mParentStatus;
+  }
+
+  WorkerStatus ParentStatus() const MOZ_REQUIRES(mMutex) {
+    mMutex.AssertCurrentThreadOwns();
+    return mParentStatus;
+  }
+
+  Worker* ParentEventTargetRef() const {
+    MOZ_DIAGNOSTIC_ASSERT(mParentEventTargetRef);
+    return mParentEventTargetRef;
+  }
+
+  void SetParentEventTargetRef(Worker* aParentEventTargetRef) {
+    MOZ_DIAGNOSTIC_ASSERT(aParentEventTargetRef);
+    MOZ_DIAGNOSTIC_ASSERT(!mParentEventTargetRef);
+    mParentEventTargetRef = aParentEventTargetRef;
+  }
+
+  // Check whether this worker is a secure context.  For use from the parent
+  // thread only; the canonical "is secure context" boolean is stored on the
+  // compartment of the worker global.  The only reason we don't
+  // AssertIsOnParentThread() here is so we can assert that this value matches
+  // the one on the compartment, which has to be done from the worker thread.
+  bool IsSecureContext() const { return mIsSecureContext; }
+
+  // Check whether we're running in automation.
+  bool IsInAutomation() const { return mIsInAutomation; }
+
+  bool IsPrivilegedAddonGlobal() const { return mIsPrivilegedAddonGlobal; }
+
+  TimeStamp CreationTimeStamp() const { return mCreationTimeStamp; }
+
+  DOMHighResTimeStamp CreationTime() const { return mCreationTimeHighRes; }
+
+  DOMHighResTimeStamp TimeStampToDOMHighRes(const TimeStamp& aTimeStamp) const {
+    MOZ_ASSERT(!aTimeStamp.IsNull());
+    TimeDuration duration = aTimeStamp - mCreationTimeStamp;
+    return duration.ToMilliseconds();
+  }
+
+  LocationInfo& GetLocationInfo() { return mLocationInfo; }
+
+  void CopyJSSettings(workerinternals::JSSettings& aSettings) {
+    mozilla::MutexAutoLock lock(mMutex);
+    aSettings = mJSSettings;
+  }
+
+  void CopyJSRealmOptions(JS::RealmOptions& aOptions) {
+    mozilla::MutexAutoLock lock(mMutex);
+    aOptions = IsChromeWorker() ? mJSSettings.chromeRealmOptions
+                                : mJSSettings.contentRealmOptions;
+  }
+
+  // The ability to be a chrome worker is orthogonal to the type of
+  // worker [Dedicated|Shared|Service].
+  bool IsChromeWorker() const { return mIsChromeWorker; }
+
+  // TODO: Invariants require that the parent worker out-live any child
+  // worker, so WorkerPrivate* should be safe in the moment of calling.
+  // We would like to have stronger type-system annotated/enforced handling.
+  WorkerPrivate* GetParent() const { return mParent; }
+
+  bool IsFrozen() const {
+    AssertIsOnParentThread();
+    return mParentFrozen;
+  }
+
+  bool IsParentWindowPaused() const {
+    AssertIsOnParentThread();
+    return mParentWindowPaused;
+  }
+
+  // When we debug a worker, we want to disconnect the window and the worker
+  // communication. This happens calling this method.
+  // Note: this method doesn't suspend the worker! Use Freeze/Thaw instead.
+  void ParentWindowPaused();
+
+  void ParentWindowResumed();
+
+  const nsString& ScriptURL() const { return mScriptURL; }
+
+  const nsString& WorkerName() const { return mWorkerName; }
+  RequestCredentials WorkerCredentials() const { return mCredentialsMode; }
+  enum WorkerType WorkerType() const { return mWorkerType; }
+
+  WorkerKind Kind() const { return mWorkerKind; }
+
+  bool IsDedicatedWorker() const { return mWorkerKind == WorkerKindDedicated; }
+
+  bool IsSharedWorker() const { return mWorkerKind == WorkerKindShared; }
+
+  bool IsServiceWorker() const { return mWorkerKind == WorkerKindService; }
+
+  nsContentPolicyType ContentPolicyType() const {
+    return ContentPolicyType(mWorkerKind);
+  }
+
+  static nsContentPolicyType ContentPolicyType(WorkerKind aWorkerKind) {
+    switch (aWorkerKind) {
+      case WorkerKindDedicated:
+        return nsIContentPolicy::TYPE_INTERNAL_WORKER;
+      case WorkerKindShared:
+        return nsIContentPolicy::TYPE_INTERNAL_SHARED_WORKER;
+      case WorkerKindService:
+        return nsIContentPolicy::TYPE_INTERNAL_SERVICE_WORKER;
+      default:
+        MOZ_ASSERT_UNREACHABLE("Invalid worker type");
+        return nsIContentPolicy::TYPE_INVALID;
+    }
+  }
+
+  nsIScriptContext* GetScriptContext() const {
+    AssertIsOnMainThread();
+    return mLoadInfo.mScriptContext;
+  }
+
+  const nsCString& Domain() const { return mLoadInfo.mDomain; }
+
+  bool IsFromWindow() const { return mLoadInfo.mFromWindow; }
+
+  nsLoadFlags GetLoadFlags() const { return mLoadInfo.mLoadFlags; }
+
+  uint64_t WindowID() const { return mLoadInfo.mWindowID; }
+
+  uint64_t AssociatedBrowsingContextID() const {
+    return mLoadInfo.mAssociatedBrowsingContextID;
+  }
+
+  uint64_t ServiceWorkerID() const { return GetServiceWorkerDescriptor().Id(); }
+
+  const nsCString& ServiceWorkerScope() const {
+    return GetServiceWorkerDescriptor().Scope();
+  }
+
+  // This value should never change after the script load completes. Before
+  // then, it may only be called on the main thread.
+  nsIURI* GetBaseURI() const { return mLoadInfo.mBaseURI; }
+
+  void SetBaseURI(nsIURI* aBaseURI);
+
+  nsIURI* GetResolvedScriptURI() const { return mLoadInfo.mResolvedScriptURI; }
+
+  const nsString& ServiceWorkerCacheName() const {
+    MOZ_DIAGNOSTIC_ASSERT(IsServiceWorker());
+    AssertIsOnMainThread();
+    return mLoadInfo.mServiceWorkerCacheName;
+  }
+
+  const ServiceWorkerDescriptor& GetServiceWorkerDescriptor() const {
+    MOZ_DIAGNOSTIC_ASSERT(IsServiceWorker());
+    MOZ_DIAGNOSTIC_ASSERT(mLoadInfo.mServiceWorkerDescriptor.isSome());
+    return mLoadInfo.mServiceWorkerDescriptor.ref();
+  }
+
+  const ServiceWorkerRegistrationDescriptor&
+  GetServiceWorkerRegistrationDescriptor() const {
+    MOZ_DIAGNOSTIC_ASSERT(IsServiceWorker());
+    MOZ_DIAGNOSTIC_ASSERT(
+        mLoadInfo.mServiceWorkerRegistrationDescriptor.isSome());
+    return mLoadInfo.mServiceWorkerRegistrationDescriptor.ref();
+  }
+
+  void UpdateServiceWorkerState(ServiceWorkerState aState) {
+    MOZ_DIAGNOSTIC_ASSERT(IsServiceWorker());
+    MOZ_DIAGNOSTIC_ASSERT(mLoadInfo.mServiceWorkerDescriptor.isSome());
+    return mLoadInfo.mServiceWorkerDescriptor.ref().SetState(aState);
+  }
+
+  const Maybe<ServiceWorkerDescriptor>& GetParentController() const {
+    return mLoadInfo.mParentController;
+  }
+
+  const ChannelInfo& GetChannelInfo() const { return mLoadInfo.mChannelInfo; }
+
+  void SetChannelInfo(const ChannelInfo& aChannelInfo) {
+    AssertIsOnMainThread();
+    MOZ_ASSERT(!mLoadInfo.mChannelInfo.IsInitialized());
+    MOZ_ASSERT(aChannelInfo.IsInitialized());
+    mLoadInfo.mChannelInfo = aChannelInfo;
+  }
+
+  void InitChannelInfo(nsIChannel* aChannel) {
+    mLoadInfo.mChannelInfo.InitFromChannel(aChannel);
+  }
+
+  void InitChannelInfo(const ChannelInfo& aChannelInfo) {
+    mLoadInfo.mChannelInfo = aChannelInfo;
+  }
+
+  nsIPrincipal* GetPrincipal() const { return mLoadInfo.mPrincipal; }
+
+  nsIPrincipal* GetLoadingPrincipal() const {
+    return mLoadInfo.mLoadingPrincipal;
+  }
+
+  nsIPrincipal* GetPartitionedPrincipal() const {
+    return mLoadInfo.mPartitionedPrincipal;
+  }
+
+  nsIPrincipal* GetEffectiveStoragePrincipal() const;
+
+  nsILoadGroup* GetLoadGroup() const {
+    AssertIsOnMainThread();
+    return mLoadInfo.mLoadGroup;
+  }
+
+  bool UsesSystemPrincipal() const {
+    return GetPrincipal()->IsSystemPrincipal();
+  }
+  bool UsesAddonOrExpandedAddonPrincipal() const {
+    return GetPrincipal()->GetIsAddonOrExpandedAddonPrincipal();
+  }
+
+  const mozilla::ipc::PrincipalInfo& GetPrincipalInfo() const {
+    return *mLoadInfo.mPrincipalInfo;
+  }
+
+  const mozilla::ipc::PrincipalInfo& GetPartitionedPrincipalInfo() const {
+    return *mLoadInfo.mPartitionedPrincipalInfo;
+  }
+
+  const mozilla::ipc::PrincipalInfo& GetEffectiveStoragePrincipalInfo() const;
+
+  already_AddRefed<nsIChannel> ForgetWorkerChannel() {
+    AssertIsOnMainThread();
+    return mLoadInfo.mChannel.forget();
+  }
+
+  nsPIDOMWindowInner* GetWindow() const {
+    AssertIsOnMainThread();
+    return mLoadInfo.mWindow;
+  }
+
+  nsPIDOMWindowInner* GetAncestorWindow() const;
+
+  void EvictFromBFCache();
+
+  nsIContentSecurityPolicy* GetCsp() const {
+    AssertIsOnMainThread();
+    return mLoadInfo.mCSP;
+  }
+
+  void SetCsp(nsIContentSecurityPolicy* aCSP);
+
+  nsresult SetCSPFromHeaderValues(const nsACString& aCSPHeaderValue,
+                                  const nsACString& aCSPReportOnlyHeaderValue);
+
+  void StoreCSPOnClient();
+
+  const mozilla::ipc::CSPInfo& GetCSPInfo() const {
+    return *mLoadInfo.mCSPInfo;
+  }
+
+  void UpdateReferrerInfoFromHeader(
+      const nsACString& aReferrerPolicyHeaderValue);
+
+  nsIReferrerInfo* GetReferrerInfo() const { return mLoadInfo.mReferrerInfo; }
+
+  ReferrerPolicy GetReferrerPolicy() const {
+    return mLoadInfo.mReferrerInfo->ReferrerPolicy();
+  }
+
+  void SetReferrerInfo(nsIReferrerInfo* aReferrerInfo) {
+    mLoadInfo.mReferrerInfo = aReferrerInfo;
+  }
+
+  bool IsEvalAllowed() const { return mLoadInfo.mEvalAllowed; }
+
+  void SetEvalAllowed(bool aAllowed) { mLoadInfo.mEvalAllowed = aAllowed; }
+
+  bool GetReportEvalCSPViolations() const {
+    return mLoadInfo.mReportEvalCSPViolations;
+  }
+
+  void SetReportEvalCSPViolations(bool aReport) {
+    mLoadInfo.mReportEvalCSPViolations = aReport;
+  }
+
+  bool IsWasmEvalAllowed() const { return mLoadInfo.mWasmEvalAllowed; }
+
+  void SetWasmEvalAllowed(bool aAllowed) {
+    mLoadInfo.mWasmEvalAllowed = aAllowed;
+  }
+
+  bool GetReportWasmEvalCSPViolations() const {
+    return mLoadInfo.mReportWasmEvalCSPViolations;
+  }
+
+  void SetReportWasmEvalCSPViolations(bool aReport) {
+    mLoadInfo.mReportWasmEvalCSPViolations = aReport;
+  }
+
+  bool XHRParamsAllowed() const { return mLoadInfo.mXHRParamsAllowed; }
+
+  void SetXHRParamsAllowed(bool aAllowed) {
+    mLoadInfo.mXHRParamsAllowed = aAllowed;
+  }
+
+  mozilla::StorageAccess StorageAccess() const {
+    AssertIsOnWorkerThread();
+    if (mLoadInfo.mUsingStorageAccess) {
+      return mozilla::StorageAccess::eAllow;
+    }
+
+    return mLoadInfo.mStorageAccess;
+  }
+
+  bool UseRegularPrincipal() const {
+    AssertIsOnWorkerThread();
+    return mLoadInfo.mUseRegularPrincipal;
+  }
+
+  bool UsingStorageAccess() const {
+    AssertIsOnWorkerThread();
+    return mLoadInfo.mUsingStorageAccess;
+  }
+
+  nsICookieJarSettings* CookieJarSettings() const {
+    // Any thread.
+    MOZ_ASSERT(mLoadInfo.mCookieJarSettings);
+    return mLoadInfo.mCookieJarSettings;
+  }
+
+  const net::CookieJarSettingsArgs& CookieJarSettingsArgs() const {
+    MOZ_ASSERT(mLoadInfo.mCookieJarSettings);
+    return mLoadInfo.mCookieJarSettingsArgs;
+  }
+
+  const OriginAttributes& GetOriginAttributes() const {
+    return mLoadInfo.mOriginAttributes;
+  }
+
+  // Determine if the SW testing per-window flag is set by devtools
+  bool ServiceWorkersTestingInWindow() const {
+    return mLoadInfo.mServiceWorkersTestingInWindow;
+  }
+
+  // Determine if the worker was created under a third-party context.
+  bool IsThirdPartyContextToTopWindow() const {
+    return mLoadInfo.mIsThirdPartyContextToTopWindow;
+  }
+
+  bool IsWatchedByDevTools() const { return mLoadInfo.mWatchedByDevTools; }
+
+  bool ShouldResistFingerprinting(RFPTarget aTarget) const;
+
+  const Maybe<RFPTarget>& GetOverriddenFingerprintingSettings() const {
+    return mLoadInfo.mOverriddenFingerprintingSettings;
+  }
+
+  RemoteWorkerChild* GetRemoteWorkerController();
+
+  void SetRemoteWorkerController(RemoteWorkerChild* aController);
+
+  RefPtr<GenericPromise> SetServiceWorkerSkipWaitingFlag();
+
+  // We can assume that an nsPIDOMWindow will be available for Freeze, Thaw
+  // as these are only used for globals going in and out of the bfcache.
+  bool Freeze(const nsPIDOMWindowInner* aWindow);
+
+  bool Thaw(const nsPIDOMWindowInner* aWindow);
+
+  void PropagateStorageAccessPermissionGranted();
+
+  void EnableDebugger();
+
+  void DisableDebugger();
+
+  already_AddRefed<WorkerRunnable> MaybeWrapAsWorkerRunnable(
+      already_AddRefed<nsIRunnable> aRunnable);
+
+  bool ProxyReleaseMainThreadObjects();
+
+  void SetLowMemoryState(bool aState);
+
+  void GarbageCollect(bool aShrinking);
+
+  void CycleCollect();
+
+  nsresult SetPrincipalsAndCSPOnMainThread(nsIPrincipal* aPrincipal,
+                                           nsIPrincipal* aPartitionedPrincipal,
+                                           nsILoadGroup* aLoadGroup,
+                                           nsIContentSecurityPolicy* aCsp);
+
+  nsresult SetPrincipalsAndCSPFromChannel(nsIChannel* aChannel);
+
+  bool FinalChannelPrincipalIsValid(nsIChannel* aChannel);
+
+#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
+  bool PrincipalURIMatchesScriptURL();
+#endif
+
+  void UpdateOverridenLoadGroup(nsILoadGroup* aBaseLoadGroup);
+
+  void WorkerScriptLoaded();
+
+  Document* GetDocument() const;
+
+  void MemoryPressure();
+
+  void UpdateContextOptions(const JS::ContextOptions& aContextOptions);
+
+  void UpdateLanguages(const nsTArray<nsString>& aLanguages);
+
+  void UpdateJSWorkerMemoryParameter(JSGCParamKey key, Maybe<uint32_t> value);
+
+#ifdef JS_GC_ZEAL
+  void UpdateGCZeal(uint8_t aGCZeal, uint32_t aFrequency);
+#endif
+
+  void OfflineStatusChangeEvent(bool aIsOffline);
+
+  nsresult Dispatch(already_AddRefed<WorkerRunnable> aRunnable,
+                    nsIEventTarget* aSyncLoopTarget = nullptr);
+
+  nsresult DispatchControlRunnable(
+      already_AddRefed<WorkerControlRunnable> aWorkerControlRunnable);
+
+  nsresult DispatchDebuggerRunnable(
+      already_AddRefed<WorkerRunnable> aDebuggerRunnable);
+
+  bool IsOnParentThread() const;
+
+#ifdef DEBUG
+  void AssertIsOnParentThread() const;
+
+  void AssertInnerWindowIsCorrect() const;
+#else
+  void AssertIsOnParentThread() const {}
+
+  void AssertInnerWindowIsCorrect() const {}
+#endif
+
+#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
+  bool PrincipalIsValid() const;
+#endif
+
+  void StartCancelingTimer();
+
+  const nsAString& Id();
+
+  const nsID& AgentClusterId() const { return mAgentClusterId; }
+
+  bool IsSharedMemoryAllowed() const;
+
+  // https://whatpr.org/html/4734/structured-data.html#cross-origin-isolated
+  bool CrossOriginIsolated() const;
+
+  void SetUseCounter(UseCounterWorker aUseCounter) {
+    MOZ_ASSERT(!mReportedUseCounters);
+    MOZ_ASSERT(aUseCounter > UseCounterWorker::Unknown);
+    AssertIsOnWorkerThread();
+    mUseCounters[static_cast<size_t>(aUseCounter)] = true;
+  }
+
+  /**
+   * COEP Methods
+   *
+   * If browser.tabs.remote.useCrossOriginEmbedderPolicy=false, these methods
+   * will, depending on the return type, return a value that will avoid
+   * assertion failures or a value that won't block loads.
+   */
+  nsILoadInfo::CrossOriginEmbedderPolicy GetEmbedderPolicy() const;
+
+  // Fails if a policy has already been set or if `aPolicy` violates the owner's
+  // policy, if an owner exists.
+  mozilla::Result<Ok, nsresult> SetEmbedderPolicy(
+      nsILoadInfo::CrossOriginEmbedderPolicy aPolicy);
+
+  // `aRequest` is the request loading the worker and must be QI-able to
+  // `nsIChannel*`. It's used to verify that the worker can indeed inherit its
+  // owner's COEP (when an owner exists).
+  //
+  // TODO: remove `aRequest`; currently, it's required because instances may not
+  // always know its final, resolved script URL or have access internally to
+  // `aRequest`.
+  void InheritOwnerEmbedderPolicyOrNull(nsIRequest* aRequest);
+
+  // Requires a policy to already have been set.
+  bool MatchEmbedderPolicy(
+      nsILoadInfo::CrossOriginEmbedderPolicy aPolicy) const;
+
+  nsILoadInfo::CrossOriginEmbedderPolicy GetOwnerEmbedderPolicy() const;
+
+  void SetCCCollectedAnything(bool collectedAnything);
+  bool isLastCCCollectedAnything();
+
+  uint32_t GetCurrentTimerNestingLevel() const {
+    auto data = mWorkerThreadAccessible.Access();
+    return data->mCurrentTimerNestingLevel;
+  }
+
+  void IncreaseTopLevelWorkerFinishedRunnableCount() {
+    ++mTopLevelWorkerFinishedRunnableCount;
+  }
+  void DecreaseTopLevelWorkerFinishedRunnableCount() {
+    --mTopLevelWorkerFinishedRunnableCount;
+  }
+  void IncreaseWorkerFinishedRunnableCount() { ++mWorkerFinishedRunnableCount; }
+  void DecreaseWorkerFinishedRunnableCount() { --mWorkerFinishedRunnableCount; }
+
+  void RunShutdownTasks();
+
+  bool CancelBeforeWorkerScopeConstructed() const {
+    auto data = mWorkerThreadAccessible.Access();
+    return data->mCancelBeforeWorkerScopeConstructed;
+  }
+
+  enum class CCFlag : uint8_t {
+    EligibleForWorkerRef,
+    IneligibleForWorkerRef,
+    EligibleForChildWorker,
+    IneligibleForChildWorker,
+    EligibleForTimeout,
+    IneligibleForTimeout,
+    CheckBackgroundActors,
+  };
+
+  // When create/release a StrongWorkerRef, child worker, and timeout, this
+  // method is used to setup if mParentEventTargetRef can get into
+  // cycle-collection.
+  // When this method is called, it will also checks if any background actor
+  // should block the mParentEventTargetRef cycle-collection when there is no
+  // StrongWorkerRef/ChildWorker/Timeout.
+  // Worker thread only.
+  void UpdateCCFlag(const CCFlag);
+
+  // This is used in WorkerPrivate::Traverse() to checking if
+  // mParentEventTargetRef should get into cycle-collection.
+  // Parent thread only method.
+  bool IsEligibleForCC();
+
+  // A method which adjusts the count of background actors which should not
+  // block WorkerPrivate::mParentEventTargetRef cycle-collection.
+  // Worker thread only.
+  void AdjustNonblockingCCBackgroundActorCount(int32_t aCount);
+
+ private:
+  WorkerPrivate(
+      WorkerPrivate* aParent, const nsAString& aScriptURL, bool aIsChromeWorker,
+      WorkerKind aWorkerKind, RequestCredentials aRequestCredentials,
+      enum WorkerType aWorkerType, const nsAString& aWorkerName,
+      const nsACString& aServiceWorkerScope, WorkerLoadInfo& aLoadInfo,
+      nsString&& aId, const nsID& aAgentClusterId,
+      const nsILoadInfo::CrossOriginOpenerPolicy aAgentClusterOpenerPolicy,
+      CancellationCallback&& aCancellationCallback,
+      TerminationCallback&& aTerminationCallback);
+
+  ~WorkerPrivate();
+
+  struct AgentClusterIdAndCoop {
+    nsID mId;
+    nsILoadInfo::CrossOriginOpenerPolicy mCoop;
+  };
+
+  static AgentClusterIdAndCoop ComputeAgentClusterIdAndCoop(
+      WorkerPrivate* aParent, WorkerKind aWorkerKind,
+      WorkerLoadInfo* aLoadInfo);
+
+  bool MayContinueRunning() {
+    AssertIsOnWorkerThread();
+
+    WorkerStatus status;
+    {
+      MutexAutoLock lock(mMutex);
+      status = mStatus;
+    }
+
+    if (status < Canceling) {
+      return true;
+    }
+
+    return false;
+  }
+
+  void CancelAllTimeouts();
+
+  enum class ProcessAllControlRunnablesResult {
+    // We did not process anything.
+    Nothing,
+    // We did process something, states may have changed, but we can keep
+    // executing script.
+    MayContinue,
+    // We did process something, and should not continue executing script.
+    Abort
+  };
+
+  ProcessAllControlRunnablesResult ProcessAllControlRunnables() {
+    MutexAutoLock lock(mMutex);
+    return ProcessAllControlRunnablesLocked();
+  }
+
+  ProcessAllControlRunnablesResult ProcessAllControlRunnablesLocked()
+      MOZ_REQUIRES(mMutex);
+
+  void EnableMemoryReporter();
+
+  void DisableMemoryReporter();
+
+  void WaitForWorkerEvents() MOZ_REQUIRES(mMutex);
+
+  // If the worker shutdown status is equal or greater then aFailStatus, this
+  // operation will fail and nullptr will be returned. See WorkerStatus.h for
+  // more information about the correct value to use.
+  already_AddRefed<nsISerialEventTarget> CreateNewSyncLoop(
+      WorkerStatus aFailStatus);
+
+  nsresult RunCurrentSyncLoop();
+
+  nsresult DestroySyncLoop(uint32_t aLoopIndex);
+
+  void InitializeGCTimers();
+
+  enum GCTimerMode { PeriodicTimer = 0, IdleTimer, NoTimer };
+
+  void SetGCTimerMode(GCTimerMode aMode);
+
+ public:
+  void CancelGCTimers() { SetGCTimerMode(NoTimer); }
+
+ private:
+  void ShutdownGCTimers();
+
+  friend class WorkerRef;
+
+  bool AddWorkerRef(WorkerRef* aWorkerRefer, WorkerStatus aFailStatus);
+
+  void RemoveWorkerRef(WorkerRef* aWorkerRef);
+
+  void NotifyWorkerRefs(WorkerStatus aStatus);
+
+  bool HasActiveWorkerRefs() {
+    auto data = mWorkerThreadAccessible.Access();
+    return !(data->mChildWorkers.IsEmpty() && data->mTimeouts.IsEmpty() &&
+             data->mWorkerRefs.IsEmpty());
+  }
+
+  friend class WorkerEventTarget;
+
+  nsresult RegisterShutdownTask(nsITargetShutdownTask* aTask);
+
+  nsresult UnregisterShutdownTask(nsITargetShutdownTask* aTask);
+
+  // Internal logic to dispatch a runnable. This is separate from Dispatch()
+  // to allow runnables to be atomically dispatched in bulk.
+  nsresult DispatchLockHeld(already_AddRefed<WorkerRunnable> aRunnable,
+                            nsIEventTarget* aSyncLoopTarget,
+                            const MutexAutoLock& aProofOfLock)
+      MOZ_REQUIRES(mMutex);
+
+  // This method dispatches a simple runnable that starts the shutdown procedure
+  // after a self.close(). This method is called after a ClearMainEventQueue()
+  // to be sure that the canceling runnable is the only one in the queue.  We
+  // need this async operation to be sure that all the current JS code is
+  // executed.
+  void DispatchCancelingRunnable();
+
+  bool GetUseCounter(UseCounterWorker aUseCounter) {
+    MOZ_ASSERT(aUseCounter > UseCounterWorker::Unknown);
+    AssertIsOnWorkerThread();
+    return mUseCounters[static_cast<size_t>(aUseCounter)];
+  }
+
+  void ReportUseCounters();
+
+  UniquePtr<ClientSource> CreateClientSource();
+
+  // This method is called when corresponding script loader processes the COEP
+  // header for the worker.
+  // This method should be called only once in the main thread.
+  // After this method is called the COEP value owner(window/parent worker) is
+  // cached in mOwnerEmbedderPolicy such that it can be accessed in other
+  // threads, i.e. WorkerThread.
+  void EnsureOwnerEmbedderPolicy();
+
+  class EventTarget;
+  friend class EventTarget;
+  friend class AutoSyncLoopHolder;
+
+  struct TimeoutInfo;
+
+  class MemoryReporter;
+  friend class MemoryReporter;
+
+  friend class mozilla::dom::WorkerThread;
+
+  SharedMutex mMutex;
+  mozilla::CondVar mCondVar MOZ_GUARDED_BY(mMutex);
+
+  // We cannot make this CheckedUnsafePtr<WorkerPrivate> as this would violate
+  // our static assert
+  MOZ_NON_OWNING_REF WorkerPrivate* const mParent;
+
+  const nsString mScriptURL;
+
+  // This is the worker name for shared workers and dedicated workers.
+  const nsString mWorkerName;
+  const RequestCredentials mCredentialsMode;
+  enum WorkerType mWorkerType;
+
+  const WorkerKind mWorkerKind;
+
+  // The worker is owned by its thread, which is represented here.  This is set
+  // in Constructor() and emptied by WorkerFinishedRunnable, and conditionally
+  // traversed by the cycle collector if no other things preventing shutdown.
+  //
+  // There are 4 ways a worker can be terminated:
+  // 1. GC/CC - When the worker is in idle state (busycount == 0), it allows to
+  //    traverse the 'hidden' mParentEventTargetRef pointer. This is the exposed
+  //    Worker webidl object. Doing this, CC will be able to detect a cycle and
+  //    Unlink is called. In Unlink, Worker calls Cancel().
+  // 2. Worker::Cancel() is called - the shutdown procedure starts immediately.
+  // 3. WorkerScope::Close() is called - Similar to point 2.
+  // 4. xpcom-shutdown notification - We call Kill().
+  RefPtr<Worker> mParentEventTargetRef;
+  RefPtr<WorkerPrivate> mSelfRef;
+
+  CancellationCallback mCancellationCallback;
+
+  // The termination callback is passed into the constructor on the parent
+  // thread and invoked by `ClearSelfAndParentEventTargetRef` just before it
+  // drops its self-ref.
+  TerminationCallback mTerminationCallback;
+
+  // The lifetime of these objects within LoadInfo is managed explicitly;
+  // they do not need to be cycle collected.
+  WorkerLoadInfo mLoadInfo;
+  LocationInfo mLocationInfo;
+
+  // Protected by mMutex.
+  workerinternals::JSSettings mJSSettings MOZ_GUARDED_BY(mMutex);
+
+  WorkerDebugger* mDebugger;
+
+  workerinternals::Queue<WorkerControlRunnable*, 4> mControlQueue;
+  workerinternals::Queue<WorkerRunnable*, 4> mDebuggerQueue;
+
+  // Touched on multiple threads, protected with mMutex. Only modified on the
+  // worker thread
+  JSContext* mJSContext MOZ_GUARDED_BY(mMutex);
+  // mThread is only modified on the Worker thread, before calling DoRunLoop
+  RefPtr<WorkerThread> mThread MOZ_GUARDED_BY(mMutex);
+  // mPRThread is only modified on another thread in ScheduleWorker(), and is
+  // constant for the duration of DoRunLoop.  Static mutex analysis doesn't help
+  // here
+  PRThread* mPRThread;
+
+  // Accessed from main thread
+  RefPtr<ThrottledEventQueue> mMainThreadEventTargetForMessaging;
+  RefPtr<ThrottledEventQueue> mMainThreadEventTarget;
+
+  // Accessed from worker thread and destructing thread
+  RefPtr<WorkerEventTarget> mWorkerControlEventTarget;
+  RefPtr<WorkerEventTarget> mWorkerHybridEventTarget;
+
+  // A pauseable queue for WorkerDebuggeeRunnables directed at the main thread.
+  // See WorkerDebuggeeRunnable for details.
+  RefPtr<ThrottledEventQueue> mMainThreadDebuggeeEventTarget;
+
+  struct SyncLoopInfo {
+    explicit SyncLoopInfo(EventTarget* aEventTarget);
+
+    RefPtr<EventTarget> mEventTarget;
+    nsresult mResult;
+    bool mCompleted;
+#ifdef DEBUG
+    bool mHasRun;
+#endif
+  };
+
+  // This is only modified on the worker thread, but in DEBUG builds
+  // AssertValidSyncLoop function iterates it on other threads. Therefore
+  // modifications are done with mMutex held *only* in DEBUG builds.
+  nsTArray<UniquePtr<SyncLoopInfo>> mSyncLoopStack;
+
+  nsCOMPtr<nsITimer> mCancelingTimer;
+
+  // fired on the main thread if the worker script fails to load
+  nsCOMPtr<nsIRunnable> mLoadFailedRunnable;
+
+  RefPtr<PerformanceStorage> mPerformanceStorage;
+
+  RefPtr<WorkerCSPEventListener> mCSPEventListener;
+
+  // Protected by mMutex.
+  nsTArray<RefPtr<WorkerRunnable>> mPreStartRunnables MOZ_GUARDED_BY(mMutex);
+
+  // Only touched on the parent thread.  Used for both SharedWorker and
+  // ServiceWorker RemoteWorkers.
+  RefPtr<RemoteWorkerChild> mRemoteWorkerController;
+
+  JS::UniqueChars mDefaultLocale;  // nulled during worker JSContext init
+  TimeStamp mKillTime;
+  WorkerStatus mParentStatus MOZ_GUARDED_BY(mMutex);
+  WorkerStatus mStatus MOZ_GUARDED_BY(mMutex);
+
+  TimeStamp mCreationTimeStamp;
+  DOMHighResTimeStamp mCreationTimeHighRes;
+
+  // Flags for use counters used directly by this worker.
+  static_assert(sizeof(UseCounterWorker) <= sizeof(size_t),
+                "UseCounterWorker is too big");
+  static_assert(UseCounterWorker::Count >= static_cast<UseCounterWorker>(0),
+                "Should be non-negative value and safe to cast to unsigned");
+  std::bitset<static_cast<size_t>(UseCounterWorker::Count)> mUseCounters;
+  bool mReportedUseCounters;
+
+  // This is created while creating the WorkerPrivate, so it's safe to be
+  // touched on any thread.
+  const nsID mAgentClusterId;
+
+  // Things touched on worker thread only.
+  struct WorkerThreadAccessible {
+    explicit WorkerThreadAccessible(WorkerPrivate* aParent);
+
+    RefPtr<WorkerGlobalScope> mScope;
+    RefPtr<WorkerDebuggerGlobalScope> mDebuggerScope;
+    // We cannot make this CheckedUnsafePtr<WorkerPrivate> as this would violate
+    // our static assert
+    nsTArray<WorkerPrivate*> mChildWorkers;
+    nsTObserverArray<WorkerRef*> mWorkerRefs;
+    nsTArray<UniquePtr<TimeoutInfo>> mTimeouts;
+
+    nsCOMPtr<nsITimer> mTimer;
+    nsCOMPtr<nsITimerCallback> mTimerRunnable;
+
+    nsCOMPtr<nsITimer> mPeriodicGCTimer;
+    nsCOMPtr<nsITimer> mIdleGCTimer;
+
+    RefPtr<MemoryReporter> mMemoryReporter;
+
+    // While running a nested event loop, whether a sync loop or a debugger
+    // event loop we want to keep track of which global is running it, if any,
+    // so runnables that run off that event loop can get at that information. In
+    // practice this only matters for various worker debugger runnables running
+    // against sandboxes, because all other runnables know which globals they
+    // belong to already.  We could also address this by threading the relevant
+    // global through the chains of runnables involved, but we'd need to thread
+    // it through some runnables that run on the main thread, and that would
+    // require some care to make sure things get released on the correct thread,
+    // which we'd rather avoid.  This member is only accessed on the worker
+    // thread.
+    nsCOMPtr<nsIGlobalObject> mCurrentEventLoopGlobal;
+
+    // Timer that triggers an interrupt on expiration of the current time slice
+    nsCOMPtr<nsITimer> mTSTimer;
+
+    // Execution manager used to regulate execution for this worker.
+    RefPtr<JSExecutionManager> mExecutionManager;
+
+    // Used to relinguish clearance for CTypes Callbacks.
+    nsTArray<AutoYieldJSThreadExecution> mYieldJSThreadExecution;
+
+    uint32_t mNumWorkerRefsPreventingShutdownStart;
+    uint32_t mDebuggerEventLoopLevel;
+
+    // This is the count of background actors that binding with IPCWorkerRefs.
+    // This count would be used in WorkerPrivate::UpdateCCFlag for checking if
+    // CC should be blocked by background actors.
+    uint32_t mNonblockingCCBackgroundActorCount;
+
+    uint32_t mErrorHandlerRecursionCount;
+    int32_t mNextTimeoutId;
+
+    // Tracks the current setTimeout/setInterval nesting level.
+    // When there isn't a TimeoutHandler on the stack, this will be 0.
+    // Whenever setTimeout/setInterval are called, a new TimeoutInfo will be
+    // created with a nesting level one more than the current nesting level,
+    // saturating at the kClampTimeoutNestingLevel.
+    //
+    // When RunExpiredTimeouts is run, it sets this value to the
+    // TimeoutInfo::mNestingLevel for the duration of
+    // the WorkerScriptTimeoutHandler::Call which will explicitly trigger a
+    // microtask checkpoint so that any immediately-resolved promises will
+    // still see the nesting level.
+    uint32_t mCurrentTimerNestingLevel;
+
+    bool mFrozen;
+    bool mTimerRunning;
+    bool mRunningExpiredTimeouts;
+    bool mPeriodicGCTimerRunning;
+    bool mIdleGCTimerRunning;
+    bool mOnLine;
+    bool mJSThreadExecutionGranted;
+    bool mCCCollectedAnything;
+    FlippedOnce<false> mDeletionScheduled;
+    FlippedOnce<false> mCancelBeforeWorkerScopeConstructed;
+    FlippedOnce<false> mPerformedShutdownAfterLastContentTaskExecuted;
+#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
+    bool mIsPotentiallyLastGCCCRunning = false;
+#endif
+  };
+  ThreadBound<WorkerThreadAccessible> mWorkerThreadAccessible;
+
+  class MOZ_RAII AutoPushEventLoopGlobal {
+   public:
+    AutoPushEventLoopGlobal(WorkerPrivate* aWorkerPrivate, JSContext* aCx);
+    ~AutoPushEventLoopGlobal();
+
+   private:
+    // We cannot make this CheckedUnsafePtr<WorkerPrivate> as this would violate
+    // our static assert
+    MOZ_NON_OWNING_REF WorkerPrivate* mWorkerPrivate;
+    nsCOMPtr<nsIGlobalObject> mOldEventLoopGlobal;
+  };
+  friend class AutoPushEventLoopGlobal;
+
+  uint32_t mPostSyncLoopOperations;
+
+  // List of operations to do at the end of the last sync event loop.
+  enum {
+    eDispatchCancelingRunnable = 0x02,
+  };
+
+  bool mParentWindowPaused;
+
+  bool mWorkerScriptExecutedSuccessfully;
+  bool mFetchHandlerWasAdded;
+  bool mMainThreadObjectsForgotten;
+  bool mIsChromeWorker;
+  bool mParentFrozen;
+
+  // mIsSecureContext is set once in our constructor; after that it can be read
+  // from various threads.
+  //
+  // It's a bit unfortunate that we have to have an out-of-band boolean for
+  // this, but we need access to this state from the parent thread, and we can't
+  // use our global object's secure state there.
+  const bool mIsSecureContext;
+
+  bool mDebuggerRegistered MOZ_GUARDED_BY(mMutex);
+
+  // During registration, this worker may be marked as not being ready to
+  // execute debuggee runnables or content.
+  //
+  // Protected by mMutex.
+  bool mDebuggerReady;
+  nsTArray<RefPtr<WorkerRunnable>> mDelayedDebuggeeRunnables;
+
+  // Whether this worker should have access to the WebExtension API bindings
+  // (currently only the Extension Background ServiceWorker declared in the
+  // extension manifest is allowed to access any WebExtension API bindings).
+  // This default to false, and it is eventually set to true by
+  // RemoteWorkerChild::ExecWorkerOnMainThread if the needed conditions
+  // are met.
+  bool mExtensionAPIAllowed;
+
+  // mIsInAutomation is true when we're running in test automation.
+  // We expose some extra testing functions in that case.
+  bool mIsInAutomation;
+
+  nsString mId;
+
+  // This is used to check if it's allowed to share the memory across the agent
+  // cluster.
+  const nsILoadInfo::CrossOriginOpenerPolicy mAgentClusterOpenerPolicy;
+
+  // Member variable of this class rather than the worker global scope because
+  // it's received on the main thread, but the global scope is thread-bound
+  // to the worker thread, so storing the value in the global scope would
+  // involve sacrificing the thread-bound-ness or using a WorkerRunnable, and
+  // there isn't a strong reason to store it on the global scope other than
+  // better consistency with the COEP spec.
+  Maybe<nsILoadInfo::CrossOriginEmbedderPolicy> mEmbedderPolicy;
+  Maybe<nsILoadInfo::CrossOriginEmbedderPolicy> mOwnerEmbedderPolicy;
+
+  /* Privileged add-on flag extracted from the AddonPolicy on the nsIPrincipal
+   * on the main thread when constructing a top-level worker. The flag is
+   * propagated to nested workers. The flag is only allowed to take effect in
+   * extension processes and is forbidden in content scripts in content
+   * processes. The flag may be read on either the parent/owner thread as well
+   * as on the worker thread itself. When bug 1443925 is fixed allowing
+   * nsIPrincipal to be used OMT, it may be possible to remove this flag. */
+  bool mIsPrivilegedAddonGlobal;
+
+  Atomic<uint32_t> mTopLevelWorkerFinishedRunnableCount;
+  Atomic<uint32_t> mWorkerFinishedRunnableCount;
+
+  nsTArray<nsCOMPtr<nsITargetShutdownTask>> mShutdownTasks
+      MOZ_GUARDED_BY(mMutex);
+  bool mShutdownTasksRun MOZ_GUARDED_BY(mMutex) = false;
+
+  bool mCCFlagSaysEligible MOZ_GUARDED_BY(mMutex){true};
+
+  // The flag indicates if the worke is idle for events in the main event loop.
+  bool mWorkerLoopIsIdle MOZ_GUARDED_BY(mMutex){false};
+};
+
+class AutoSyncLoopHolder {
+  CheckedUnsafePtr<WorkerPrivate> mWorkerPrivate;
+  nsCOMPtr<nsISerialEventTarget> mTarget;
+  uint32_t mIndex;
+
+ public:
+  // See CreateNewSyncLoop() for more information about the correct value to use
+  // for aFailStatus.
+  AutoSyncLoopHolder(WorkerPrivate* aWorkerPrivate, WorkerStatus aFailStatus)
+      : mWorkerPrivate(aWorkerPrivate),
+        mTarget(aWorkerPrivate->CreateNewSyncLoop(aFailStatus)),
+        mIndex(aWorkerPrivate->mSyncLoopStack.Length() - 1) {
+    aWorkerPrivate->AssertIsOnWorkerThread();
+  }
+
+  ~AutoSyncLoopHolder() {
+    if (mWorkerPrivate && mTarget) {
+      mWorkerPrivate->AssertIsOnWorkerThread();
+      mWorkerPrivate->StopSyncLoop(mTarget, NS_ERROR_FAILURE);
+      mWorkerPrivate->DestroySyncLoop(mIndex);
+    }
+  }
+
+  nsresult Run() {
+    CheckedUnsafePtr<WorkerPrivate> workerPrivate = mWorkerPrivate;
+    mWorkerPrivate = nullptr;
+
+    workerPrivate->AssertIsOnWorkerThread();
+
+    return workerPrivate->RunCurrentSyncLoop();
+  }
+
+  nsISerialEventTarget* GetSerialEventTarget() const {
+    // This can be null if CreateNewSyncLoop() fails.
+    return mTarget;
+  }
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif /* mozilla_dom_workers_workerprivate_h__ */
diff --git a/dom/workers/WorkerRef.cpp b/dom/workers/WorkerRef.cpp
new file mode 100644
index 0000000000..9ba9841041
--- /dev/null
+++ b/dom/workers/WorkerRef.cpp
@@ -0,0 +1,267 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/WorkerRef.h"
+
+#include "nsDebug.h"
+#include "WorkerRunnable.h"
+#include "WorkerPrivate.h"
+
+namespace mozilla::dom {
+
+namespace {
+
+// This runnable is used to release the StrongWorkerRef on the worker thread
+// when a ThreadSafeWorkerRef is released.
+class ReleaseRefControlRunnable final : public WorkerControlRunnable {
+ public:
+  ReleaseRefControlRunnable(WorkerPrivate* aWorkerPrivate,
+                            already_AddRefed<StrongWorkerRef> aRef)
+      : WorkerControlRunnable(aWorkerPrivate, "ReleaseRefControlRunnable",
+                              WorkerThread),
+        mRef(std::move(aRef)) {
+    MOZ_ASSERT(mRef);
+  }
+
+  bool PreDispatch(WorkerPrivate* aWorkerPrivate) override { return true; }
+
+  void PostDispatch(WorkerPrivate* aWorkerPrivate,
+                    bool aDispatchResult) override {}
+
+  bool WorkerRun(JSContext* aCx, WorkerPrivate* aWorkerPrivate) override {
+    mRef = nullptr;
+    return true;
+  }
+
+ private:
+  RefPtr<StrongWorkerRef> mRef;
+};
+
+}  // namespace
+
+// ----------------------------------------------------------------------------
+// WorkerRef
+
+WorkerRef::WorkerRef(WorkerPrivate* aWorkerPrivate, const char* aName,
+                     bool aIsPreventingShutdown)
+    :
+#ifdef DEBUG
+      mDebugMutex("WorkerRef"),
+#endif
+      mWorkerPrivate(aWorkerPrivate),
+      mName(aName),
+      mIsPreventingShutdown(aIsPreventingShutdown),
+      mHolding(false) {
+  MOZ_ASSERT(aWorkerPrivate);
+  MOZ_ASSERT(aName);
+
+  aWorkerPrivate->AssertIsOnWorkerThread();
+}
+
+WorkerRef::~WorkerRef() {
+  NS_ASSERT_OWNINGTHREAD(WorkerRef);
+  ReleaseWorker();
+}
+
+void WorkerRef::ReleaseWorker() {
+  if (mHolding) {
+    MOZ_ASSERT(mWorkerPrivate);
+
+    if (mIsPreventingShutdown) {
+      mWorkerPrivate->AssertIsNotPotentiallyLastGCCCRunning();
+    }
+    mWorkerPrivate->RemoveWorkerRef(this);
+    mWorkerPrivate = nullptr;
+
+    mHolding = false;
+  }
+}
+
+bool WorkerRef::HoldWorker(WorkerStatus aStatus) {
+  MOZ_ASSERT(mWorkerPrivate);
+  MOZ_ASSERT(!mHolding);
+
+  if (NS_WARN_IF(!mWorkerPrivate->AddWorkerRef(this, aStatus))) {
+    return false;
+  }
+
+  mHolding = true;
+  return true;
+}
+
+void WorkerRef::Notify() {
+  NS_ASSERT_OWNINGTHREAD(WorkerRef);
+
+  if (!mCallback) {
+    return;
+  }
+
+  MoveOnlyFunction<void()> callback = std::move(mCallback);
+  MOZ_ASSERT(!mCallback);
+
+  callback();
+}
+
+// ----------------------------------------------------------------------------
+// WeakWorkerRef
+
+/* static */
+already_AddRefed<WeakWorkerRef> WeakWorkerRef::Create(
+    WorkerPrivate* aWorkerPrivate, MoveOnlyFunction<void()>&& aCallback) {
+  MOZ_ASSERT(aWorkerPrivate);
+  aWorkerPrivate->AssertIsOnWorkerThread();
+
+  RefPtr<WeakWorkerRef> ref = new WeakWorkerRef(aWorkerPrivate);
+  if (!ref->HoldWorker(Canceling)) {
+    return nullptr;
+  }
+
+  ref->mCallback = std::move(aCallback);
+
+  return ref.forget();
+}
+
+WeakWorkerRef::WeakWorkerRef(WorkerPrivate* aWorkerPrivate)
+    : WorkerRef(aWorkerPrivate, "WeakWorkerRef", false) {}
+
+WeakWorkerRef::~WeakWorkerRef() = default;
+
+void WeakWorkerRef::Notify() {
+  MOZ_ASSERT(mHolding);
+  MOZ_ASSERT(mWorkerPrivate);
+
+  // Notify could drop the last reference to this object. We must keep it alive
+  // in order to call ReleaseWorker() immediately after.
+  RefPtr<WeakWorkerRef> kungFuGrip = this;
+
+  WorkerRef::Notify();
+  ReleaseWorker();
+}
+
+WorkerPrivate* WeakWorkerRef::GetPrivate() const {
+  NS_ASSERT_OWNINGTHREAD(WeakWorkerRef);
+  return mWorkerPrivate;
+}
+
+WorkerPrivate* WeakWorkerRef::GetUnsafePrivate() const {
+  return mWorkerPrivate;
+}
+
+// ----------------------------------------------------------------------------
+// StrongWorkerRef
+
+/* static */
+already_AddRefed<StrongWorkerRef> StrongWorkerRef::Create(
+    WorkerPrivate* const aWorkerPrivate, const char* const aName,
+    MoveOnlyFunction<void()>&& aCallback) {
+  if (RefPtr<StrongWorkerRef> ref =
+          CreateImpl(aWorkerPrivate, aName, Canceling)) {
+    ref->mCallback = std::move(aCallback);
+    return ref.forget();
+  }
+  return nullptr;
+}
+
+/* static */
+already_AddRefed<StrongWorkerRef> StrongWorkerRef::CreateForcibly(
+    WorkerPrivate* const aWorkerPrivate, const char* const aName) {
+  return CreateImpl(aWorkerPrivate, aName, Killing);
+}
+
+/* static */
+already_AddRefed<StrongWorkerRef> StrongWorkerRef::CreateImpl(
+    WorkerPrivate* const aWorkerPrivate, const char* const aName,
+    WorkerStatus const aFailStatus) {
+  MOZ_ASSERT(aWorkerPrivate);
+  MOZ_ASSERT(aName);
+
+  RefPtr<StrongWorkerRef> ref = new StrongWorkerRef(aWorkerPrivate, aName);
+  if (!ref->HoldWorker(aFailStatus)) {
+    return nullptr;
+  }
+
+  return ref.forget();
+}
+
+StrongWorkerRef::StrongWorkerRef(WorkerPrivate* aWorkerPrivate,
+                                 const char* aName)
+    : WorkerRef(aWorkerPrivate, aName, true) {}
+
+StrongWorkerRef::~StrongWorkerRef() = default;
+
+WorkerPrivate* StrongWorkerRef::Private() const {
+  NS_ASSERT_OWNINGTHREAD(StrongWorkerRef);
+  return mWorkerPrivate;
+}
+
+// ----------------------------------------------------------------------------
+// ThreadSafeWorkerRef
+
+ThreadSafeWorkerRef::ThreadSafeWorkerRef(StrongWorkerRef* aRef) : mRef(aRef) {
+  MOZ_ASSERT(aRef);
+  aRef->Private()->AssertIsOnWorkerThread();
+}
+
+ThreadSafeWorkerRef::~ThreadSafeWorkerRef() {
+  // Let's release the StrongWorkerRef on the correct thread.
+  if (!mRef->mWorkerPrivate->IsOnWorkerThread()) {
+    WorkerPrivate* workerPrivate = mRef->mWorkerPrivate;
+    RefPtr<ReleaseRefControlRunnable> r =
+        new ReleaseRefControlRunnable(workerPrivate, mRef.forget());
+    r->Dispatch();
+    return;
+  }
+}
+
+WorkerPrivate* ThreadSafeWorkerRef::Private() const {
+  return mRef->mWorkerPrivate;
+}
+
+// ----------------------------------------------------------------------------
+// IPCWorkerRef
+
+/* static */
+already_AddRefed<IPCWorkerRef> IPCWorkerRef::Create(
+    WorkerPrivate* aWorkerPrivate, const char* aName,
+    MoveOnlyFunction<void()>&& aCallback) {
+  MOZ_ASSERT(aWorkerPrivate);
+  aWorkerPrivate->AssertIsOnWorkerThread();
+
+  RefPtr<IPCWorkerRef> ref = new IPCWorkerRef(aWorkerPrivate, aName);
+  if (!ref->HoldWorker(Canceling)) {
+    return nullptr;
+  }
+  ref->SetActorCount(1);
+  ref->mCallback = std::move(aCallback);
+
+  return ref.forget();
+}
+
+IPCWorkerRef::IPCWorkerRef(WorkerPrivate* aWorkerPrivate, const char* aName)
+    : WorkerRef(aWorkerPrivate, aName, false), mActorCount(0) {}
+
+IPCWorkerRef::~IPCWorkerRef() {
+  NS_ASSERT_OWNINGTHREAD(IPCWorkerRef);
+  // explicit type convertion to avoid undefined behavior of uint32_t overflow.
+  mWorkerPrivate->AdjustNonblockingCCBackgroundActorCount(
+      (int32_t)-mActorCount);
+  ReleaseWorker();
+};
+
+WorkerPrivate* IPCWorkerRef::Private() const {
+  NS_ASSERT_OWNINGTHREAD(IPCWorkerRef);
+  return mWorkerPrivate;
+}
+
+void IPCWorkerRef::SetActorCount(uint32_t aCount) {
+  NS_ASSERT_OWNINGTHREAD(IPCWorkerRef);
+  // explicit type convertion to avoid undefined behavior of uint32_t overflow.
+  mWorkerPrivate->AdjustNonblockingCCBackgroundActorCount((int32_t)aCount -
+                                                          (int32_t)mActorCount);
+  mActorCount = aCount;
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/workers/WorkerRef.h b/dom/workers/WorkerRef.h
new file mode 100644
index 0000000000..e41ef07bfd
--- /dev/null
+++ b/dom/workers/WorkerRef.h
@@ -0,0 +1,276 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_workers_WorkerRef_h
+#define mozilla_dom_workers_WorkerRef_h
+
+#include "mozilla/dom/WorkerStatus.h"
+#include "mozilla/MoveOnlyFunction.h"
+#include "mozilla/RefPtr.h"
+#include "nsISupports.h"
+#include "nsTString.h"
+
+#ifdef DEBUG
+#  include "mozilla/Mutex.h"
+#endif
+
+namespace mozilla::dom {
+
+/*
+ * If you want to play with a DOM Worker, you must know that it can go away
+ * at any time if nothing prevents its shutting down. This documentation helps
+ * to understand how to play with DOM Workers correctly.
+ *
+ * There are several reasons why a DOM Worker could go away. Here is the
+ * complete list:
+ *
+ * a. GC/CC - If the DOM Worker thread is idle and the Worker object is garbage
+ *    collected, it goes away.
+ * b. The worker script can call self.close()
+ * c. The Worker object calls worker.terminate()
+ * d. Firefox is shutting down.
+ *
+ * When a DOM Worker goes away, it does several steps. See more in
+ * WorkerStatus.h. The DOM Worker thread will basically stop scheduling
+ * WorkerRunnables, and eventually WorkerControlRunnables. But if there is
+ * something preventing the shutting down, it will always possible to dispatch
+ * WorkerControlRunnables.  Of course, at some point, the worker _must_ be
+ * released, otherwise firefox will leak it and the browser shutdown will hang.
+ *
+ * WeakWorkerRef is a refcounted, NON thread-safe object.
+ *
+ * From this object, you can obtain a WorkerPrivate, calling
+ * WeakWorkerRef::GetPrivate(). It returns nullptr if the worker is shutting
+ * down or if it is already gone away.
+ *
+ * If you want to know when a DOM Worker starts the shutting down procedure,
+ * pass a callback to the mozilla::dom::WeakWorkerRef::Create() method.
+ * Your function will be called. Note that _after_ the callback,
+ * WeakWorkerRef::GetPrivate() will return nullptr.
+ *
+ * How to keep a DOM Worker alive?
+ * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ *
+ * If you need to keep the worker alive, you must use StrongWorkerRef.
+ * You can have this refcounted, NON thread-safe object, calling
+ * mozilla::dom::StrongWorkerRef::Create(WorkerPrivate* aWorkerPrivate);
+ *
+ * If you have a StrongWorkerRef:
+ * a. the DOM Worker is kept alive.
+ * b. you can have access to the WorkerPrivate, calling: Private().
+ * c. WorkerControlRunnable can be dispatched.
+ *
+ * Note that the DOM Worker shutdown can start at any time, but having a
+ * StrongWorkerRef prevents the full shutdown. Also with StrongWorkerRef, you
+ * can pass a callback when calling mozilla::dom::StrongWorkerRef::Create().
+ *
+ * When the DOM Worker shutdown starts, WorkerRunnable cannot be dispatched
+ * anymore. At this point, you should dispatch WorkerControlRunnable just to
+ * release resources.
+ *
+ * How to have a thread-safe DOM Worker reference?
+ * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ *
+ * Sometimes you need to play with threads and you need a thread-safe worker
+ * reference. ThreadSafeWorkerRef is what you want.
+ *
+ * Just because this object can be sent to different threads, we don't allow the
+ * setting of a callback. It would be confusing.
+ *
+ * ThreadSafeWorkerRef can be destroyed in any thread. Internally it keeps a
+ * reference to its StrongWorkerRef creator and this ref will be dropped on the
+ * correct thread when the ThreadSafeWorkerRef is deleted.
+ *
+ * IPC WorkerRef
+ * ~~~~~~~~~~~~~
+ *
+ * IPDL protocols require a correct shutdown sequence. Because of this, they
+ * need a special configuration:
+ * 1. they need to be informed when the Worker starts the shutting down
+ * 2. they don't want to prevent the shutdown
+ * 3. but at the same time, they need to block the shutdown until the WorkerRef
+ *    is not longer alive.
+ *
+ * Point 1 is a standard feature of WorkerRef; point 2 is similar to
+ * WeakWorkerRef; point 3 is similar to StrongWorkerRef.
+ *
+ * You can create a special IPC WorkerRef using this static method:
+ * mozilla::dom::IPCWorkerRef::Create(WorkerPrivate* aWorkerPrivate,
+ *                                    const char* * aName);
+ */
+
+class WorkerPrivate;
+class StrongWorkerRef;
+class ThreadSafeWorkerRef;
+
+#ifdef DEBUG  // In debug mode, provide a way for clients to annotate WorkerRefs
+#  define SET_WORKERREF_DEBUG_STATUS(workerref, str) \
+    ((workerref)->DebugSetWorkerRefStatus(str))
+#  define GET_WORKERREF_DEBUG_STATUS(workerref) \
+    ((workerref)->DebugGetWorkerRefStatus())
+#else
+#  define SET_WORKERREF_DEBUG_STATUS(workerref, str) (void())
+#  define GET_WORKERREF_DEBUG_STATUS(workerref) (EmptyCString())
+#endif
+
+class WorkerRef {
+  friend class WorkerPrivate;
+
+ public:
+  NS_INLINE_DECL_REFCOUNTING(WorkerRef)
+
+#ifdef DEBUG
+  mutable Mutex mDebugMutex;
+  nsCString mDebugStatus MOZ_GUARDED_BY(mDebugMutex);
+
+  void DebugSetWorkerRefStatus(const nsCString& aStatus) {
+    MutexAutoLock lock(mDebugMutex);
+    mDebugStatus = aStatus;
+  }
+
+  const nsCString DebugGetWorkerRefStatus() const {
+    MutexAutoLock lock(mDebugMutex);
+    return mDebugStatus;
+  }
+#endif
+
+ protected:
+  WorkerRef(WorkerPrivate* aWorkerPrivate, const char* aName,
+            bool aIsPreventingShutdown);
+  virtual ~WorkerRef();
+
+  virtual void Notify();
+
+  bool HoldWorker(WorkerStatus aStatus);
+  void ReleaseWorker();
+
+  bool IsPreventingShutdown() const { return mIsPreventingShutdown; }
+
+  const char* Name() const { return mName; }
+
+  WorkerPrivate* mWorkerPrivate;
+
+  MoveOnlyFunction<void()> mCallback;
+  const char* const mName;
+  const bool mIsPreventingShutdown;
+
+  // True if this WorkerRef has been added to a WorkerPrivate.
+  bool mHolding;
+};
+
+class WeakWorkerRef final : public WorkerRef {
+ public:
+  static already_AddRefed<WeakWorkerRef> Create(
+      WorkerPrivate* aWorkerPrivate,
+      MoveOnlyFunction<void()>&& aCallback = nullptr);
+
+  WorkerPrivate* GetPrivate() const;
+
+  // This can be called on any thread. It's racy and, in general, the wrong
+  // choice.
+  WorkerPrivate* GetUnsafePrivate() const;
+
+ private:
+  explicit WeakWorkerRef(WorkerPrivate* aWorkerPrivate);
+  ~WeakWorkerRef();
+
+  void Notify() override;
+};
+
+class StrongWorkerRef final : public WorkerRef {
+ public:
+  static already_AddRefed<StrongWorkerRef> Create(
+      WorkerPrivate* aWorkerPrivate, const char* aName,
+      MoveOnlyFunction<void()>&& aCallback = nullptr);
+
+  // This function creates a StrongWorkerRef even when in the Canceling state of
+  // the worker's lifecycle. It's intended to be used by system code, e.g. code
+  // that needs to perform IPC.
+  //
+  // This method should only be used in cases where the StrongWorkerRef will be
+  // used for an extremely bounded duration that cannot be impacted by content.
+  // For example, IPCStreams use this type of ref in order to immediately
+  // migrate to an actor on another thread. Whether the IPCStream ever actually
+  // is streamed does not matter; the ref will be dropped once the new actor is
+  // created. For this reason, this method does not take a callback. It's
+  // expected and required that callers will drop the reference when they are
+  // done.
+  static already_AddRefed<StrongWorkerRef> CreateForcibly(
+      WorkerPrivate* aWorkerPrivate, const char* aName);
+
+  WorkerPrivate* Private() const;
+
+ private:
+  friend class WeakWorkerRef;
+  friend class ThreadSafeWorkerRef;
+
+  static already_AddRefed<StrongWorkerRef> CreateImpl(
+      WorkerPrivate* aWorkerPrivate, const char* aName,
+      WorkerStatus aFailStatus);
+
+  StrongWorkerRef(WorkerPrivate* aWorkerPrivate, const char* aName);
+  ~StrongWorkerRef();
+};
+
+class ThreadSafeWorkerRef final {
+ public:
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(ThreadSafeWorkerRef)
+
+  explicit ThreadSafeWorkerRef(StrongWorkerRef* aRef);
+
+  WorkerPrivate* Private() const;
+
+#ifdef DEBUG
+  RefPtr<StrongWorkerRef>& Ref() { return mRef; }
+#endif
+
+ private:
+  friend class StrongWorkerRef;
+
+  ~ThreadSafeWorkerRef();
+
+  RefPtr<StrongWorkerRef> mRef;
+};
+
+class IPCWorkerRef final : public WorkerRef {
+ public:
+  static already_AddRefed<IPCWorkerRef> Create(
+      WorkerPrivate* aWorkerPrivate, const char* aName,
+      MoveOnlyFunction<void()>&& aCallback = nullptr);
+
+  WorkerPrivate* Private() const;
+
+  void SetActorCount(uint32_t aCount);
+
+ private:
+  IPCWorkerRef(WorkerPrivate* aWorkerPrivate, const char* aName);
+  ~IPCWorkerRef();
+
+  // The count of background actors which binding with this IPCWorkerRef.
+  uint32_t mActorCount;
+};
+
+// Template class to keep an Actor pointer, as a raw pointer, in a ref-counted
+// way when passed to lambdas.
+template <class ActorPtr>
+class IPCWorkerRefHelper final {
+ public:
+  NS_INLINE_DECL_REFCOUNTING(IPCWorkerRefHelper);
+
+  explicit IPCWorkerRefHelper(ActorPtr* aActor) : mActor(aActor) {}
+
+  ActorPtr* Actor() const { return mActor; }
+
+ private:
+  ~IPCWorkerRefHelper() = default;
+
+  // Raw pointer
+  ActorPtr* mActor;
+};
+
+}  // namespace mozilla::dom
+
+#endif /* mozilla_dom_workers_WorkerRef_h */
diff --git a/dom/workers/WorkerRunnable.cpp b/dom/workers/WorkerRunnable.cpp
new file mode 100644
index 0000000000..ff2178d16e
--- /dev/null
+++ b/dom/workers/WorkerRunnable.cpp
@@ -0,0 +1,705 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "WorkerRunnable.h"
+
+#include "WorkerScope.h"
+#include "js/RootingAPI.h"
+#include "jsapi.h"
+#include "jsfriendapi.h"
+#include "mozilla/AlreadyAddRefed.h"
+#include "mozilla/AppShutdown.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/CycleCollectedJSContext.h"
+#include "mozilla/DebugOnly.h"
+#include "mozilla/ErrorResult.h"
+#include "mozilla/Logging.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/Telemetry.h"
+#include "mozilla/TelemetryHistogramEnums.h"
+#include "mozilla/TimeStamp.h"
+#include "mozilla/Unused.h"
+#include "mozilla/dom/ScriptSettings.h"
+#include "mozilla/dom/Worker.h"
+#include "mozilla/dom/WorkerCommon.h"
+#include "nsDebug.h"
+#include "nsGlobalWindowInner.h"
+#include "nsID.h"
+#include "nsIEventTarget.h"
+#include "nsIGlobalObject.h"
+#include "nsIRunnable.h"
+#include "nsThreadUtils.h"
+#include "nsWrapperCacheInlines.h"
+
+namespace mozilla::dom {
+
+static mozilla::LazyLogModule sWorkerRunnableLog("WorkerRunnable");
+
+#ifdef LOG
+#  undef LOG
+#endif
+#define LOG(args) MOZ_LOG(sWorkerRunnableLog, LogLevel::Verbose, args);
+
+namespace {
+
+const nsIID kWorkerRunnableIID = {
+    0x320cc0b5,
+    0xef12,
+    0x4084,
+    {0x88, 0x6e, 0xca, 0x6a, 0x81, 0xe4, 0x1d, 0x68}};
+
+}  // namespace
+
+#ifdef DEBUG
+WorkerRunnable::WorkerRunnable(WorkerPrivate* aWorkerPrivate, const char* aName,
+                               Target aTarget)
+    : mWorkerPrivate(aWorkerPrivate),
+      mTarget(aTarget),
+#  ifdef MOZ_COLLECTING_RUNNABLE_TELEMETRY
+      mName(aName),
+#  endif
+      mCallingCancelWithinRun(false) {
+  LOG(("WorkerRunnable::WorkerRunnable [%p]", this));
+  MOZ_ASSERT(aWorkerPrivate);
+}
+#endif
+
+bool WorkerRunnable::IsDebuggerRunnable() const { return false; }
+
+nsIGlobalObject* WorkerRunnable::DefaultGlobalObject() const {
+  if (IsDebuggerRunnable()) {
+    return mWorkerPrivate->DebuggerGlobalScope();
+  } else {
+    return mWorkerPrivate->GlobalScope();
+  }
+}
+
+bool WorkerRunnable::PreDispatch(WorkerPrivate* aWorkerPrivate) {
+#ifdef DEBUG
+  MOZ_ASSERT(aWorkerPrivate);
+
+  switch (mTarget) {
+    case ParentThread:
+      aWorkerPrivate->AssertIsOnWorkerThread();
+      break;
+
+    case WorkerThread:
+      aWorkerPrivate->AssertIsOnParentThread();
+      break;
+
+    default:
+      MOZ_ASSERT_UNREACHABLE("Unknown behavior!");
+  }
+#endif
+  return true;
+}
+
+bool WorkerRunnable::Dispatch() {
+  bool ok = PreDispatch(mWorkerPrivate);
+  if (ok) {
+    ok = DispatchInternal();
+  }
+  PostDispatch(mWorkerPrivate, ok);
+  return ok;
+}
+
+bool WorkerRunnable::DispatchInternal() {
+  LOG(("WorkerRunnable::DispatchInternal [%p]", this));
+  RefPtr<WorkerRunnable> runnable(this);
+
+  if (mTarget == WorkerThread) {
+    if (IsDebuggerRunnable()) {
+      return NS_SUCCEEDED(
+          mWorkerPrivate->DispatchDebuggerRunnable(runnable.forget()));
+    } else {
+      return NS_SUCCEEDED(mWorkerPrivate->Dispatch(runnable.forget()));
+    }
+  }
+
+  MOZ_ASSERT(mTarget == ParentThread);
+
+  if (WorkerPrivate* parent = mWorkerPrivate->GetParent()) {
+    return NS_SUCCEEDED(parent->Dispatch(runnable.forget()));
+  }
+
+  if (IsDebuggeeRunnable()) {
+    RefPtr<WorkerDebuggeeRunnable> debuggeeRunnable =
+        runnable.forget().downcast<WorkerDebuggeeRunnable>();
+    return NS_SUCCEEDED(mWorkerPrivate->DispatchDebuggeeToMainThread(
+        debuggeeRunnable.forget(), NS_DISPATCH_NORMAL));
+  }
+
+  return NS_SUCCEEDED(mWorkerPrivate->DispatchToMainThread(runnable.forget()));
+}
+
+void WorkerRunnable::PostDispatch(WorkerPrivate* aWorkerPrivate,
+                                  bool aDispatchResult) {
+  MOZ_ASSERT(aWorkerPrivate);
+
+#ifdef DEBUG
+  switch (mTarget) {
+    case ParentThread:
+      aWorkerPrivate->AssertIsOnWorkerThread();
+      break;
+
+    case WorkerThread:
+      aWorkerPrivate->AssertIsOnParentThread();
+      break;
+
+    default:
+      MOZ_ASSERT_UNREACHABLE("Unknown behavior!");
+  }
+#endif
+}
+
+bool WorkerRunnable::PreRun(WorkerPrivate* aWorkerPrivate) { return true; }
+
+void WorkerRunnable::PostRun(JSContext* aCx, WorkerPrivate* aWorkerPrivate,
+                             bool aRunResult) {
+  MOZ_ASSERT(aCx);
+  MOZ_ASSERT(aWorkerPrivate);
+
+#ifdef DEBUG
+  switch (mTarget) {
+    case ParentThread:
+      aWorkerPrivate->AssertIsOnParentThread();
+      break;
+
+    case WorkerThread:
+      aWorkerPrivate->AssertIsOnWorkerThread();
+      break;
+
+    default:
+      MOZ_ASSERT_UNREACHABLE("Unknown behavior!");
+  }
+#endif
+}
+
+// static
+WorkerRunnable* WorkerRunnable::FromRunnable(nsIRunnable* aRunnable) {
+  MOZ_ASSERT(aRunnable);
+
+  WorkerRunnable* runnable;
+  nsresult rv = aRunnable->QueryInterface(kWorkerRunnableIID,
+                                          reinterpret_cast<void**>(&runnable));
+  if (NS_FAILED(rv)) {
+    return nullptr;
+  }
+
+  MOZ_ASSERT(runnable);
+  return runnable;
+}
+
+NS_IMPL_ADDREF(WorkerRunnable)
+NS_IMPL_RELEASE(WorkerRunnable)
+
+#ifdef MOZ_COLLECTING_RUNNABLE_TELEMETRY
+NS_IMETHODIMP
+WorkerRunnable::GetName(nsACString& aName) {
+  if (mName) {
+    aName.AssignASCII(mName);
+  } else {
+    aName.Truncate();
+  }
+  return NS_OK;
+}
+#endif
+
+NS_INTERFACE_MAP_BEGIN(WorkerRunnable)
+  NS_INTERFACE_MAP_ENTRY(nsIRunnable)
+#ifdef MOZ_COLLECTING_RUNNABLE_TELEMETRY
+  NS_INTERFACE_MAP_ENTRY(nsINamed)
+#endif
+  NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, nsIRunnable)
+  // kWorkerRunnableIID is special in that it does not AddRef its result.
+  if (aIID.Equals(kWorkerRunnableIID)) {
+    *aInstancePtr = this;
+    return NS_OK;
+  } else
+NS_INTERFACE_MAP_END
+
+NS_IMETHODIMP
+WorkerRunnable::Run() {
+  LOG(("WorkerRunnable::Run [%p]", this));
+  bool targetIsWorkerThread = mTarget == WorkerThread;
+
+  if (targetIsWorkerThread) {
+    // On a worker thread, a WorkerRunnable should only run when there is an
+    // underlying WorkerThreadPrimaryRunnable active, which means we should
+    // find a CycleCollectedJSContext.
+    if (!CycleCollectedJSContext::Get()) {
+#if (defined(MOZ_COLLECTING_RUNNABLE_TELEMETRY) && defined(NIGHTLY_BUILD))
+      // We will only leak the static name string of the WorkerRunnable type
+      // we are trying to execute.
+      MOZ_CRASH_UNSAFE_PRINTF(
+          "Runnable '%s' executed after WorkerThreadPrimaryRunnable ended.",
+          this->mName);
+#endif
+      return NS_OK;
+    }
+  }
+
+#ifdef DEBUG
+  if (targetIsWorkerThread) {
+    mWorkerPrivate->AssertIsOnWorkerThread();
+  } else {
+    MOZ_ASSERT(mTarget == ParentThread);
+    mWorkerPrivate->AssertIsOnParentThread();
+  }
+#endif
+
+  if (targetIsWorkerThread && !mCallingCancelWithinRun &&
+      mWorkerPrivate->CancelBeforeWorkerScopeConstructed()) {
+    mCallingCancelWithinRun = true;
+    Cancel();
+    mCallingCancelWithinRun = false;
+    return NS_OK;
+  }
+
+  bool result = PreRun(mWorkerPrivate);
+  if (!result) {
+    MOZ_ASSERT(targetIsWorkerThread,
+               "The only PreRun implementation that can fail is "
+               "ScriptExecutorRunnable");
+    mWorkerPrivate->AssertIsOnWorkerThread();
+    MOZ_ASSERT(!JS_IsExceptionPending(mWorkerPrivate->GetJSContext()));
+    // We can't enter a useful realm on the JSContext here; just pass it
+    // in as-is.
+    PostRun(mWorkerPrivate->GetJSContext(), mWorkerPrivate, false);
+    return NS_ERROR_FAILURE;
+  }
+
+  // Track down the appropriate global, if any, to use for the AutoEntryScript.
+  nsCOMPtr<nsIGlobalObject> globalObject;
+  bool isMainThread = !targetIsWorkerThread && !mWorkerPrivate->GetParent();
+  MOZ_ASSERT(isMainThread == NS_IsMainThread());
+  RefPtr<WorkerPrivate> kungFuDeathGrip;
+  if (targetIsWorkerThread) {
+    globalObject = mWorkerPrivate->GetCurrentEventLoopGlobal();
+    if (!globalObject) {
+      globalObject = DefaultGlobalObject();
+      // Our worker thread may not be in a good state here if there is no
+      // JSContext avaliable.  The way this manifests itself is that
+      // globalObject ends up null (though it's not clear to me how we can be
+      // running runnables at all when DefaultGlobalObject() is returning
+      // false!) and then when we try to init the AutoJSAPI either
+      // CycleCollectedJSContext::Get() returns null or it has a null JSContext.
+      // In any case, we used to have a check for
+      // GetCurrentWorkerThreadJSContext() being non-null here and that seems to
+      // avoid the problem, so let's keep doing that check even if we don't need
+      // the JSContext here at all.
+      if (NS_WARN_IF(!globalObject && !GetCurrentWorkerThreadJSContext())) {
+        return NS_ERROR_FAILURE;
+      }
+    }
+
+    // We may still not have a globalObject here: in the case of
+    // CompileScriptRunnable, we don't actually create the global object until
+    // we have the script data, which happens in a syncloop under
+    // CompileScriptRunnable::WorkerRun, so we can't assert that it got created
+    // in the PreRun call above.
+  } else {
+    kungFuDeathGrip = mWorkerPrivate;
+    if (isMainThread) {
+      globalObject = nsGlobalWindowInner::Cast(mWorkerPrivate->GetWindow());
+    } else {
+      globalObject = mWorkerPrivate->GetParent()->GlobalScope();
+    }
+  }
+
+  // We might run script as part of WorkerRun, so we need an AutoEntryScript.
+  // This is part of the HTML spec for workers at:
+  // http://www.whatwg.org/specs/web-apps/current-work/#run-a-worker
+  // If we don't have a globalObject we have to use an AutoJSAPI instead, but
+  // this is OK as we won't be running script in these circumstances.
+  Maybe<mozilla::dom::AutoJSAPI> maybeJSAPI;
+  Maybe<mozilla::dom::AutoEntryScript> aes;
+  JSContext* cx;
+  AutoJSAPI* jsapi;
+  if (globalObject) {
+    aes.emplace(globalObject, "Worker runnable", isMainThread);
+    jsapi = aes.ptr();
+    cx = aes->cx();
+  } else {
+    maybeJSAPI.emplace();
+    maybeJSAPI->Init();
+    jsapi = maybeJSAPI.ptr();
+    cx = jsapi->cx();
+  }
+
+  // Note that we can't assert anything about
+  // mWorkerPrivate->ParentEventTargetRef()->GetWrapper()
+  // existing, since it may in fact have been GCed (and we may be one of the
+  // runnables cleaning up the worker as a result).
+
+  // If we are on the parent thread and that thread is not the main thread,
+  // then we must be a dedicated worker (because there are no
+  // Shared/ServiceWorkers whose parent is itself a worker) and then we
+  // definitely have a globalObject.  If it _is_ the main thread, globalObject
+  // can be null for workers started from JSMs or other non-window contexts,
+  // sadly.
+  MOZ_ASSERT_IF(!targetIsWorkerThread && !isMainThread,
+                mWorkerPrivate->IsDedicatedWorker() && globalObject);
+
+  // If we're on the parent thread we might be in a null realm in the
+  // situation described above when globalObject is null.  Make sure to enter
+  // the realm of the worker's reflector if there is one.  There might
+  // not be one if we're just starting to compile the script for this worker.
+  Maybe<JSAutoRealm> ar;
+  if (!targetIsWorkerThread && mWorkerPrivate->IsDedicatedWorker() &&
+      mWorkerPrivate->ParentEventTargetRef()->GetWrapper()) {
+    JSObject* wrapper = mWorkerPrivate->ParentEventTargetRef()->GetWrapper();
+
+    // If we're on the parent thread and have a reflector and a globalObject,
+    // then the realms of cx, globalObject, and the worker's reflector
+    // should all match.
+    MOZ_ASSERT_IF(globalObject,
+                  js::GetNonCCWObjectRealm(wrapper) == js::GetContextRealm(cx));
+    MOZ_ASSERT_IF(globalObject,
+                  js::GetNonCCWObjectRealm(wrapper) ==
+                      js::GetNonCCWObjectRealm(
+                          globalObject->GetGlobalJSObjectPreserveColor()));
+
+    // If we're on the parent thread and have a reflector, then our
+    // JSContext had better be either in the null realm (and hence
+    // have no globalObject) or in the realm of our reflector.
+    MOZ_ASSERT(!js::GetContextRealm(cx) ||
+                   js::GetNonCCWObjectRealm(wrapper) == js::GetContextRealm(cx),
+               "Must either be in the null compartment or in our reflector "
+               "compartment");
+
+    ar.emplace(cx, wrapper);
+  }
+
+  MOZ_ASSERT(!jsapi->HasException());
+  result = WorkerRun(cx, mWorkerPrivate);
+  jsapi->ReportException();
+
+  // We can't even assert that this didn't create our global, since in the case
+  // of CompileScriptRunnable it _does_.
+
+  // It would be nice to avoid passing a JSContext to PostRun, but in the case
+  // of ScriptExecutorRunnable we need to know the current compartment on the
+  // JSContext (the one we set up based on the global returned from PreRun) so
+  // that we can sanely do exception reporting.  In particular, we want to make
+  // sure that we do our JS_SetPendingException while still in that compartment,
+  // because otherwise we might end up trying to create a cross-compartment
+  // wrapper when we try to move the JS exception from our runnable's
+  // ErrorResult to the JSContext, and that's not desirable in this case.
+  //
+  // We _could_ skip passing a JSContext here and then in
+  // ScriptExecutorRunnable::PostRun end up grabbing it from the WorkerPrivate
+  // and looking at its current compartment.  But that seems like slightly weird
+  // action-at-a-distance...
+  //
+  // In any case, we do NOT try to change the compartment on the JSContext at
+  // this point; in the one case in which we could do that
+  // (CompileScriptRunnable) it actually doesn't matter which compartment we're
+  // in for PostRun.
+  PostRun(cx, mWorkerPrivate, result);
+  MOZ_ASSERT(!jsapi->HasException());
+
+  return result ? NS_OK : NS_ERROR_FAILURE;
+}
+
+nsresult WorkerRunnable::Cancel() {
+  LOG(("WorkerRunnable::Cancel [%p]", this));
+  return NS_OK;
+}
+
+void WorkerDebuggerRunnable::PostDispatch(WorkerPrivate* aWorkerPrivate,
+                                          bool aDispatchResult) {}
+
+WorkerSyncRunnable::WorkerSyncRunnable(WorkerPrivate* aWorkerPrivate,
+                                       nsIEventTarget* aSyncLoopTarget,
+                                       const char* aName)
+    : WorkerRunnable(aWorkerPrivate, aName, WorkerThread),
+      mSyncLoopTarget(aSyncLoopTarget) {
+#ifdef DEBUG
+  if (mSyncLoopTarget) {
+    mWorkerPrivate->AssertValidSyncLoop(mSyncLoopTarget);
+  }
+#endif
+}
+
+WorkerSyncRunnable::WorkerSyncRunnable(
+    WorkerPrivate* aWorkerPrivate, nsCOMPtr<nsIEventTarget>&& aSyncLoopTarget,
+    const char* aName)
+    : WorkerRunnable(aWorkerPrivate, aName, WorkerThread),
+      mSyncLoopTarget(std::move(aSyncLoopTarget)) {
+#ifdef DEBUG
+  if (mSyncLoopTarget) {
+    mWorkerPrivate->AssertValidSyncLoop(mSyncLoopTarget);
+  }
+#endif
+}
+
+WorkerSyncRunnable::~WorkerSyncRunnable() = default;
+
+bool WorkerSyncRunnable::DispatchInternal() {
+  if (mSyncLoopTarget) {
+    RefPtr<WorkerSyncRunnable> runnable(this);
+    return NS_SUCCEEDED(
+        mSyncLoopTarget->Dispatch(runnable.forget(), NS_DISPATCH_NORMAL));
+  }
+
+  return WorkerRunnable::DispatchInternal();
+}
+
+void MainThreadWorkerSyncRunnable::PostDispatch(WorkerPrivate* aWorkerPrivate,
+                                                bool aDispatchResult) {}
+
+MainThreadStopSyncLoopRunnable::MainThreadStopSyncLoopRunnable(
+    WorkerPrivate* aWorkerPrivate, nsCOMPtr<nsIEventTarget>&& aSyncLoopTarget,
+    nsresult aResult)
+    : WorkerSyncRunnable(aWorkerPrivate, std::move(aSyncLoopTarget)),
+      mResult(aResult) {
+  LOG(("MainThreadStopSyncLoopRunnable::MainThreadStopSyncLoopRunnable [%p]",
+       this));
+
+  AssertIsOnMainThread();
+#ifdef DEBUG
+  mWorkerPrivate->AssertValidSyncLoop(mSyncLoopTarget);
+#endif
+}
+
+nsresult MainThreadStopSyncLoopRunnable::Cancel() {
+  LOG(("MainThreadStopSyncLoopRunnable::Cancel [%p]", this));
+  nsresult rv = Run();
+  NS_WARNING_ASSERTION(NS_SUCCEEDED(rv), "Run() failed");
+
+  return rv;
+}
+
+bool MainThreadStopSyncLoopRunnable::WorkerRun(JSContext* aCx,
+                                               WorkerPrivate* aWorkerPrivate) {
+  aWorkerPrivate->AssertIsOnWorkerThread();
+  MOZ_ASSERT(mSyncLoopTarget);
+
+  nsCOMPtr<nsIEventTarget> syncLoopTarget;
+  mSyncLoopTarget.swap(syncLoopTarget);
+
+  aWorkerPrivate->StopSyncLoop(syncLoopTarget, mResult);
+  return true;
+}
+
+bool MainThreadStopSyncLoopRunnable::DispatchInternal() {
+  MOZ_ASSERT(mSyncLoopTarget);
+
+  RefPtr<MainThreadStopSyncLoopRunnable> runnable(this);
+  return NS_SUCCEEDED(
+      mSyncLoopTarget->Dispatch(runnable.forget(), NS_DISPATCH_NORMAL));
+}
+
+void MainThreadStopSyncLoopRunnable::PostDispatch(WorkerPrivate* aWorkerPrivate,
+                                                  bool aDispatchResult) {}
+
+#ifdef DEBUG
+WorkerControlRunnable::WorkerControlRunnable(WorkerPrivate* aWorkerPrivate,
+                                             const char* aName, Target aTarget)
+    : WorkerRunnable(aWorkerPrivate, aName, aTarget) {
+  MOZ_ASSERT(aWorkerPrivate);
+}
+#endif
+
+nsresult WorkerControlRunnable::Cancel() {
+  LOG(("WorkerControlRunnable::Cancel [%p]", this));
+  if (NS_FAILED(Run())) {
+    NS_WARNING("WorkerControlRunnable::Run() failed.");
+  }
+
+  return NS_OK;
+}
+
+bool WorkerControlRunnable::DispatchInternal() {
+  RefPtr<WorkerControlRunnable> runnable(this);
+
+  if (mTarget == WorkerThread) {
+    return NS_SUCCEEDED(
+        mWorkerPrivate->DispatchControlRunnable(runnable.forget()));
+  }
+
+  if (WorkerPrivate* parent = mWorkerPrivate->GetParent()) {
+    return NS_SUCCEEDED(parent->DispatchControlRunnable(runnable.forget()));
+  }
+
+  return NS_SUCCEEDED(mWorkerPrivate->DispatchToMainThread(runnable.forget()));
+}
+
+WorkerMainThreadRunnable::WorkerMainThreadRunnable(
+    WorkerPrivate* aWorkerPrivate, const nsACString& aTelemetryKey)
+    : mozilla::Runnable("dom::WorkerMainThreadRunnable"),
+      mWorkerPrivate(aWorkerPrivate),
+      mTelemetryKey(aTelemetryKey) {
+  mWorkerPrivate->AssertIsOnWorkerThread();
+}
+
+WorkerMainThreadRunnable::~WorkerMainThreadRunnable() = default;
+
+void WorkerMainThreadRunnable::Dispatch(WorkerStatus aFailStatus,
+                                        mozilla::ErrorResult& aRv) {
+  mWorkerPrivate->AssertIsOnWorkerThread();
+
+  TimeStamp startTime = TimeStamp::NowLoRes();
+
+  AutoSyncLoopHolder syncLoop(mWorkerPrivate, aFailStatus);
+
+  mSyncLoopTarget = syncLoop.GetSerialEventTarget();
+  if (!mSyncLoopTarget) {
+    // SyncLoop creation can fail if the worker is shutting down.
+    aRv.Throw(NS_ERROR_DOM_INVALID_STATE_ERR);
+    return;
+  }
+
+  DebugOnly<nsresult> rv = mWorkerPrivate->DispatchToMainThread(this);
+  MOZ_ASSERT(
+      NS_SUCCEEDED(rv),
+      "Should only fail after xpcom-shutdown-threads and we're gone by then");
+
+  bool success = NS_SUCCEEDED(syncLoop.Run());
+
+  Telemetry::Accumulate(
+      Telemetry::SYNC_WORKER_OPERATION, mTelemetryKey,
+      static_cast<uint32_t>(
+          (TimeStamp::NowLoRes() - startTime).ToMilliseconds()));
+
+  Unused << startTime;  // Shut the compiler up.
+
+  if (!success) {
+    aRv.ThrowUncatchableException();
+  }
+}
+
+NS_IMETHODIMP
+WorkerMainThreadRunnable::Run() {
+  AssertIsOnMainThread();
+
+  // This shouldn't be necessary once we're better about making sure no workers
+  // are created during shutdown in earlier phases.
+  if (AppShutdown::IsInOrBeyond(ShutdownPhase::XPCOMShutdownThreads)) {
+    return NS_ERROR_ILLEGAL_DURING_SHUTDOWN;
+  }
+
+  bool runResult = MainThreadRun();
+
+  RefPtr<MainThreadStopSyncLoopRunnable> response =
+      new MainThreadStopSyncLoopRunnable(mWorkerPrivate,
+                                         std::move(mSyncLoopTarget),
+                                         runResult ? NS_OK : NS_ERROR_FAILURE);
+
+  MOZ_ALWAYS_TRUE(response->Dispatch());
+
+  return NS_OK;
+}
+
+bool WorkerSameThreadRunnable::PreDispatch(WorkerPrivate* aWorkerPrivate) {
+  aWorkerPrivate->AssertIsOnWorkerThread();
+  return true;
+}
+
+void WorkerSameThreadRunnable::PostDispatch(WorkerPrivate* aWorkerPrivate,
+                                            bool aDispatchResult) {
+  aWorkerPrivate->AssertIsOnWorkerThread();
+}
+
+WorkerProxyToMainThreadRunnable::WorkerProxyToMainThreadRunnable()
+    : mozilla::Runnable("dom::WorkerProxyToMainThreadRunnable") {}
+
+WorkerProxyToMainThreadRunnable::~WorkerProxyToMainThreadRunnable() = default;
+
+bool WorkerProxyToMainThreadRunnable::Dispatch(WorkerPrivate* aWorkerPrivate) {
+  MOZ_ASSERT(aWorkerPrivate);
+  aWorkerPrivate->AssertIsOnWorkerThread();
+
+  RefPtr<StrongWorkerRef> workerRef = StrongWorkerRef::Create(
+      aWorkerPrivate, "WorkerProxyToMainThreadRunnable");
+  if (NS_WARN_IF(!workerRef)) {
+    RunBackOnWorkerThreadForCleanup(aWorkerPrivate);
+    return false;
+  }
+
+  MOZ_ASSERT(!mWorkerRef);
+  mWorkerRef = new ThreadSafeWorkerRef(workerRef);
+
+  if (ForMessaging()
+          ? NS_WARN_IF(NS_FAILED(
+                aWorkerPrivate->DispatchToMainThreadForMessaging(this)))
+          : NS_WARN_IF(NS_FAILED(aWorkerPrivate->DispatchToMainThread(this)))) {
+    ReleaseWorker();
+    RunBackOnWorkerThreadForCleanup(aWorkerPrivate);
+    return false;
+  }
+
+  return true;
+}
+
+NS_IMETHODIMP
+WorkerProxyToMainThreadRunnable::Run() {
+  AssertIsOnMainThread();
+  RunOnMainThread(mWorkerRef->Private());
+  PostDispatchOnMainThread();
+  return NS_OK;
+}
+
+void WorkerProxyToMainThreadRunnable::PostDispatchOnMainThread() {
+  class ReleaseRunnable final : public MainThreadWorkerControlRunnable {
+    RefPtr<WorkerProxyToMainThreadRunnable> mRunnable;
+
+   public:
+    ReleaseRunnable(WorkerPrivate* aWorkerPrivate,
+                    WorkerProxyToMainThreadRunnable* aRunnable)
+        : MainThreadWorkerControlRunnable(aWorkerPrivate),
+          mRunnable(aRunnable) {
+      MOZ_ASSERT(aRunnable);
+    }
+
+    virtual nsresult Cancel() override {
+      Unused << WorkerRun(nullptr, mWorkerPrivate);
+      return NS_OK;
+    }
+
+    virtual bool WorkerRun(JSContext* aCx,
+                           WorkerPrivate* aWorkerPrivate) override {
+      MOZ_ASSERT(aWorkerPrivate);
+      aWorkerPrivate->AssertIsOnWorkerThread();
+
+      if (mRunnable) {
+        mRunnable->RunBackOnWorkerThreadForCleanup(aWorkerPrivate);
+
+        // Let's release the worker thread.
+        mRunnable->ReleaseWorker();
+        mRunnable = nullptr;
+      }
+
+      return true;
+    }
+
+   private:
+    ~ReleaseRunnable() = default;
+  };
+
+  RefPtr<WorkerControlRunnable> runnable =
+      new ReleaseRunnable(mWorkerRef->Private(), this);
+  Unused << NS_WARN_IF(!runnable->Dispatch());
+}
+
+void WorkerProxyToMainThreadRunnable::ReleaseWorker() { mWorkerRef = nullptr; }
+
+bool WorkerDebuggeeRunnable::PreDispatch(WorkerPrivate* aWorkerPrivate) {
+  if (mTarget == ParentThread) {
+    RefPtr<StrongWorkerRef> strongRef = StrongWorkerRef::Create(
+        aWorkerPrivate, "WorkerDebuggeeRunnable::mSender");
+    if (!strongRef) {
+      return false;
+    }
+
+    mSender = new ThreadSafeWorkerRef(strongRef);
+  }
+
+  return WorkerRunnable::PreDispatch(aWorkerPrivate);
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/workers/WorkerRunnable.h b/dom/workers/WorkerRunnable.h
new file mode 100644
index 0000000000..d133f11ea2
--- /dev/null
+++ b/dom/workers/WorkerRunnable.h
@@ -0,0 +1,503 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_workers_workerrunnable_h__
+#define mozilla_dom_workers_workerrunnable_h__
+
+#include <cstdint>
+#include <utility>
+#include "MainThreadUtils.h"
+#include "mozilla/Atomics.h"
+#include "mozilla/RefPtr.h"
+#include "mozilla/dom/WorkerRef.h"
+#include "mozilla/dom/WorkerStatus.h"
+#include "nsCOMPtr.h"
+#include "nsIRunnable.h"
+#include "nsISupports.h"
+#include "nsStringFwd.h"
+#include "nsThreadUtils.h"
+#include "nscore.h"
+
+struct JSContext;
+class nsIEventTarget;
+class nsIGlobalObject;
+
+namespace mozilla {
+
+class ErrorResult;
+
+namespace dom {
+
+class WorkerPrivate;
+
+// Use this runnable to communicate from the worker to its parent or vice-versa.
+class WorkerRunnable : public nsIRunnable
+#ifdef MOZ_COLLECTING_RUNNABLE_TELEMETRY
+    ,
+                       public nsINamed
+#endif
+{
+ public:
+  enum Target {
+    // Target the main thread for top-level workers, otherwise target the
+    // WorkerThread of the worker's parent.
+    ParentThread,
+
+    // Target the thread where the worker event loop runs.
+    WorkerThread,
+  };
+
+ protected:
+  // The WorkerPrivate that this runnable is associated with.
+  WorkerPrivate* mWorkerPrivate;
+
+  // See above.
+  Target mTarget;
+
+#ifdef MOZ_COLLECTING_RUNNABLE_TELEMETRY
+  const char* mName = nullptr;
+#endif
+
+ private:
+  // Whether or not Cancel() is currently being called from inside the Run()
+  // method. Avoids infinite recursion when a subclass calls Run() from inside
+  // Cancel(). Only checked and modified on the target thread.
+  bool mCallingCancelWithinRun;
+
+ public:
+  NS_DECL_THREADSAFE_ISUPPORTS
+#ifdef MOZ_COLLECTING_RUNNABLE_TELEMETRY
+  NS_DECL_NSINAMED
+#endif
+
+  virtual nsresult Cancel();
+
+  // The return value is true if and only if both PreDispatch and
+  // DispatchInternal return true.
+  bool Dispatch();
+
+  // True if this runnable is handled by running JavaScript in some global that
+  // could possibly be a debuggee, and thus needs to be deferred when the target
+  // is paused in the debugger, until the JavaScript invocation in progress has
+  // run to completion. Examples are MessageEventRunnable and
+  // ReportErrorRunnable. These runnables are segregated into separate
+  // ThrottledEventQueues, which the debugger pauses.
+  //
+  // Note that debugger runnables do not fall in this category, since we don't
+  // support debugging the debugger server at the moment.
+  virtual bool IsDebuggeeRunnable() const { return false; }
+
+  static WorkerRunnable* FromRunnable(nsIRunnable* aRunnable);
+
+ protected:
+  WorkerRunnable(WorkerPrivate* aWorkerPrivate,
+                 const char* aName = "WorkerRunnable",
+                 Target aTarget = WorkerThread)
+#ifdef DEBUG
+      ;
+#else
+      : mWorkerPrivate(aWorkerPrivate),
+        mTarget(aTarget),
+#  ifdef MOZ_COLLECTING_RUNNABLE_TELEMETRY
+        mName(aName),
+#  endif
+        mCallingCancelWithinRun(false) {
+  }
+#endif
+
+  // This class is reference counted.
+  virtual ~WorkerRunnable() = default;
+
+  // Returns true if this runnable should be dispatched to the debugger queue,
+  // and false otherwise.
+  virtual bool IsDebuggerRunnable() const;
+
+  nsIGlobalObject* DefaultGlobalObject() const;
+
+  // By default asserts that Dispatch() is being called on the right thread
+  // (ParentThread if |mTarget| is WorkerThread).
+  virtual bool PreDispatch(WorkerPrivate* aWorkerPrivate);
+
+  // By default asserts that Dispatch() is being called on the right thread
+  // (ParentThread if |mTarget| is WorkerThread).
+  virtual void PostDispatch(WorkerPrivate* aWorkerPrivate,
+                            bool aDispatchResult);
+
+  // May be implemented by subclasses if desired if they need to do some sort of
+  // setup before we try to set up our JSContext and compartment for real.
+  // Typically the only thing that should go in here is creation of the worker's
+  // global.
+  //
+  // If false is returned, WorkerRun will not be called at all.  PostRun will
+  // still be called, with false passed for aRunResult.
+  virtual bool PreRun(WorkerPrivate* aWorkerPrivate);
+
+  // Must be implemented by subclasses. Called on the target thread.  The return
+  // value will be passed to PostRun().  The JSContext passed in here comes from
+  // an AutoJSAPI (or AutoEntryScript) that we set up on the stack.  If
+  // mTarget is ParentThread, it is in the compartment of
+  // mWorkerPrivate's reflector (i.e. the worker object in the parent thread),
+  // unless that reflector is null, in which case it's in the compartment of the
+  // parent global (which is the compartment reflector would have been in), or
+  // in the null compartment if there is no parent global.  For other mTarget
+  // values, we're running on the worker thread and aCx is in whatever
+  // compartment GetCurrentWorkerThreadJSContext() was in when
+  // nsIRunnable::Run() got called.  This is actually important for cases when a
+  // runnable spins a syncloop and wants everything that happens during the
+  // syncloop to happen in the compartment that runnable set up (which may, for
+  // example, be a debugger sandbox compartment!).  If aCx wasn't in a
+  // compartment to start with, aCx will be in either the debugger global's
+  // compartment or the worker's global's compartment depending on whether
+  // IsDebuggerRunnable() is true.
+  //
+  // Immediately after WorkerRun returns, the caller will assert that either it
+  // returns false or there is no exception pending on aCx.  Then it will report
+  // any pending exceptions on aCx.
+  virtual bool WorkerRun(JSContext* aCx, WorkerPrivate* aWorkerPrivate) = 0;
+
+  // By default asserts that Run() (and WorkerRun()) were called on the correct
+  // thread.
+  //
+  // The aCx passed here is the same one as was passed to WorkerRun and is
+  // still in the same compartment.  PostRun implementations must NOT leave an
+  // exception on the JSContext and must not run script, because the incoming
+  // JSContext may be in the null compartment.
+  virtual void PostRun(JSContext* aCx, WorkerPrivate* aWorkerPrivate,
+                       bool aRunResult);
+
+  virtual bool DispatchInternal();
+
+  // Calling Run() directly is not supported. Just call Dispatch() and
+  // WorkerRun() will be called on the correct thread automatically.
+  NS_DECL_NSIRUNNABLE
+};
+
+// This runnable is used to send a message to a worker debugger.
+class WorkerDebuggerRunnable : public WorkerRunnable {
+ protected:
+  explicit WorkerDebuggerRunnable(WorkerPrivate* aWorkerPrivate,
+                                  const char* aName = "WorkerDebuggerRunnable")
+      : WorkerRunnable(aWorkerPrivate, aName, WorkerThread) {}
+
+  virtual ~WorkerDebuggerRunnable() = default;
+
+ private:
+  virtual bool IsDebuggerRunnable() const override { return true; }
+
+  bool PreDispatch(WorkerPrivate* aWorkerPrivate) final {
+    AssertIsOnMainThread();
+
+    return true;
+  }
+
+  virtual void PostDispatch(WorkerPrivate* aWorkerPrivate,
+                            bool aDispatchResult) override;
+};
+
+// This runnable is used to send a message directly to a worker's sync loop.
+class WorkerSyncRunnable : public WorkerRunnable {
+ protected:
+  nsCOMPtr<nsIEventTarget> mSyncLoopTarget;
+
+  // Passing null for aSyncLoopTarget is allowed and will result in the behavior
+  // of a normal WorkerRunnable.
+  WorkerSyncRunnable(WorkerPrivate* aWorkerPrivate,
+                     nsIEventTarget* aSyncLoopTarget,
+                     const char* aName = "WorkerSyncRunnable");
+
+  WorkerSyncRunnable(WorkerPrivate* aWorkerPrivate,
+                     nsCOMPtr<nsIEventTarget>&& aSyncLoopTarget,
+                     const char* aName = "WorkerSyncRunnable");
+
+  virtual ~WorkerSyncRunnable();
+
+  virtual bool DispatchInternal() override;
+};
+
+// This runnable is identical to WorkerSyncRunnable except it is meant to be
+// created on and dispatched from the main thread only.  Its WorkerRun/PostRun
+// will run on the worker thread.
+class MainThreadWorkerSyncRunnable : public WorkerSyncRunnable {
+ protected:
+  // Passing null for aSyncLoopTarget is allowed and will result in the behavior
+  // of a normal WorkerRunnable.
+  MainThreadWorkerSyncRunnable(
+      WorkerPrivate* aWorkerPrivate, nsIEventTarget* aSyncLoopTarget,
+      const char* aName = "MainThreadWorkerSyncRunnable")
+      : WorkerSyncRunnable(aWorkerPrivate, aSyncLoopTarget, aName) {
+    AssertIsOnMainThread();
+  }
+
+  MainThreadWorkerSyncRunnable(
+      WorkerPrivate* aWorkerPrivate, nsCOMPtr<nsIEventTarget>&& aSyncLoopTarget,
+      const char* aName = "MainThreadWorkerSyncRunnable")
+      : WorkerSyncRunnable(aWorkerPrivate, std::move(aSyncLoopTarget), aName) {
+    AssertIsOnMainThread();
+  }
+
+  virtual ~MainThreadWorkerSyncRunnable() = default;
+
+ private:
+  virtual bool PreDispatch(WorkerPrivate* aWorkerPrivate) override {
+    AssertIsOnMainThread();
+    return true;
+  }
+
+  virtual void PostDispatch(WorkerPrivate* aWorkerPrivate,
+                            bool aDispatchResult) override;
+};
+
+// This runnable is processed as soon as it is received by the worker,
+// potentially running before previously queued runnables and perhaps even with
+// other JS code executing on the stack. These runnables must not alter the
+// state of the JS runtime and should only twiddle state values.
+class WorkerControlRunnable : public WorkerRunnable {
+  friend class WorkerPrivate;
+
+ protected:
+  WorkerControlRunnable(WorkerPrivate* aWorkerPrivate,
+                        const char* aName = "WorkerControlRunnable",
+                        Target aTarget = WorkerThread)
+#ifdef DEBUG
+      ;
+#else
+      : WorkerRunnable(aWorkerPrivate, aName, aTarget) {
+  }
+#endif
+
+  virtual ~WorkerControlRunnable() = default;
+
+  nsresult Cancel() override;
+
+ public:
+  NS_INLINE_DECL_REFCOUNTING_INHERITED(WorkerControlRunnable, WorkerRunnable)
+
+ private:
+  virtual bool DispatchInternal() override;
+
+  // Should only be called by WorkerPrivate::DoRunLoop.
+  using WorkerRunnable::Cancel;
+};
+
+// A convenience class for WorkerRunnables that are originated on the main
+// thread.
+class MainThreadWorkerRunnable : public WorkerRunnable {
+ protected:
+  explicit MainThreadWorkerRunnable(
+      WorkerPrivate* aWorkerPrivate,
+      const char* aName = "MainThreadWorkerRunnable")
+      : WorkerRunnable(aWorkerPrivate, aName, WorkerThread) {
+    AssertIsOnMainThread();
+  }
+
+  virtual ~MainThreadWorkerRunnable() = default;
+
+  virtual bool PreDispatch(WorkerPrivate* aWorkerPrivate) override {
+    AssertIsOnMainThread();
+    return true;
+  }
+
+  virtual void PostDispatch(WorkerPrivate* aWorkerPrivate,
+                            bool aDispatchResult) override {
+    AssertIsOnMainThread();
+  }
+};
+
+// A convenience class for WorkerControlRunnables that originate on the main
+// thread.
+class MainThreadWorkerControlRunnable : public WorkerControlRunnable {
+ protected:
+  explicit MainThreadWorkerControlRunnable(
+      WorkerPrivate* aWorkerPrivate,
+      const char* aName = "MainThreadWorkerControlRunnable")
+      : WorkerControlRunnable(aWorkerPrivate, aName, WorkerThread) {}
+
+  virtual ~MainThreadWorkerControlRunnable() = default;
+
+  virtual bool PreDispatch(WorkerPrivate* aWorkerPrivate) override {
+    AssertIsOnMainThread();
+    return true;
+  }
+
+  virtual void PostDispatch(WorkerPrivate* aWorkerPrivate,
+                            bool aDispatchResult) override {
+    AssertIsOnMainThread();
+  }
+};
+
+// A WorkerRunnable that should be dispatched from the worker to itself for
+// async tasks.
+//
+// Async tasks will almost always want to use this since
+// a WorkerSameThreadRunnable keeps the Worker from being GCed.
+class WorkerSameThreadRunnable : public WorkerRunnable {
+ protected:
+  explicit WorkerSameThreadRunnable(
+      WorkerPrivate* aWorkerPrivate,
+      const char* aName = "WorkerSameThreadRunnable")
+      : WorkerRunnable(aWorkerPrivate, aName, WorkerThread) {}
+
+  virtual ~WorkerSameThreadRunnable() = default;
+
+  virtual bool PreDispatch(WorkerPrivate* aWorkerPrivate) override;
+
+  virtual void PostDispatch(WorkerPrivate* aWorkerPrivate,
+                            bool aDispatchResult) override;
+
+  // We just delegate PostRun to WorkerRunnable, since it does exactly
+  // what we want.
+};
+
+// Base class for the runnable objects, which makes a synchronous call to
+// dispatch the tasks from the worker thread to the main thread.
+//
+// Note that the derived class must override MainThreadRun.
+class WorkerMainThreadRunnable : public Runnable {
+ protected:
+  WorkerPrivate* mWorkerPrivate;
+  nsCOMPtr<nsISerialEventTarget> mSyncLoopTarget;
+  const nsCString mTelemetryKey;
+
+  explicit WorkerMainThreadRunnable(WorkerPrivate* aWorkerPrivate,
+                                    const nsACString& aTelemetryKey);
+  ~WorkerMainThreadRunnable();
+
+  virtual bool MainThreadRun() = 0;
+
+ public:
+  // Dispatch the runnable to the main thread.  If dispatch to main thread
+  // fails, or if the worker is in a state equal or greater of aFailStatus, an
+  // error will be reported on aRv. Normally you want to use 'Canceling' for
+  // aFailStatus, except if you want an infallible runnable. In this case, use
+  // 'Killing'.
+  // In that case the error MUST be propagated out to script.
+  void Dispatch(WorkerStatus aFailStatus, ErrorResult& aRv);
+
+ private:
+  NS_IMETHOD Run() override;
+};
+
+// This runnable is an helper class for dispatching something from a worker
+// thread to the main-thread and back to the worker-thread. During this
+// operation, this class will keep the worker alive.
+// The purpose of RunBackOnWorkerThreadForCleanup() must be used, as the name
+// says, only to release resources, no JS has to be executed, no timers, or
+// other things. The reason of such limitations is that, in order to execute
+// this method in any condition (also when the worker is shutting down), a
+// Control Runnable is used, and, this could generate a reordering of existing
+// runnables.
+class WorkerProxyToMainThreadRunnable : public Runnable {
+ protected:
+  WorkerProxyToMainThreadRunnable();
+
+  virtual ~WorkerProxyToMainThreadRunnable();
+
+  // First this method is called on the main-thread.
+  virtual void RunOnMainThread(WorkerPrivate* aWorkerPrivate) = 0;
+
+  // After this second method is called on the worker-thread.
+  virtual void RunBackOnWorkerThreadForCleanup(
+      WorkerPrivate* aWorkerPrivate) = 0;
+
+ public:
+  bool Dispatch(WorkerPrivate* aWorkerPrivate);
+
+  virtual bool ForMessaging() const { return false; }
+
+ private:
+  NS_IMETHOD Run() override;
+
+  void PostDispatchOnMainThread();
+
+  void ReleaseWorker();
+
+  RefPtr<ThreadSafeWorkerRef> mWorkerRef;
+};
+
+// This runnable is used to stop a sync loop and it's meant to be used on the
+// main-thread only.
+class MainThreadStopSyncLoopRunnable : public WorkerSyncRunnable {
+  nsresult mResult;
+
+ public:
+  // Passing null for aSyncLoopTarget is not allowed.
+  MainThreadStopSyncLoopRunnable(WorkerPrivate* aWorkerPrivate,
+                                 nsCOMPtr<nsIEventTarget>&& aSyncLoopTarget,
+                                 nsresult aResult);
+
+  // By default StopSyncLoopRunnables cannot be canceled since they could leave
+  // a sync loop spinning forever.
+  nsresult Cancel() override;
+
+ protected:
+  virtual ~MainThreadStopSyncLoopRunnable() = default;
+
+ private:
+  bool PreDispatch(WorkerPrivate* aWorkerPrivate) final {
+    AssertIsOnMainThread();
+    return true;
+  }
+
+  virtual void PostDispatch(WorkerPrivate* aWorkerPrivate,
+                            bool aDispatchResult) override;
+
+  virtual bool WorkerRun(JSContext* aCx,
+                         WorkerPrivate* aWorkerPrivate) override;
+
+  bool DispatchInternal() final;
+};
+
+// Runnables handled by content JavaScript (MessageEventRunnable, JavaScript
+// error reports, and so on) must not be delivered while that content is in the
+// midst of being debugged; the debuggee must be allowed to complete its current
+// JavaScript invocation and return to its own event loop. Only then is it
+// prepared for messages sent from the worker.
+//
+// Runnables that need to be deferred in this way should inherit from this
+// class. They will be routed to mMainThreadDebuggeeEventTarget, which is paused
+// while the window is suspended, as it is whenever the debugger spins its
+// nested event loop. When the debugger leaves its nested event loop, it resumes
+// the window, so that mMainThreadDebuggeeEventTarget will resume delivering
+// runnables from the worker when control returns to the main event loop.
+//
+// When a page enters the bfcache, it freezes all its workers. Since a frozen
+// worker processes only control runnables, it doesn't take any special
+// consideration to prevent WorkerDebuggeeRunnables sent from child to parent
+// workers from running; they'll never run anyway. But WorkerDebuggeeRunnables
+// from a top-level frozen worker to its parent window must not be delivered
+// either, even as the main thread event loop continues to spin. Thus, freezing
+// a top-level worker also pauses mMainThreadDebuggeeEventTarget.
+class WorkerDebuggeeRunnable : public WorkerRunnable {
+ protected:
+  WorkerDebuggeeRunnable(WorkerPrivate* aWorkerPrivate,
+                         const char* aName = "WorkerDebuggeeRunnable",
+                         Target aTarget = ParentThread)
+      : WorkerRunnable(aWorkerPrivate, aName, aTarget) {}
+
+  bool PreDispatch(WorkerPrivate* aWorkerPrivate) override;
+
+ private:
+  // This override is deliberately private: it doesn't make sense to call it if
+  // we know statically that we are a WorkerDebuggeeRunnable.
+  bool IsDebuggeeRunnable() const override { return true; }
+
+  // Runnables sent upwards, to the content window or parent worker, must keep
+  // their sender alive until they are delivered: they check back with the
+  // sender in case it has been terminated after having dispatched the runnable
+  // (in which case it should not be acted upon); and runnables sent to content
+  // wait until delivery to determine the target window, since
+  // WorkerPrivate::GetWindow may only be used on the main thread.
+  //
+  // Runnables sent downwards, from content to a worker or from a worker to a
+  // child, keep the sender alive because they are WorkerThread
+  // runnables, and so leave this null.
+  RefPtr<ThreadSafeWorkerRef> mSender;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_workers_workerrunnable_h__
diff --git a/dom/workers/WorkerScope.cpp b/dom/workers/WorkerScope.cpp
new file mode 100644
index 0000000000..159829f4a8
--- /dev/null
+++ b/dom/workers/WorkerScope.cpp
@@ -0,0 +1,1406 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/dom/WorkerScope.h"
+
+#include <stdio.h>
+#include <new>
+#include <utility>
+#include "Crypto.h"
+#include "GeckoProfiler.h"
+#include "MainThreadUtils.h"
+#include "ScriptLoader.h"
+#include "js/CompilationAndEvaluation.h"
+#include "js/CompileOptions.h"
+#include "js/RealmOptions.h"
+#include "js/RootingAPI.h"
+#include "js/SourceText.h"
+#include "js/Value.h"
+#include "js/Wrapper.h"
+#include "jsapi.h"
+#include "jsfriendapi.h"
+#include "mozilla/AlreadyAddRefed.h"
+#include "mozilla/BaseProfilerMarkersPrerequisites.h"
+#include "mozilla/CycleCollectedJSContext.h"
+#include "mozilla/ErrorResult.h"
+#include "mozilla/EventListenerManager.h"
+#include "mozilla/Logging.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/MozPromise.h"
+#include "mozilla/Mutex.h"
+#include "mozilla/NotNull.h"
+#include "mozilla/RefPtr.h"
+#include "mozilla/Result.h"
+#include "mozilla/StaticAnalysisFunctions.h"
+#include "mozilla/StorageAccess.h"
+#include "mozilla/UniquePtr.h"
+#include "mozilla/Unused.h"
+#include "mozilla/dom/AutoEntryScript.h"
+#include "mozilla/ipc/BackgroundChild.h"
+#include "mozilla/dom/BindingDeclarations.h"
+#include "mozilla/dom/BindingUtils.h"
+#include "mozilla/dom/BlobURLProtocolHandler.h"
+#include "mozilla/dom/CSPEvalChecker.h"
+#include "mozilla/dom/CallbackDebuggerNotification.h"
+#include "mozilla/dom/ClientSource.h"
+#include "mozilla/dom/Clients.h"
+#include "mozilla/dom/Console.h"
+#include "mozilla/dom/DOMMozPromiseRequestHolder.h"
+#include "mozilla/dom/DebuggerNotification.h"
+#include "mozilla/dom/DebuggerNotificationBinding.h"
+#include "mozilla/dom/DebuggerNotificationManager.h"
+#include "mozilla/dom/DedicatedWorkerGlobalScopeBinding.h"
+#include "mozilla/dom/DOMString.h"
+#include "mozilla/dom/Fetch.h"
+#include "mozilla/dom/FontFaceSet.h"
+#include "mozilla/dom/IDBFactory.h"
+#include "mozilla/dom/ImageBitmap.h"
+#include "mozilla/dom/ImageBitmapSource.h"
+#include "mozilla/dom/MessagePortBinding.h"
+#include "mozilla/ipc/PBackgroundChild.h"
+#include "mozilla/ipc/PBackgroundSharedTypes.h"
+#include "mozilla/dom/Performance.h"
+#include "mozilla/dom/Promise.h"
+#include "mozilla/dom/PromiseWorkerProxy.h"
+#include "mozilla/dom/WebTaskSchedulerWorker.h"
+#include "mozilla/dom/ScriptSettings.h"
+#include "mozilla/dom/SerializedStackHolder.h"
+#include "mozilla/dom/ServiceWorkerDescriptor.h"
+#include "mozilla/dom/ServiceWorkerGlobalScopeBinding.h"
+#include "mozilla/dom/ServiceWorkerManager.h"
+#include "mozilla/dom/ServiceWorkerRegistration.h"
+#include "mozilla/dom/ServiceWorkerRegistrationDescriptor.h"
+#include "mozilla/dom/ServiceWorkerUtils.h"
+#include "mozilla/dom/SharedWorkerGlobalScopeBinding.h"
+#include "mozilla/dom/SimpleGlobalObject.h"
+#include "mozilla/dom/TimeoutHandler.h"
+#include "mozilla/dom/TestUtils.h"
+#include "mozilla/dom/WorkerCommon.h"
+#include "mozilla/dom/WorkerDebuggerGlobalScopeBinding.h"
+#include "mozilla/dom/WorkerGlobalScopeBinding.h"
+#include "mozilla/dom/WorkerLocation.h"
+#include "mozilla/dom/WorkerNavigator.h"
+#include "mozilla/dom/WorkerPrivate.h"
+#include "mozilla/dom/WorkerRunnable.h"
+#include "mozilla/dom/WorkerDocumentListener.h"
+#include "mozilla/dom/VsyncWorkerChild.h"
+#include "mozilla/dom/cache/CacheStorage.h"
+#include "mozilla/dom/cache/Types.h"
+#include "mozilla/extensions/ExtensionBrowser.h"
+#include "mozilla/fallible.h"
+#include "mozilla/gfx/Rect.h"
+#include "nsAtom.h"
+#include "nsCOMPtr.h"
+#include "nsContentUtils.h"
+#include "nsDebug.h"
+#include "nsGkAtoms.h"
+#include "nsIEventTarget.h"
+#include "nsIGlobalObject.h"
+#include "nsIScriptError.h"
+#include "nsISerialEventTarget.h"
+#include "nsIWeakReference.h"
+#include "nsJSUtils.h"
+#include "nsLiteralString.h"
+#include "nsQueryObject.h"
+#include "nsReadableUtils.h"
+#include "nsRFPService.h"
+#include "nsString.h"
+#include "nsTArray.h"
+#include "nsTLiteralString.h"
+#include "nsThreadUtils.h"
+#include "nsWeakReference.h"
+#include "nsWrapperCacheInlines.h"
+#include "nscore.h"
+#include "xpcpublic.h"
+
+#ifdef ANDROID
+#  include <android/log.h>
+#endif
+
+#ifdef XP_WIN
+#  undef PostMessage
+#endif
+
+using mozilla::dom::cache::CacheStorage;
+using mozilla::dom::workerinternals::NamedWorkerGlobalScopeMixin;
+using mozilla::ipc::BackgroundChild;
+using mozilla::ipc::PBackgroundChild;
+using mozilla::ipc::PrincipalInfo;
+
+namespace mozilla::dom {
+
+static mozilla::LazyLogModule sWorkerScopeLog("WorkerScope");
+
+#ifdef LOG
+#  undef LOG
+#endif
+#define LOG(args) MOZ_LOG(sWorkerScopeLog, LogLevel::Debug, args);
+
+class WorkerScriptTimeoutHandler final : public ScriptTimeoutHandler {
+ public:
+  NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(WorkerScriptTimeoutHandler,
+                                           ScriptTimeoutHandler)
+
+  WorkerScriptTimeoutHandler(JSContext* aCx, nsIGlobalObject* aGlobal,
+                             const nsAString& aExpression)
+      : ScriptTimeoutHandler(aCx, aGlobal, aExpression) {}
+
+  MOZ_CAN_RUN_SCRIPT virtual bool Call(const char* aExecutionReason) override;
+
+ private:
+  virtual ~WorkerScriptTimeoutHandler() = default;
+};
+
+NS_IMPL_CYCLE_COLLECTION_INHERITED(WorkerScriptTimeoutHandler,
+                                   ScriptTimeoutHandler)
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(WorkerScriptTimeoutHandler)
+NS_INTERFACE_MAP_END_INHERITING(ScriptTimeoutHandler)
+
+NS_IMPL_ADDREF_INHERITED(WorkerScriptTimeoutHandler, ScriptTimeoutHandler)
+NS_IMPL_RELEASE_INHERITED(WorkerScriptTimeoutHandler, ScriptTimeoutHandler)
+
+bool WorkerScriptTimeoutHandler::Call(const char* aExecutionReason) {
+  nsAutoMicroTask mt;
+  AutoEntryScript aes(mGlobal, aExecutionReason, false);
+
+  JSContext* cx = aes.cx();
+  JS::CompileOptions options(cx);
+  options.setFileAndLine(mFileName.get(), mLineNo).setNoScriptRval(true);
+  options.setIntroductionType("domTimer");
+
+  JS::Rooted<JS::Value> unused(cx);
+  JS::SourceText<char16_t> srcBuf;
+  if (!srcBuf.init(cx, mExpr.BeginReading(), mExpr.Length(),
+                   JS::SourceOwnership::Borrowed) ||
+      !JS::Evaluate(cx, options, srcBuf, &unused)) {
+    if (!JS_IsExceptionPending(cx)) {
+      return false;
+    }
+  }
+
+  return true;
+};
+
+namespace workerinternals {
+void NamedWorkerGlobalScopeMixin::GetName(DOMString& aName) const {
+  aName.AsAString() = mName;
+}
+}  // namespace workerinternals
+
+NS_IMPL_CYCLE_COLLECTION_CLASS(WorkerGlobalScopeBase)
+
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(WorkerGlobalScopeBase,
+                                                  DOMEventTargetHelper)
+  tmp->AssertIsOnWorkerThread();
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mConsole)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mModuleLoader)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mSerialEventTarget)
+  tmp->TraverseObjectsInGlobal(cb);
+  // If we already exited WorkerThreadPrimaryRunnable, we will find it
+  // nullptr and there is nothing left to do here on the WorkerPrivate,
+  // in particular the timeouts have already been canceled and unlinked.
+  if (tmp->mWorkerPrivate) {
+    tmp->mWorkerPrivate->TraverseTimeouts(cb);
+  }
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED(WorkerGlobalScopeBase,
+                                                DOMEventTargetHelper)
+  tmp->AssertIsOnWorkerThread();
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mConsole)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mModuleLoader)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mSerialEventTarget)
+  tmp->UnlinkObjectsInGlobal();
+  // If we already exited WorkerThreadPrimaryRunnable, we will find it
+  // nullptr and there is nothing left to do here on the WorkerPrivate,
+  // in particular the timeouts have already been canceled and unlinked.
+  if (tmp->mWorkerPrivate) {
+    tmp->mWorkerPrivate->UnlinkTimeouts();
+  }
+  NS_IMPL_CYCLE_COLLECTION_UNLINK_WEAK_REFERENCE
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+
+NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN_INHERITED(WorkerGlobalScopeBase,
+                                               DOMEventTargetHelper)
+  tmp->AssertIsOnWorkerThread();
+NS_IMPL_CYCLE_COLLECTION_TRACE_END
+
+NS_IMPL_ADDREF_INHERITED(WorkerGlobalScopeBase, DOMEventTargetHelper)
+NS_IMPL_RELEASE_INHERITED(WorkerGlobalScopeBase, DOMEventTargetHelper)
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(WorkerGlobalScopeBase)
+  NS_INTERFACE_MAP_ENTRY(nsIGlobalObject)
+  NS_INTERFACE_MAP_ENTRY(nsISupportsWeakReference)
+NS_INTERFACE_MAP_END_INHERITING(DOMEventTargetHelper)
+
+WorkerGlobalScopeBase::WorkerGlobalScopeBase(
+    WorkerPrivate* aWorkerPrivate, UniquePtr<ClientSource> aClientSource)
+    : mWorkerPrivate(aWorkerPrivate),
+      mClientSource(std::move(aClientSource)),
+      mSerialEventTarget(aWorkerPrivate->HybridEventTarget()) {
+  LOG(("WorkerGlobalScopeBase::WorkerGlobalScopeBase [%p]", this));
+  MOZ_ASSERT(mWorkerPrivate);
+#ifdef DEBUG
+  mWorkerPrivate->AssertIsOnWorkerThread();
+  mWorkerThreadUsedOnlyForAssert = PR_GetCurrentThread();
+#endif
+  MOZ_ASSERT(mClientSource);
+
+  MOZ_DIAGNOSTIC_ASSERT(
+      mSerialEventTarget,
+      "There should be an event target when a worker global is created.");
+
+  // In workers, each DETH must have an owner. Because the global scope doesn't
+  // have one, let's set it as owner of itself.
+  BindToOwner(static_cast<nsIGlobalObject*>(this));
+}
+
+WorkerGlobalScopeBase::~WorkerGlobalScopeBase() = default;
+
+JSObject* WorkerGlobalScopeBase::GetGlobalJSObject() {
+  AssertIsOnWorkerThread();
+  return GetWrapper();
+}
+
+JSObject* WorkerGlobalScopeBase::GetGlobalJSObjectPreserveColor() const {
+  AssertIsOnWorkerThread();
+  return GetWrapperPreserveColor();
+}
+
+bool WorkerGlobalScopeBase::IsSharedMemoryAllowed() const {
+  AssertIsOnWorkerThread();
+  return mWorkerPrivate->IsSharedMemoryAllowed();
+}
+
+bool WorkerGlobalScopeBase::ShouldResistFingerprinting(
+    RFPTarget aTarget) const {
+  AssertIsOnWorkerThread();
+  return mWorkerPrivate->ShouldResistFingerprinting(aTarget);
+}
+
+OriginTrials WorkerGlobalScopeBase::Trials() const {
+  AssertIsOnWorkerThread();
+  return mWorkerPrivate->Trials();
+}
+
+StorageAccess WorkerGlobalScopeBase::GetStorageAccess() {
+  AssertIsOnWorkerThread();
+  return mWorkerPrivate->StorageAccess();
+}
+
+Maybe<ClientInfo> WorkerGlobalScopeBase::GetClientInfo() const {
+  return Some(mClientSource->Info());
+}
+
+Maybe<ServiceWorkerDescriptor> WorkerGlobalScopeBase::GetController() const {
+  return mClientSource->GetController();
+}
+
+mozilla::Result<mozilla::ipc::PrincipalInfo, nsresult>
+WorkerGlobalScopeBase::GetStorageKey() {
+  AssertIsOnWorkerThread();
+
+  const mozilla::ipc::PrincipalInfo& principalInfo =
+      mWorkerPrivate->GetEffectiveStoragePrincipalInfo();
+
+  // Block expanded and null principals, let content and system through.
+  if (principalInfo.type() !=
+          mozilla::ipc::PrincipalInfo::TContentPrincipalInfo &&
+      principalInfo.type() !=
+          mozilla::ipc::PrincipalInfo::TSystemPrincipalInfo) {
+    return Err(NS_ERROR_DOM_SECURITY_ERR);
+  }
+
+  return principalInfo;
+}
+
+void WorkerGlobalScopeBase::Control(
+    const ServiceWorkerDescriptor& aServiceWorker) {
+  AssertIsOnWorkerThread();
+  MOZ_DIAGNOSTIC_ASSERT(!mWorkerPrivate->IsChromeWorker());
+  MOZ_DIAGNOSTIC_ASSERT(mWorkerPrivate->Kind() != WorkerKindService);
+
+  if (IsBlobURI(mWorkerPrivate->GetBaseURI())) {
+    // Blob URL workers can only become controlled by inheriting from
+    // their parent.  Make sure to note this properly.
+    mClientSource->InheritController(aServiceWorker);
+  } else {
+    // Otherwise this is a normal interception and we simply record the
+    // controller locally.
+    mClientSource->SetController(aServiceWorker);
+  }
+}
+
+nsresult WorkerGlobalScopeBase::Dispatch(
+    already_AddRefed<nsIRunnable>&& aRunnable) const {
+  return SerialEventTarget()->Dispatch(std::move(aRunnable),
+                                       NS_DISPATCH_NORMAL);
+}
+
+nsISerialEventTarget* WorkerGlobalScopeBase::SerialEventTarget() const {
+  AssertIsOnWorkerThread();
+  return mSerialEventTarget;
+}
+
+// See also AutoJSAPI::ReportException
+void WorkerGlobalScopeBase::ReportError(JSContext* aCx,
+                                        JS::Handle<JS::Value> aError,
+                                        CallerType, ErrorResult& aRv) {
+  JS::ErrorReportBuilder jsReport(aCx);
+  JS::ExceptionStack exnStack(aCx, aError, nullptr);
+  if (!jsReport.init(aCx, exnStack, JS::ErrorReportBuilder::NoSideEffects)) {
+    return aRv.NoteJSContextException(aCx);
+  }
+
+  // Before invoking ReportError, put the exception back on the context,
+  // because it may want to put it in its error events and has no other way
+  // to get hold of it.  After we invoke ReportError, clear the exception on
+  // cx(), just in case ReportError didn't.
+  JS::SetPendingExceptionStack(aCx, exnStack);
+  mWorkerPrivate->ReportError(aCx, jsReport.toStringResult(),
+                              jsReport.report());
+  JS_ClearPendingException(aCx);
+}
+
+void WorkerGlobalScopeBase::Atob(const nsAString& aAtob, nsAString& aOut,
+                                 ErrorResult& aRv) const {
+  AssertIsOnWorkerThread();
+  aRv = nsContentUtils::Atob(aAtob, aOut);
+}
+
+void WorkerGlobalScopeBase::Btoa(const nsAString& aBtoa, nsAString& aOut,
+                                 ErrorResult& aRv) const {
+  AssertIsOnWorkerThread();
+  aRv = nsContentUtils::Btoa(aBtoa, aOut);
+}
+
+already_AddRefed<Console> WorkerGlobalScopeBase::GetConsole(ErrorResult& aRv) {
+  AssertIsOnWorkerThread();
+
+  if (!mConsole) {
+    mConsole = Console::Create(mWorkerPrivate->GetJSContext(), nullptr, aRv);
+    if (NS_WARN_IF(aRv.Failed())) {
+      return nullptr;
+    }
+  }
+
+  RefPtr<Console> console = mConsole;
+  return console.forget();
+}
+
+uint64_t WorkerGlobalScopeBase::WindowID() const {
+  return mWorkerPrivate->WindowID();
+}
+
+NS_IMPL_CYCLE_COLLECTION_CLASS(WorkerGlobalScope)
+
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(WorkerGlobalScope,
+                                                  WorkerGlobalScopeBase)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mCrypto)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mPerformance)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mWebTaskScheduler)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mLocation)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mNavigator)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mFontFaceSet)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mIndexedDB)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mCacheStorage)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mDebuggerNotificationManager)
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED(WorkerGlobalScope,
+                                                WorkerGlobalScopeBase)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mCrypto)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mPerformance)
+  if (tmp->mWebTaskScheduler) {
+    tmp->mWebTaskScheduler->Disconnect();
+    NS_IMPL_CYCLE_COLLECTION_UNLINK(mWebTaskScheduler)
+  }
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mLocation)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mNavigator)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mFontFaceSet)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mIndexedDB)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mCacheStorage)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mDebuggerNotificationManager)
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+
+NS_IMPL_ISUPPORTS_CYCLE_COLLECTION_INHERITED_0(WorkerGlobalScope,
+                                               WorkerGlobalScopeBase)
+
+WorkerGlobalScope::~WorkerGlobalScope() = default;
+
+void WorkerGlobalScope::NoteTerminating() {
+  LOG(("WorkerGlobalScope::NoteTerminating [%p]", this));
+  if (IsDying()) {
+    return;
+  }
+
+  StartDying();
+}
+
+void WorkerGlobalScope::NoteShuttingDown() {
+  MOZ_ASSERT(IsDying());
+  LOG(("WorkerGlobalScope::NoteShuttingDown [%p]", this));
+
+  if (mNavigator) {
+    mNavigator->Invalidate();
+    mNavigator = nullptr;
+  }
+}
+
+Crypto* WorkerGlobalScope::GetCrypto(ErrorResult& aError) {
+  AssertIsOnWorkerThread();
+
+  if (!mCrypto) {
+    mCrypto = new Crypto(this);
+  }
+
+  return mCrypto;
+}
+
+already_AddRefed<CacheStorage> WorkerGlobalScope::GetCaches(ErrorResult& aRv) {
+  if (!mCacheStorage) {
+    mCacheStorage = CacheStorage::CreateOnWorker(cache::DEFAULT_NAMESPACE, this,
+                                                 mWorkerPrivate, aRv);
+  }
+
+  RefPtr<CacheStorage> ref = mCacheStorage;
+  return ref.forget();
+}
+
+bool WorkerGlobalScope::IsSecureContext() const {
+  bool globalSecure = JS::GetIsSecureContext(
+      js::GetNonCCWObjectRealm(GetWrapperPreserveColor()));
+  MOZ_ASSERT(globalSecure == mWorkerPrivate->IsSecureContext());
+  return globalSecure;
+}
+
+already_AddRefed<WorkerLocation> WorkerGlobalScope::Location() {
+  AssertIsOnWorkerThread();
+
+  if (!mLocation) {
+    mLocation = WorkerLocation::Create(mWorkerPrivate->GetLocationInfo());
+    MOZ_ASSERT(mLocation);
+  }
+
+  RefPtr<WorkerLocation> location = mLocation;
+  return location.forget();
+}
+
+already_AddRefed<WorkerNavigator> WorkerGlobalScope::Navigator() {
+  AssertIsOnWorkerThread();
+
+  if (!mNavigator) {
+    mNavigator = WorkerNavigator::Create(mWorkerPrivate->OnLine());
+    MOZ_ASSERT(mNavigator);
+  }
+
+  RefPtr<WorkerNavigator> navigator = mNavigator;
+  return navigator.forget();
+}
+
+already_AddRefed<WorkerNavigator> WorkerGlobalScope::GetExistingNavigator()
+    const {
+  AssertIsOnWorkerThread();
+
+  RefPtr<WorkerNavigator> navigator = mNavigator;
+  return navigator.forget();
+}
+
+FontFaceSet* WorkerGlobalScope::GetFonts(ErrorResult& aRv) {
+  AssertIsOnWorkerThread();
+
+  if (!mFontFaceSet) {
+    mFontFaceSet = FontFaceSet::CreateForWorker(this, mWorkerPrivate);
+    if (MOZ_UNLIKELY(!mFontFaceSet)) {
+      aRv.ThrowInvalidStateError("Couldn't acquire worker reference");
+      return nullptr;
+    }
+  }
+
+  return mFontFaceSet;
+}
+
+OnErrorEventHandlerNonNull* WorkerGlobalScope::GetOnerror() {
+  AssertIsOnWorkerThread();
+
+  EventListenerManager* elm = GetExistingListenerManager();
+  return elm ? elm->GetOnErrorEventHandler() : nullptr;
+}
+
+void WorkerGlobalScope::SetOnerror(OnErrorEventHandlerNonNull* aHandler) {
+  AssertIsOnWorkerThread();
+
+  EventListenerManager* elm = GetOrCreateListenerManager();
+  if (elm) {
+    elm->SetEventHandler(aHandler);
+  }
+}
+
+void WorkerGlobalScope::ImportScripts(JSContext* aCx,
+                                      const Sequence<nsString>& aScriptURLs,
+                                      ErrorResult& aRv) {
+  AssertIsOnWorkerThread();
+
+  UniquePtr<SerializedStackHolder> stack;
+  if (mWorkerPrivate->IsWatchedByDevTools()) {
+    stack = GetCurrentStackForNetMonitor(aCx);
+  }
+
+  {
+    AUTO_PROFILER_MARKER_TEXT(
+        "ImportScripts", JS, MarkerStack::Capture(),
+        profiler_thread_is_being_profiled_for_markers()
+            ? StringJoin(","_ns, aScriptURLs,
+                         [](nsACString& dest, const auto& scriptUrl) {
+                           AppendUTF16toUTF8(
+                               Substring(
+                                   scriptUrl, 0,
+                                   std::min(size_t(128), scriptUrl.Length())),
+                               dest);
+                         })
+            : nsAutoCString{});
+    workerinternals::Load(mWorkerPrivate, std::move(stack), aScriptURLs,
+                          WorkerScript, aRv);
+  }
+}
+
+int32_t WorkerGlobalScope::SetTimeout(JSContext* aCx, Function& aHandler,
+                                      const int32_t aTimeout,
+                                      const Sequence<JS::Value>& aArguments,
+                                      ErrorResult& aRv) {
+  return SetTimeoutOrInterval(aCx, aHandler, aTimeout, aArguments, false, aRv);
+}
+
+int32_t WorkerGlobalScope::SetTimeout(JSContext* aCx, const nsAString& aHandler,
+                                      const int32_t aTimeout,
+                                      const Sequence<JS::Value>& /* unused */,
+                                      ErrorResult& aRv) {
+  return SetTimeoutOrInterval(aCx, aHandler, aTimeout, false, aRv);
+}
+
+void WorkerGlobalScope::ClearTimeout(int32_t aHandle) {
+  AssertIsOnWorkerThread();
+
+  DebuggerNotificationDispatch(this, DebuggerNotificationType::ClearTimeout);
+
+  mWorkerPrivate->ClearTimeout(aHandle, Timeout::Reason::eTimeoutOrInterval);
+}
+
+int32_t WorkerGlobalScope::SetInterval(JSContext* aCx, Function& aHandler,
+                                       const int32_t aTimeout,
+                                       const Sequence<JS::Value>& aArguments,
+                                       ErrorResult& aRv) {
+  return SetTimeoutOrInterval(aCx, aHandler, aTimeout, aArguments, true, aRv);
+}
+
+int32_t WorkerGlobalScope::SetInterval(JSContext* aCx,
+                                       const nsAString& aHandler,
+                                       const int32_t aTimeout,
+                                       const Sequence<JS::Value>& /* unused */,
+                                       ErrorResult& aRv) {
+  return SetTimeoutOrInterval(aCx, aHandler, aTimeout, true, aRv);
+}
+
+void WorkerGlobalScope::ClearInterval(int32_t aHandle) {
+  AssertIsOnWorkerThread();
+
+  DebuggerNotificationDispatch(this, DebuggerNotificationType::ClearInterval);
+
+  mWorkerPrivate->ClearTimeout(aHandle, Timeout::Reason::eTimeoutOrInterval);
+}
+
+int32_t WorkerGlobalScope::SetTimeoutOrInterval(
+    JSContext* aCx, Function& aHandler, const int32_t aTimeout,
+    const Sequence<JS::Value>& aArguments, bool aIsInterval, ErrorResult& aRv) {
+  AssertIsOnWorkerThread();
+
+  DebuggerNotificationDispatch(
+      this, aIsInterval ? DebuggerNotificationType::SetInterval
+                        : DebuggerNotificationType::SetTimeout);
+
+  nsTArray<JS::Heap<JS::Value>> args;
+  if (!args.AppendElements(aArguments, fallible)) {
+    aRv.Throw(NS_ERROR_OUT_OF_MEMORY);
+    return 0;
+  }
+
+  RefPtr<TimeoutHandler> handler =
+      new CallbackTimeoutHandler(aCx, this, &aHandler, std::move(args));
+
+  return mWorkerPrivate->SetTimeout(aCx, handler, aTimeout, aIsInterval,
+                                    Timeout::Reason::eTimeoutOrInterval, aRv);
+}
+
+int32_t WorkerGlobalScope::SetTimeoutOrInterval(JSContext* aCx,
+                                                const nsAString& aHandler,
+                                                const int32_t aTimeout,
+                                                bool aIsInterval,
+                                                ErrorResult& aRv) {
+  AssertIsOnWorkerThread();
+
+  DebuggerNotificationDispatch(
+      this, aIsInterval ? DebuggerNotificationType::SetInterval
+                        : DebuggerNotificationType::SetTimeout);
+
+  bool allowEval = false;
+  aRv =
+      CSPEvalChecker::CheckForWorker(aCx, mWorkerPrivate, aHandler, &allowEval);
+  if (NS_WARN_IF(aRv.Failed()) || !allowEval) {
+    return 0;
+  }
+
+  RefPtr<TimeoutHandler> handler =
+      new WorkerScriptTimeoutHandler(aCx, this, aHandler);
+
+  return mWorkerPrivate->SetTimeout(aCx, handler, aTimeout, aIsInterval,
+                                    Timeout::Reason::eTimeoutOrInterval, aRv);
+}
+
+void WorkerGlobalScope::GetOrigin(nsAString& aOrigin) const {
+  AssertIsOnWorkerThread();
+  nsContentUtils::GetWebExposedOriginSerialization(
+      mWorkerPrivate->GetPrincipal(), aOrigin);
+}
+
+bool WorkerGlobalScope::CrossOriginIsolated() const {
+  return mWorkerPrivate->CrossOriginIsolated();
+}
+
+void WorkerGlobalScope::Dump(const Optional<nsAString>& aString) const {
+  AssertIsOnWorkerThread();
+
+  if (!aString.WasPassed()) {
+    return;
+  }
+
+  if (!nsJSUtils::DumpEnabled()) {
+    return;
+  }
+
+  NS_ConvertUTF16toUTF8 str(aString.Value());
+
+  MOZ_LOG(nsContentUtils::DOMDumpLog(), LogLevel::Debug,
+          ("[Worker.Dump] %s", str.get()));
+#ifdef ANDROID
+  __android_log_print(ANDROID_LOG_INFO, "Gecko", "%s", str.get());
+#endif
+  fputs(str.get(), stdout);
+  fflush(stdout);
+}
+
+Performance* WorkerGlobalScope::GetPerformance() {
+  AssertIsOnWorkerThread();
+
+  if (!mPerformance) {
+    mPerformance = Performance::CreateForWorker(this);
+  }
+
+  return mPerformance;
+}
+
+bool WorkerGlobalScope::IsInAutomation(JSContext* aCx, JSObject* /* unused */) {
+  return GetWorkerPrivateFromContext(aCx)->IsInAutomation();
+}
+
+void WorkerGlobalScope::GetJSTestingFunctions(
+    JSContext* aCx, JS::MutableHandle<JSObject*> aFunctions, ErrorResult& aRv) {
+  JSObject* obj = js::GetTestingFunctions(aCx);
+  if (!obj) {
+    aRv.Throw(NS_ERROR_OUT_OF_MEMORY);
+    return;
+  }
+
+  aFunctions.set(obj);
+}
+
+already_AddRefed<Promise> WorkerGlobalScope::Fetch(
+    const RequestOrUSVString& aInput, const RequestInit& aInit,
+    CallerType aCallerType, ErrorResult& aRv) {
+  return FetchRequest(this, aInput, aInit, aCallerType, aRv);
+}
+
+already_AddRefed<IDBFactory> WorkerGlobalScope::GetIndexedDB(
+    JSContext* aCx, ErrorResult& aErrorResult) {
+  AssertIsOnWorkerThread();
+
+  RefPtr<IDBFactory> indexedDB = mIndexedDB;
+
+  if (!indexedDB) {
+    StorageAccess access = mWorkerPrivate->StorageAccess();
+
+    if (access == StorageAccess::eDeny) {
+      NS_WARNING("IndexedDB is not allowed in this worker!");
+      aErrorResult = NS_ERROR_DOM_SECURITY_ERR;
+      return nullptr;
+    }
+
+    if (ShouldPartitionStorage(access) &&
+        !StoragePartitioningEnabled(access,
+                                    mWorkerPrivate->CookieJarSettings())) {
+      NS_WARNING("IndexedDB is not allowed in this worker!");
+      aErrorResult = NS_ERROR_DOM_SECURITY_ERR;
+      return nullptr;
+    }
+
+    const PrincipalInfo& principalInfo =
+        mWorkerPrivate->GetEffectiveStoragePrincipalInfo();
+
+    auto res = IDBFactory::CreateForWorker(this, principalInfo,
+                                           mWorkerPrivate->WindowID());
+    if (NS_WARN_IF(res.isErr())) {
+      aErrorResult = res.unwrapErr();
+      return nullptr;
+    }
+
+    indexedDB = res.unwrap();
+    mIndexedDB = indexedDB;
+  }
+
+  return indexedDB.forget();
+}
+
+WebTaskScheduler* WorkerGlobalScope::Scheduler() {
+  mWorkerPrivate->AssertIsOnWorkerThread();
+
+  if (!mWebTaskScheduler) {
+    mWebTaskScheduler = WebTaskScheduler::CreateForWorker(mWorkerPrivate);
+  }
+
+  MOZ_ASSERT(mWebTaskScheduler);
+  return mWebTaskScheduler;
+}
+
+WebTaskScheduler* WorkerGlobalScope::GetExistingScheduler() const {
+  return mWebTaskScheduler;
+}
+
+already_AddRefed<Promise> WorkerGlobalScope::CreateImageBitmap(
+    const ImageBitmapSource& aImage, const ImageBitmapOptions& aOptions,
+    ErrorResult& aRv) {
+  return ImageBitmap::Create(this, aImage, Nothing(), aOptions, aRv);
+}
+
+already_AddRefed<Promise> WorkerGlobalScope::CreateImageBitmap(
+    const ImageBitmapSource& aImage, int32_t aSx, int32_t aSy, int32_t aSw,
+    int32_t aSh, const ImageBitmapOptions& aOptions, ErrorResult& aRv) {
+  return ImageBitmap::Create(
+      this, aImage, Some(gfx::IntRect(aSx, aSy, aSw, aSh)), aOptions, aRv);
+}
+
+// https://html.spec.whatwg.org/#structured-cloning
+void WorkerGlobalScope::StructuredClone(
+    JSContext* aCx, JS::Handle<JS::Value> aValue,
+    const StructuredSerializeOptions& aOptions,
+    JS::MutableHandle<JS::Value> aRetval, ErrorResult& aError) {
+  nsContentUtils::StructuredClone(aCx, this, aValue, aOptions, aRetval, aError);
+}
+
+mozilla::dom::DebuggerNotificationManager*
+WorkerGlobalScope::GetOrCreateDebuggerNotificationManager() {
+  if (!mDebuggerNotificationManager) {
+    mDebuggerNotificationManager = new DebuggerNotificationManager(this);
+  }
+
+  return mDebuggerNotificationManager;
+}
+
+mozilla::dom::DebuggerNotificationManager*
+WorkerGlobalScope::GetExistingDebuggerNotificationManager() {
+  return mDebuggerNotificationManager;
+}
+
+Maybe<EventCallbackDebuggerNotificationType>
+WorkerGlobalScope::GetDebuggerNotificationType() const {
+  return Some(EventCallbackDebuggerNotificationType::Global);
+}
+
+RefPtr<ServiceWorkerRegistration>
+WorkerGlobalScope::GetServiceWorkerRegistration(
+    const ServiceWorkerRegistrationDescriptor& aDescriptor) const {
+  AssertIsOnWorkerThread();
+  RefPtr<ServiceWorkerRegistration> ref;
+  ForEachGlobalTeardownObserver(
+      [&](GlobalTeardownObserver* aObserver, bool* aDoneOut) {
+        RefPtr<ServiceWorkerRegistration> swr = do_QueryObject(aObserver);
+        if (!swr || !swr->MatchesDescriptor(aDescriptor)) {
+          return;
+        }
+
+        ref = std::move(swr);
+        *aDoneOut = true;
+      });
+  return ref;
+}
+
+RefPtr<ServiceWorkerRegistration>
+WorkerGlobalScope::GetOrCreateServiceWorkerRegistration(
+    const ServiceWorkerRegistrationDescriptor& aDescriptor) {
+  AssertIsOnWorkerThread();
+  RefPtr<ServiceWorkerRegistration> ref =
+      GetServiceWorkerRegistration(aDescriptor);
+  if (!ref) {
+    ref = ServiceWorkerRegistration::CreateForWorker(mWorkerPrivate, this,
+                                                     aDescriptor);
+  }
+  return ref;
+}
+
+mozilla::dom::StorageManager* WorkerGlobalScope::GetStorageManager() {
+  return RefPtr(Navigator())->Storage();
+}
+
+// https://html.spec.whatwg.org/multipage/web-messaging.html#eligible-for-messaging
+// * a WorkerGlobalScope object whose closing flag is false and whose worker
+//   is not a suspendable worker.
+bool WorkerGlobalScope::IsEligibleForMessaging() {
+  return mIsEligibleForMessaging;
+}
+void WorkerGlobalScope::StorageAccessPermissionGranted() {
+  // Reset the IndexedDB factory.
+  mIndexedDB = nullptr;
+
+  // Reset DOM Cache
+  mCacheStorage = nullptr;
+}
+
+bool WorkerGlobalScope::WindowInteractionAllowed() const {
+  AssertIsOnWorkerThread();
+  return mWindowInteractionsAllowed > 0;
+}
+
+void WorkerGlobalScope::AllowWindowInteraction() {
+  AssertIsOnWorkerThread();
+  mWindowInteractionsAllowed++;
+}
+
+void WorkerGlobalScope::ConsumeWindowInteraction() {
+  AssertIsOnWorkerThread();
+  MOZ_ASSERT(mWindowInteractionsAllowed);
+  mWindowInteractionsAllowed--;
+}
+
+NS_IMPL_CYCLE_COLLECTION_INHERITED(DedicatedWorkerGlobalScope,
+                                   WorkerGlobalScope, mFrameRequestManager)
+
+NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN_INHERITED(DedicatedWorkerGlobalScope,
+                                               WorkerGlobalScope)
+NS_IMPL_CYCLE_COLLECTION_TRACE_END
+
+NS_IMPL_ISUPPORTS_CYCLE_COLLECTION_INHERITED_0(DedicatedWorkerGlobalScope,
+                                               WorkerGlobalScope)
+
+DedicatedWorkerGlobalScope::DedicatedWorkerGlobalScope(
+    WorkerPrivate* aWorkerPrivate, UniquePtr<ClientSource> aClientSource,
+    const nsString& aName)
+    : WorkerGlobalScope(std::move(aWorkerPrivate), std::move(aClientSource)),
+      NamedWorkerGlobalScopeMixin(aName) {}
+
+bool DedicatedWorkerGlobalScope::WrapGlobalObject(
+    JSContext* aCx, JS::MutableHandle<JSObject*> aReflector) {
+  AssertIsOnWorkerThread();
+  MOZ_ASSERT(!mWorkerPrivate->IsSharedWorker());
+
+  JS::RealmOptions options;
+  mWorkerPrivate->CopyJSRealmOptions(options);
+
+  xpc::SetPrefableRealmOptions(options);
+
+  return DedicatedWorkerGlobalScope_Binding::Wrap(
+      aCx, this, this, options,
+      nsJSPrincipals::get(mWorkerPrivate->GetPrincipal()), aReflector);
+}
+
+void DedicatedWorkerGlobalScope::PostMessage(
+    JSContext* aCx, JS::Handle<JS::Value> aMessage,
+    const Sequence<JSObject*>& aTransferable, ErrorResult& aRv) {
+  AssertIsOnWorkerThread();
+  mWorkerPrivate->PostMessageToParent(aCx, aMessage, aTransferable, aRv);
+}
+
+void DedicatedWorkerGlobalScope::PostMessage(
+    JSContext* aCx, JS::Handle<JS::Value> aMessage,
+    const StructuredSerializeOptions& aOptions, ErrorResult& aRv) {
+  AssertIsOnWorkerThread();
+  mWorkerPrivate->PostMessageToParent(aCx, aMessage, aOptions.mTransfer, aRv);
+}
+
+void DedicatedWorkerGlobalScope::Close() {
+  AssertIsOnWorkerThread();
+  mWorkerPrivate->CloseInternal();
+}
+
+int32_t DedicatedWorkerGlobalScope::RequestAnimationFrame(
+    FrameRequestCallback& aCallback, ErrorResult& aError) {
+  AssertIsOnWorkerThread();
+
+  DebuggerNotificationDispatch(this,
+                               DebuggerNotificationType::RequestAnimationFrame);
+
+  // Ensure the worker is associated with a window.
+  if (mWorkerPrivate->WindowID() == UINT64_MAX) {
+    aError.ThrowNotSupportedError("Worker has no associated owner Window");
+    return 0;
+  }
+
+  if (!mVsyncChild) {
+    PBackgroundChild* bgChild = BackgroundChild::GetOrCreateForCurrentThread();
+    mVsyncChild = MakeRefPtr<VsyncWorkerChild>();
+
+    if (!bgChild || !mVsyncChild->Initialize(mWorkerPrivate) ||
+        !bgChild->SendPVsyncConstructor(mVsyncChild)) {
+      mVsyncChild->Destroy();
+      mVsyncChild = nullptr;
+      aError.ThrowNotSupportedError(
+          "Worker failed to register for vsync to drive event loop");
+      return 0;
+    }
+  }
+
+  if (!mDocListener) {
+    mDocListener = WorkerDocumentListener::Create(mWorkerPrivate);
+    if (!mDocListener) {
+      aError.ThrowNotSupportedError(
+          "Worker failed to register for document visibility events");
+      return 0;
+    }
+  }
+
+  int32_t handle = 0;
+  aError = mFrameRequestManager.Schedule(aCallback, &handle);
+  if (!aError.Failed() && mDocumentVisible) {
+    mVsyncChild->TryObserve();
+  }
+  return handle;
+}
+
+void DedicatedWorkerGlobalScope::CancelAnimationFrame(int32_t aHandle,
+                                                      ErrorResult& aError) {
+  AssertIsOnWorkerThread();
+
+  DebuggerNotificationDispatch(this,
+                               DebuggerNotificationType::CancelAnimationFrame);
+
+  // Ensure the worker is associated with a window.
+  if (mWorkerPrivate->WindowID() == UINT64_MAX) {
+    aError.ThrowNotSupportedError("Worker has no associated owner Window");
+    return;
+  }
+
+  mFrameRequestManager.Cancel(aHandle);
+  if (mVsyncChild && mFrameRequestManager.IsEmpty()) {
+    mVsyncChild->TryUnobserve();
+  }
+}
+
+void DedicatedWorkerGlobalScope::OnDocumentVisible(bool aVisible) {
+  AssertIsOnWorkerThread();
+
+  mDocumentVisible = aVisible;
+
+  // We only change state immediately when we become visible. If we become
+  // hidden, then we wait for the next vsync tick to apply that.
+  if (aVisible && !mFrameRequestManager.IsEmpty()) {
+    mVsyncChild->TryObserve();
+  }
+}
+
+void DedicatedWorkerGlobalScope::OnVsync(const VsyncEvent& aVsync) {
+  AssertIsOnWorkerThread();
+
+  if (mFrameRequestManager.IsEmpty() || !mDocumentVisible) {
+    // If we ever receive a vsync event, and there are still no callbacks to
+    // process, or we remain hidden, we should disable observing them. By
+    // waiting an extra tick, we ensure we minimize extra IPC for content that
+    // does not call requestFrameAnimation directly during the callback, or
+    // that is rapidly toggling between hidden and visible.
+    mVsyncChild->TryUnobserve();
+    return;
+  }
+
+  nsTArray<FrameRequest> callbacks;
+  mFrameRequestManager.Take(callbacks);
+
+  RefPtr<DedicatedWorkerGlobalScope> scope(this);
+  CallbackDebuggerNotificationGuard guard(
+      scope, DebuggerNotificationType::RequestAnimationFrameCallback);
+
+  // This is similar to what we do in nsRefreshDriver::RunFrameRequestCallbacks
+  // and Performance::TimeStampToDOMHighResForRendering in order to have the
+  // same behaviour for requestAnimationFrame on both the main and worker
+  // threads.
+  DOMHighResTimeStamp timeStamp = 0;
+  if (!aVsync.mTime.IsNull()) {
+    timeStamp = mWorkerPrivate->TimeStampToDOMHighRes(aVsync.mTime);
+    // 0 is an inappropriate mixin for this this area; however CSS Animations
+    // needs to have it's Time Reduction Logic refactored, so it's currently
+    // only clamping for RFP mode. RFP mode gives a much lower time precision,
+    // so we accept the security leak here for now.
+    timeStamp = nsRFPService::ReduceTimePrecisionAsMSecsRFPOnly(
+        timeStamp, 0, this->GetRTPCallerType());
+  }
+
+  for (auto& callback : callbacks) {
+    if (mFrameRequestManager.IsCanceled(callback.mHandle)) {
+      continue;
+    }
+
+    // MOZ_KnownLive is OK, because the stack array `callbacks` keeps the
+    // callback alive and the mCallback strong reference can't be mutated by
+    // the call.
+    LogFrameRequestCallback::Run run(callback.mCallback);
+    MOZ_KnownLive(callback.mCallback)->Call(timeStamp);
+  }
+}
+
+SharedWorkerGlobalScope::SharedWorkerGlobalScope(
+    WorkerPrivate* aWorkerPrivate, UniquePtr<ClientSource> aClientSource,
+    const nsString& aName)
+    : WorkerGlobalScope(std::move(aWorkerPrivate), std::move(aClientSource)),
+      NamedWorkerGlobalScopeMixin(aName) {}
+
+bool SharedWorkerGlobalScope::WrapGlobalObject(
+    JSContext* aCx, JS::MutableHandle<JSObject*> aReflector) {
+  AssertIsOnWorkerThread();
+  MOZ_ASSERT(mWorkerPrivate->IsSharedWorker());
+
+  JS::RealmOptions options;
+  mWorkerPrivate->CopyJSRealmOptions(options);
+
+  return SharedWorkerGlobalScope_Binding::Wrap(
+      aCx, this, this, options,
+      nsJSPrincipals::get(mWorkerPrivate->GetPrincipal()), aReflector);
+}
+
+void SharedWorkerGlobalScope::Close() {
+  AssertIsOnWorkerThread();
+  mWorkerPrivate->CloseInternal();
+}
+
+NS_IMPL_CYCLE_COLLECTION_INHERITED(ServiceWorkerGlobalScope, WorkerGlobalScope,
+                                   mClients, mExtensionBrowser, mRegistration)
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(ServiceWorkerGlobalScope)
+NS_INTERFACE_MAP_END_INHERITING(WorkerGlobalScope)
+
+NS_IMPL_ADDREF_INHERITED(ServiceWorkerGlobalScope, WorkerGlobalScope)
+NS_IMPL_RELEASE_INHERITED(ServiceWorkerGlobalScope, WorkerGlobalScope)
+
+ServiceWorkerGlobalScope::ServiceWorkerGlobalScope(
+    WorkerPrivate* aWorkerPrivate, UniquePtr<ClientSource> aClientSource,
+    const ServiceWorkerRegistrationDescriptor& aRegistrationDescriptor)
+    : WorkerGlobalScope(std::move(aWorkerPrivate), std::move(aClientSource)),
+      mScope(NS_ConvertUTF8toUTF16(aRegistrationDescriptor.Scope()))
+
+      // Eagerly create the registration because we will need to receive
+      // updates about the state of the registration.  We can't wait until
+      // first access to start receiving these.
+      ,
+      mRegistration(
+          GetOrCreateServiceWorkerRegistration(aRegistrationDescriptor)) {}
+
+ServiceWorkerGlobalScope::~ServiceWorkerGlobalScope() = default;
+
+bool ServiceWorkerGlobalScope::WrapGlobalObject(
+    JSContext* aCx, JS::MutableHandle<JSObject*> aReflector) {
+  AssertIsOnWorkerThread();
+  MOZ_ASSERT(mWorkerPrivate->IsServiceWorker());
+
+  JS::RealmOptions options;
+  mWorkerPrivate->CopyJSRealmOptions(options);
+
+  return ServiceWorkerGlobalScope_Binding::Wrap(
+      aCx, this, this, options,
+      nsJSPrincipals::get(mWorkerPrivate->GetPrincipal()), aReflector);
+}
+
+already_AddRefed<Clients> ServiceWorkerGlobalScope::GetClients() {
+  if (!mClients) {
+    mClients = new Clients(this);
+  }
+
+  RefPtr<Clients> ref = mClients;
+  return ref.forget();
+}
+
+ServiceWorkerRegistration* ServiceWorkerGlobalScope::Registration() {
+  return mRegistration;
+}
+
+EventHandlerNonNull* ServiceWorkerGlobalScope::GetOnfetch() {
+  AssertIsOnWorkerThread();
+
+  return GetEventHandler(nsGkAtoms::onfetch);
+}
+
+namespace {
+
+class ReportFetchListenerWarningRunnable final : public Runnable {
+  const nsCString mScope;
+  nsString mSourceSpec;
+  uint32_t mLine;
+  uint32_t mColumn;
+
+ public:
+  explicit ReportFetchListenerWarningRunnable(const nsString& aScope)
+      : mozilla::Runnable("ReportFetchListenerWarningRunnable"),
+        mScope(NS_ConvertUTF16toUTF8(aScope)) {
+    WorkerPrivate* workerPrivate = GetCurrentThreadWorkerPrivate();
+    MOZ_ASSERT(workerPrivate);
+    JSContext* cx = workerPrivate->GetJSContext();
+    MOZ_ASSERT(cx);
+
+    nsJSUtils::GetCallingLocation(cx, mSourceSpec, &mLine, &mColumn);
+  }
+
+  NS_IMETHOD
+  Run() override {
+    AssertIsOnMainThread();
+
+    ServiceWorkerManager::LocalizeAndReportToAllClients(
+        mScope, "ServiceWorkerNoFetchHandler", nsTArray<nsString>{},
+        nsIScriptError::warningFlag, mSourceSpec, u""_ns, mLine, mColumn);
+
+    return NS_OK;
+  }
+};
+
+}  // anonymous namespace
+
+void ServiceWorkerGlobalScope::NoteFetchHandlerWasAdded() const {
+  if (mWorkerPrivate->WorkerScriptExecutedSuccessfully()) {
+    RefPtr<Runnable> r = new ReportFetchListenerWarningRunnable(mScope);
+    mWorkerPrivate->DispatchToMainThreadForMessaging(r.forget());
+  }
+  mWorkerPrivate->SetFetchHandlerWasAdded();
+}
+
+void ServiceWorkerGlobalScope::SetOnfetch(
+    mozilla::dom::EventHandlerNonNull* aCallback) {
+  AssertIsOnWorkerThread();
+
+  if (aCallback) {
+    NoteFetchHandlerWasAdded();
+  }
+  SetEventHandler(nsGkAtoms::onfetch, aCallback);
+}
+
+void ServiceWorkerGlobalScope::EventListenerAdded(nsAtom* aType) {
+  AssertIsOnWorkerThread();
+
+  if (aType == nsGkAtoms::onfetch) {
+    NoteFetchHandlerWasAdded();
+  }
+}
+
+already_AddRefed<Promise> ServiceWorkerGlobalScope::SkipWaiting(
+    ErrorResult& aRv) {
+  AssertIsOnWorkerThread();
+  MOZ_ASSERT(mWorkerPrivate->IsServiceWorker());
+
+  RefPtr<Promise> promise = Promise::Create(this, aRv);
+  if (NS_WARN_IF(aRv.Failed())) {
+    return nullptr;
+  }
+
+  using MozPromiseType =
+      decltype(mWorkerPrivate->SetServiceWorkerSkipWaitingFlag())::element_type;
+  auto holder = MakeRefPtr<DOMMozPromiseRequestHolder<MozPromiseType>>(this);
+
+  mWorkerPrivate->SetServiceWorkerSkipWaitingFlag()
+      ->Then(GetCurrentSerialEventTarget(), __func__,
+             [holder, promise](const MozPromiseType::ResolveOrRejectValue&) {
+               holder->Complete();
+               promise->MaybeResolveWithUndefined();
+             })
+      ->Track(*holder);
+
+  return promise.forget();
+}
+
+SafeRefPtr<extensions::ExtensionBrowser>
+ServiceWorkerGlobalScope::AcquireExtensionBrowser() {
+  if (!mExtensionBrowser) {
+    mExtensionBrowser = MakeSafeRefPtr<extensions::ExtensionBrowser>(this);
+  }
+
+  return mExtensionBrowser.clonePtr();
+}
+
+bool WorkerDebuggerGlobalScope::WrapGlobalObject(
+    JSContext* aCx, JS::MutableHandle<JSObject*> aReflector) {
+  AssertIsOnWorkerThread();
+
+  JS::RealmOptions options;
+  mWorkerPrivate->CopyJSRealmOptions(options);
+
+  return WorkerDebuggerGlobalScope_Binding::Wrap(
+      aCx, this, this, options,
+      nsJSPrincipals::get(mWorkerPrivate->GetPrincipal()), aReflector);
+}
+
+void WorkerDebuggerGlobalScope::GetGlobal(JSContext* aCx,
+                                          JS::MutableHandle<JSObject*> aGlobal,
+                                          ErrorResult& aRv) {
+  WorkerGlobalScope* scope = mWorkerPrivate->GetOrCreateGlobalScope(aCx);
+  if (!scope) {
+    aRv.Throw(NS_ERROR_FAILURE);
+    return;
+  }
+
+  aGlobal.set(scope->GetWrapper());
+}
+
+void WorkerDebuggerGlobalScope::CreateSandbox(
+    JSContext* aCx, const nsAString& aName, JS::Handle<JSObject*> aPrototype,
+    JS::MutableHandle<JSObject*> aResult, ErrorResult& aRv) {
+  AssertIsOnWorkerThread();
+
+  aResult.set(nullptr);
+
+  JS::Rooted<JS::Value> protoVal(aCx);
+  protoVal.setObjectOrNull(aPrototype);
+  JS::Rooted<JSObject*> sandbox(
+      aCx,
+      SimpleGlobalObject::Create(
+          SimpleGlobalObject::GlobalType::WorkerDebuggerSandbox, protoVal));
+
+  if (!sandbox) {
+    aRv.Throw(NS_ERROR_OUT_OF_MEMORY);
+    return;
+  }
+
+  if (!JS_WrapObject(aCx, &sandbox)) {
+    aRv.NoteJSContextException(aCx);
+    return;
+  }
+
+  aResult.set(sandbox);
+}
+
+void WorkerDebuggerGlobalScope::LoadSubScript(
+    JSContext* aCx, const nsAString& aURL,
+    const Optional<JS::Handle<JSObject*>>& aSandbox, ErrorResult& aRv) {
+  AssertIsOnWorkerThread();
+
+  Maybe<JSAutoRealm> ar;
+  if (aSandbox.WasPassed()) {
+    // We only care about worker debugger sandbox objects here, so
+    // CheckedUnwrapStatic is fine.
+    JS::Rooted<JSObject*> sandbox(aCx,
+                                  js::CheckedUnwrapStatic(aSandbox.Value()));
+    if (!sandbox || !IsWorkerDebuggerSandbox(sandbox)) {
+      aRv.Throw(NS_ERROR_INVALID_ARG);
+      return;
+    }
+
+    ar.emplace(aCx, sandbox);
+  }
+
+  nsTArray<nsString> urls;
+  urls.AppendElement(aURL);
+  workerinternals::Load(mWorkerPrivate, nullptr, urls, DebuggerScript, aRv);
+}
+
+void WorkerDebuggerGlobalScope::EnterEventLoop() {
+  // We're on the worker thread here, and WorkerPrivate's refcounting is
+  // non-threadsafe: you can only do it on the parent thread.  What that
+  // means in practice is that we're relying on it being kept alive while
+  // we run.  Hopefully.
+  MOZ_KnownLive(mWorkerPrivate)->EnterDebuggerEventLoop();
+}
+
+void WorkerDebuggerGlobalScope::LeaveEventLoop() {
+  mWorkerPrivate->LeaveDebuggerEventLoop();
+}
+
+void WorkerDebuggerGlobalScope::PostMessage(const nsAString& aMessage) {
+  mWorkerPrivate->PostMessageToDebugger(aMessage);
+}
+
+void WorkerDebuggerGlobalScope::SetImmediate(Function& aHandler,
+                                             ErrorResult& aRv) {
+  mWorkerPrivate->SetDebuggerImmediate(aHandler, aRv);
+}
+
+void WorkerDebuggerGlobalScope::ReportError(JSContext* aCx,
+                                            const nsAString& aMessage) {
+  JS::AutoFilename chars;
+  uint32_t lineno = 0;
+  JS::DescribeScriptedCaller(aCx, &chars, &lineno);
+  nsString filename(NS_ConvertUTF8toUTF16(chars.get()));
+  mWorkerPrivate->ReportErrorToDebugger(filename, lineno, aMessage);
+}
+
+void WorkerDebuggerGlobalScope::RetrieveConsoleEvents(
+    JSContext* aCx, nsTArray<JS::Value>& aEvents, ErrorResult& aRv) {
+  WorkerGlobalScope* scope = mWorkerPrivate->GetOrCreateGlobalScope(aCx);
+  if (!scope) {
+    aRv.Throw(NS_ERROR_FAILURE);
+    return;
+  }
+
+  RefPtr<Console> console = scope->GetConsole(aRv);
+  if (NS_WARN_IF(aRv.Failed())) {
+    return;
+  }
+
+  console->RetrieveConsoleEvents(aCx, aEvents, aRv);
+}
+
+void WorkerDebuggerGlobalScope::ClearConsoleEvents(JSContext* aCx,
+                                                   ErrorResult& aRv) {
+  WorkerGlobalScope* scope = mWorkerPrivate->GetOrCreateGlobalScope(aCx);
+  if (!scope) {
+    aRv.Throw(NS_ERROR_FAILURE);
+    return;
+  }
+
+  RefPtr<Console> console = scope->GetConsoleIfExists();
+  if (console) {
+    console->ClearStorage();
+  }
+}
+
+void WorkerDebuggerGlobalScope::SetConsoleEventHandler(JSContext* aCx,
+                                                       AnyCallback* aHandler,
+                                                       ErrorResult& aRv) {
+  WorkerGlobalScope* scope = mWorkerPrivate->GetOrCreateGlobalScope(aCx);
+  if (!scope) {
+    aRv.Throw(NS_ERROR_FAILURE);
+    return;
+  }
+
+  RefPtr<Console> console = scope->GetConsole(aRv);
+  if (NS_WARN_IF(aRv.Failed())) {
+    return;
+  }
+
+  console->SetConsoleEventHandler(aHandler);
+}
+
+void WorkerDebuggerGlobalScope::Dump(JSContext* aCx,
+                                     const Optional<nsAString>& aString) const {
+  WorkerGlobalScope* scope = mWorkerPrivate->GetOrCreateGlobalScope(aCx);
+  if (scope) {
+    scope->Dump(aString);
+  }
+}
+
+bool IsWorkerGlobal(JSObject* object) {
+  return IS_INSTANCE_OF(WorkerGlobalScope, object);
+}
+
+bool IsWorkerDebuggerGlobal(JSObject* object) {
+  return IS_INSTANCE_OF(WorkerDebuggerGlobalScope, object);
+}
+
+bool IsWorkerDebuggerSandbox(JSObject* object) {
+  return SimpleGlobalObject::SimpleGlobalType(object) ==
+         SimpleGlobalObject::GlobalType::WorkerDebuggerSandbox;
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/workers/WorkerScope.h b/dom/workers/WorkerScope.h
new file mode 100644
index 0000000000..7e00f9b59b
--- /dev/null
+++ b/dom/workers/WorkerScope.h
@@ -0,0 +1,557 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_workerscope_h__
+#define mozilla_dom_workerscope_h__
+
+#include "js/TypeDecls.h"
+#include "js/loader/ModuleLoaderBase.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/DOMEventTargetHelper.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/NotNull.h"
+#include "mozilla/RefPtr.h"
+#include "mozilla/UniquePtr.h"
+#include "mozilla/TimeStamp.h"
+#include "mozilla/dom/AnimationFrameProvider.h"
+#include "mozilla/dom/ImageBitmapBinding.h"
+#include "mozilla/dom/ImageBitmapSource.h"
+#include "mozilla/dom/PerformanceWorker.h"
+#include "mozilla/dom/SafeRefPtr.h"
+#include "mozilla/dom/WorkerPrivate.h"
+#include "nsCOMPtr.h"
+#include "nsCycleCollectionParticipant.h"
+#include "nsIGlobalObject.h"
+#include "nsISupports.h"
+#include "nsWeakReference.h"
+
+#ifdef XP_WIN
+#  undef PostMessage
+#endif
+
+class nsAtom;
+class nsISerialEventTarget;
+
+namespace mozilla {
+class ErrorResult;
+struct VsyncEvent;
+
+namespace extensions {
+
+class ExtensionBrowser;
+
+}  // namespace extensions
+
+namespace dom {
+
+class AnyCallback;
+enum class CallerType : uint32_t;
+class ClientInfo;
+class ClientSource;
+class Clients;
+class Console;
+class Crypto;
+class DOMString;
+class DebuggerNotificationManager;
+enum class EventCallbackDebuggerNotificationType : uint8_t;
+class EventHandlerNonNull;
+class FontFaceSet;
+class Function;
+class IDBFactory;
+class OnErrorEventHandlerNonNull;
+template <typename T>
+class Optional;
+class Performance;
+class Promise;
+class RequestOrUSVString;
+template <typename T>
+class Sequence;
+class ServiceWorkerDescriptor;
+class ServiceWorkerRegistration;
+class ServiceWorkerRegistrationDescriptor;
+struct StructuredSerializeOptions;
+class WorkerDocumentListener;
+class WorkerLocation;
+class WorkerNavigator;
+class WorkerPrivate;
+class VsyncWorkerChild;
+class WebTaskScheduler;
+class WebTaskSchedulerWorker;
+struct RequestInit;
+
+namespace cache {
+
+class CacheStorage;
+
+}  // namespace cache
+
+class WorkerGlobalScopeBase : public DOMEventTargetHelper,
+                              public nsSupportsWeakReference,
+                              public nsIGlobalObject {
+  friend class WorkerPrivate;
+
+ public:
+  NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS_INHERITED(WorkerGlobalScopeBase,
+                                                         DOMEventTargetHelper)
+
+  WorkerGlobalScopeBase(WorkerPrivate* aWorkerPrivate,
+                        UniquePtr<ClientSource> aClientSource);
+
+  virtual bool WrapGlobalObject(JSContext* aCx,
+                                JS::MutableHandle<JSObject*> aReflector) = 0;
+
+  // EventTarget implementation
+  JSObject* WrapObject(JSContext* aCx,
+                       JS::Handle<JSObject*> aGivenProto) final {
+    MOZ_CRASH("WrapObject not supported; use WrapGlobalObject.");
+  }
+
+  // nsIGlobalObject implementation
+  JSObject* GetGlobalJSObject() final;
+
+  JSObject* GetGlobalJSObjectPreserveColor() const final;
+
+  bool IsSharedMemoryAllowed() const final;
+
+  bool ShouldResistFingerprinting(RFPTarget aTarget) const final;
+
+  OriginTrials Trials() const final;
+
+  StorageAccess GetStorageAccess() final;
+
+  Maybe<ClientInfo> GetClientInfo() const final;
+
+  Maybe<ServiceWorkerDescriptor> GetController() const final;
+
+  mozilla::Result<mozilla::ipc::PrincipalInfo, nsresult> GetStorageKey() final;
+
+  virtual void Control(const ServiceWorkerDescriptor& aServiceWorker);
+
+  // DispatcherTrait implementation
+  nsresult Dispatch(already_AddRefed<nsIRunnable>&& aRunnable) const final;
+  nsISerialEventTarget* SerialEventTarget() const final;
+
+  MOZ_CAN_RUN_SCRIPT
+  void ReportError(JSContext* aCx, JS::Handle<JS::Value> aError,
+                   CallerType aCallerType, ErrorResult& aRv);
+
+  // atob, btoa, and dump are declared (separately) by both WorkerGlobalScope
+  // and WorkerDebuggerGlobalScope WebIDL interfaces
+  void Atob(const nsAString& aAtob, nsAString& aOut, ErrorResult& aRv) const;
+
+  void Btoa(const nsAString& aBtoa, nsAString& aOut, ErrorResult& aRv) const;
+
+  already_AddRefed<Console> GetConsole(ErrorResult& aRv);
+
+  Console* GetConsoleIfExists() const { return mConsole; }
+
+  void InitModuleLoader(JS::loader::ModuleLoaderBase* aModuleLoader) {
+    if (!mModuleLoader) {
+      mModuleLoader = aModuleLoader;
+    }
+  }
+
+  // The nullptr here is not used, but is required to make the override method
+  // have the same signature as other GetModuleLoader methods on globals.
+  JS::loader::ModuleLoaderBase* GetModuleLoader(
+      JSContext* aCx = nullptr) override {
+    return mModuleLoader;
+  };
+
+  uint64_t WindowID() const;
+
+  // Usually global scope dies earlier than the WorkerPrivate, but if we see
+  // it leak at least we can tell it to not carry away a dead pointer.
+  void NoteWorkerTerminated() { mWorkerPrivate = nullptr; }
+
+  ClientSource& MutableClientSourceRef() const { return *mClientSource; }
+
+  // WorkerPrivate wants to be able to forbid script when its state machine
+  // demands it.
+  void WorkerPrivateSaysForbidScript() { StartForbiddingScript(); }
+  void WorkerPrivateSaysAllowScript() { StopForbiddingScript(); }
+
+ protected:
+  ~WorkerGlobalScopeBase();
+
+  CheckedUnsafePtr<WorkerPrivate> mWorkerPrivate;
+
+  void AssertIsOnWorkerThread() const {
+    MOZ_ASSERT(mWorkerThreadUsedOnlyForAssert == PR_GetCurrentThread());
+  }
+
+ private:
+  RefPtr<Console> mConsole;
+  RefPtr<JS::loader::ModuleLoaderBase> mModuleLoader;
+  const UniquePtr<ClientSource> mClientSource;
+  nsCOMPtr<nsISerialEventTarget> mSerialEventTarget;
+#ifdef DEBUG
+  PRThread* mWorkerThreadUsedOnlyForAssert;
+#endif
+};
+
+namespace workerinternals {
+
+class NamedWorkerGlobalScopeMixin {
+ public:
+  explicit NamedWorkerGlobalScopeMixin(const nsAString& aName) : mName(aName) {}
+
+  void GetName(DOMString& aName) const;
+
+ protected:
+  ~NamedWorkerGlobalScopeMixin() = default;
+
+ private:
+  const nsString mName;
+};
+
+}  // namespace workerinternals
+
+class WorkerGlobalScope : public WorkerGlobalScopeBase {
+ public:
+  NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(WorkerGlobalScope,
+                                           WorkerGlobalScopeBase)
+
+  using WorkerGlobalScopeBase::WorkerGlobalScopeBase;
+
+  void NoteTerminating();
+
+  void NoteShuttingDown();
+
+  // nsIGlobalObject implementation
+  RefPtr<ServiceWorkerRegistration> GetServiceWorkerRegistration(
+      const ServiceWorkerRegistrationDescriptor& aDescriptor) const final;
+
+  RefPtr<ServiceWorkerRegistration> GetOrCreateServiceWorkerRegistration(
+      const ServiceWorkerRegistrationDescriptor& aDescriptor) final;
+
+  DebuggerNotificationManager* GetOrCreateDebuggerNotificationManager() final;
+
+  DebuggerNotificationManager* GetExistingDebuggerNotificationManager() final;
+
+  Maybe<EventCallbackDebuggerNotificationType> GetDebuggerNotificationType()
+      const final;
+
+  mozilla::dom::StorageManager* GetStorageManager() final;
+
+  void SetIsNotEligibleForMessaging() { mIsEligibleForMessaging = false; }
+
+  bool IsEligibleForMessaging() final;
+
+  // WorkerGlobalScope WebIDL implementation
+  WorkerGlobalScope* Self() { return this; }
+
+  already_AddRefed<WorkerLocation> Location();
+
+  already_AddRefed<WorkerNavigator> Navigator();
+
+  already_AddRefed<WorkerNavigator> GetExistingNavigator() const;
+
+  FontFaceSet* GetFonts(ErrorResult&);
+  FontFaceSet* GetFonts() final { return GetFonts(IgnoreErrors()); }
+
+  void ImportScripts(JSContext* aCx, const Sequence<nsString>& aScriptURLs,
+                     ErrorResult& aRv);
+
+  OnErrorEventHandlerNonNull* GetOnerror();
+
+  void SetOnerror(OnErrorEventHandlerNonNull* aHandler);
+
+  IMPL_EVENT_HANDLER(languagechange)
+  IMPL_EVENT_HANDLER(offline)
+  IMPL_EVENT_HANDLER(online)
+  IMPL_EVENT_HANDLER(rejectionhandled)
+  IMPL_EVENT_HANDLER(unhandledrejection)
+
+  void Dump(const Optional<nsAString>& aString) const;
+
+  Performance* GetPerformance();
+
+  Performance* GetPerformanceIfExists() const { return mPerformance; }
+
+  static bool IsInAutomation(JSContext* aCx, JSObject*);
+
+  void GetJSTestingFunctions(JSContext* aCx,
+                             JS::MutableHandle<JSObject*> aFunctions,
+                             ErrorResult& aRv);
+
+  // GlobalCrypto WebIDL implementation
+  Crypto* GetCrypto(ErrorResult& aError);
+
+  // WindowOrWorkerGlobalScope WebIDL implementation
+  void GetOrigin(nsAString& aOrigin) const;
+
+  bool CrossOriginIsolated() const final;
+
+  MOZ_CAN_RUN_SCRIPT
+  int32_t SetTimeout(JSContext* aCx, Function& aHandler, int32_t aTimeout,
+                     const Sequence<JS::Value>& aArguments, ErrorResult& aRv);
+
+  MOZ_CAN_RUN_SCRIPT
+  int32_t SetTimeout(JSContext* aCx, const nsAString& aHandler,
+                     int32_t aTimeout, const Sequence<JS::Value>&,
+                     ErrorResult& aRv);
+
+  MOZ_CAN_RUN_SCRIPT
+  void ClearTimeout(int32_t aHandle);
+
+  MOZ_CAN_RUN_SCRIPT
+  int32_t SetInterval(JSContext* aCx, Function& aHandler, int32_t aTimeout,
+                      const Sequence<JS::Value>& aArguments, ErrorResult& aRv);
+  MOZ_CAN_RUN_SCRIPT
+  int32_t SetInterval(JSContext* aCx, const nsAString& aHandler,
+                      int32_t aTimeout, const Sequence<JS::Value>&,
+                      ErrorResult& aRv);
+
+  MOZ_CAN_RUN_SCRIPT
+  void ClearInterval(int32_t aHandle);
+
+  already_AddRefed<Promise> CreateImageBitmap(
+      const ImageBitmapSource& aImage, const ImageBitmapOptions& aOptions,
+      ErrorResult& aRv);
+
+  already_AddRefed<Promise> CreateImageBitmap(
+      const ImageBitmapSource& aImage, int32_t aSx, int32_t aSy, int32_t aSw,
+      int32_t aSh, const ImageBitmapOptions& aOptions, ErrorResult& aRv);
+
+  void StructuredClone(JSContext* aCx, JS::Handle<JS::Value> aValue,
+                       const StructuredSerializeOptions& aOptions,
+                       JS::MutableHandle<JS::Value> aRetval,
+                       ErrorResult& aError);
+
+  already_AddRefed<Promise> Fetch(const RequestOrUSVString& aInput,
+                                  const RequestInit& aInit,
+                                  CallerType aCallerType, ErrorResult& aRv);
+
+  bool IsSecureContext() const;
+
+  already_AddRefed<IDBFactory> GetIndexedDB(JSContext* aCx,
+                                            ErrorResult& aErrorResult);
+
+  already_AddRefed<cache::CacheStorage> GetCaches(ErrorResult& aRv);
+
+  WebTaskScheduler* Scheduler();
+  WebTaskScheduler* GetExistingScheduler() const;
+
+  bool WindowInteractionAllowed() const;
+
+  void AllowWindowInteraction();
+
+  void ConsumeWindowInteraction();
+
+  void StorageAccessPermissionGranted();
+
+  virtual void OnDocumentVisible(bool aVisible) {}
+
+  MOZ_CAN_RUN_SCRIPT_BOUNDARY
+  virtual void OnVsync(const VsyncEvent& aVsync) {}
+
+ protected:
+  ~WorkerGlobalScope();
+
+ private:
+  MOZ_CAN_RUN_SCRIPT
+  int32_t SetTimeoutOrInterval(JSContext* aCx, Function& aHandler,
+                               int32_t aTimeout,
+                               const Sequence<JS::Value>& aArguments,
+                               bool aIsInterval, ErrorResult& aRv);
+
+  MOZ_CAN_RUN_SCRIPT
+  int32_t SetTimeoutOrInterval(JSContext* aCx, const nsAString& aHandler,
+                               int32_t aTimeout, bool aIsInterval,
+                               ErrorResult& aRv);
+
+  RefPtr<Crypto> mCrypto;
+  RefPtr<WorkerLocation> mLocation;
+  RefPtr<WorkerNavigator> mNavigator;
+  RefPtr<FontFaceSet> mFontFaceSet;
+  RefPtr<Performance> mPerformance;
+  RefPtr<IDBFactory> mIndexedDB;
+  RefPtr<cache::CacheStorage> mCacheStorage;
+  RefPtr<DebuggerNotificationManager> mDebuggerNotificationManager;
+  RefPtr<WebTaskSchedulerWorker> mWebTaskScheduler;
+  uint32_t mWindowInteractionsAllowed = 0;
+  bool mIsEligibleForMessaging{true};
+};
+
+class DedicatedWorkerGlobalScope final
+    : public WorkerGlobalScope,
+      public workerinternals::NamedWorkerGlobalScopeMixin {
+ public:
+  NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS_INHERITED(
+      DedicatedWorkerGlobalScope, WorkerGlobalScope)
+
+  DedicatedWorkerGlobalScope(WorkerPrivate* aWorkerPrivate,
+                             UniquePtr<ClientSource> aClientSource,
+                             const nsString& aName);
+
+  bool WrapGlobalObject(JSContext* aCx,
+                        JS::MutableHandle<JSObject*> aReflector) override;
+
+  void PostMessage(JSContext* aCx, JS::Handle<JS::Value> aMessage,
+                   const Sequence<JSObject*>& aTransferable, ErrorResult& aRv);
+
+  void PostMessage(JSContext* aCx, JS::Handle<JS::Value> aMessage,
+                   const StructuredSerializeOptions& aOptions,
+                   ErrorResult& aRv);
+
+  void Close();
+
+  MOZ_CAN_RUN_SCRIPT
+  int32_t RequestAnimationFrame(FrameRequestCallback& aCallback,
+                                ErrorResult& aError);
+
+  MOZ_CAN_RUN_SCRIPT
+  void CancelAnimationFrame(int32_t aHandle, ErrorResult& aError);
+
+  void OnDocumentVisible(bool aVisible) override;
+
+  MOZ_CAN_RUN_SCRIPT_BOUNDARY
+  void OnVsync(const VsyncEvent& aVsync) override;
+
+  IMPL_EVENT_HANDLER(message)
+  IMPL_EVENT_HANDLER(messageerror)
+  IMPL_EVENT_HANDLER(rtctransform)
+
+ private:
+  ~DedicatedWorkerGlobalScope() = default;
+
+  FrameRequestManager mFrameRequestManager;
+  RefPtr<VsyncWorkerChild> mVsyncChild;
+  RefPtr<WorkerDocumentListener> mDocListener;
+  bool mDocumentVisible = false;
+};
+
+class SharedWorkerGlobalScope final
+    : public WorkerGlobalScope,
+      public workerinternals::NamedWorkerGlobalScopeMixin {
+ public:
+  SharedWorkerGlobalScope(WorkerPrivate* aWorkerPrivate,
+                          UniquePtr<ClientSource> aClientSource,
+                          const nsString& aName);
+
+  bool WrapGlobalObject(JSContext* aCx,
+                        JS::MutableHandle<JSObject*> aReflector) override;
+
+  void Close();
+
+  IMPL_EVENT_HANDLER(connect)
+
+ private:
+  ~SharedWorkerGlobalScope() = default;
+};
+
+class ServiceWorkerGlobalScope final : public WorkerGlobalScope {
+ public:
+  NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(ServiceWorkerGlobalScope,
+                                           WorkerGlobalScope)
+
+  ServiceWorkerGlobalScope(
+      WorkerPrivate* aWorkerPrivate, UniquePtr<ClientSource> aClientSource,
+      const ServiceWorkerRegistrationDescriptor& aRegistrationDescriptor);
+
+  bool WrapGlobalObject(JSContext* aCx,
+                        JS::MutableHandle<JSObject*> aReflector) override;
+
+  already_AddRefed<Clients> GetClients();
+
+  ServiceWorkerRegistration* Registration();
+
+  already_AddRefed<Promise> SkipWaiting(ErrorResult& aRv);
+
+  SafeRefPtr<extensions::ExtensionBrowser> AcquireExtensionBrowser();
+
+  IMPL_EVENT_HANDLER(install)
+  IMPL_EVENT_HANDLER(activate)
+
+  EventHandlerNonNull* GetOnfetch();
+
+  void SetOnfetch(EventHandlerNonNull* aCallback);
+
+  void EventListenerAdded(nsAtom* aType) override;
+
+  IMPL_EVENT_HANDLER(message)
+  IMPL_EVENT_HANDLER(messageerror)
+
+  IMPL_EVENT_HANDLER(notificationclick)
+  IMPL_EVENT_HANDLER(notificationclose)
+
+  IMPL_EVENT_HANDLER(push)
+  IMPL_EVENT_HANDLER(pushsubscriptionchange)
+
+ private:
+  ~ServiceWorkerGlobalScope();
+
+  void NoteFetchHandlerWasAdded() const;
+
+  RefPtr<Clients> mClients;
+  const nsString mScope;
+  RefPtr<ServiceWorkerRegistration> mRegistration;
+  SafeRefPtr<extensions::ExtensionBrowser> mExtensionBrowser;
+};
+
+class WorkerDebuggerGlobalScope final : public WorkerGlobalScopeBase {
+ public:
+  using WorkerGlobalScopeBase::WorkerGlobalScopeBase;
+
+  bool WrapGlobalObject(JSContext* aCx,
+                        JS::MutableHandle<JSObject*> aReflector) override;
+
+  void Control(const ServiceWorkerDescriptor& aServiceWorker) override {
+    MOZ_CRASH("Can't control debugger workers.");
+  }
+
+  void GetGlobal(JSContext* aCx, JS::MutableHandle<JSObject*> aGlobal,
+                 ErrorResult& aRv);
+
+  void CreateSandbox(JSContext* aCx, const nsAString& aName,
+                     JS::Handle<JSObject*> aPrototype,
+                     JS::MutableHandle<JSObject*> aResult, ErrorResult& aRv);
+
+  void LoadSubScript(JSContext* aCx, const nsAString& aUrl,
+                     const Optional<JS::Handle<JSObject*>>& aSandbox,
+                     ErrorResult& aRv);
+
+  MOZ_CAN_RUN_SCRIPT void EnterEventLoop();
+
+  void LeaveEventLoop();
+
+  void PostMessage(const nsAString& aMessage);
+
+  void SetImmediate(Function& aHandler, ErrorResult& aRv);
+
+  void ReportError(JSContext* aCx, const nsAString& aMessage);
+
+  void RetrieveConsoleEvents(JSContext* aCx, nsTArray<JS::Value>& aEvents,
+                             ErrorResult& aRv);
+
+  void ClearConsoleEvents(JSContext* aCx, ErrorResult& aRv);
+
+  void SetConsoleEventHandler(JSContext* aCx, AnyCallback* aHandler,
+                              ErrorResult& aRv);
+
+  void Dump(JSContext* aCx, const Optional<nsAString>& aString) const;
+
+  IMPL_EVENT_HANDLER(message)
+  IMPL_EVENT_HANDLER(messageerror)
+
+ private:
+  ~WorkerDebuggerGlobalScope() = default;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+inline nsISupports* ToSupports(mozilla::dom::WorkerGlobalScope* aScope) {
+  return static_cast<mozilla::dom::EventTarget*>(aScope);
+}
+
+#endif /* mozilla_dom_workerscope_h__ */
diff --git a/dom/workers/WorkerStatus.h b/dom/workers/WorkerStatus.h
new file mode 100644
index 0000000000..696abc5d2c
--- /dev/null
+++ b/dom/workers/WorkerStatus.h
@@ -0,0 +1,58 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_workers_WorkerStatus_h
+#define mozilla_dom_workers_WorkerStatus_h
+
+namespace mozilla::dom {
+
+/**
+ * Use this chart to help figure out behavior during each of the closing
+ * statuses. Details below.
+ *
+ * +========================================================+
+ * |                     Closing Statuses                   |
+ * +=============+=============+=================+==========+
+ * |    status   | clear queue | abort execution | notified |
+ * +=============+=============+=================+==========+
+ * |   Closing   |     yes     |       no        |    no    |
+ * +-------------+-------------+-----------------+----------+
+ * |  Canceling  |     yes     |       yes       |   yes    |
+ * +-------------+-------------+-----------------+----------+
+ * |   Killing   |     yes     |       yes       |   yes    |
+ * +-------------+-------------+-----------------+----------+
+ */
+
+enum WorkerStatus {
+  // Not yet scheduled.
+  Pending = 0,
+
+  // This status means that the worker is active.
+  Running,
+
+  // Inner script called close() on the worker global scope. Setting this
+  // status causes the worker to clear its queue of events but does not abort
+  // the currently running script. WorkerRef objects are not going to be
+  // notified because the behavior of APIs/Components should not change during
+  // this status yet.
+  Closing,
+
+  // Either the user navigated away from the owning page or the owning page fell
+  // out of bfcache. Setting this status causes the worker to abort immediately.
+  // Since the page has gone away the worker may not post any messages.
+  Canceling,
+
+  // The application is shutting down. Setting this status causes the worker to
+  // abort immediately.
+  Killing,
+
+  // The worker is effectively dead.
+  Dead
+};
+
+}  // namespace mozilla::dom
+
+#endif /* mozilla_dom_workers_WorkerStatus_h */
diff --git a/dom/workers/WorkerTestUtils.cpp b/dom/workers/WorkerTestUtils.cpp
new file mode 100644
index 0000000000..81fa41b03c
--- /dev/null
+++ b/dom/workers/WorkerTestUtils.cpp
@@ -0,0 +1,21 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/ErrorResult.h"
+#include "mozilla/dom/WorkerPrivate.h"
+#include "mozilla/dom/WorkerTestUtils.h"
+
+namespace mozilla::dom {
+
+uint32_t WorkerTestUtils::CurrentTimerNestingLevel(const GlobalObject& aGlobal,
+                                                   ErrorResult& aErr) {
+  MOZ_ASSERT(!NS_IsMainThread());
+  WorkerPrivate* worker = GetCurrentThreadWorkerPrivate();
+  MOZ_ASSERT(worker);
+  return worker->GetCurrentTimerNestingLevel();
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/workers/WorkerTestUtils.h b/dom/workers/WorkerTestUtils.h
new file mode 100644
index 0000000000..6668fdf1f7
--- /dev/null
+++ b/dom/workers/WorkerTestUtils.h
@@ -0,0 +1,40 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_WorkerTestUtils__
+#define mozilla_dom_WorkerTestUtils__
+
+namespace mozilla {
+
+class ErrorResult;
+
+namespace dom {
+
+/**
+ * dom/webidl/WorkerTestUtils.webidl defines APIs to expose worker's internal
+ * status for glass-box testing. The APIs are only exposed to Workers with prefs
+ * dom.workers.testing.enabled.
+ *
+ * WorkerTestUtils is the implementation of dom/webidl/WorkerTestUtils.webidl
+ */
+class WorkerTestUtils final {
+ public:
+  /**
+   *  Expose the worker's current timer nesting level.
+   *
+   *  The worker's current timer nesting level means the executing timer
+   *  handler's timer nesting level. When there is no executing timer handler, 0
+   *  should be returned by this API. The maximum timer nesting level is 5.
+   *
+   *  https://html.spec.whatwg.org/#timer-initialisation-steps
+   */
+  static uint32_t CurrentTimerNestingLevel(const GlobalObject&,
+                                           ErrorResult& aErr);
+};
+
+}  // namespace dom
+}  // namespace mozilla
+#endif
diff --git a/dom/workers/WorkerThread.cpp b/dom/workers/WorkerThread.cpp
new file mode 100644
index 0000000000..19cf9cb364
--- /dev/null
+++ b/dom/workers/WorkerThread.cpp
@@ -0,0 +1,367 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "WorkerThread.h"
+
+#include <utility>
+#include "WorkerPrivate.h"
+#include "WorkerRunnable.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/Atomics.h"
+#include "mozilla/CycleCollectedJSContext.h"
+#include "mozilla/EventQueue.h"
+#include "mozilla/MacroForEach.h"
+#include "mozilla/NotNull.h"
+#include "mozilla/ThreadEventQueue.h"
+#include "mozilla/UniquePtr.h"
+#include "mozilla/ipc/BackgroundChild.h"
+#include "nsCOMPtr.h"
+#include "nsDebug.h"
+#include "nsICancelableRunnable.h"
+#include "nsIEventTarget.h"
+#include "nsIRunnable.h"
+#include "nsIThreadInternal.h"
+#include "nsString.h"
+#include "prthread.h"
+
+namespace mozilla {
+
+using namespace ipc;
+
+namespace dom {
+
+namespace {
+
+// The C stack size. We use the same stack size on all platforms for
+// consistency.
+//
+// Note: Our typical equation of 256 machine words works out to 2MB on 64-bit
+// platforms. Since that works out to the size of a VM huge page, that can
+// sometimes lead to an OS allocating an entire huge page for the stack at once.
+// To avoid this, we subtract the size of 2 pages, to be safe.
+const uint32_t kWorkerStackSize = 256 * sizeof(size_t) * 1024 - 8192;
+
+}  // namespace
+
+WorkerThreadFriendKey::WorkerThreadFriendKey() {
+  MOZ_COUNT_CTOR(WorkerThreadFriendKey);
+}
+
+WorkerThreadFriendKey::~WorkerThreadFriendKey() {
+  MOZ_COUNT_DTOR(WorkerThreadFriendKey);
+}
+
+class WorkerThread::Observer final : public nsIThreadObserver {
+  WorkerPrivate* mWorkerPrivate;
+
+ public:
+  explicit Observer(WorkerPrivate* aWorkerPrivate)
+      : mWorkerPrivate(aWorkerPrivate) {
+    MOZ_ASSERT(aWorkerPrivate);
+    aWorkerPrivate->AssertIsOnWorkerThread();
+  }
+
+  NS_DECL_THREADSAFE_ISUPPORTS
+
+ private:
+  ~Observer() { mWorkerPrivate->AssertIsOnWorkerThread(); }
+
+  NS_DECL_NSITHREADOBSERVER
+};
+
+WorkerThread::WorkerThread(ConstructorKey)
+    : nsThread(
+          MakeNotNull<ThreadEventQueue*>(MakeUnique<mozilla::EventQueue>()),
+          nsThread::NOT_MAIN_THREAD, {.stackSize = kWorkerStackSize}),
+      mLock("WorkerThread::mLock"),
+      mWorkerPrivateCondVar(mLock, "WorkerThread::mWorkerPrivateCondVar"),
+      mWorkerPrivate(nullptr),
+      mOtherThreadsDispatchingViaEventTarget(0)
+#ifdef DEBUG
+      ,
+      mAcceptingNonWorkerRunnables(true)
+#endif
+{
+}
+
+WorkerThread::~WorkerThread() {
+  MOZ_ASSERT(!mWorkerPrivate);
+  MOZ_ASSERT(!mOtherThreadsDispatchingViaEventTarget);
+  MOZ_ASSERT(mAcceptingNonWorkerRunnables);
+}
+
+// static
+SafeRefPtr<WorkerThread> WorkerThread::Create(
+    const WorkerThreadFriendKey& /* aKey */) {
+  SafeRefPtr<WorkerThread> thread =
+      MakeSafeRefPtr<WorkerThread>(ConstructorKey());
+  if (NS_FAILED(thread->Init("DOM Worker"_ns))) {
+    NS_WARNING("Failed to create new thread!");
+    return nullptr;
+  }
+
+  return thread;
+}
+
+void WorkerThread::SetWorker(const WorkerThreadFriendKey& /* aKey */,
+                             WorkerPrivate* aWorkerPrivate) {
+  MOZ_ASSERT(PR_GetCurrentThread() == mThread);
+
+  if (aWorkerPrivate) {
+    {
+      MutexAutoLock lock(mLock);
+
+      MOZ_ASSERT(!mWorkerPrivate);
+      MOZ_ASSERT(mAcceptingNonWorkerRunnables);
+
+      mWorkerPrivate = aWorkerPrivate;
+#ifdef DEBUG
+      mAcceptingNonWorkerRunnables = false;
+#endif
+    }
+
+    mObserver = new Observer(aWorkerPrivate);
+    MOZ_ALWAYS_SUCCEEDS(AddObserver(mObserver));
+  } else {
+    MOZ_ALWAYS_SUCCEEDS(RemoveObserver(mObserver));
+    mObserver = nullptr;
+
+    {
+      MutexAutoLock lock(mLock);
+
+      MOZ_ASSERT(mWorkerPrivate);
+      MOZ_ASSERT(!mAcceptingNonWorkerRunnables);
+      // mOtherThreadsDispatchingViaEventTarget can still be non-zero here
+      // because WorkerThread::Dispatch isn't atomic so a thread initiating
+      // dispatch can have dispatched a runnable at this thread allowing us to
+      // begin shutdown before that thread gets a chance to decrement
+      // mOtherThreadsDispatchingViaEventTarget back to 0.  So we need to wait
+      // for that.
+      while (mOtherThreadsDispatchingViaEventTarget) {
+        mWorkerPrivateCondVar.Wait();
+      }
+
+#ifdef DEBUG
+      mAcceptingNonWorkerRunnables = true;
+#endif
+      mWorkerPrivate = nullptr;
+    }
+  }
+}
+
+nsresult WorkerThread::DispatchPrimaryRunnable(
+    const WorkerThreadFriendKey& /* aKey */,
+    already_AddRefed<nsIRunnable> aRunnable) {
+  nsCOMPtr<nsIRunnable> runnable(aRunnable);
+
+#ifdef DEBUG
+  MOZ_ASSERT(PR_GetCurrentThread() != mThread);
+  MOZ_ASSERT(runnable);
+  {
+    MutexAutoLock lock(mLock);
+
+    MOZ_ASSERT(!mWorkerPrivate);
+    MOZ_ASSERT(mAcceptingNonWorkerRunnables);
+  }
+#endif
+
+  nsresult rv = nsThread::Dispatch(runnable.forget(), NS_DISPATCH_NORMAL);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  return NS_OK;
+}
+
+nsresult WorkerThread::DispatchAnyThread(
+    const WorkerThreadFriendKey& /* aKey */,
+    already_AddRefed<WorkerRunnable> aWorkerRunnable) {
+  // May be called on any thread!
+
+#ifdef DEBUG
+  {
+    const bool onWorkerThread = PR_GetCurrentThread() == mThread;
+    {
+      MutexAutoLock lock(mLock);
+
+      MOZ_ASSERT(mWorkerPrivate);
+      MOZ_ASSERT(!mAcceptingNonWorkerRunnables);
+
+      if (onWorkerThread) {
+        mWorkerPrivate->AssertIsOnWorkerThread();
+      }
+    }
+  }
+#endif
+
+  nsCOMPtr<nsIRunnable> runnable(aWorkerRunnable);
+
+  nsresult rv = nsThread::Dispatch(runnable.forget(), NS_DISPATCH_NORMAL);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  // We don't need to notify the worker's condition variable here because we're
+  // being called from worker-controlled code and it will make sure to wake up
+  // the worker thread if needed.
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WorkerThread::DispatchFromScript(nsIRunnable* aRunnable, uint32_t aFlags) {
+  nsCOMPtr<nsIRunnable> runnable(aRunnable);
+  return Dispatch(runnable.forget(), aFlags);
+}
+
+NS_IMETHODIMP
+WorkerThread::Dispatch(already_AddRefed<nsIRunnable> aRunnable,
+                       uint32_t aFlags) {
+  // May be called on any thread!
+  nsCOMPtr<nsIRunnable> runnable(aRunnable);  // in case we exit early
+
+  // Workers only support asynchronous dispatch.
+  if (NS_WARN_IF(aFlags != NS_DISPATCH_NORMAL)) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  const bool onWorkerThread = PR_GetCurrentThread() == mThread;
+
+  WorkerPrivate* workerPrivate = nullptr;
+  if (onWorkerThread) {
+    // No need to lock here because it is only modified on this thread.
+    MOZ_ASSERT(mWorkerPrivate);
+    mWorkerPrivate->AssertIsOnWorkerThread();
+
+    workerPrivate = mWorkerPrivate;
+  } else {
+    MutexAutoLock lock(mLock);
+
+    MOZ_ASSERT(mOtherThreadsDispatchingViaEventTarget < UINT32_MAX);
+
+    if (mWorkerPrivate) {
+      workerPrivate = mWorkerPrivate;
+
+      // Incrementing this counter will make the worker thread sleep if it
+      // somehow tries to unset mWorkerPrivate while we're using it.
+      mOtherThreadsDispatchingViaEventTarget++;
+    }
+  }
+
+  nsresult rv;
+  if (runnable && onWorkerThread) {
+    RefPtr<WorkerRunnable> workerRunnable =
+        workerPrivate->MaybeWrapAsWorkerRunnable(runnable.forget());
+    rv = nsThread::Dispatch(workerRunnable.forget(), NS_DISPATCH_NORMAL);
+  } else {
+    rv = nsThread::Dispatch(runnable.forget(), NS_DISPATCH_NORMAL);
+  }
+
+  if (!onWorkerThread && workerPrivate) {
+    // We need to wake the worker thread if we're not already on the right
+    // thread and the dispatch succeeded.
+    if (NS_SUCCEEDED(rv)) {
+      MutexAutoLock workerLock(workerPrivate->mMutex);
+
+      workerPrivate->mCondVar.Notify();
+    }
+
+    // Now unset our waiting flag.
+    {
+      MutexAutoLock lock(mLock);
+
+      MOZ_ASSERT(mOtherThreadsDispatchingViaEventTarget);
+
+      if (!--mOtherThreadsDispatchingViaEventTarget) {
+        mWorkerPrivateCondVar.Notify();
+      }
+    }
+  }
+
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WorkerThread::DelayedDispatch(already_AddRefed<nsIRunnable>, uint32_t) {
+  return NS_ERROR_NOT_IMPLEMENTED;
+}
+
+uint32_t WorkerThread::RecursionDepth(
+    const WorkerThreadFriendKey& /* aKey */) const {
+  MOZ_ASSERT(PR_GetCurrentThread() == mThread);
+
+  return mNestedEventLoopDepth;
+}
+
+NS_IMETHODIMP
+WorkerThread::HasPendingEvents(bool* aResult) {
+  MOZ_ASSERT(aResult);
+  const bool onWorkerThread = PR_GetCurrentThread() == mThread;
+  // If is on the worker thread, call nsThread::HasPendingEvents directly.
+  if (onWorkerThread) {
+    return nsThread::HasPendingEvents(aResult);
+  }
+  // Checking if is on the parent thread, otherwise, returns unexpected error.
+  {
+    MutexAutoLock lock(mLock);
+    // return directly if the mWorkerPrivate has not yet set or had already
+    // unset
+    if (!mWorkerPrivate) {
+      *aResult = false;
+      return NS_OK;
+    }
+    if (!mWorkerPrivate->IsOnParentThread()) {
+      *aResult = false;
+      return NS_ERROR_UNEXPECTED;
+    }
+  }
+  *aResult = mEvents->HasPendingEvent();
+  return NS_OK;
+}
+
+NS_IMPL_ISUPPORTS(WorkerThread::Observer, nsIThreadObserver)
+
+NS_IMETHODIMP
+WorkerThread::Observer::OnDispatchedEvent() {
+  MOZ_CRASH("OnDispatchedEvent() should never be called!");
+}
+
+NS_IMETHODIMP
+WorkerThread::Observer::OnProcessNextEvent(nsIThreadInternal* /* aThread */,
+                                           bool aMayWait) {
+  mWorkerPrivate->AssertIsOnWorkerThread();
+
+  // If the PBackground child is not created yet, then we must permit
+  // blocking event processing to support
+  // BackgroundChild::GetOrCreateCreateForCurrentThread(). If this occurs
+  // then we are spinning on the event queue at the start of
+  // PrimaryWorkerRunnable::Run() and don't want to process the event in
+  // mWorkerPrivate yet.
+  if (aMayWait) {
+    MOZ_ASSERT(CycleCollectedJSContext::Get()->RecursionDepth() == 2);
+    MOZ_ASSERT(!BackgroundChild::GetForCurrentThread());
+    return NS_OK;
+  }
+
+  mWorkerPrivate->OnProcessNextEvent();
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+WorkerThread::Observer::AfterProcessNextEvent(nsIThreadInternal* /* aThread */,
+                                              bool /* aEventWasProcessed */) {
+  mWorkerPrivate->AssertIsOnWorkerThread();
+
+  mWorkerPrivate->AfterProcessNextEvent();
+  return NS_OK;
+}
+
+}  // namespace dom
+}  // namespace mozilla
diff --git a/dom/workers/WorkerThread.h b/dom/workers/WorkerThread.h
new file mode 100644
index 0000000000..06624f60c1
--- /dev/null
+++ b/dom/workers/WorkerThread.h
@@ -0,0 +1,112 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_workers_WorkerThread_h__
+#define mozilla_dom_workers_WorkerThread_h__
+
+#include "mozilla/AlreadyAddRefed.h"
+#include "mozilla/CondVar.h"
+#include "mozilla/Mutex.h"
+#include "mozilla/RefPtr.h"
+#include "mozilla/dom/SafeRefPtr.h"
+#include "nsISupports.h"
+#include "nsThread.h"
+#include "nscore.h"
+
+class nsIRunnable;
+
+namespace mozilla {
+class Runnable;
+
+namespace dom {
+
+class WorkerRunnable;
+class WorkerPrivate;
+template <class>
+class WorkerPrivateParent;
+
+namespace workerinternals {
+class RuntimeService;
+}
+
+// This class lets us restrict the public methods that can be called on
+// WorkerThread to RuntimeService and WorkerPrivate without letting them gain
+// full access to private methods (as would happen if they were simply friends).
+class WorkerThreadFriendKey {
+  friend class workerinternals::RuntimeService;
+  friend class WorkerPrivate;
+  friend class WorkerPrivateParent<WorkerPrivate>;
+
+  WorkerThreadFriendKey();
+  ~WorkerThreadFriendKey();
+};
+
+class WorkerThread final : public nsThread {
+  class Observer;
+
+  Mutex mLock MOZ_UNANNOTATED;
+  CondVar mWorkerPrivateCondVar;
+
+  // Protected by nsThread::mLock.
+  WorkerPrivate* mWorkerPrivate;
+
+  // Only touched on the target thread.
+  RefPtr<Observer> mObserver;
+
+  // Protected by nsThread::mLock and waited on with mWorkerPrivateCondVar.
+  uint32_t mOtherThreadsDispatchingViaEventTarget;
+
+#ifdef DEBUG
+  // Protected by nsThread::mLock.
+  bool mAcceptingNonWorkerRunnables;
+#endif
+
+  // Using this struct we restrict access to the constructor while still being
+  // able to use MakeSafeRefPtr.
+  struct ConstructorKey {};
+
+ public:
+  explicit WorkerThread(ConstructorKey);
+
+  static SafeRefPtr<WorkerThread> Create(const WorkerThreadFriendKey& aKey);
+
+  void SetWorker(const WorkerThreadFriendKey& aKey,
+                 WorkerPrivate* aWorkerPrivate);
+
+  nsresult DispatchPrimaryRunnable(const WorkerThreadFriendKey& aKey,
+                                   already_AddRefed<nsIRunnable> aRunnable);
+
+  nsresult DispatchAnyThread(const WorkerThreadFriendKey& aKey,
+                             already_AddRefed<WorkerRunnable> aWorkerRunnable);
+
+  uint32_t RecursionDepth(const WorkerThreadFriendKey& aKey) const;
+
+  // Override HasPendingEvents to allow HasPendingEvents could be accessed by
+  // the parent thread. WorkerPrivate::IsEligibleForCC calls this method on the
+  // parent thread to check if there is any pending events on the worker thread.
+  NS_IMETHOD HasPendingEvents(bool* aHasPendingEvents) override;
+
+  NS_INLINE_DECL_REFCOUNTING_INHERITED(WorkerThread, nsThread)
+
+ private:
+  ~WorkerThread();
+
+  // This should only be called by consumers that have an
+  // nsIEventTarget/nsIThread pointer.
+  NS_IMETHOD
+  Dispatch(already_AddRefed<nsIRunnable> aRunnable, uint32_t aFlags) override;
+
+  NS_IMETHOD
+  DispatchFromScript(nsIRunnable* aRunnable, uint32_t aFlags) override;
+
+  NS_IMETHOD
+  DelayedDispatch(already_AddRefed<nsIRunnable>, uint32_t) override;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_workers_WorkerThread_h__
diff --git a/dom/workers/loader/CacheLoadHandler.cpp b/dom/workers/loader/CacheLoadHandler.cpp
new file mode 100644
index 0000000000..16f992e837
--- /dev/null
+++ b/dom/workers/loader/CacheLoadHandler.cpp
@@ -0,0 +1,651 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "CacheLoadHandler.h"
+#include "ScriptResponseHeaderProcessor.h"  // ScriptResponseHeaderProcessor
+#include "WorkerLoadContext.h"              // WorkerLoadContext
+
+#include "nsIPrincipal.h"
+
+#include "nsIThreadRetargetableRequest.h"
+#include "nsIXPConnect.h"
+
+#include "jsapi.h"
+#include "nsNetUtil.h"
+
+#include "mozilla/Assertions.h"
+#include "mozilla/Encoding.h"
+#include "mozilla/dom/CacheBinding.h"
+#include "mozilla/dom/cache/CacheTypes.h"
+#include "mozilla/dom/Response.h"
+#include "mozilla/dom/ServiceWorkerBinding.h"  // ServiceWorkerState
+#include "mozilla/Result.h"
+#include "mozilla/TaskQueue.h"
+#include "mozilla/UniquePtr.h"
+#include "mozilla/dom/Document.h"
+#include "mozilla/dom/WorkerScope.h"
+
+#include "mozilla/dom/workerinternals/ScriptLoader.h"  // WorkerScriptLoader
+
+namespace mozilla {
+namespace dom {
+
+namespace workerinternals::loader {
+
+NS_IMPL_ISUPPORTS0(CacheCreator)
+
+NS_IMPL_ISUPPORTS(CacheLoadHandler, nsIStreamLoaderObserver)
+
+NS_IMPL_ISUPPORTS0(CachePromiseHandler)
+
+CachePromiseHandler::CachePromiseHandler(
+    WorkerScriptLoader* aLoader, ThreadSafeRequestHandle* aRequestHandle)
+    : mLoader(aLoader), mRequestHandle(aRequestHandle) {
+  AssertIsOnMainThread();
+  MOZ_ASSERT(mLoader);
+}
+
+void CachePromiseHandler::ResolvedCallback(JSContext* aCx,
+                                           JS::Handle<JS::Value> aValue,
+                                           ErrorResult& aRv) {
+  AssertIsOnMainThread();
+  if (mRequestHandle->IsEmpty()) {
+    return;
+  }
+  WorkerLoadContext* loadContext = mRequestHandle->GetContext();
+
+  // May already have been canceled by CacheLoadHandler::Fail from
+  // CancelMainThread.
+  MOZ_ASSERT(loadContext->mCacheStatus == WorkerLoadContext::WritingToCache ||
+             loadContext->mCacheStatus == WorkerLoadContext::Cancel);
+  MOZ_ASSERT_IF(loadContext->mCacheStatus == WorkerLoadContext::Cancel,
+                !loadContext->mCachePromise);
+
+  if (loadContext->mCachePromise) {
+    loadContext->mCacheStatus = WorkerLoadContext::Cached;
+    loadContext->mCachePromise = nullptr;
+    mRequestHandle->MaybeExecuteFinishedScripts();
+  }
+}
+
+void CachePromiseHandler::RejectedCallback(JSContext* aCx,
+                                           JS::Handle<JS::Value> aValue,
+                                           ErrorResult& aRv) {
+  AssertIsOnMainThread();
+  if (mRequestHandle->IsEmpty()) {
+    return;
+  }
+  WorkerLoadContext* loadContext = mRequestHandle->GetContext();
+
+  // May already have been canceled by CacheLoadHandler::Fail from
+  // CancelMainThread.
+  MOZ_ASSERT(loadContext->mCacheStatus == WorkerLoadContext::WritingToCache ||
+             loadContext->mCacheStatus == WorkerLoadContext::Cancel);
+  loadContext->mCacheStatus = WorkerLoadContext::Cancel;
+
+  loadContext->mCachePromise = nullptr;
+
+  // This will delete the cache object and will call LoadingFinished() with an
+  // error for each ongoing operation.
+  auto* cacheCreator = mRequestHandle->GetCacheCreator();
+  if (cacheCreator) {
+    cacheCreator->DeleteCache(NS_ERROR_FAILURE);
+  }
+}
+
+CacheCreator::CacheCreator(WorkerPrivate* aWorkerPrivate)
+    : mCacheName(aWorkerPrivate->ServiceWorkerCacheName()),
+      mOriginAttributes(aWorkerPrivate->GetOriginAttributes()) {
+  MOZ_ASSERT(aWorkerPrivate->IsServiceWorker());
+}
+
+nsresult CacheCreator::CreateCacheStorage(nsIPrincipal* aPrincipal) {
+  AssertIsOnMainThread();
+  MOZ_ASSERT(!mCacheStorage);
+  MOZ_ASSERT(aPrincipal);
+
+  nsIXPConnect* xpc = nsContentUtils::XPConnect();
+  MOZ_ASSERT(xpc, "This should never be null!");
+
+  AutoJSAPI jsapi;
+  jsapi.Init();
+  JSContext* cx = jsapi.cx();
+  JS::Rooted<JSObject*> sandbox(cx);
+  nsresult rv = xpc->CreateSandbox(cx, aPrincipal, sandbox.address());
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  // The JSContext is not in a realm, so CreateSandbox returned an unwrapped
+  // global.
+  MOZ_ASSERT(JS_IsGlobalObject(sandbox));
+
+  mSandboxGlobalObject = xpc::NativeGlobal(sandbox);
+  if (NS_WARN_IF(!mSandboxGlobalObject)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  // If we're in private browsing mode, don't even try to create the
+  // CacheStorage.  Instead, just fail immediately to terminate the
+  // ServiceWorker load.
+  if (NS_WARN_IF(mOriginAttributes.mPrivateBrowsingId > 0)) {
+    return NS_ERROR_DOM_SECURITY_ERR;
+  }
+
+  // Create a CacheStorage bypassing its trusted origin checks.  The
+  // ServiceWorker has already performed its own checks before getting
+  // to this point.
+  ErrorResult error;
+  mCacheStorage = CacheStorage::CreateOnMainThread(
+      mozilla::dom::cache::CHROME_ONLY_NAMESPACE, mSandboxGlobalObject,
+      aPrincipal, true /* force trusted origin */, error);
+  if (NS_WARN_IF(error.Failed())) {
+    return error.StealNSResult();
+  }
+
+  return NS_OK;
+}
+
+nsresult CacheCreator::Load(nsIPrincipal* aPrincipal) {
+  AssertIsOnMainThread();
+  MOZ_ASSERT(!mLoaders.IsEmpty());
+
+  nsresult rv = CreateCacheStorage(aPrincipal);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  ErrorResult error;
+  MOZ_ASSERT(!mCacheName.IsEmpty());
+  RefPtr<Promise> promise = mCacheStorage->Open(mCacheName, error);
+  if (NS_WARN_IF(error.Failed())) {
+    return error.StealNSResult();
+  }
+
+  promise->AppendNativeHandler(this);
+  return NS_OK;
+}
+
+void CacheCreator::FailLoaders(nsresult aRv) {
+  AssertIsOnMainThread();
+
+  // Fail() can call LoadingFinished() which may call ExecuteFinishedScripts()
+  // which sets mCacheCreator to null, so hold a ref.
+  RefPtr<CacheCreator> kungfuDeathGrip = this;
+
+  for (uint32_t i = 0, len = mLoaders.Length(); i < len; ++i) {
+    mLoaders[i]->Fail(aRv);
+  }
+
+  mLoaders.Clear();
+}
+
+void CacheCreator::RejectedCallback(JSContext* aCx,
+                                    JS::Handle<JS::Value> aValue,
+                                    ErrorResult& aRv) {
+  AssertIsOnMainThread();
+  FailLoaders(NS_ERROR_FAILURE);
+}
+
+void CacheCreator::ResolvedCallback(JSContext* aCx,
+                                    JS::Handle<JS::Value> aValue,
+                                    ErrorResult& aRv) {
+  AssertIsOnMainThread();
+  if (!aValue.isObject()) {
+    FailLoaders(NS_ERROR_FAILURE);
+    return;
+  }
+
+  JS::Rooted<JSObject*> obj(aCx, &aValue.toObject());
+  Cache* cache = nullptr;
+  nsresult rv = UNWRAP_OBJECT(Cache, &obj, cache);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    FailLoaders(NS_ERROR_FAILURE);
+    return;
+  }
+
+  mCache = cache;
+  MOZ_DIAGNOSTIC_ASSERT(mCache);
+
+  // If the worker is canceled, CancelMainThread() will have cleared the
+  // loaders via DeleteCache().
+  for (uint32_t i = 0, len = mLoaders.Length(); i < len; ++i) {
+    mLoaders[i]->Load(cache);
+  }
+}
+
+void CacheCreator::DeleteCache(nsresult aReason) {
+  AssertIsOnMainThread();
+
+  // This is called when the load is canceled which can occur before
+  // mCacheStorage is initialized.
+  if (mCacheStorage) {
+    // It's safe to do this while Cache::Match() and Cache::Put() calls are
+    // running.
+    RefPtr<Promise> promise = mCacheStorage->Delete(mCacheName, IgnoreErrors());
+
+    // We don't care to know the result of the promise object.
+  }
+
+  // Always call this here to ensure the loaders array is cleared.
+  FailLoaders(NS_ERROR_FAILURE);
+}
+
+CacheLoadHandler::CacheLoadHandler(ThreadSafeWorkerRef* aWorkerRef,
+                                   ThreadSafeRequestHandle* aRequestHandle,
+                                   bool aIsWorkerScript,
+                                   bool aOnlyExistingCachedResourcesAllowed,
+                                   WorkerScriptLoader* aLoader)
+    : mRequestHandle(aRequestHandle),
+      mLoader(aLoader),
+      mWorkerRef(aWorkerRef),
+      mIsWorkerScript(aIsWorkerScript),
+      mFailed(false),
+      mOnlyExistingCachedResourcesAllowed(aOnlyExistingCachedResourcesAllowed) {
+  MOZ_ASSERT(aWorkerRef);
+  MOZ_ASSERT(aWorkerRef->Private()->IsServiceWorker());
+  mMainThreadEventTarget = aWorkerRef->Private()->MainThreadEventTarget();
+  MOZ_ASSERT(mMainThreadEventTarget);
+  mBaseURI = mLoader->GetBaseURI();
+  AssertIsOnMainThread();
+
+  // Worker scripts are always decoded as UTF-8 per spec.
+  mDecoder = MakeUnique<ScriptDecoder>(UTF_8_ENCODING,
+                                       ScriptDecoder::BOMHandling::Remove);
+}
+
+void CacheLoadHandler::Fail(nsresult aRv) {
+  AssertIsOnMainThread();
+  MOZ_ASSERT(NS_FAILED(aRv));
+
+  if (mFailed) {
+    return;
+  }
+
+  mFailed = true;
+
+  if (mPump) {
+    MOZ_ASSERT_IF(!mRequestHandle->IsEmpty(),
+                  mRequestHandle->GetContext()->mCacheStatus ==
+                      WorkerLoadContext::ReadingFromCache);
+    mPump->Cancel(aRv);
+    mPump = nullptr;
+  }
+  if (mRequestHandle->IsEmpty()) {
+    return;
+  }
+
+  WorkerLoadContext* loadContext = mRequestHandle->GetContext();
+
+  loadContext->mCacheStatus = WorkerLoadContext::Cancel;
+
+  if (loadContext->mCachePromise) {
+    loadContext->mCachePromise->MaybeReject(aRv);
+  }
+
+  loadContext->mCachePromise = nullptr;
+
+  mRequestHandle->LoadingFinished(aRv);
+}
+
+void CacheLoadHandler::Load(Cache* aCache) {
+  AssertIsOnMainThread();
+  MOZ_ASSERT(aCache);
+  MOZ_ASSERT(!mRequestHandle->IsEmpty());
+  WorkerLoadContext* loadContext = mRequestHandle->GetContext();
+
+  nsCOMPtr<nsIURI> uri;
+  nsresult rv = NS_NewURI(getter_AddRefs(uri), loadContext->mRequest->mURL,
+                          nullptr, mBaseURI);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    Fail(rv);
+    return;
+  }
+
+  nsAutoCString spec;
+  rv = uri->GetSpec(spec);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    Fail(rv);
+    return;
+  }
+
+  MOZ_ASSERT(loadContext->mFullURL.IsEmpty());
+  CopyUTF8toUTF16(spec, loadContext->mFullURL);
+
+  mozilla::dom::RequestOrUSVString request;
+  request.SetAsUSVString().ShareOrDependUpon(loadContext->mFullURL);
+
+  mozilla::dom::CacheQueryOptions params;
+
+  // This JSContext will not end up executing JS code because here there are
+  // no ReadableStreams involved.
+  AutoJSAPI jsapi;
+  jsapi.Init();
+
+  ErrorResult error;
+  RefPtr<Promise> promise = aCache->Match(jsapi.cx(), request, params, error);
+  if (NS_WARN_IF(error.Failed())) {
+    Fail(error.StealNSResult());
+    return;
+  }
+
+  promise->AppendNativeHandler(this);
+}
+
+void CacheLoadHandler::RejectedCallback(JSContext* aCx,
+                                        JS::Handle<JS::Value> aValue,
+                                        ErrorResult& aRv) {
+  AssertIsOnMainThread();
+  MOZ_ASSERT(!mRequestHandle->IsEmpty());
+
+  MOZ_ASSERT(mRequestHandle->GetContext()->mCacheStatus ==
+             WorkerLoadContext::Uncached);
+  Fail(NS_ERROR_FAILURE);
+}
+
+void CacheLoadHandler::ResolvedCallback(JSContext* aCx,
+                                        JS::Handle<JS::Value> aValue,
+                                        ErrorResult& aRv) {
+  AssertIsOnMainThread();
+  MOZ_ASSERT(!mRequestHandle->IsEmpty());
+  WorkerLoadContext* loadContext = mRequestHandle->GetContext();
+
+  // If we have already called 'Fail', we should not proceed. If we cancelled,
+  // we should similarily not proceed.
+  if (mFailed) {
+    return;
+  }
+
+  MOZ_ASSERT(loadContext->mCacheStatus == WorkerLoadContext::Uncached);
+
+  nsresult rv;
+
+  // The ServiceWorkerScriptCache will store data for any scripts it
+  // it knows about.  This is always at least the top level script.
+  // Depending on if a previous version of the service worker has
+  // been installed or not it may also know about importScripts().  We
+  // must handle loading and offlining new importScripts() here, however.
+  if (aValue.isUndefined()) {
+    // If this is the main script or we're not loading a new service worker
+    // then this is an error.  This can happen for internal reasons, like
+    // storage was probably wiped without removing the service worker
+    // registration.  It can also happen for exposed reasons like the
+    // service worker script calling importScripts() after install.
+    if (NS_WARN_IF(mIsWorkerScript || mOnlyExistingCachedResourcesAllowed)) {
+      Fail(NS_ERROR_DOM_INVALID_STATE_ERR);
+      return;
+    }
+
+    loadContext->mCacheStatus = WorkerLoadContext::ToBeCached;
+    rv = mLoader->LoadScript(mRequestHandle);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      Fail(rv);
+    }
+    return;
+  }
+
+  MOZ_ASSERT(aValue.isObject());
+
+  JS::Rooted<JSObject*> obj(aCx, &aValue.toObject());
+  mozilla::dom::Response* response = nullptr;
+  rv = UNWRAP_OBJECT(Response, &obj, response);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    Fail(rv);
+    return;
+  }
+
+  InternalHeaders* headers = response->GetInternalHeaders();
+
+  headers->Get("content-security-policy"_ns, mCSPHeaderValue, IgnoreErrors());
+  headers->Get("content-security-policy-report-only"_ns,
+               mCSPReportOnlyHeaderValue, IgnoreErrors());
+  headers->Get("referrer-policy"_ns, mReferrerPolicyHeaderValue,
+               IgnoreErrors());
+
+  nsAutoCString coepHeader;
+  headers->Get("cross-origin-embedder-policy"_ns, coepHeader, IgnoreErrors());
+
+  nsILoadInfo::CrossOriginEmbedderPolicy coep =
+      NS_GetCrossOriginEmbedderPolicyFromHeader(
+          coepHeader, mWorkerRef->Private()->Trials().IsEnabled(
+                          OriginTrial::CoepCredentialless));
+
+  rv = ScriptResponseHeaderProcessor::ProcessCrossOriginEmbedderPolicyHeader(
+      mWorkerRef->Private(), coep, loadContext->IsTopLevel());
+
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    Fail(rv);
+    return;
+  }
+
+  nsCOMPtr<nsIInputStream> inputStream;
+  response->GetBody(getter_AddRefs(inputStream));
+  mChannelInfo = response->GetChannelInfo();
+  const UniquePtr<PrincipalInfo>& pInfo = response->GetPrincipalInfo();
+  if (pInfo) {
+    mPrincipalInfo = mozilla::MakeUnique<PrincipalInfo>(*pInfo);
+  }
+
+  if (!inputStream) {
+    loadContext->mCacheStatus = WorkerLoadContext::Cached;
+
+    if (mRequestHandle->IsCancelled()) {
+      auto* cacheCreator = mRequestHandle->GetCacheCreator();
+      if (cacheCreator) {
+        cacheCreator->DeleteCache(mRequestHandle->GetCancelResult());
+      }
+      return;
+    }
+
+    nsresult rv = DataReceivedFromCache(
+        (uint8_t*)"", 0, mChannelInfo, std::move(mPrincipalInfo),
+        mCSPHeaderValue, mCSPReportOnlyHeaderValue, mReferrerPolicyHeaderValue);
+
+    mRequestHandle->OnStreamComplete(rv);
+    return;
+  }
+
+  MOZ_ASSERT(!mPump);
+  rv = NS_NewInputStreamPump(getter_AddRefs(mPump), inputStream.forget(),
+                             0,     /* default segsize */
+                             0,     /* default segcount */
+                             false, /* default closeWhenDone */
+                             mMainThreadEventTarget);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    Fail(rv);
+    return;
+  }
+
+  nsCOMPtr<nsIStreamLoader> loader;
+  rv = NS_NewStreamLoader(getter_AddRefs(loader), this);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    Fail(rv);
+    return;
+  }
+
+  rv = mPump->AsyncRead(loader);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    mPump = nullptr;
+    Fail(rv);
+    return;
+  }
+
+  nsCOMPtr<nsIThreadRetargetableRequest> rr = do_QueryInterface(mPump);
+  if (rr) {
+    nsCOMPtr<nsIEventTarget> sts =
+        do_GetService(NS_STREAMTRANSPORTSERVICE_CONTRACTID);
+    RefPtr<TaskQueue> queue =
+        TaskQueue::Create(sts.forget(), "CacheLoadHandler STS Delivery Queue");
+    rv = rr->RetargetDeliveryTo(queue);
+    if (NS_FAILED(rv)) {
+      NS_WARNING("Failed to dispatch the nsIInputStreamPump to a IO thread.");
+    }
+  }
+
+  loadContext->mCacheStatus = WorkerLoadContext::ReadingFromCache;
+}
+
+NS_IMETHODIMP
+CacheLoadHandler::OnStreamComplete(nsIStreamLoader* aLoader,
+                                   nsISupports* aContext, nsresult aStatus,
+                                   uint32_t aStringLen,
+                                   const uint8_t* aString) {
+  AssertIsOnMainThread();
+  if (mRequestHandle->IsEmpty()) {
+    return NS_OK;
+  }
+  WorkerLoadContext* loadContext = mRequestHandle->GetContext();
+
+  mPump = nullptr;
+
+  if (NS_FAILED(aStatus)) {
+    MOZ_ASSERT(loadContext->mCacheStatus ==
+                   WorkerLoadContext::ReadingFromCache ||
+               loadContext->mCacheStatus == WorkerLoadContext::Cancel);
+    Fail(aStatus);
+    return NS_OK;
+  }
+
+  MOZ_ASSERT(loadContext->mCacheStatus == WorkerLoadContext::ReadingFromCache);
+  loadContext->mCacheStatus = WorkerLoadContext::Cached;
+
+  MOZ_ASSERT(mPrincipalInfo);
+
+  nsresult rv = DataReceivedFromCache(
+      aString, aStringLen, mChannelInfo, std::move(mPrincipalInfo),
+      mCSPHeaderValue, mCSPReportOnlyHeaderValue, mReferrerPolicyHeaderValue);
+  return mRequestHandle->OnStreamComplete(rv);
+}
+
+nsresult CacheLoadHandler::DataReceivedFromCache(
+    const uint8_t* aString, uint32_t aStringLen,
+    const mozilla::dom::ChannelInfo& aChannelInfo,
+    UniquePtr<PrincipalInfo> aPrincipalInfo, const nsACString& aCSPHeaderValue,
+    const nsACString& aCSPReportOnlyHeaderValue,
+    const nsACString& aReferrerPolicyHeaderValue) {
+  AssertIsOnMainThread();
+  if (mRequestHandle->IsEmpty()) {
+    return NS_OK;
+  }
+  WorkerLoadContext* loadContext = mRequestHandle->GetContext();
+
+  MOZ_ASSERT(loadContext->mCacheStatus == WorkerLoadContext::Cached);
+  MOZ_ASSERT(loadContext->mRequest);
+
+  auto responsePrincipalOrErr = PrincipalInfoToPrincipal(*aPrincipalInfo);
+  MOZ_DIAGNOSTIC_ASSERT(responsePrincipalOrErr.isOk());
+
+  nsIPrincipal* principal = mWorkerRef->Private()->GetPrincipal();
+  if (!principal) {
+    WorkerPrivate* parentWorker = mWorkerRef->Private()->GetParent();
+    MOZ_ASSERT(parentWorker, "Must have a parent!");
+    principal = parentWorker->GetPrincipal();
+  }
+
+  nsCOMPtr<nsIPrincipal> responsePrincipal = responsePrincipalOrErr.unwrap();
+
+  loadContext->mMutedErrorFlag.emplace(!principal->Subsumes(responsePrincipal));
+
+  // May be null.
+  Document* parentDoc = mWorkerRef->Private()->GetDocument();
+
+  // Use the regular ScriptDecoder Decoder for this grunt work! Should be just
+  // fine because we're running on the main thread.
+  nsresult rv;
+
+  // Set the Source type to "text" for decoding.
+  loadContext->mRequest->SetTextSource(loadContext);
+
+  rv = mDecoder->DecodeRawData(loadContext->mRequest, aString, aStringLen,
+                               /* aEndOfStream = */ true);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  if (!loadContext->mRequest->ScriptTextLength()) {
+    nsContentUtils::ReportToConsole(nsIScriptError::warningFlag, "DOM"_ns,
+                                    parentDoc, nsContentUtils::eDOM_PROPERTIES,
+                                    "EmptyWorkerSourceWarning");
+  }
+
+  nsCOMPtr<nsIURI> finalURI;
+  rv = NS_NewURI(getter_AddRefs(finalURI), loadContext->mFullURL);
+  if (!loadContext->mRequest->mBaseURL) {
+    loadContext->mRequest->mBaseURL = finalURI;
+  }
+  if (loadContext->IsTopLevel()) {
+    if (NS_SUCCEEDED(rv)) {
+      mWorkerRef->Private()->SetBaseURI(finalURI);
+    }
+
+#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
+    nsIPrincipal* principal = mWorkerRef->Private()->GetPrincipal();
+    MOZ_DIAGNOSTIC_ASSERT(principal);
+
+    bool equal = false;
+    MOZ_ALWAYS_SUCCEEDS(responsePrincipal->Equals(principal, &equal));
+    MOZ_DIAGNOSTIC_ASSERT(equal);
+
+    nsCOMPtr<nsIContentSecurityPolicy> csp;
+    if (parentDoc) {
+      csp = parentDoc->GetCsp();
+    }
+    MOZ_DIAGNOSTIC_ASSERT(!csp);
+#endif
+
+    mWorkerRef->Private()->InitChannelInfo(aChannelInfo);
+
+    nsILoadGroup* loadGroup = mWorkerRef->Private()->GetLoadGroup();
+    MOZ_DIAGNOSTIC_ASSERT(loadGroup);
+
+    // Override the principal on the WorkerPrivate.  This is only necessary
+    // in order to get a principal with exactly the correct URL.  The fetch
+    // referrer logic depends on the WorkerPrivate principal having a URL
+    // that matches the worker script URL.  If bug 1340694 is ever fixed
+    // this can be removed.
+    // XXX: force the partitionedPrincipal to be equal to the response one.
+    // This is OK for now because we don't want to expose partitionedPrincipal
+    // functionality in ServiceWorkers yet.
+    rv = mWorkerRef->Private()->SetPrincipalsAndCSPOnMainThread(
+        responsePrincipal, responsePrincipal, loadGroup, nullptr);
+    MOZ_DIAGNOSTIC_ASSERT(NS_SUCCEEDED(rv));
+
+    rv = mWorkerRef->Private()->SetCSPFromHeaderValues(
+        aCSPHeaderValue, aCSPReportOnlyHeaderValue);
+    MOZ_DIAGNOSTIC_ASSERT(NS_SUCCEEDED(rv));
+
+    mWorkerRef->Private()->UpdateReferrerInfoFromHeader(
+        aReferrerPolicyHeaderValue);
+  }
+
+  if (NS_SUCCEEDED(rv)) {
+    DataReceived();
+  }
+
+  return rv;
+}
+
+void CacheLoadHandler::DataReceived() {
+  MOZ_ASSERT(!mRequestHandle->IsEmpty());
+  WorkerLoadContext* loadContext = mRequestHandle->GetContext();
+
+  if (loadContext->IsTopLevel()) {
+    WorkerPrivate* parent = mWorkerRef->Private()->GetParent();
+
+    if (parent) {
+      // XHR Params Allowed
+      mWorkerRef->Private()->SetXHRParamsAllowed(parent->XHRParamsAllowed());
+
+      // Set Eval and ContentSecurityPolicy
+      mWorkerRef->Private()->SetCsp(parent->GetCsp());
+      mWorkerRef->Private()->SetEvalAllowed(parent->IsEvalAllowed());
+      mWorkerRef->Private()->SetWasmEvalAllowed(parent->IsWasmEvalAllowed());
+    }
+  }
+}
+
+}  // namespace workerinternals::loader
+
+}  // namespace dom
+}  // namespace mozilla
diff --git a/dom/workers/loader/CacheLoadHandler.h b/dom/workers/loader/CacheLoadHandler.h
new file mode 100644
index 0000000000..b1e164b79e
--- /dev/null
+++ b/dom/workers/loader/CacheLoadHandler.h
@@ -0,0 +1,221 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_workers_CacheLoadHandler_h__
+#define mozilla_dom_workers_CacheLoadHandler_h__
+
+#include "nsIContentPolicy.h"
+#include "nsIInputStreamPump.h"
+#include "nsIStreamLoader.h"
+#include "nsStringFwd.h"
+#include "nsStreamUtils.h"
+
+#include "mozilla/StaticPrefs_browser.h"
+#include "mozilla/dom/CacheBinding.h"
+#include "mozilla/dom/ChannelInfo.h"
+#include "mozilla/dom/Promise.h"
+#include "mozilla/dom/PromiseNativeHandler.h"
+#include "mozilla/dom/ScriptLoadHandler.h"
+#include "mozilla/dom/cache/Cache.h"
+#include "mozilla/dom/cache/CacheStorage.h"
+#include "mozilla/dom/WorkerCommon.h"
+#include "mozilla/dom/WorkerRef.h"
+
+#include "mozilla/dom/workerinternals/ScriptLoader.h"
+
+using mozilla::dom::cache::Cache;
+using mozilla::dom::cache::CacheStorage;
+using mozilla::ipc::PrincipalInfo;
+
+namespace mozilla::dom {
+
+class WorkerLoadContext;
+
+namespace workerinternals::loader {
+
+/*
+ * [DOMDOC] CacheLoadHandler for Workers
+ *
+ * A LoadHandler is a ScriptLoader helper class that reacts to an
+ * nsIStreamLoader's events for loading JS scripts. It is primarily responsible
+ * for decoding the stream into UTF8 or UTF16. Additionally, it takes care of
+ * any work that needs to follow the completion of a stream. Every LoadHandler
+ * also manages additional tasks for the type of load that it is doing.
+ *
+ * CacheLoadHandler is a specialized LoadHandler used by ServiceWorkers to
+ * implement the installation model used by ServiceWorkers to support running
+ * offline. When a ServiceWorker is installed, its main script is evaluated and
+ * all script resources that are loaded are saved. The spec does not specify the
+ * storage mechanism for this, but we chose to reuse the Cache API[1] mechanism
+ * that we expose to content to also store the script and its dependencies. We
+ * store the script resources in a special chrome namespace CacheStorage that is
+ * not visible to content. Each distinct ServiceWorker installation gets its own
+ * Cache keyed by a randomly-generated UUID.
+ *
+ * In terms of specification, this class implements step 4 of
+ * https://w3c.github.io/ServiceWorker/#importscripts
+ *
+ * Relationship to NetworkLoadHandler
+ *
+ * During ServiceWorker installation, the CacheLoadHandler falls back on the
+ * NetworkLoadHandler by calling `mLoader->LoadScript(...)`. If a script has not
+ * been seen before, then we will fall back on loading from the network.
+ * However, if the ServiceWorker is already installed, an error will be
+ * generated and the ServiceWorker will fail to load, per spec.
+ *
+ * CacheLoadHandler does not persist some pieces of information, such as the
+ * sourceMapUrl. Also, the DOM Cache API storage does not yet support alternate
+ * data streams for JS Bytecode or WASM caching; this is tracked by Bug 1336199.
+ *
+ * [1]: https://developer.mozilla.org/en-US/docs/Web/API/caches
+ *
+ */
+
+class CacheLoadHandler final : public PromiseNativeHandler,
+                               public nsIStreamLoaderObserver {
+ public:
+  NS_DECL_ISUPPORTS
+  NS_DECL_NSISTREAMLOADEROBSERVER
+
+  CacheLoadHandler(ThreadSafeWorkerRef* aWorkerRef,
+                   ThreadSafeRequestHandle* aRequestHandle,
+                   bool aIsWorkerScript,
+                   bool aOnlyExistingCachedResourcesAllowed,
+                   WorkerScriptLoader* aLoader);
+
+  void Fail(nsresult aRv);
+
+  void Load(Cache* aCache);
+
+  virtual void ResolvedCallback(JSContext* aCx, JS::Handle<JS::Value> aValue,
+                                ErrorResult& aRv) override;
+
+  virtual void RejectedCallback(JSContext* aCx, JS::Handle<JS::Value> aValue,
+                                ErrorResult& aRv) override;
+
+ private:
+  ~CacheLoadHandler() { AssertIsOnMainThread(); }
+
+  nsresult DataReceivedFromCache(const uint8_t* aString, uint32_t aStringLen,
+                                 const mozilla::dom::ChannelInfo& aChannelInfo,
+                                 UniquePtr<PrincipalInfo> aPrincipalInfo,
+                                 const nsACString& aCSPHeaderValue,
+                                 const nsACString& aCSPReportOnlyHeaderValue,
+                                 const nsACString& aReferrerPolicyHeaderValue);
+  void DataReceived();
+
+  RefPtr<ThreadSafeRequestHandle> mRequestHandle;
+  const RefPtr<WorkerScriptLoader> mLoader;
+  RefPtr<ThreadSafeWorkerRef> mWorkerRef;
+  const bool mIsWorkerScript;
+  bool mFailed;
+  bool mOnlyExistingCachedResourcesAllowed;
+  nsCOMPtr<nsIInputStreamPump> mPump;
+  nsCOMPtr<nsIURI> mBaseURI;
+  mozilla::dom::ChannelInfo mChannelInfo;
+  UniquePtr<PrincipalInfo> mPrincipalInfo;
+  UniquePtr<ScriptDecoder> mDecoder;
+  nsCString mCSPHeaderValue;
+  nsCString mCSPReportOnlyHeaderValue;
+  nsCString mReferrerPolicyHeaderValue;
+  nsCOMPtr<nsISerialEventTarget> mMainThreadEventTarget;
+};
+
+/*
+ * CacheCreator
+ *
+ * The CacheCreator is responsible for maintaining a CacheStorage for the
+ * purposes of caching ServiceWorkers (see comment on CacheLoadHandler). In
+ * addition, it tracks all CacheLoadHandlers and is used for cleanup once
+ * loading has finished.
+ *
+ */
+
+class CacheCreator final : public PromiseNativeHandler {
+ public:
+  NS_DECL_ISUPPORTS
+
+  explicit CacheCreator(WorkerPrivate* aWorkerPrivate);
+
+  void AddLoader(MovingNotNull<RefPtr<CacheLoadHandler>> aLoader) {
+    AssertIsOnMainThread();
+    MOZ_ASSERT(!mCacheStorage);
+    mLoaders.AppendElement(std::move(aLoader));
+  }
+
+  virtual void ResolvedCallback(JSContext* aCx, JS::Handle<JS::Value> aValue,
+                                ErrorResult& aRv) override;
+
+  virtual void RejectedCallback(JSContext* aCx, JS::Handle<JS::Value> aValue,
+                                ErrorResult& aRv) override;
+
+  // Try to load from cache with aPrincipal used for cache access.
+  nsresult Load(nsIPrincipal* aPrincipal);
+
+  Cache* Cache_() const {
+    AssertIsOnMainThread();
+    MOZ_ASSERT(mCache);
+    return mCache;
+  }
+
+  nsIGlobalObject* Global() const {
+    AssertIsOnMainThread();
+    MOZ_ASSERT(mSandboxGlobalObject);
+    return mSandboxGlobalObject;
+  }
+
+  void DeleteCache(nsresult aReason);
+
+ private:
+  ~CacheCreator() = default;
+
+  nsresult CreateCacheStorage(nsIPrincipal* aPrincipal);
+
+  void FailLoaders(nsresult aRv);
+
+  RefPtr<Cache> mCache;
+  RefPtr<CacheStorage> mCacheStorage;
+  nsCOMPtr<nsIGlobalObject> mSandboxGlobalObject;
+  nsTArray<NotNull<RefPtr<CacheLoadHandler>>> mLoaders;
+
+  nsString mCacheName;
+  OriginAttributes mOriginAttributes;
+};
+
+/*
+ * CachePromiseHandler
+ *
+ * This promise handler is used to track if a ServiceWorker has been written to
+ * Cache. It is responsible for tracking the state of the ServiceWorker being
+ * cached. It also handles cancelling caching of a ServiceWorker if loading is
+ * interrupted. It is initialized by the NetworkLoadHandler as part of the first
+ * load of a ServiceWorker.
+ *
+ */
+class CachePromiseHandler final : public PromiseNativeHandler {
+ public:
+  NS_DECL_ISUPPORTS
+
+  CachePromiseHandler(WorkerScriptLoader* aLoader,
+                      ThreadSafeRequestHandle* aRequestHandle);
+
+  virtual void ResolvedCallback(JSContext* aCx, JS::Handle<JS::Value> aValue,
+                                ErrorResult& aRv) override;
+
+  virtual void RejectedCallback(JSContext* aCx, JS::Handle<JS::Value> aValue,
+                                ErrorResult& aRv) override;
+
+ private:
+  ~CachePromiseHandler() { AssertIsOnMainThread(); }
+
+  RefPtr<WorkerScriptLoader> mLoader;
+  RefPtr<ThreadSafeRequestHandle> mRequestHandle;
+};
+
+}  // namespace workerinternals::loader
+}  // namespace mozilla::dom
+
+#endif /* mozilla_dom_workers_CacheLoadHandler_h__ */
diff --git a/dom/workers/loader/NetworkLoadHandler.cpp b/dom/workers/loader/NetworkLoadHandler.cpp
new file mode 100644
index 0000000000..9c2c243066
--- /dev/null
+++ b/dom/workers/loader/NetworkLoadHandler.cpp
@@ -0,0 +1,393 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "NetworkLoadHandler.h"
+#include "CacheLoadHandler.h"  // CachePromiseHandler
+
+#include "nsContentUtils.h"
+#include "nsIChannel.h"
+#include "nsIHttpChannel.h"
+#include "nsIHttpChannelInternal.h"
+#include "nsIPrincipal.h"
+#include "nsIScriptError.h"
+#include "nsNetUtil.h"
+
+#include "mozilla/Encoding.h"
+#include "mozilla/dom/BlobURLProtocolHandler.h"
+#include "mozilla/dom/InternalResponse.h"
+#include "mozilla/dom/ServiceWorkerBinding.h"
+#include "mozilla/dom/ServiceWorkerManager.h"
+#include "mozilla/dom/ScriptLoader.h"
+#include "mozilla/dom/Response.h"
+#include "mozilla/dom/WorkerScope.h"
+
+#include "mozilla/dom/workerinternals/ScriptLoader.h"  // WorkerScriptLoader
+
+using mozilla::ipc::PrincipalInfo;
+
+namespace mozilla {
+namespace dom {
+
+namespace workerinternals::loader {
+
+NS_IMPL_ISUPPORTS(NetworkLoadHandler, nsIStreamLoaderObserver,
+                  nsIRequestObserver)
+
+NetworkLoadHandler::NetworkLoadHandler(WorkerScriptLoader* aLoader,
+                                       ThreadSafeRequestHandle* aRequestHandle)
+    : mLoader(aLoader),
+      mWorkerRef(aLoader->mWorkerRef),
+      mRequestHandle(aRequestHandle) {
+  MOZ_ASSERT(mLoader);
+
+  // Worker scripts are always decoded as UTF-8 per spec.
+  mDecoder = MakeUnique<ScriptDecoder>(UTF_8_ENCODING,
+                                       ScriptDecoder::BOMHandling::Remove);
+}
+
+NS_IMETHODIMP
+NetworkLoadHandler::OnStreamComplete(nsIStreamLoader* aLoader,
+                                     nsISupports* aContext, nsresult aStatus,
+                                     uint32_t aStringLen,
+                                     const uint8_t* aString) {
+  // If we have cancelled, or we have no mRequest, it means that the loader has
+  // shut down and we can exit early. If the cancel result is still NS_OK
+  if (mRequestHandle->IsEmpty()) {
+    return NS_OK;
+  }
+  nsresult rv = DataReceivedFromNetwork(aLoader, aStatus, aStringLen, aString);
+  return mRequestHandle->OnStreamComplete(rv);
+}
+
+nsresult NetworkLoadHandler::DataReceivedFromNetwork(nsIStreamLoader* aLoader,
+                                                     nsresult aStatus,
+                                                     uint32_t aStringLen,
+                                                     const uint8_t* aString) {
+  AssertIsOnMainThread();
+  MOZ_ASSERT(!mRequestHandle->IsEmpty());
+  WorkerLoadContext* loadContext = mRequestHandle->GetContext();
+
+  if (!loadContext->mChannel) {
+    return NS_BINDING_ABORTED;
+  }
+
+  loadContext->mChannel = nullptr;
+
+  if (NS_FAILED(aStatus)) {
+    return aStatus;
+  }
+
+  if (mRequestHandle->IsCancelled()) {
+    return mRequestHandle->GetCancelResult();
+  }
+
+  NS_ASSERTION(aString, "This should never be null!");
+
+  nsCOMPtr<nsIRequest> request;
+  nsresult rv = aLoader->GetRequest(getter_AddRefs(request));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  nsCOMPtr<nsIChannel> channel = do_QueryInterface(request);
+  MOZ_ASSERT(channel);
+
+  nsIScriptSecurityManager* ssm = nsContentUtils::GetSecurityManager();
+  NS_ASSERTION(ssm, "Should never be null!");
+
+  nsCOMPtr<nsIPrincipal> channelPrincipal;
+  rv =
+      ssm->GetChannelResultPrincipal(channel, getter_AddRefs(channelPrincipal));
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  nsIPrincipal* principal = mWorkerRef->Private()->GetPrincipal();
+  if (!principal) {
+    WorkerPrivate* parentWorker = mWorkerRef->Private()->GetParent();
+    MOZ_ASSERT(parentWorker, "Must have a parent!");
+    principal = parentWorker->GetPrincipal();
+  }
+
+#ifdef DEBUG
+  if (loadContext->IsTopLevel()) {
+    nsCOMPtr<nsIPrincipal> loadingPrincipal =
+        mWorkerRef->Private()->GetLoadingPrincipal();
+    // if we are not in a ServiceWorker, and the principal is not null, then
+    // the loading principal must subsume the worker principal if it is not a
+    // nullPrincipal (sandbox).
+    MOZ_ASSERT(!loadingPrincipal || loadingPrincipal->GetIsNullPrincipal() ||
+               principal->GetIsNullPrincipal() ||
+               loadingPrincipal->Subsumes(principal));
+  }
+#endif
+
+  // We don't mute the main worker script becase we've already done
+  // same-origin checks on them so we should be able to see their errors.
+  // Note that for data: url, where we allow it through the same-origin check
+  // but then give it a different origin.
+  loadContext->mMutedErrorFlag.emplace(!loadContext->IsTopLevel() &&
+                                       !principal->Subsumes(channelPrincipal));
+
+  // Make sure we're not seeing the result of a 404 or something by checking
+  // the 'requestSucceeded' attribute on the http channel.
+  nsCOMPtr<nsIHttpChannel> httpChannel = do_QueryInterface(request);
+  nsAutoCString tCspHeaderValue, tCspROHeaderValue, tRPHeaderCValue;
+
+  if (httpChannel) {
+    bool requestSucceeded;
+    rv = httpChannel->GetRequestSucceeded(&requestSucceeded);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    if (!requestSucceeded) {
+      return NS_ERROR_NOT_AVAILABLE;
+    }
+
+    Unused << httpChannel->GetResponseHeader("content-security-policy"_ns,
+                                             tCspHeaderValue);
+
+    Unused << httpChannel->GetResponseHeader(
+        "content-security-policy-report-only"_ns, tCspROHeaderValue);
+
+    Unused << httpChannel->GetResponseHeader("referrer-policy"_ns,
+                                             tRPHeaderCValue);
+
+    nsAutoCString sourceMapURL;
+    if (nsContentUtils::GetSourceMapURL(httpChannel, sourceMapURL)) {
+      loadContext->mRequest->mSourceMapURL =
+          Some(NS_ConvertUTF8toUTF16(sourceMapURL));
+    }
+  }
+
+  // May be null.
+  Document* parentDoc = mWorkerRef->Private()->GetDocument();
+
+  // Set the Source type to "text" for decoding.
+  loadContext->mRequest->SetTextSource(loadContext);
+
+  // Use the regular ScriptDecoder Decoder for this grunt work! Should be just
+  // fine because we're running on the main thread.
+  rv = mDecoder->DecodeRawData(loadContext->mRequest, aString, aStringLen,
+                               /* aEndOfStream = */ true);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  if (!loadContext->mRequest->ScriptTextLength()) {
+    nsContentUtils::ReportToConsole(nsIScriptError::warningFlag, "DOM"_ns,
+                                    parentDoc, nsContentUtils::eDOM_PROPERTIES,
+                                    "EmptyWorkerSourceWarning");
+  }
+
+  // For modules, we need to store the base URI on the module request object,
+  // rather than on the worker private (as we do for classic scripts). This is
+  // because module loading is shared across multiple components, with
+  // ScriptLoadRequests being the common structure among them. This specific
+  // use of the base url is used when resolving the module specifier for child
+  // modules.
+  nsCOMPtr<nsIURI> uri;
+  rv = channel->GetOriginalURI(getter_AddRefs(uri));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  loadContext->mRequest->SetBaseURLFromChannelAndOriginalURI(channel, uri);
+
+  // Figure out what we actually loaded.
+  nsCOMPtr<nsIURI> finalURI;
+  rv = NS_GetFinalChannelURI(channel, getter_AddRefs(finalURI));
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  if (principal->IsSameOrigin(finalURI)) {
+    nsCString filename;
+    rv = finalURI->GetSpec(filename);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    if (!filename.IsEmpty()) {
+      // This will help callers figure out what their script url resolved to
+      // in case of errors, and is used for debugging.
+      // The full URL shouldn't be exposed to the debugger if cross origin.
+      // See Bug 1634872.
+      loadContext->mRequest->mURL = filename;
+    }
+  }
+
+  // Update the principal of the worker and its base URI if we just loaded the
+  // worker's primary script.
+  bool isDynamic = loadContext->mRequest->IsModuleRequest() &&
+                   loadContext->mRequest->AsModuleRequest()->IsDynamicImport();
+  if (loadContext->IsTopLevel() && !isDynamic) {
+    // Take care of the base URI first.
+    mWorkerRef->Private()->SetBaseURI(finalURI);
+
+    // Store the channel info if needed.
+    mWorkerRef->Private()->InitChannelInfo(channel);
+
+    // Our final channel principal should match the loading principal
+    // in terms of the origin.  This used to be an assert, but it seems
+    // there are some rare cases where this check can fail in practice.
+    // Perhaps some browser script setting nsIChannel.owner, etc.
+    NS_ENSURE_TRUE(mWorkerRef->Private()->FinalChannelPrincipalIsValid(channel),
+                   NS_ERROR_FAILURE);
+
+    // However, we must still override the principal since the nsIPrincipal
+    // URL may be different due to same-origin redirects.  Unfortunately this
+    // URL must exactly match the final worker script URL in order to
+    // properly set the referrer header on fetch/xhr requests.  If bug 1340694
+    // is ever fixed this can be removed.
+    rv = mWorkerRef->Private()->SetPrincipalsAndCSPFromChannel(channel);
+    NS_ENSURE_SUCCESS(rv, rv);
+
+    nsCOMPtr<nsIContentSecurityPolicy> csp = mWorkerRef->Private()->GetCsp();
+    // We did inherit CSP in bug 1223647. If we do not already have a CSP, we
+    // should get it from the HTTP headers on the worker script.
+    if (!csp) {
+      rv = mWorkerRef->Private()->SetCSPFromHeaderValues(tCspHeaderValue,
+                                                         tCspROHeaderValue);
+      NS_ENSURE_SUCCESS(rv, rv);
+    } else {
+      csp->EnsureEventTarget(mWorkerRef->Private()->MainThreadEventTarget());
+    }
+
+    mWorkerRef->Private()->UpdateReferrerInfoFromHeader(tRPHeaderCValue);
+
+    WorkerPrivate* parent = mWorkerRef->Private()->GetParent();
+    if (parent) {
+      // XHR Params Allowed
+      mWorkerRef->Private()->SetXHRParamsAllowed(parent->XHRParamsAllowed());
+    }
+
+    nsCOMPtr<nsILoadInfo> chanLoadInfo = channel->LoadInfo();
+    if (chanLoadInfo) {
+      mLoader->SetController(chanLoadInfo->GetController());
+    }
+
+    // If we are loading a blob URL we must inherit the controller
+    // from the parent.  This is a bit odd as the blob URL may have
+    // been created in a different context with a different controller.
+    // For now, though, this is what the spec says.  See:
+    //
+    // https://github.com/w3c/ServiceWorker/issues/1261
+    //
+    if (IsBlobURI(mWorkerRef->Private()->GetBaseURI())) {
+      MOZ_DIAGNOSTIC_ASSERT(mLoader->GetController().isNothing());
+      mLoader->SetController(mWorkerRef->Private()->GetParentController());
+    }
+  }
+
+  return NS_OK;
+}
+
+NS_IMETHODIMP
+NetworkLoadHandler::OnStartRequest(nsIRequest* aRequest) {
+  nsresult rv = PrepareForRequest(aRequest);
+
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    aRequest->Cancel(rv);
+  }
+
+  return rv;
+}
+
+nsresult NetworkLoadHandler::PrepareForRequest(nsIRequest* aRequest) {
+  AssertIsOnMainThread();
+  MOZ_ASSERT(!mRequestHandle->IsEmpty());
+  WorkerLoadContext* loadContext = mRequestHandle->GetContext();
+
+  // If one load info cancels or hits an error, it can race with the start
+  // callback coming from another load info.
+  if (mRequestHandle->IsCancelled()) {
+    return NS_ERROR_FAILURE;
+  }
+
+  nsCOMPtr<nsIChannel> channel = do_QueryInterface(aRequest);
+
+  // Checking the MIME type is only required for ServiceWorkers'
+  // importScripts, per step 10 of
+  // https://w3c.github.io/ServiceWorker/#importscripts
+  //
+  // "Extract a MIME type from the response’s header list. If this MIME type
+  // (ignoring parameters) is not a JavaScript MIME type, return a network
+  // error."
+  if (mWorkerRef->Private()->IsServiceWorker()) {
+    nsAutoCString mimeType;
+    channel->GetContentType(mimeType);
+
+    if (!nsContentUtils::IsJavascriptMIMEType(
+            NS_ConvertUTF8toUTF16(mimeType))) {
+      const nsCString& scope = mWorkerRef->Private()
+                                   ->GetServiceWorkerRegistrationDescriptor()
+                                   .Scope();
+
+      ServiceWorkerManager::LocalizeAndReportToAllClients(
+          scope, "ServiceWorkerRegisterMimeTypeError2",
+          nsTArray<nsString>{
+              NS_ConvertUTF8toUTF16(scope), NS_ConvertUTF8toUTF16(mimeType),
+              NS_ConvertUTF8toUTF16(loadContext->mRequest->mURL)});
+
+      return NS_ERROR_DOM_NETWORK_ERR;
+    }
+  }
+
+  // We synthesize the result code, but its never exposed to content.
+  SafeRefPtr<mozilla::dom::InternalResponse> ir =
+      MakeSafeRefPtr<mozilla::dom::InternalResponse>(200, "OK"_ns);
+  ir->SetBody(loadContext->mCacheReadStream,
+              InternalResponse::UNKNOWN_BODY_SIZE);
+
+  // Drop our reference to the stream now that we've passed it along, so it
+  // doesn't hang around once the cache is done with it and keep data alive.
+  loadContext->mCacheReadStream = nullptr;
+
+  // Set the channel info of the channel on the response so that it's
+  // saved in the cache.
+  ir->InitChannelInfo(channel);
+
+  // Save the principal of the channel since its URI encodes the script URI
+  // rather than the ServiceWorkerRegistrationInfo URI.
+  nsIScriptSecurityManager* ssm = nsContentUtils::GetSecurityManager();
+  NS_ASSERTION(ssm, "Should never be null!");
+
+  nsCOMPtr<nsIPrincipal> channelPrincipal;
+  MOZ_TRY(ssm->GetChannelResultPrincipal(channel,
+                                         getter_AddRefs(channelPrincipal)));
+
+  UniquePtr<PrincipalInfo> principalInfo(new PrincipalInfo());
+  MOZ_TRY(PrincipalToPrincipalInfo(channelPrincipal, principalInfo.get()));
+
+  ir->SetPrincipalInfo(std::move(principalInfo));
+  ir->Headers()->FillResponseHeaders(channel);
+
+  RefPtr<mozilla::dom::Response> response = new mozilla::dom::Response(
+      mRequestHandle->GetCacheCreator()->Global(), std::move(ir), nullptr);
+
+  mozilla::dom::RequestOrUSVString request;
+
+  MOZ_ASSERT(!loadContext->mFullURL.IsEmpty());
+  request.SetAsUSVString().ShareOrDependUpon(loadContext->mFullURL);
+
+  // This JSContext will not end up executing JS code because here there are
+  // no ReadableStreams involved.
+  AutoJSAPI jsapi;
+  jsapi.Init();
+
+  ErrorResult error;
+  RefPtr<Promise> cachePromise =
+      mRequestHandle->GetCacheCreator()->Cache_()->Put(jsapi.cx(), request,
+                                                       *response, error);
+  error.WouldReportJSException();
+  if (NS_WARN_IF(error.Failed())) {
+    return error.StealNSResult();
+  }
+
+  RefPtr<CachePromiseHandler> promiseHandler =
+      new CachePromiseHandler(mLoader, mRequestHandle);
+  cachePromise->AppendNativeHandler(promiseHandler);
+
+  loadContext->mCachePromise.swap(cachePromise);
+  loadContext->mCacheStatus = WorkerLoadContext::WritingToCache;
+
+  return NS_OK;
+}
+
+}  // namespace workerinternals::loader
+
+}  // namespace dom
+}  // namespace mozilla
diff --git a/dom/workers/loader/NetworkLoadHandler.h b/dom/workers/loader/NetworkLoadHandler.h
new file mode 100644
index 0000000000..b32c9d8d8e
--- /dev/null
+++ b/dom/workers/loader/NetworkLoadHandler.h
@@ -0,0 +1,79 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_workers_NetworkLoadHandler_h__
+#define mozilla_dom_workers_NetworkLoadHandler_h__
+
+#include "nsIStreamLoader.h"
+#include "mozilla/dom/WorkerLoadContext.h"
+#include "mozilla/dom/ScriptLoadHandler.h"
+#include "mozilla/dom/WorkerRef.h"
+
+namespace mozilla::dom::workerinternals::loader {
+
+class WorkerScriptLoader;
+
+/*
+ * [DOMDOC] NetworkLoadHandler for Workers
+ *
+ * A LoadHandler is a ScriptLoader helper class that reacts to an
+ * nsIStreamLoader's events for
+ * loading JS scripts. It is primarily responsible for decoding the stream into
+ * UTF8 or UTF16. Additionally, it takes care of any work that needs to follow
+ * the completion of a stream. Every LoadHandler also manages additional tasks
+ * for the type of load that it is doing.
+ *
+ * As part of worker loading we have an number of tasks that we need to take
+ * care of after a successfully completed stream, including setting a final URI
+ * on the WorkerPrivate if we have loaded a main script, or handling CSP issues.
+ * These are handled in DataReceivedFromNetwork, and implement roughly the same
+ * set of tasks as you will find in the CacheLoadhandler, which has a companion
+ * method DataReceivedFromcache.
+ *
+ * In the worker context, the LoadHandler is run on the main thread, and all
+ * work in this file ultimately is done by the main thread, including decoding.
+ *
+ */
+
+class NetworkLoadHandler final : public nsIStreamLoaderObserver,
+                                 public nsIRequestObserver {
+ public:
+  NS_DECL_ISUPPORTS
+
+  NetworkLoadHandler(WorkerScriptLoader* aLoader,
+                     ThreadSafeRequestHandle* aRequestHandle);
+
+  NS_IMETHOD
+  OnStreamComplete(nsIStreamLoader* aLoader, nsISupports* aContext,
+                   nsresult aStatus, uint32_t aStringLen,
+                   const uint8_t* aString) override;
+
+  nsresult DataReceivedFromNetwork(nsIStreamLoader* aLoader, nsresult aStatus,
+                                   uint32_t aStringLen, const uint8_t* aString);
+
+  NS_IMETHOD
+  OnStartRequest(nsIRequest* aRequest) override;
+
+  nsresult PrepareForRequest(nsIRequest* aRequest);
+
+  NS_IMETHOD
+  OnStopRequest(nsIRequest* aRequest, nsresult aStatusCode) override {
+    // Nothing to do here!
+    return NS_OK;
+  }
+
+ private:
+  ~NetworkLoadHandler() = default;
+
+  RefPtr<WorkerScriptLoader> mLoader;
+  UniquePtr<ScriptDecoder> mDecoder;
+  RefPtr<ThreadSafeWorkerRef> mWorkerRef;
+  RefPtr<ThreadSafeRequestHandle> mRequestHandle;
+};
+
+}  // namespace mozilla::dom::workerinternals::loader
+
+#endif /* mozilla_dom_workers_NetworkLoadHandler_h__ */
diff --git a/dom/workers/loader/ScriptResponseHeaderProcessor.cpp b/dom/workers/loader/ScriptResponseHeaderProcessor.cpp
new file mode 100644
index 0000000000..6dc5c9e1ef
--- /dev/null
+++ b/dom/workers/loader/ScriptResponseHeaderProcessor.cpp
@@ -0,0 +1,79 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "ScriptResponseHeaderProcessor.h"
+#include "mozilla/Try.h"
+#include "mozilla/dom/WorkerScope.h"
+
+namespace mozilla {
+namespace dom {
+
+namespace workerinternals {
+
+namespace loader {
+
+NS_IMPL_ISUPPORTS(ScriptResponseHeaderProcessor, nsIRequestObserver);
+
+nsresult ScriptResponseHeaderProcessor::ProcessCrossOriginEmbedderPolicyHeader(
+    WorkerPrivate* aWorkerPrivate,
+    nsILoadInfo::CrossOriginEmbedderPolicy aPolicy, bool aIsMainScript) {
+  MOZ_ASSERT(aWorkerPrivate);
+
+  if (aIsMainScript) {
+    MOZ_TRY(aWorkerPrivate->SetEmbedderPolicy(aPolicy));
+  } else {
+    // NOTE: Spec doesn't mention non-main scripts must match COEP header with
+    // the main script, but it must pass CORP checking.
+    // see: wpt window-simple-success.https.html, the worker import script
+    // test-incrementer.js without coep header.
+    Unused << NS_WARN_IF(!aWorkerPrivate->MatchEmbedderPolicy(aPolicy));
+  }
+
+  return NS_OK;
+}
+
+// Enforce strict MIME type checks for worker-imported scripts
+// https://github.com/whatwg/html/pull/4001
+nsresult ScriptResponseHeaderProcessor::EnsureJavaScriptMimeType(
+    nsIRequest* aRequest) {
+  nsCOMPtr<nsIChannel> channel = do_QueryInterface(aRequest);
+  MOZ_ASSERT(channel);
+  nsAutoCString mimeType;
+  channel->GetContentType(mimeType);
+  if (!nsContentUtils::IsJavascriptMIMEType(NS_ConvertUTF8toUTF16(mimeType))) {
+    return NS_ERROR_DOM_NETWORK_ERR;
+  }
+  return NS_OK;
+}
+
+nsresult ScriptResponseHeaderProcessor::ProcessCrossOriginEmbedderPolicyHeader(
+    nsIRequest* aRequest) {
+  nsCOMPtr<nsIHttpChannelInternal> httpChannel = do_QueryInterface(aRequest);
+
+  // NOTE: the spec doesn't say what to do with non-HTTP workers.
+  // See: https://github.com/whatwg/html/issues/4916
+  if (!httpChannel) {
+    if (mIsMainScript) {
+      mWorkerPrivate->InheritOwnerEmbedderPolicyOrNull(aRequest);
+    }
+
+    return NS_OK;
+  }
+
+  nsILoadInfo::CrossOriginEmbedderPolicy coep;
+  MOZ_TRY(httpChannel->GetResponseEmbedderPolicy(
+      mWorkerPrivate->Trials().IsEnabled(OriginTrial::CoepCredentialless),
+      &coep));
+
+  return ProcessCrossOriginEmbedderPolicyHeader(mWorkerPrivate, coep,
+                                                mIsMainScript);
+}
+
+}  // namespace loader
+}  // namespace workerinternals
+
+}  // namespace dom
+}  // namespace mozilla
diff --git a/dom/workers/loader/ScriptResponseHeaderProcessor.h b/dom/workers/loader/ScriptResponseHeaderProcessor.h
new file mode 100644
index 0000000000..43a9bfde42
--- /dev/null
+++ b/dom/workers/loader/ScriptResponseHeaderProcessor.h
@@ -0,0 +1,94 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_workers_ScriptResponseHeaderProcessor_h__
+#define mozilla_dom_workers_ScriptResponseHeaderProcessor_h__
+
+#include "mozilla/dom/WorkerCommon.h"
+
+#include "nsIHttpChannel.h"
+#include "nsIHttpChannelInternal.h"
+#include "nsIStreamLoader.h"
+#include "nsStreamUtils.h"
+#include "mozilla/StaticPrefs_browser.h"
+#include "mozilla/StaticPrefs_dom.h"
+
+namespace mozilla::dom {
+
+class WorkerPrivate;
+
+namespace workerinternals::loader {
+
+/* ScriptResponseHeaderProcessor
+ *
+ * This class handles Policy headers. It can be used as a RequestObserver in a
+ * Tee, as it is for NetworkLoadHandler in WorkerScriptLoader, or the static
+ * method can be called directly, as it is in CacheLoadHandler.
+ *
+ */
+
+class ScriptResponseHeaderProcessor final : public nsIRequestObserver {
+ public:
+  NS_DECL_ISUPPORTS
+
+  ScriptResponseHeaderProcessor(WorkerPrivate* aWorkerPrivate,
+                                bool aIsMainScript, bool aIsImportScript)
+      : mWorkerPrivate(aWorkerPrivate),
+        mIsMainScript(aIsMainScript),
+        mIsImportScript(aIsImportScript) {
+    AssertIsOnMainThread();
+  }
+
+  NS_IMETHOD OnStartRequest(nsIRequest* aRequest) override {
+    nsresult rv = NS_OK;
+    if (mIsImportScript &&
+        StaticPrefs::dom_workers_importScripts_enforceStrictMimeType()) {
+      rv = EnsureJavaScriptMimeType(aRequest);
+      if (NS_WARN_IF(NS_FAILED(rv))) {
+        aRequest->Cancel(rv);
+        return NS_OK;
+      }
+    }
+
+    if (!StaticPrefs::browser_tabs_remote_useCrossOriginEmbedderPolicy()) {
+      return NS_OK;
+    }
+
+    rv = ProcessCrossOriginEmbedderPolicyHeader(aRequest);
+
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      aRequest->Cancel(rv);
+    }
+
+    return rv;
+  }
+
+  NS_IMETHOD OnStopRequest(nsIRequest* aRequest,
+                           nsresult aStatusCode) override {
+    return NS_OK;
+  }
+
+  static nsresult ProcessCrossOriginEmbedderPolicyHeader(
+      WorkerPrivate* aWorkerPrivate,
+      nsILoadInfo::CrossOriginEmbedderPolicy aPolicy, bool aIsMainScript);
+
+ private:
+  ~ScriptResponseHeaderProcessor() = default;
+
+  nsresult EnsureJavaScriptMimeType(nsIRequest* aRequest);
+
+  nsresult ProcessCrossOriginEmbedderPolicyHeader(nsIRequest* aRequest);
+
+  WorkerPrivate* const mWorkerPrivate;
+  const bool mIsMainScript;
+  const bool mIsImportScript;
+};
+
+}  // namespace workerinternals::loader
+
+}  // namespace mozilla::dom
+
+#endif /* mozilla_dom_workers_ScriptResponseHeaderProcessor_h__ */
diff --git a/dom/workers/loader/WorkerLoadContext.cpp b/dom/workers/loader/WorkerLoadContext.cpp
new file mode 100644
index 0000000000..a788d5173c
--- /dev/null
+++ b/dom/workers/loader/WorkerLoadContext.cpp
@@ -0,0 +1,78 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "WorkerLoadContext.h"
+#include "mozilla/dom/workerinternals/ScriptLoader.h"
+#include "CacheLoadHandler.h"  // CacheCreator
+
+namespace mozilla {
+namespace dom {
+
+WorkerLoadContext::WorkerLoadContext(
+    Kind aKind, const Maybe<ClientInfo>& aClientInfo,
+    workerinternals::loader::WorkerScriptLoader* aScriptLoader,
+    bool aOnlyExistingCachedResourcesAllowed)
+    : JS::loader::LoadContextBase(JS::loader::ContextKind::Worker),
+      mKind(aKind),
+      mClientInfo(aClientInfo),
+      mScriptLoader(aScriptLoader),
+      mOnlyExistingCachedResourcesAllowed(
+          aOnlyExistingCachedResourcesAllowed){};
+
+ThreadSafeRequestHandle::ThreadSafeRequestHandle(
+    JS::loader::ScriptLoadRequest* aRequest, nsISerialEventTarget* aSyncTarget)
+    : mRequest(aRequest), mOwningEventTarget(aSyncTarget) {}
+
+already_AddRefed<JS::loader::ScriptLoadRequest>
+ThreadSafeRequestHandle::ReleaseRequest() {
+  RefPtr<JS::loader::ScriptLoadRequest> request;
+  mRequest.swap(request);
+  mRunnable = nullptr;
+  return request.forget();
+}
+
+nsresult ThreadSafeRequestHandle::OnStreamComplete(nsresult aStatus) {
+  return mRunnable->OnStreamComplete(this, aStatus);
+}
+
+void ThreadSafeRequestHandle::LoadingFinished(nsresult aRv) {
+  mRunnable->LoadingFinished(this, aRv);
+}
+
+void ThreadSafeRequestHandle::MaybeExecuteFinishedScripts() {
+  mRunnable->MaybeExecuteFinishedScripts(this);
+}
+
+bool ThreadSafeRequestHandle::IsCancelled() { return mRunnable->IsCancelled(); }
+
+nsresult ThreadSafeRequestHandle::GetCancelResult() {
+  return mRunnable->GetCancelResult();
+}
+
+workerinternals::loader::CacheCreator*
+ThreadSafeRequestHandle::GetCacheCreator() {
+  AssertIsOnMainThread();
+  return mRunnable->GetCacheCreator();
+}
+
+ThreadSafeRequestHandle::~ThreadSafeRequestHandle() {
+  // Normally we only touch mStrongRef on the owning thread.  This is safe,
+  // however, because when we do use mStrongRef on the owning thread we are
+  // always holding a strong ref to the ThreadsafeHandle via the owning
+  // runnable.  So we cannot run the ThreadsafeHandle destructor simultaneously.
+  if (!mRequest || mOwningEventTarget->IsOnCurrentThread()) {
+    return;
+  }
+
+  // Dispatch in NS_ProxyRelease is guaranteed to succeed here because we block
+  // shutdown until all Contexts have been destroyed. Therefore it is ok to have
+  // MOZ_ALWAYS_SUCCEED here.
+  MOZ_ALWAYS_SUCCEEDS(NS_ProxyRelease("ThreadSafeRequestHandle::mRequest",
+                                      mOwningEventTarget, mRequest.forget()));
+}
+
+}  // namespace dom
+}  // namespace mozilla
diff --git a/dom/workers/loader/WorkerLoadContext.h b/dom/workers/loader/WorkerLoadContext.h
new file mode 100644
index 0000000000..97362f2871
--- /dev/null
+++ b/dom/workers/loader/WorkerLoadContext.h
@@ -0,0 +1,219 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_workers_WorkerLoadContext_h__
+#define mozilla_dom_workers_WorkerLoadContext_h__
+
+#include "nsIChannel.h"
+#include "nsIInputStream.h"
+#include "nsIRequest.h"
+#include "mozilla/CORSMode.h"
+#include "mozilla/dom/Promise.h"
+#include "js/loader/ScriptKind.h"
+#include "js/loader/ScriptLoadRequest.h"
+#include "js/loader/LoadContextBase.h"
+
+class nsIReferrerInfo;
+class nsIURI;
+
+namespace mozilla::dom {
+
+class ClientInfo;
+class WorkerPrivate;
+
+namespace workerinternals::loader {
+class CacheCreator;
+class ScriptLoaderRunnable;
+class WorkerScriptLoader;
+}  // namespace workerinternals::loader
+
+/*
+ * WorkerLoadContext (for all workers)
+ *
+ * LoadContexts augment the loading of a ScriptLoadRequest. They
+ * describe how a ScriptLoadRequests loading and evaluation needs to be
+ * augmented, based on the information provided by the loading context. The
+ * WorkerLoadContext has the following generic fields applied to all worker
+ * ScriptLoadRequests (and primarily used for error handling):
+ *
+ *    * mMutedErrorFlag
+ *        Set when we finish loading a script, and used to determine whether a
+ *        given error is thrown or muted.
+ *    * mLoadResult
+ *        In order to report errors correctly in the worker thread, we need to
+ *        move them from the main thread to the worker. This field records the
+ *        load error, for throwing when we return to the worker thread.
+ *    * mKind
+ *        See documentation of WorkerLoadContext::Kind.
+ *    * mClientInfo
+ *        A snapshot of a global living in the system (see documentation for
+ *        ClientInfo). In worker loading, this field is important for CSP
+ *        information and knowing what to intercept for Service Worker
+ *        interception.
+ *    * mChannel
+ *        The channel used by this request for it's load. Used for cancellation,
+ *        in order to cancel the stream.
+ *
+ * The rest of the fields on this class focus on enabling the ServiceWorker
+ * usecase, in particular -- using the Cache API to store the worker so that
+ * in the case of (for example) a page refresh, the service worker itself is
+ * persisted so that it can do other work. For more details see the
+ * CacheLoadHandler.h file.
+ *
+ */
+
+class WorkerLoadContext : public JS::loader::LoadContextBase {
+ public:
+  /* Worker Load Context Kinds
+   *
+   * A script that is loaded and run as a worker can be one of several species.
+   * Each may have slightly different behavior, but they fall into roughly two
+   * categories: the Main Worker Script (the script that triggers the first
+   * load) and scripts that are attached to this main worker script.
+   *
+   * In the specification, the Main Worker Script is referred to as the "top
+   * level script" and is defined here:
+   * https://html.spec.whatwg.org/multipage/webappapis.html#fetching-scripts-is-top-level
+   */
+
+  enum Kind {
+    // Indicates that the is-top-level bit is true. This may be a Classic script
+    // or a Module script.
+    MainScript,
+    // We are importing a script from the worker via ImportScript. This may only
+    // be a Classic script.
+    ImportScript,
+    // We are importing a script from the worker via a Static Import. This may
+    // only
+    // be a Module script.
+    StaticImport,
+    DynamicImport,
+    // We have an attached debugger, and these should be treated specially and
+    // not like a main script (regardless of their type). This is not part of
+    // the specification.
+    DebuggerScript
+  };
+
+  WorkerLoadContext(Kind aKind, const Maybe<ClientInfo>& aClientInfo,
+                    workerinternals::loader::WorkerScriptLoader* aScriptLoader,
+                    bool aOnlyExistingCachedResourcesAllowed);
+
+  // Used to detect if the `is top-level` bit is set on a given module.
+  bool IsTopLevel() {
+    return mRequest->IsTopLevel() && (mKind == Kind::MainScript);
+  };
+
+  static Kind GetKind(bool isMainScript, bool isDebuggerScript) {
+    if (isDebuggerScript) {
+      return Kind::DebuggerScript;
+    }
+    if (isMainScript) {
+      return Kind::MainScript;
+    }
+    return Kind::ImportScript;
+  };
+
+  /* These fields are used by all workers */
+  Maybe<bool> mMutedErrorFlag;
+  nsresult mLoadResult = NS_ERROR_NOT_INITIALIZED;
+  bool mLoadingFinished = false;
+  bool mIsTopLevel = true;
+  Kind mKind;
+  Maybe<ClientInfo> mClientInfo;
+  nsCOMPtr<nsIChannel> mChannel;
+  RefPtr<workerinternals::loader::WorkerScriptLoader> mScriptLoader;
+
+  /* These fields are only used by service workers */
+  /* TODO: Split out a ServiceWorkerLoadContext */
+  // This full URL string is populated only if this object is used in a
+  // ServiceWorker.
+  nsString mFullURL;
+
+  // This promise is set only when the script is for a ServiceWorker but
+  // it's not in the cache yet. The promise is resolved when the full body is
+  // stored into the cache.  mCachePromise will be set to nullptr after
+  // resolution.
+  RefPtr<Promise> mCachePromise;
+
+  // The reader stream the cache entry should be filled from, for those cases
+  // when we're going to have an mCachePromise.
+  nsCOMPtr<nsIInputStream> mCacheReadStream;
+
+  enum CacheStatus {
+    // By default a normal script is just loaded from the network. But for
+    // ServiceWorkers, we have to check if the cache contains the script and
+    // load it from the cache.
+    Uncached,
+
+    WritingToCache,
+
+    ReadingFromCache,
+
+    // This script has been loaded from the ServiceWorker cache.
+    Cached,
+
+    // This script must be stored in the ServiceWorker cache.
+    ToBeCached,
+
+    // Something went wrong or the worker went away.
+    Cancel
+  };
+
+  CacheStatus mCacheStatus = Uncached;
+
+  // If the requested script is not currently in the cache, should we initiate
+  // a request to fetch and cache it?  Only ServiceWorkers that are being
+  // installed are allowed to go to the network (and then cache the result).
+  bool mOnlyExistingCachedResourcesAllowed = false;
+
+  bool IsAwaitingPromise() const { return bool(mCachePromise); }
+};
+
+class ThreadSafeRequestHandle final {
+ public:
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(ThreadSafeRequestHandle)
+
+  ThreadSafeRequestHandle(JS::loader::ScriptLoadRequest* aRequest,
+                          nsISerialEventTarget* aSyncTarget);
+
+  JS::loader::ScriptLoadRequest* GetRequest() const { return mRequest; }
+
+  WorkerLoadContext* GetContext() { return mRequest->GetWorkerLoadContext(); }
+
+  bool IsEmpty() { return !mRequest; }
+
+  // Runnable controls
+  nsresult OnStreamComplete(nsresult aStatus);
+
+  void LoadingFinished(nsresult aRv);
+
+  void MaybeExecuteFinishedScripts();
+
+  bool IsCancelled();
+
+  bool Finished() {
+    return GetContext()->mLoadingFinished && !GetContext()->IsAwaitingPromise();
+  }
+
+  nsresult GetCancelResult();
+
+  already_AddRefed<JS::loader::ScriptLoadRequest> ReleaseRequest();
+
+  workerinternals::loader::CacheCreator* GetCacheCreator();
+
+  RefPtr<workerinternals::loader::ScriptLoaderRunnable> mRunnable;
+
+  bool mExecutionScheduled = false;
+
+ private:
+  ~ThreadSafeRequestHandle();
+
+  RefPtr<JS::loader::ScriptLoadRequest> mRequest;
+  nsCOMPtr<nsISerialEventTarget> mOwningEventTarget;
+};
+
+}  // namespace mozilla::dom
+#endif /* mozilla_dom_workers_WorkerLoadContext_h__ */
diff --git a/dom/workers/loader/WorkerModuleLoader.cpp b/dom/workers/loader/WorkerModuleLoader.cpp
new file mode 100644
index 0000000000..da340c89bd
--- /dev/null
+++ b/dom/workers/loader/WorkerModuleLoader.cpp
@@ -0,0 +1,225 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "js/experimental/JSStencil.h"  // JS::Stencil, JS::CompileModuleScriptToStencil, JS::InstantiateModuleStencil
+#include "js/loader/ModuleLoadRequest.h"
+#include "mozilla/dom/RequestBinding.h"
+#include "mozilla/dom/WorkerLoadContext.h"
+#include "mozilla/dom/WorkerPrivate.h"
+#include "mozilla/dom/workerinternals/ScriptLoader.h"
+#include "mozilla/dom/WorkerScope.h"
+#include "WorkerModuleLoader.h"
+
+#include "nsISupportsImpl.h"
+
+namespace mozilla::dom::workerinternals::loader {
+
+//////////////////////////////////////////////////////////////
+// WorkerModuleLoader
+//////////////////////////////////////////////////////////////
+
+NS_IMPL_ADDREF_INHERITED(WorkerModuleLoader, JS::loader::ModuleLoaderBase)
+NS_IMPL_RELEASE_INHERITED(WorkerModuleLoader, JS::loader::ModuleLoaderBase)
+
+NS_IMPL_CYCLE_COLLECTION_INHERITED(WorkerModuleLoader,
+                                   JS::loader::ModuleLoaderBase)
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(WorkerModuleLoader)
+NS_INTERFACE_MAP_END_INHERITING(JS::loader::ModuleLoaderBase)
+
+WorkerModuleLoader::WorkerModuleLoader(WorkerScriptLoader* aScriptLoader,
+                                       nsIGlobalObject* aGlobalObject)
+    : ModuleLoaderBase(aScriptLoader, aGlobalObject) {}
+
+nsIURI* WorkerModuleLoader::GetBaseURI() const {
+  WorkerPrivate* workerPrivate = GetCurrentThreadWorkerPrivate();
+  return workerPrivate->GetBaseURI();
+}
+
+already_AddRefed<ModuleLoadRequest> WorkerModuleLoader::CreateStaticImport(
+    nsIURI* aURI, ModuleLoadRequest* aParent) {
+  // We are intentionally deviating from the specification here and using the
+  // worker's CSP rather than the document CSP. The spec otherwise requires our
+  // service worker integration to be changed, and additionally the decision
+  // here did not make sense as we are treating static imports as different from
+  // other kinds of subresources.
+  // See Discussion in https://github.com/w3c/webappsec-csp/issues/336
+  Maybe<ClientInfo> clientInfo = GetGlobalObject()->GetClientInfo();
+
+  RefPtr<WorkerLoadContext> loadContext = new WorkerLoadContext(
+      WorkerLoadContext::Kind::StaticImport, clientInfo,
+      aParent->GetWorkerLoadContext()->mScriptLoader,
+      aParent->GetWorkerLoadContext()->mOnlyExistingCachedResourcesAllowed);
+  RefPtr<ModuleLoadRequest> request = new ModuleLoadRequest(
+      aURI, aParent->ReferrerPolicy(), aParent->mFetchOptions, SRIMetadata(),
+      aParent->mURI, loadContext, false, /* is top level */
+      false,                             /* is dynamic import */
+      this, aParent->mVisitedSet, aParent->GetRootModule());
+
+  request->mURL = request->mURI->GetSpecOrDefault();
+  request->NoCacheEntryFound();
+  return request.forget();
+}
+
+bool WorkerModuleLoader::CreateDynamicImportLoader() {
+  WorkerPrivate* workerPrivate = GetCurrentThreadWorkerPrivate();
+  workerPrivate->AssertIsOnWorkerThread();
+
+  IgnoredErrorResult rv;
+  RefPtr<WorkerScriptLoader> loader = loader::WorkerScriptLoader::Create(
+      workerPrivate, nullptr, nullptr,
+      GetCurrentScriptLoader()->GetWorkerScriptType(), rv);
+  if (NS_WARN_IF(rv.Failed())) {
+    return false;
+  }
+
+  SetScriptLoader(loader);
+  return true;
+}
+
+already_AddRefed<ModuleLoadRequest> WorkerModuleLoader::CreateDynamicImport(
+    JSContext* aCx, nsIURI* aURI, LoadedScript* aMaybeActiveScript,
+    JS::Handle<JSString*> aSpecifier, JS::Handle<JSObject*> aPromise) {
+  WorkerPrivate* workerPrivate = GetCurrentThreadWorkerPrivate();
+
+  if (!CreateDynamicImportLoader()) {
+    return nullptr;
+  }
+
+  // Not supported for Service Workers.
+  // https://github.com/w3c/ServiceWorker/issues/1585 covers existing discussion
+  // about potentially supporting use of import().
+  if (workerPrivate->IsServiceWorker()) {
+    return nullptr;
+  }
+  MOZ_ASSERT(aSpecifier);
+  MOZ_ASSERT(aPromise);
+
+  RefPtr<ScriptFetchOptions> options;
+  nsIURI* baseURL = nullptr;
+  if (aMaybeActiveScript) {
+    // https://html.spec.whatwg.org/multipage/webappapis.html#hostloadimportedmodule
+    // Step 6.3. Set fetchOptions to the new descendant script fetch options for
+    // referencingScript's fetch options.
+    options = aMaybeActiveScript->GetFetchOptions();
+    baseURL = aMaybeActiveScript->BaseURL();
+  } else {
+    // https://html.spec.whatwg.org/multipage/webappapis.html#hostloadimportedmodule
+    // Step 4. Let fetchOptions be the default classic script fetch options.
+    //
+    // https://html.spec.whatwg.org/multipage/webappapis.html#default-classic-script-fetch-options
+    // The default classic script fetch options are a script fetch options whose
+    // cryptographic nonce is the empty string, integrity metadata is the empty
+    // string, parser metadata is "not-parser-inserted", credentials mode is
+    // "same-origin", referrer policy is the empty string, and fetch priority is
+    // "auto".
+    options = new ScriptFetchOptions(
+        CORSMode::CORS_NONE, /* aNonce = */ u""_ns, RequestPriority::Auto,
+        JS::loader::ParserMetadata::NotParserInserted, nullptr);
+    baseURL = GetBaseURI();
+  }
+
+  Maybe<ClientInfo> clientInfo = GetGlobalObject()->GetClientInfo();
+
+  RefPtr<WorkerLoadContext> context = new WorkerLoadContext(
+      WorkerLoadContext::Kind::DynamicImport, clientInfo,
+      GetCurrentScriptLoader(),
+      // When dynamic import is supported in ServiceWorkers,
+      // the current plan in onlyExistingCachedResourcesAllowed
+      // is that only existing cached resources will be
+      // allowed.  (`import()` will not be used for caching
+      // side effects, but instead a specific method will be
+      // used during installation.)
+      true);
+
+  ReferrerPolicy referrerPolicy = workerPrivate->GetReferrerPolicy();
+  RefPtr<ModuleLoadRequest> request = new ModuleLoadRequest(
+      aURI, referrerPolicy, options, SRIMetadata(), baseURL, context, true,
+      /* is top level */ true, /* is dynamic import */
+      this, ModuleLoadRequest::NewVisitedSetForTopLevelImport(aURI), nullptr);
+
+  request->SetDynamicImport(aMaybeActiveScript, aSpecifier, aPromise);
+  request->NoCacheEntryFound();
+
+  return request.forget();
+}
+
+bool WorkerModuleLoader::CanStartLoad(ModuleLoadRequest* aRequest,
+                                      nsresult* aRvOut) {
+  return true;
+}
+
+nsresult WorkerModuleLoader::StartFetch(ModuleLoadRequest* aRequest) {
+  if (!GetScriptLoaderFor(aRequest)->DispatchLoadScript(aRequest)) {
+    return NS_ERROR_FAILURE;
+  }
+  return NS_OK;
+}
+
+nsresult WorkerModuleLoader::CompileFetchedModule(
+    JSContext* aCx, JS::Handle<JSObject*> aGlobal, JS::CompileOptions& aOptions,
+    ModuleLoadRequest* aRequest, JS::MutableHandle<JSObject*> aModuleScript) {
+  RefPtr<JS::Stencil> stencil;
+  MOZ_ASSERT(aRequest->IsTextSource());
+  MaybeSourceText maybeSource;
+  nsresult rv = aRequest->GetScriptSource(aCx, &maybeSource,
+                                          aRequest->mLoadContext.get());
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  auto compile = [&](auto& source) {
+    return JS::CompileModuleScriptToStencil(aCx, aOptions, source);
+  };
+  stencil = maybeSource.mapNonEmpty(compile);
+
+  if (!stencil) {
+    return NS_ERROR_FAILURE;
+  }
+
+  JS::InstantiateOptions instantiateOptions(aOptions);
+  aModuleScript.set(
+      JS::InstantiateModuleStencil(aCx, instantiateOptions, stencil));
+  if (!aModuleScript) {
+    return NS_ERROR_FAILURE;
+  }
+
+  return NS_OK;
+}
+
+WorkerScriptLoader* WorkerModuleLoader::GetCurrentScriptLoader() {
+  return static_cast<WorkerScriptLoader*>(mLoader.get());
+}
+
+WorkerScriptLoader* WorkerModuleLoader::GetScriptLoaderFor(
+    ModuleLoadRequest* aRequest) {
+  return aRequest->GetWorkerLoadContext()->mScriptLoader;
+}
+
+void WorkerModuleLoader::OnModuleLoadComplete(ModuleLoadRequest* aRequest) {
+  if (aRequest->IsTopLevel()) {
+    AutoJSAPI jsapi;
+    if (NS_WARN_IF(!jsapi.Init(GetGlobalObject()))) {
+      return;
+    }
+    RefPtr<WorkerScriptLoader> requestScriptLoader =
+        GetScriptLoaderFor(aRequest);
+    if (aRequest->IsDynamicImport()) {
+      aRequest->ProcessDynamicImport();
+      requestScriptLoader->TryShutdown();
+    } else {
+      requestScriptLoader->MaybeMoveToLoadedList(aRequest);
+      requestScriptLoader->ProcessPendingRequests(jsapi.cx());
+    }
+  }
+}
+
+bool WorkerModuleLoader::IsModuleEvaluationAborted(
+    ModuleLoadRequest* aRequest) {
+  WorkerPrivate* workerPrivate = GetCurrentThreadWorkerPrivate();
+  return !workerPrivate || !workerPrivate->GlobalScope() ||
+         workerPrivate->GlobalScope()->IsDying();
+}
+
+}  // namespace mozilla::dom::workerinternals::loader
diff --git a/dom/workers/loader/WorkerModuleLoader.h b/dom/workers/loader/WorkerModuleLoader.h
new file mode 100644
index 0000000000..6ad45b42a0
--- /dev/null
+++ b/dom/workers/loader/WorkerModuleLoader.h
@@ -0,0 +1,83 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_loader_WorkerModuleLoader_h
+#define mozilla_loader_WorkerModuleLoader_h
+
+#include "js/loader/ModuleLoaderBase.h"
+#include "js/loader/ScriptFetchOptions.h"
+#include "mozilla/dom/SerializedStackHolder.h"
+#include "mozilla/UniquePtr.h"
+
+namespace mozilla::dom::workerinternals::loader {
+class WorkerScriptLoader;
+
+// alias common classes
+using ScriptFetchOptions = JS::loader::ScriptFetchOptions;
+using ScriptKind = JS::loader::ScriptKind;
+using ScriptLoadRequest = JS::loader::ScriptLoadRequest;
+using ScriptLoadRequestList = JS::loader::ScriptLoadRequestList;
+using ModuleLoadRequest = JS::loader::ModuleLoadRequest;
+
+// WorkerModuleLoader
+//
+// The WorkerModuleLoader provides the methods that implement specification
+// step 5 from "To fetch a worklet/module worker script graph", specifically for
+// workers. In addition, this implements worker specific initialization for
+// Static imports and Dynamic imports.
+//
+// The steps are outlined in "To fetch the descendants of and link a module
+// script" and are common for all Modules. Thus we delegate to ModuleLoaderBase
+// for those steps.
+class WorkerModuleLoader : public JS::loader::ModuleLoaderBase {
+ public:
+  NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(WorkerModuleLoader,
+                                           JS::loader::ModuleLoaderBase)
+
+  WorkerModuleLoader(WorkerScriptLoader* aScriptLoader,
+                     nsIGlobalObject* aGlobalObject);
+
+ private:
+  ~WorkerModuleLoader() = default;
+
+  bool CreateDynamicImportLoader();
+  void SetScriptLoader(JS::loader::ScriptLoaderInterface* aLoader) {
+    mLoader = aLoader;
+  }
+
+  WorkerScriptLoader* GetCurrentScriptLoader();
+
+  WorkerScriptLoader* GetScriptLoaderFor(ModuleLoadRequest* aRequest);
+
+  nsIURI* GetBaseURI() const override;
+
+  already_AddRefed<ModuleLoadRequest> CreateStaticImport(
+      nsIURI* aURI, ModuleLoadRequest* aParent) override;
+
+  already_AddRefed<ModuleLoadRequest> CreateDynamicImport(
+      JSContext* aCx, nsIURI* aURI, LoadedScript* aMaybeActiveScript,
+      JS::Handle<JSString*> aSpecifier,
+      JS::Handle<JSObject*> aPromise) override;
+
+  bool CanStartLoad(ModuleLoadRequest* aRequest, nsresult* aRvOut) override;
+
+  // StartFetch is special for worker modules, as we need to move back to the
+  // main thread to start a new load.
+  nsresult StartFetch(ModuleLoadRequest* aRequest) override;
+
+  nsresult CompileFetchedModule(
+      JSContext* aCx, JS::Handle<JSObject*> aGlobal,
+      JS::CompileOptions& aOptions, ModuleLoadRequest* aRequest,
+      JS::MutableHandle<JSObject*> aModuleScript) override;
+
+  void OnModuleLoadComplete(ModuleLoadRequest* aRequest) override;
+
+  bool IsModuleEvaluationAborted(ModuleLoadRequest* aRequest) override;
+};
+
+}  // namespace mozilla::dom::workerinternals::loader
+#endif  // mozilla_loader_WorkerModuleLoader_h
diff --git a/dom/workers/loader/moz.build b/dom/workers/loader/moz.build
new file mode 100644
index 0000000000..d39a6acb24
--- /dev/null
+++ b/dom/workers/loader/moz.build
@@ -0,0 +1,34 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+with Files("**"):
+    BUG_COMPONENT = ("Core", "DOM: Workers")
+
+# Public stuff.
+EXPORTS.mozilla.dom += [
+    "WorkerLoadContext.h",
+]
+
+# Private stuff.
+EXPORTS.mozilla.dom.workerinternals += [
+    "CacheLoadHandler.h",
+    "NetworkLoadHandler.h",
+    "ScriptResponseHeaderProcessor.h",
+    "WorkerModuleLoader.h",
+]
+
+UNIFIED_SOURCES += [
+    "CacheLoadHandler.cpp",
+    "NetworkLoadHandler.cpp",
+    "ScriptResponseHeaderProcessor.cpp",
+    "WorkerLoadContext.cpp",
+    "WorkerModuleLoader.cpp",
+]
+
+
+include("/ipc/chromium/chromium-config.mozbuild")
+
+FINAL_LIBRARY = "xul"
diff --git a/dom/workers/moz.build b/dom/workers/moz.build
new file mode 100644
index 0000000000..c7818826d1
--- /dev/null
+++ b/dom/workers/moz.build
@@ -0,0 +1,114 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+with Files("**"):
+    BUG_COMPONENT = ("Core", "DOM: Workers")
+
+DIRS += ["remoteworkers", "sharedworkers", "loader"]
+
+# Public stuff.
+EXPORTS.mozilla.dom += [
+    "ChromeWorker.h",
+    "EventWithOptionsRunnable.h",
+    "JSExecutionManager.h",
+    "Worker.h",
+    "WorkerChannelInfo.h",
+    "WorkerCommon.h",
+    "WorkerDebugger.h",
+    "WorkerDebuggerManager.h",
+    "WorkerDocumentListener.h",
+    "WorkerError.h",
+    "WorkerIPCUtils.h",
+    "WorkerLoadInfo.h",
+    "WorkerLocation.h",
+    "WorkerNavigator.h",
+    "WorkerPrivate.h",
+    "WorkerRef.h",
+    "WorkerRunnable.h",
+    "WorkerScope.h",
+    "WorkerStatus.h",
+    "WorkerTestUtils.h",
+]
+
+# Private stuff.
+EXPORTS.mozilla.dom.workerinternals += [
+    "JSSettings.h",
+    "Queue.h",
+    "RuntimeService.h",
+    "ScriptLoader.h",
+]
+
+XPIDL_MODULE = "dom_workers"
+
+XPIDL_SOURCES += [
+    "nsIWorkerChannelInfo.idl",
+    "nsIWorkerDebugger.idl",
+    "nsIWorkerDebuggerManager.idl",
+]
+
+UNIFIED_SOURCES += [
+    "ChromeWorker.cpp",
+    "ChromeWorkerScope.cpp",
+    "EventWithOptionsRunnable.cpp",
+    "JSExecutionManager.cpp",
+    "MessageEventRunnable.cpp",
+    "RegisterBindings.cpp",
+    "RuntimeService.cpp",
+    "ScriptLoader.cpp",
+    "Worker.cpp",
+    "WorkerChannelInfo.cpp",
+    "WorkerCSPEventListener.cpp",
+    "WorkerDebugger.cpp",
+    "WorkerDebuggerManager.cpp",
+    "WorkerDocumentListener.cpp",
+    "WorkerError.cpp",
+    "WorkerEventTarget.cpp",
+    "WorkerLoadInfo.cpp",
+    "WorkerLocation.cpp",
+    "WorkerNavigator.cpp",
+    "WorkerPrivate.cpp",
+    "WorkerRef.cpp",
+    "WorkerRunnable.cpp",
+    "WorkerScope.cpp",
+    "WorkerTestUtils.cpp",
+    "WorkerThread.cpp",
+]
+
+LOCAL_INCLUDES += [
+    "/caps",
+    "/dom/base",
+    "/dom/bindings",
+    "/dom/system",
+    "/dom/workers/remoteworkers",
+    "/js/xpconnect/loader",
+    "/netwerk/base",
+    "/xpcom/build",
+    "/xpcom/threads",
+]
+
+if CONFIG["MOZ_WIDGET_TOOLKIT"] == "cocoa":
+    LOCAL_INCLUDES += [
+        "/xpcom/base",
+    ]
+
+
+include("/ipc/chromium/chromium-config.mozbuild")
+
+FINAL_LIBRARY = "xul"
+
+MOCHITEST_MANIFESTS += [
+    "test/mochitest.toml",
+]
+
+MOCHITEST_CHROME_MANIFESTS += [
+    "test/chrome.toml",
+]
+
+MARIONETTE_MANIFESTS += ["test/marionette/manifest.toml"]
+
+XPCSHELL_TESTS_MANIFESTS += ["test/xpcshell/xpcshell.toml"]
+
+BROWSER_CHROME_MANIFESTS += ["test/browser.toml"]
diff --git a/dom/workers/nsIWorkerChannelInfo.idl b/dom/workers/nsIWorkerChannelInfo.idl
new file mode 100644
index 0000000000..5cf3305749
--- /dev/null
+++ b/dom/workers/nsIWorkerChannelInfo.idl
@@ -0,0 +1,22 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsISupports.idl"
+
+webidl BrowsingContext;
+
+[scriptable, builtinclass, uuid(bf9a175a-03bc-4d7b-ba2f-76347cf40d7b)]
+interface nsIWorkerChannelLoadInfo : nsISupports
+{
+  [infallible] attribute unsigned long long workerAssociatedBrowsingContextID;
+  [infallible] readonly attribute BrowsingContext workerAssociatedBrowsingContext;
+};
+
+[scriptable, builtinclass, uuid(df1fffe4-dac6-487e-979a-629ac8c64831)]
+interface nsIWorkerChannelInfo : nsISupports
+{
+  attribute nsIWorkerChannelLoadInfo loadInfo;
+  [must_use] readonly attribute uint64_t channelId;
+};
diff --git a/dom/workers/nsIWorkerDebugger.idl b/dom/workers/nsIWorkerDebugger.idl
new file mode 100644
index 0000000000..931d01a4ac
--- /dev/null
+++ b/dom/workers/nsIWorkerDebugger.idl
@@ -0,0 +1,73 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+#include "nsISupports.idl"
+
+interface mozIDOMWindow;
+interface nsIPrincipal;
+
+[scriptable, uuid(9cf3b48e-361d-486a-8917-55cf8d00bb41)]
+interface nsIWorkerDebuggerListener : nsISupports
+{
+  void onClose();
+
+  void onError(in AString filename, in unsigned long lineno,
+               in AString message);
+
+  void onMessage(in AString message);
+};
+
+[scriptable, builtinclass, uuid(22f93aa3-8a05-46be-87e0-fa93bf8a8eff)]
+interface nsIWorkerDebugger : nsISupports
+{
+  const unsigned long TYPE_DEDICATED = 0;
+  const unsigned long TYPE_SHARED = 1;
+  const unsigned long TYPE_SERVICE = 2;
+
+  readonly attribute bool isClosed;
+
+  readonly attribute bool isChrome;
+
+  readonly attribute bool isInitialized;
+
+  readonly attribute nsIWorkerDebugger parent;
+
+  readonly attribute unsigned long type;
+
+  readonly attribute AString url;
+
+  // If this is a dedicated worker, the window this worker or (in the case of
+  // nested workers) its top-level ancestral worker is associated with.
+  readonly attribute mozIDOMWindow window;
+
+  readonly attribute Array<uint64_t> windowIDs;
+
+  readonly attribute nsIPrincipal principal;
+
+  readonly attribute unsigned long serviceWorkerID;
+
+  readonly attribute AString id;
+
+  void initialize(in AString url);
+
+  [binaryname(PostMessageMoz)]
+  void postMessage(in AString message);
+
+  void addListener(in nsIWorkerDebuggerListener listener);
+
+  void removeListener(in nsIWorkerDebuggerListener listener);
+
+  // Indicate whether the debugger has finished initializing. By default the
+  // debugger will be considered initialized when the onRegister hooks in all
+  // nsIWorkerDebuggerManagerListener have been called.
+  //
+  // setDebuggerReady(false) can be called during an onRegister hook to mark
+  // the debugger as not being ready yet. This will prevent all content from
+  // running in the worker, including the worker's main script and any messages
+  // posted to it. Other runnables will still execute in the worker as normal.
+  //
+  // When the debugger is ready, setDebuggerReady(true) should then be called
+  // to allow the worker to begin executing content.
+  void setDebuggerReady(in boolean ready);
+};
diff --git a/dom/workers/nsIWorkerDebuggerManager.idl b/dom/workers/nsIWorkerDebuggerManager.idl
new file mode 100644
index 0000000000..ce047cfdc9
--- /dev/null
+++ b/dom/workers/nsIWorkerDebuggerManager.idl
@@ -0,0 +1,26 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+#include "nsISupports.idl"
+
+interface nsISimpleEnumerator;
+interface nsIWorkerDebugger;
+
+[scriptable, uuid(d2aa74ee-6b98-4d5d-8173-4e23422daf1e)]
+interface nsIWorkerDebuggerManagerListener : nsISupports
+{
+  void onRegister(in nsIWorkerDebugger aDebugger);
+
+  void onUnregister(in nsIWorkerDebugger aDebugger);
+};
+
+[scriptable, builtinclass, uuid(056d7918-dc86-452a-b4e6-86da3405f015)]
+interface nsIWorkerDebuggerManager : nsISupports
+{
+  nsISimpleEnumerator getWorkerDebuggerEnumerator();
+
+  void addListener(in nsIWorkerDebuggerManagerListener listener);
+
+  void removeListener(in nsIWorkerDebuggerManagerListener listener);
+};
diff --git a/dom/workers/remoteworkers/PRemoteWorker.ipdl b/dom/workers/remoteworkers/PRemoteWorker.ipdl
new file mode 100644
index 0000000000..4da11c4840
--- /dev/null
+++ b/dom/workers/remoteworkers/PRemoteWorker.ipdl
@@ -0,0 +1,90 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+include protocol PBackground;
+include protocol PFetchEventOpProxy;
+
+include DOMTypes;
+include ServiceWorkerOpArgs;
+include RemoteWorkerTypes;
+
+namespace mozilla {
+namespace dom {
+
+struct RemoteWorkerSuspendOp
+{};
+
+struct RemoteWorkerResumeOp
+{};
+
+struct RemoteWorkerFreezeOp
+{};
+
+struct RemoteWorkerThawOp
+{};
+
+struct RemoteWorkerTerminateOp
+{};
+
+struct RemoteWorkerPortIdentifierOp
+{
+  MessagePortIdentifier portIdentifier;
+};
+
+struct RemoteWorkerAddWindowIDOp
+{
+  uint64_t windowID;
+};
+
+struct RemoteWorkerRemoveWindowIDOp
+{
+  uint64_t windowID;
+};
+
+union RemoteWorkerOp {
+  RemoteWorkerSuspendOp;
+  RemoteWorkerResumeOp;
+  RemoteWorkerFreezeOp;
+  RemoteWorkerThawOp;
+  RemoteWorkerTerminateOp;
+  RemoteWorkerPortIdentifierOp;
+  RemoteWorkerAddWindowIDOp;
+  RemoteWorkerRemoveWindowIDOp;
+};
+
+// This protocol is used to make a remote worker controllable from the parent
+// process. The parent process will receive operations from the
+// PRemoteWorkerController protocol.
+protocol PRemoteWorker
+{
+  manager PBackground;
+
+  manages PFetchEventOpProxy;
+
+parent:
+  async Created(bool aStatus);
+
+  async Error(ErrorValue aValue);
+
+  async NotifyLock(bool aCreated);
+
+  async NotifyWebTransport(bool aCreated);
+
+  async Close();
+
+  async SetServiceWorkerSkipWaitingFlag() returns (bool aOk);
+
+child:
+  async PFetchEventOpProxy(ParentToChildServiceWorkerFetchEventOpArgs aArgs);
+
+  async __delete__();
+
+  async ExecOp(RemoteWorkerOp op);
+
+  async ExecServiceWorkerOp(ServiceWorkerOpArgs aArgs)
+      returns (ServiceWorkerOpResult aResult);
+};
+
+} // namespace dom
+} // namespace mozilla
diff --git a/dom/workers/remoteworkers/PRemoteWorkerController.ipdl b/dom/workers/remoteworkers/PRemoteWorkerController.ipdl
new file mode 100644
index 0000000000..059a81f8fe
--- /dev/null
+++ b/dom/workers/remoteworkers/PRemoteWorkerController.ipdl
@@ -0,0 +1,48 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+include protocol PBackground;
+include protocol PFetchEventOp;
+
+include RemoteWorkerTypes;
+include ServiceWorkerOpArgs;
+
+namespace mozilla {
+namespace dom {
+
+/**
+ * Proxy protocol used by ServiceWorkerManager whose canonical state exists on
+ * the main thread to control/receive feedback from RemoteWorkers which are
+ * canonically controlled from the PBackground thread.  Exclusively for use from
+ * the parent process main thread to the parent process PBackground thread.
+ */
+protocol PRemoteWorkerController {
+  manager PBackground;
+
+  manages PFetchEventOp;
+
+ child:
+  async CreationFailed();
+
+  async CreationSucceeded();
+
+  async ErrorReceived(ErrorValue aError);
+
+  async Terminated();
+
+  async SetServiceWorkerSkipWaitingFlag() returns (bool aOk);
+
+ parent:
+  async PFetchEventOp(ParentToParentServiceWorkerFetchEventOpArgs aArgs);
+
+  async __delete__();
+
+  async Shutdown() returns (bool aOk);
+
+  async ExecServiceWorkerOp(ServiceWorkerOpArgs aArgs)
+      returns (ServiceWorkerOpResult aResult);
+};
+
+}  // namespace dom
+}  // namespace mozilla
diff --git a/dom/workers/remoteworkers/PRemoteWorkerService.ipdl b/dom/workers/remoteworkers/PRemoteWorkerService.ipdl
new file mode 100644
index 0000000000..6287bb56a1
--- /dev/null
+++ b/dom/workers/remoteworkers/PRemoteWorkerService.ipdl
@@ -0,0 +1,25 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+include protocol PBackground;
+
+include ProtocolTypes;
+include RemoteWorkerTypes;
+
+namespace mozilla {
+namespace dom {
+
+// Simple protocol to register any active RemoteWorkerService running on any
+// process.  Initialization/registration is delayed for preallocated processes
+// until the process takes on its final remoteType.
+protocol PRemoteWorkerService
+{
+  manager PBackground;
+
+parent:
+  async __delete__();
+};
+
+} // namespace dom
+} // namespace mozilla
diff --git a/dom/workers/remoteworkers/RemoteWorkerChild.cpp b/dom/workers/remoteworkers/RemoteWorkerChild.cpp
new file mode 100644
index 0000000000..a644439a8d
--- /dev/null
+++ b/dom/workers/remoteworkers/RemoteWorkerChild.cpp
@@ -0,0 +1,1071 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "RemoteWorkerChild.h"
+
+#include <utility>
+
+#include "MainThreadUtils.h"
+#include "nsCOMPtr.h"
+#include "nsDebug.h"
+#include "nsError.h"
+#include "nsIConsoleReportCollector.h"
+#include "nsIInterfaceRequestor.h"
+#include "nsIPrincipal.h"
+#include "nsNetUtil.h"
+#include "nsThreadUtils.h"
+#include "nsXULAppAPI.h"
+
+#include "RemoteWorkerService.h"
+#include "mozilla/ArrayAlgorithm.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/Attributes.h"
+#include "mozilla/BasePrincipal.h"
+#include "mozilla/ErrorResult.h"
+#include "mozilla/SchedulerGroup.h"
+#include "mozilla/Services.h"
+#include "mozilla/ScopeExit.h"
+#include "mozilla/Unused.h"
+#include "mozilla/dom/FetchEventOpProxyChild.h"
+#include "mozilla/dom/IndexedDatabaseManager.h"
+#include "mozilla/dom/MessagePort.h"
+#include "mozilla/dom/RemoteWorkerManager.h"  // RemoteWorkerManager::IsRemoteTypeAllowed
+#include "mozilla/dom/RemoteWorkerTypes.h"
+#include "mozilla/dom/ServiceWorkerDescriptor.h"
+#include "mozilla/dom/ServiceWorkerInterceptController.h"
+#include "mozilla/dom/ServiceWorkerOp.h"
+#include "mozilla/dom/ServiceWorkerRegistrationDescriptor.h"
+#include "mozilla/dom/ServiceWorkerShutdownState.h"
+#include "mozilla/dom/ServiceWorkerUtils.h"
+#include "mozilla/dom/workerinternals/ScriptLoader.h"
+#include "mozilla/dom/WorkerError.h"
+#include "mozilla/dom/WorkerPrivate.h"
+#include "mozilla/dom/WorkerRef.h"
+#include "mozilla/dom/WorkerRunnable.h"
+#include "mozilla/dom/WorkerScope.h"
+#include "mozilla/ipc/BackgroundUtils.h"
+#include "mozilla/ipc/URIUtils.h"
+#include "mozilla/net/CookieJarSettings.h"
+#include "mozilla/PermissionManager.h"
+
+mozilla::LazyLogModule gRemoteWorkerChildLog("RemoteWorkerChild");
+
+#ifdef LOG
+#  undef LOG
+#endif
+#define LOG(fmt) MOZ_LOG(gRemoteWorkerChildLog, mozilla::LogLevel::Verbose, fmt)
+
+namespace mozilla {
+
+using namespace ipc;
+
+namespace dom {
+
+using workerinternals::ChannelFromScriptURLMainThread;
+
+namespace {
+
+class SharedWorkerInterfaceRequestor final : public nsIInterfaceRequestor {
+ public:
+  NS_DECL_ISUPPORTS
+
+  SharedWorkerInterfaceRequestor() {
+    // This check must match the code nsDocShell::Create.
+    if (XRE_IsParentProcess()) {
+      mSWController = new ServiceWorkerInterceptController();
+    }
+  }
+
+  NS_IMETHOD
+  GetInterface(const nsIID& aIID, void** aSink) override {
+    MOZ_ASSERT(NS_IsMainThread());
+
+    if (mSWController &&
+        aIID.Equals(NS_GET_IID(nsINetworkInterceptController))) {
+      // If asked for the network intercept controller, ask the outer requestor,
+      // which could be the docshell.
+      RefPtr<ServiceWorkerInterceptController> swController = mSWController;
+      swController.forget(aSink);
+      return NS_OK;
+    }
+
+    return NS_NOINTERFACE;
+  }
+
+ private:
+  ~SharedWorkerInterfaceRequestor() = default;
+
+  RefPtr<ServiceWorkerInterceptController> mSWController;
+};
+
+NS_IMPL_ADDREF(SharedWorkerInterfaceRequestor)
+NS_IMPL_RELEASE(SharedWorkerInterfaceRequestor)
+NS_IMPL_QUERY_INTERFACE(SharedWorkerInterfaceRequestor, nsIInterfaceRequestor)
+
+// Normal runnable because AddPortIdentifier() is going to exec JS code.
+class MessagePortIdentifierRunnable final : public WorkerRunnable {
+ public:
+  MessagePortIdentifierRunnable(WorkerPrivate* aWorkerPrivate,
+                                RemoteWorkerChild* aActor,
+                                const MessagePortIdentifier& aPortIdentifier)
+      : WorkerRunnable(aWorkerPrivate, "MessagePortIdentifierRunnable"),
+        mActor(aActor),
+        mPortIdentifier(aPortIdentifier) {}
+
+ private:
+  bool WorkerRun(JSContext* aCx, WorkerPrivate* aWorkerPrivate) override {
+    if (aWorkerPrivate->GlobalScope()->IsDying()) {
+      mPortIdentifier.ForceClose();
+      return true;
+    }
+    mActor->AddPortIdentifier(aCx, aWorkerPrivate, mPortIdentifier);
+    return true;
+  }
+
+  RefPtr<RemoteWorkerChild> mActor;
+  UniqueMessagePortId mPortIdentifier;
+};
+
+// This is used to propagate the CSP violation when loading the SharedWorker
+// main-script and nothing else.
+class RemoteWorkerCSPEventListener final : public nsICSPEventListener {
+ public:
+  NS_DECL_ISUPPORTS
+
+  explicit RemoteWorkerCSPEventListener(RemoteWorkerChild* aActor)
+      : mActor(aActor){};
+
+  NS_IMETHOD OnCSPViolationEvent(const nsAString& aJSON) override {
+    mActor->CSPViolationPropagationOnMainThread(aJSON);
+    return NS_OK;
+  }
+
+ private:
+  ~RemoteWorkerCSPEventListener() = default;
+
+  RefPtr<RemoteWorkerChild> mActor;
+};
+
+NS_IMPL_ISUPPORTS(RemoteWorkerCSPEventListener, nsICSPEventListener)
+
+}  // anonymous namespace
+
+RemoteWorkerChild::RemoteWorkerChild(const RemoteWorkerData& aData)
+    : mState(VariantType<Pending>(), "RemoteWorkerChild::mState"),
+      mServiceKeepAlive(RemoteWorkerService::MaybeGetKeepAlive()),
+      mIsServiceWorker(aData.serviceWorkerData().type() ==
+                       OptionalServiceWorkerData::TServiceWorkerData) {
+  MOZ_ASSERT(RemoteWorkerService::Thread()->IsOnCurrentThread());
+}
+
+RemoteWorkerChild::~RemoteWorkerChild() {
+#ifdef DEBUG
+  auto lock = mState.Lock();
+  MOZ_ASSERT(lock->is<Killed>());
+#endif
+}
+
+void RemoteWorkerChild::ActorDestroy(ActorDestroyReason) {
+  auto launcherData = mLauncherData.Access();
+
+  Unused << NS_WARN_IF(!launcherData->mTerminationPromise.IsEmpty());
+  launcherData->mTerminationPromise.RejectIfExists(NS_ERROR_DOM_ABORT_ERR,
+                                                   __func__);
+
+  auto lock = mState.Lock();
+
+  // If the worker hasn't shutdown or begun shutdown, we need to ensure it gets
+  // canceled.
+  if (NS_WARN_IF(!lock->is<Killed>() && !lock->is<Canceled>())) {
+    // In terms of strong references to this RemoteWorkerChild, at this moment:
+    // - IPC is holding a strong reference that will be dropped in the near
+    //   future after this method returns.
+    // - If the worker has been started by ExecWorkerOnMainThread, then
+    //   WorkerPrivate::mRemoteWorkerController is a strong reference to us.
+    //   If the worker has not been started, ExecWorker's runnable lambda will
+    //   have a strong reference that will cover the call to
+    //   ExecWorkerOnMainThread.
+    //   - The WorkerPrivate cancellation and termination callbacks will also
+    //     hold strong references, but those callbacks will not outlive the
+    //     WorkerPrivate and are not exposed to callers like
+    //     mRemoteWorkerController is.
+    //
+    // Note that this call to RequestWorkerCancellation can still race worker
+    // cancellation, in which case the strong reference obtained by
+    // NewRunnableMethod can end up being the last strong reference.
+    // (RequestWorkerCancellation handles the case that the Worker is already
+    // canceled if this happens.)
+    RefPtr<nsIRunnable> runnable =
+        NewRunnableMethod("RequestWorkerCancellation", this,
+                          &RemoteWorkerChild::RequestWorkerCancellation);
+    MOZ_ALWAYS_SUCCEEDS(SchedulerGroup::Dispatch(runnable.forget()));
+  }
+}
+
+void RemoteWorkerChild::ExecWorker(const RemoteWorkerData& aData) {
+#ifdef DEBUG
+  MOZ_ASSERT(GetActorEventTarget()->IsOnCurrentThread());
+  auto launcherData = mLauncherData.Access();
+  MOZ_ASSERT(CanSend());
+#endif
+
+  RefPtr<RemoteWorkerChild> self = this;
+
+  nsCOMPtr<nsIRunnable> r = NS_NewRunnableFunction(
+      __func__, [self = std::move(self), data = aData]() mutable {
+        nsresult rv = self->ExecWorkerOnMainThread(std::move(data));
+
+        // Creation failure will already have been reported via the method
+        // above internally using ScopeExit.
+        Unused << NS_WARN_IF(NS_FAILED(rv));
+      });
+
+  MOZ_ALWAYS_SUCCEEDS(SchedulerGroup::Dispatch(r.forget()));
+}
+
+nsresult RemoteWorkerChild::ExecWorkerOnMainThread(RemoteWorkerData&& aData) {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  // Ensure that the IndexedDatabaseManager is initialized so that if any
+  // workers do any IndexedDB calls that all of IDB's prefs/etc. are
+  // initialized.
+  Unused << NS_WARN_IF(!IndexedDatabaseManager::GetOrCreate());
+
+  auto scopeExit =
+      MakeScopeExit([&] { ExceptionalErrorTransitionDuringExecWorker(); });
+
+  // Verify the the RemoteWorker should be really allowed to run in this
+  // process, and fail if it shouldn't (This shouldn't normally happen,
+  // unless the RemoteWorkerData has been tempered in the process it was
+  // sent from).
+  if (!RemoteWorkerManager::IsRemoteTypeAllowed(aData)) {
+    return NS_ERROR_UNEXPECTED;
+  }
+
+  auto principalOrErr = PrincipalInfoToPrincipal(aData.principalInfo());
+  if (NS_WARN_IF(principalOrErr.isErr())) {
+    return principalOrErr.unwrapErr();
+  }
+
+  nsCOMPtr<nsIPrincipal> principal = principalOrErr.unwrap();
+
+  auto loadingPrincipalOrErr =
+      PrincipalInfoToPrincipal(aData.loadingPrincipalInfo());
+  if (NS_WARN_IF(loadingPrincipalOrErr.isErr())) {
+    return loadingPrincipalOrErr.unwrapErr();
+  }
+
+  auto partitionedPrincipalOrErr =
+      PrincipalInfoToPrincipal(aData.partitionedPrincipalInfo());
+  if (NS_WARN_IF(partitionedPrincipalOrErr.isErr())) {
+    return partitionedPrincipalOrErr.unwrapErr();
+  }
+
+  WorkerLoadInfo info;
+  info.mBaseURI = DeserializeURI(aData.baseScriptURL());
+  info.mResolvedScriptURI = DeserializeURI(aData.resolvedScriptURL());
+
+  info.mPrincipalInfo = MakeUnique<PrincipalInfo>(aData.principalInfo());
+  info.mPartitionedPrincipalInfo =
+      MakeUnique<PrincipalInfo>(aData.partitionedPrincipalInfo());
+
+  info.mReferrerInfo = aData.referrerInfo();
+  info.mDomain = aData.domain();
+  info.mTrials = aData.originTrials();
+  info.mPrincipal = principal;
+  info.mPartitionedPrincipal = partitionedPrincipalOrErr.unwrap();
+  info.mLoadingPrincipal = loadingPrincipalOrErr.unwrap();
+  info.mStorageAccess = aData.storageAccess();
+  info.mUseRegularPrincipal = aData.useRegularPrincipal();
+  info.mUsingStorageAccess = aData.usingStorageAccess();
+  info.mIsThirdPartyContextToTopWindow = aData.isThirdPartyContextToTopWindow();
+  info.mOriginAttributes =
+      BasePrincipal::Cast(principal)->OriginAttributesRef();
+  info.mShouldResistFingerprinting = aData.shouldResistFingerprinting();
+  Maybe<RFPTarget> overriddenFingerprintingSettings;
+  if (aData.overriddenFingerprintingSettings().isSome()) {
+    overriddenFingerprintingSettings.emplace(
+        RFPTarget(aData.overriddenFingerprintingSettings().ref()));
+  }
+  info.mOverriddenFingerprintingSettings = overriddenFingerprintingSettings;
+  net::CookieJarSettings::Deserialize(aData.cookieJarSettings(),
+                                      getter_AddRefs(info.mCookieJarSettings));
+  info.mCookieJarSettingsArgs = aData.cookieJarSettings();
+
+  // Default CSP permissions for now.  These will be overrided if necessary
+  // based on the script CSP headers during load in ScriptLoader.
+  info.mEvalAllowed = true;
+  info.mReportEvalCSPViolations = false;
+  info.mWasmEvalAllowed = true;
+  info.mReportWasmEvalCSPViolations = false;
+  info.mSecureContext = aData.isSecureContext()
+                            ? WorkerLoadInfo::eSecureContext
+                            : WorkerLoadInfo::eInsecureContext;
+
+  WorkerPrivate::OverrideLoadInfoLoadGroup(info, info.mLoadingPrincipal);
+
+  RefPtr<SharedWorkerInterfaceRequestor> requestor =
+      new SharedWorkerInterfaceRequestor();
+  info.mInterfaceRequestor->SetOuterRequestor(requestor);
+
+  Maybe<ClientInfo> clientInfo;
+  if (aData.clientInfo().isSome()) {
+    clientInfo.emplace(ClientInfo(aData.clientInfo().ref()));
+  }
+
+  nsresult rv = NS_OK;
+
+  if (clientInfo.isSome()) {
+    Maybe<mozilla::ipc::CSPInfo> cspInfo = clientInfo.ref().GetCspInfo();
+    if (cspInfo.isSome()) {
+      info.mCSP = CSPInfoToCSP(cspInfo.ref(), nullptr);
+      info.mCSPInfo = MakeUnique<CSPInfo>();
+      rv = CSPToCSPInfo(info.mCSP, info.mCSPInfo.get());
+      if (NS_WARN_IF(NS_FAILED(rv))) {
+        return rv;
+      }
+    }
+  }
+
+  rv = info.SetPrincipalsAndCSPOnMainThread(
+      info.mPrincipal, info.mPartitionedPrincipal, info.mLoadGroup, info.mCSP);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  nsString workerPrivateId;
+
+  if (mIsServiceWorker) {
+    ServiceWorkerData& data = aData.serviceWorkerData().get_ServiceWorkerData();
+
+    MOZ_ASSERT(!data.id().IsEmpty());
+    workerPrivateId = std::move(data.id());
+
+    info.mServiceWorkerCacheName = data.cacheName();
+    info.mServiceWorkerDescriptor.emplace(data.descriptor());
+    info.mServiceWorkerRegistrationDescriptor.emplace(
+        data.registrationDescriptor());
+    info.mLoadFlags = static_cast<nsLoadFlags>(data.loadFlags());
+  } else {
+    // Top level workers' main script use the document charset for the script
+    // uri encoding.
+    rv = ChannelFromScriptURLMainThread(
+        info.mLoadingPrincipal, nullptr /* parent document */, info.mLoadGroup,
+        info.mResolvedScriptURI, aData.type(), aData.credentials(), clientInfo,
+        nsIContentPolicy::TYPE_INTERNAL_SHARED_WORKER, info.mCookieJarSettings,
+        info.mReferrerInfo, getter_AddRefs(info.mChannel));
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+
+    nsCOMPtr<nsILoadInfo> loadInfo = info.mChannel->LoadInfo();
+
+    auto* cspEventListener = new RemoteWorkerCSPEventListener(this);
+    rv = loadInfo->SetCspEventListener(cspEventListener);
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return rv;
+    }
+  }
+
+  info.mAgentClusterId = aData.agentClusterId();
+
+  AutoJSAPI jsapi;
+  jsapi.Init();
+
+  ErrorResult error;
+  RefPtr<RemoteWorkerChild> self = this;
+  RefPtr<WorkerPrivate> workerPrivate = WorkerPrivate::Constructor(
+      jsapi.cx(), aData.originalScriptURL(), false,
+      mIsServiceWorker ? WorkerKindService : WorkerKindShared,
+      aData.credentials(), aData.type(), aData.name(), VoidCString(), &info,
+      error, std::move(workerPrivateId),
+      [self](bool aEverRan) {
+        self->OnWorkerCancellationTransitionStateFromPendingOrRunningToCanceled();
+      },
+      // This will be invoked here on the main thread when the worker is already
+      // fully shutdown.  This replaces a prior approach where we would
+      // begin to transition when the worker thread would reach the Canceling
+      // state.  This lambda ensures that we not only wait for the Killing state
+      // to be reached but that the global shutdown has already occurred.
+      [self]() { self->TransitionStateFromCanceledToKilled(); });
+
+  if (NS_WARN_IF(error.Failed())) {
+    MOZ_ASSERT(!workerPrivate);
+
+    rv = error.StealNSResult();
+    return rv;
+  }
+
+  workerPrivate->SetRemoteWorkerController(this);
+
+  // This wants to run as a normal task sequentially after the top level script
+  // evaluation, so the hybrid target is the correct choice between hybrid and
+  // `ControlEventTarget`.
+  nsCOMPtr<nsISerialEventTarget> workerTarget =
+      workerPrivate->HybridEventTarget();
+
+  nsCOMPtr<nsIRunnable> runnable = NewCancelableRunnableMethod(
+      "InitialzeOnWorker", this, &RemoteWorkerChild::InitializeOnWorker);
+
+  {
+    MOZ_ASSERT(workerPrivate);
+    auto lock = mState.Lock();
+    // We MUST be pending here, so direct access is ok.
+    lock->as<Pending>().mWorkerPrivate = std::move(workerPrivate);
+  }
+
+  if (mIsServiceWorker) {
+    nsCOMPtr<nsIRunnable> r = NS_NewRunnableFunction(
+        __func__, [workerTarget,
+                   initializeWorkerRunnable = std::move(runnable)]() mutable {
+          Unused << NS_WARN_IF(NS_FAILED(
+              workerTarget->Dispatch(initializeWorkerRunnable.forget())));
+        });
+
+    RefPtr<PermissionManager> permissionManager =
+        PermissionManager::GetInstance();
+    if (!permissionManager) {
+      return NS_ERROR_FAILURE;
+    }
+    permissionManager->WhenPermissionsAvailable(principal, r);
+  } else {
+    if (NS_WARN_IF(NS_FAILED(workerTarget->Dispatch(runnable.forget())))) {
+      rv = NS_ERROR_FAILURE;
+      return rv;
+    }
+  }
+
+  scopeExit.release();
+
+  return NS_OK;
+}
+
+void RemoteWorkerChild::RequestWorkerCancellation() {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  LOG(("RequestWorkerCancellation[this=%p]", this));
+
+  // We want to ensure that we've requested the worker be canceled.  So if the
+  // worker is running, cancel it.  We can't do this with the lock held,
+  // however, because our lambdas will want to manipulate the state.
+  RefPtr<WorkerPrivate> cancelWith;
+  {
+    auto lock = mState.Lock();
+    if (lock->is<Pending>()) {
+      cancelWith = lock->as<Pending>().mWorkerPrivate;
+    } else if (lock->is<Running>()) {
+      cancelWith = lock->as<Running>().mWorkerPrivate;
+    }
+  }
+
+  if (cancelWith) {
+    cancelWith->Cancel();
+  }
+}
+
+// This method will be invoked on the worker after the top-level
+// CompileScriptRunnable task has succeeded and as long as the worker has not
+// been closed/canceled.  There are edge-cases related to cancellation, but we
+// have our caller ensure that we are only called as long as the worker's state
+// is Running.
+//
+// (https://bugzilla.mozilla.org/show_bug.cgi?id=1800659 will eliminate
+// cancellation, and the documentation around that bug / in design documents
+// helps provide more context about this.)
+void RemoteWorkerChild::InitializeOnWorker() {
+  nsCOMPtr<nsIRunnable> r =
+      NewRunnableMethod("TransitionStateToRunning", this,
+                        &RemoteWorkerChild::TransitionStateToRunning);
+  MOZ_ALWAYS_SUCCEEDS(SchedulerGroup::Dispatch(r.forget()));
+}
+
+RefPtr<GenericNonExclusivePromise> RemoteWorkerChild::GetTerminationPromise() {
+  auto launcherData = mLauncherData.Access();
+  return launcherData->mTerminationPromise.Ensure(__func__);
+}
+
+void RemoteWorkerChild::CreationSucceededOnAnyThread() {
+  CreationSucceededOrFailedOnAnyThread(true);
+}
+
+void RemoteWorkerChild::CreationFailedOnAnyThread() {
+  CreationSucceededOrFailedOnAnyThread(false);
+}
+
+void RemoteWorkerChild::CreationSucceededOrFailedOnAnyThread(
+    bool aDidCreationSucceed) {
+#ifdef DEBUG
+  {
+    auto lock = mState.Lock();
+    MOZ_ASSERT_IF(aDidCreationSucceed, lock->is<Running>());
+    MOZ_ASSERT_IF(!aDidCreationSucceed, lock->is<Killed>());
+  }
+#endif
+
+  RefPtr<RemoteWorkerChild> self = this;
+
+  nsCOMPtr<nsIRunnable> r = NS_NewRunnableFunction(
+      __func__,
+      [self = std::move(self), didCreationSucceed = aDidCreationSucceed] {
+        auto launcherData = self->mLauncherData.Access();
+
+        if (!self->CanSend() || launcherData->mDidSendCreated) {
+          return;
+        }
+
+        Unused << self->SendCreated(didCreationSucceed);
+        launcherData->mDidSendCreated = true;
+      });
+
+  GetActorEventTarget()->Dispatch(r.forget(), NS_DISPATCH_NORMAL);
+}
+
+void RemoteWorkerChild::CloseWorkerOnMainThread() {
+  AssertIsOnMainThread();
+
+  LOG(("CloseWorkerOnMainThread[this=%p]", this));
+
+  // We can't hold the state lock while calling WorkerPrivate::Cancel because
+  // the lambda callback will want to touch the state, so save off the
+  // WorkerPrivate so we can cancel it (if we need to cancel it).
+  RefPtr<WorkerPrivate> cancelWith;
+  {
+    auto lock = mState.Lock();
+
+    if (lock->is<Pending>()) {
+      cancelWith = lock->as<Pending>().mWorkerPrivate;
+      // There should be no way for this code to run before we
+      // ExecWorkerOnMainThread runs, which means that either it should have
+      // set a WorkerPrivate on Pending, or its error handling should already
+      // have transitioned us to Canceled and Killing in that order.  (It's
+      // also possible that it assigned a WorkerPrivate and subsequently we
+      // transitioned to Running, which would put us in the next branch.)
+      MOZ_DIAGNOSTIC_ASSERT(cancelWith);
+    } else if (lock->is<Running>()) {
+      cancelWith = lock->as<Running>().mWorkerPrivate;
+    }
+  }
+
+  // It's very okay for us to not have a WorkerPrivate here if we've already
+  // canceled the worker or if errors happened.
+  if (cancelWith) {
+    cancelWith->Cancel();
+  }
+}
+
+/**
+ * Error reporting method
+ */
+void RemoteWorkerChild::ErrorPropagation(const ErrorValue& aValue) {
+  MOZ_ASSERT(GetActorEventTarget()->IsOnCurrentThread());
+
+  if (!CanSend()) {
+    return;
+  }
+
+  Unused << SendError(aValue);
+}
+
+void RemoteWorkerChild::ErrorPropagationDispatch(nsresult aError) {
+  MOZ_ASSERT(NS_FAILED(aError));
+
+  RefPtr<RemoteWorkerChild> self = this;
+  nsCOMPtr<nsIRunnable> r = NS_NewRunnableFunction(
+      "RemoteWorkerChild::ErrorPropagationDispatch",
+      [self = std::move(self), aError]() { self->ErrorPropagation(aError); });
+
+  GetActorEventTarget()->Dispatch(r.forget(), NS_DISPATCH_NORMAL);
+}
+
+void RemoteWorkerChild::ErrorPropagationOnMainThread(
+    const WorkerErrorReport* aReport, bool aIsErrorEvent) {
+  AssertIsOnMainThread();
+
+  ErrorValue value;
+  if (aIsErrorEvent) {
+    ErrorData data(
+        aReport->mIsWarning, aReport->mLineNumber, aReport->mColumnNumber,
+        aReport->mMessage, aReport->mFilename, aReport->mLine,
+        TransformIntoNewArray(aReport->mNotes, [](const WorkerErrorNote& note) {
+          return ErrorDataNote(note.mLineNumber, note.mColumnNumber,
+                               note.mMessage, note.mFilename);
+        }));
+    value = data;
+  } else {
+    value = void_t();
+  }
+
+  RefPtr<RemoteWorkerChild> self = this;
+  nsCOMPtr<nsIRunnable> r = NS_NewRunnableFunction(
+      "RemoteWorkerChild::ErrorPropagationOnMainThread",
+      [self = std::move(self), value]() { self->ErrorPropagation(value); });
+
+  GetActorEventTarget()->Dispatch(r.forget(), NS_DISPATCH_NORMAL);
+}
+
+void RemoteWorkerChild::CSPViolationPropagationOnMainThread(
+    const nsAString& aJSON) {
+  AssertIsOnMainThread();
+
+  RefPtr<RemoteWorkerChild> self = this;
+  nsCOMPtr<nsIRunnable> r = NS_NewRunnableFunction(
+      "RemoteWorkerChild::ErrorPropagationDispatch",
+      [self = std::move(self), json = nsString(aJSON)]() {
+        CSPViolation violation(json);
+        self->ErrorPropagation(violation);
+      });
+
+  GetActorEventTarget()->Dispatch(r.forget(), NS_DISPATCH_NORMAL);
+}
+
+void RemoteWorkerChild::NotifyLock(bool aCreated) {
+  nsCOMPtr<nsIRunnable> r =
+      NS_NewRunnableFunction(__func__, [self = RefPtr(this), aCreated] {
+        if (!self->CanSend()) {
+          return;
+        }
+
+        Unused << self->SendNotifyLock(aCreated);
+      });
+
+  GetActorEventTarget()->Dispatch(r.forget(), NS_DISPATCH_NORMAL);
+}
+
+void RemoteWorkerChild::NotifyWebTransport(bool aCreated) {
+  nsCOMPtr<nsIRunnable> r =
+      NS_NewRunnableFunction(__func__, [self = RefPtr(this), aCreated] {
+        if (!self->CanSend()) {
+          return;
+        }
+
+        Unused << self->SendNotifyWebTransport(aCreated);
+      });
+
+  GetActorEventTarget()->Dispatch(r.forget(), NS_DISPATCH_NORMAL);
+}
+
+void RemoteWorkerChild::FlushReportsOnMainThread(
+    nsIConsoleReportCollector* aReporter) {
+  AssertIsOnMainThread();
+
+  bool reportErrorToBrowserConsole = true;
+
+  // Flush the reports.
+  for (uint32_t i = 0, len = mWindowIDs.Length(); i < len; ++i) {
+    aReporter->FlushReportsToConsole(
+        mWindowIDs[i], nsIConsoleReportCollector::ReportAction::Save);
+    reportErrorToBrowserConsole = false;
+  }
+
+  // Finally report to browser console if there is no any window.
+  if (reportErrorToBrowserConsole) {
+    aReporter->FlushReportsToConsole(0);
+    return;
+  }
+
+  aReporter->ClearConsoleReports();
+}
+
+/**
+ * Worker state transition methods
+ */
+RemoteWorkerChild::WorkerPrivateAccessibleState::
+    ~WorkerPrivateAccessibleState() {
+  // We should now only be performing state transitions on the main thread, so
+  // we should assert we're only releasing on the main thread.
+  MOZ_ASSERT(!mWorkerPrivate || NS_IsMainThread());
+  // mWorkerPrivate can be safely released on the main thread.
+  if (!mWorkerPrivate || NS_IsMainThread()) {
+    return;
+  }
+
+  // But as a backstop, do proxy the release to the main thread.
+  NS_ReleaseOnMainThread(
+      "RemoteWorkerChild::WorkerPrivateAccessibleState::mWorkerPrivate",
+      mWorkerPrivate.forget());
+}
+
+void RemoteWorkerChild::
+    OnWorkerCancellationTransitionStateFromPendingOrRunningToCanceled() {
+  auto lock = mState.Lock();
+
+  LOG(("TransitionStateFromPendingOrRunningToCanceled[this=%p]", this));
+
+  if (lock->is<Pending>()) {
+    TransitionStateFromPendingToCanceled(lock.ref());
+  } else if (lock->is<Running>()) {
+    *lock = VariantType<Canceled>();
+  } else {
+    MOZ_ASSERT(false, "State should have been Pending or Running");
+  }
+}
+
+void RemoteWorkerChild::TransitionStateFromPendingToCanceled(State& aState) {
+  AssertIsOnMainThread();
+  MOZ_ASSERT(aState.is<Pending>());
+  LOG(("TransitionStateFromPendingToCanceled[this=%p]", this));
+
+  CancelAllPendingOps(aState);
+
+  aState = VariantType<Canceled>();
+}
+
+void RemoteWorkerChild::TransitionStateFromCanceledToKilled() {
+  AssertIsOnMainThread();
+
+  LOG(("TransitionStateFromCanceledToKilled[this=%p]", this));
+
+  auto lock = mState.Lock();
+  MOZ_ASSERT(lock->is<Canceled>());
+
+  *lock = VariantType<Killed>();
+
+  RefPtr<RemoteWorkerChild> self = this;
+  nsCOMPtr<nsIRunnable> r = NS_NewRunnableFunction(__func__, [self]() {
+    auto launcherData = self->mLauncherData.Access();
+
+    // (We maintain the historical ordering of resolving this promise prior to
+    // calling SendClose, however the previous code used 2 separate dispatches
+    // to this thread for the resolve and SendClose, and there inherently
+    // would be a race between the runnables resulting from the resolved
+    // promise and the promise containing the call to SendClose.  Now it's
+    // entirely clear that our call to SendClose will effectively run before
+    // any of the resolved promises are able to do anything.)
+    launcherData->mTerminationPromise.ResolveIfExists(true, __func__);
+
+    if (self->CanSend()) {
+      Unused << self->SendClose();
+    }
+  });
+
+  GetActorEventTarget()->Dispatch(r.forget(), NS_DISPATCH_NORMAL);
+}
+
+void RemoteWorkerChild::TransitionStateToRunning() {
+  AssertIsOnMainThread();
+
+  LOG(("TransitionStateToRunning[this=%p]", this));
+
+  nsTArray<RefPtr<Op>> pendingOps;
+
+  {
+    auto lock = mState.Lock();
+
+    // Because this is an async notification sent from the worker to the main
+    // thread, it's very possible that we've already decided on the main thread
+    // to transition to the Canceled state, in which case there is nothing for
+    // us to do here.
+    if (!lock->is<Pending>()) {
+      LOG(("State is already not pending in TransitionStateToRunning[this=%p]!",
+           this));
+      return;
+    }
+
+    RefPtr<WorkerPrivate> workerPrivate =
+        std::move(lock->as<Pending>().mWorkerPrivate);
+    pendingOps = std::move(lock->as<Pending>().mPendingOps);
+
+    // Move the worker private into place to avoid gratuitous ref churn; prior
+    // comments here suggest the Variant can't accept a move.
+    *lock = VariantType<Running>();
+    lock->as<Running>().mWorkerPrivate = std::move(workerPrivate);
+  }
+
+  CreationSucceededOnAnyThread();
+
+  RefPtr<RemoteWorkerChild> self = this;
+  for (auto& op : pendingOps) {
+    op->StartOnMainThread(self);
+  }
+}
+
+void RemoteWorkerChild::ExceptionalErrorTransitionDuringExecWorker() {
+  AssertIsOnMainThread();
+
+  LOG(("ExceptionalErrorTransitionDuringExecWorker[this=%p]", this));
+
+  // This method is called synchronously by ExecWorkerOnMainThread in the event
+  // of any error.  Because we only transition to Running on the main thread
+  // as the result of a notification from the worker, we know our state will be
+  // Pending, but mWorkerPrivate may or may not be null, as we may not have
+  // gotten to spawning the worker.
+  //
+  // In the event the worker exists, we need to Cancel() it.  We must do this
+  // without the lock held because our call to Cancel() will invoke the
+  // cancellation callback we created which will call TransitionStateToCanceled,
+  // and we can't be holding the lock when that happens.
+
+  RefPtr<WorkerPrivate> cancelWith;
+
+  {
+    auto lock = mState.Lock();
+
+    MOZ_ASSERT(lock->is<Pending>());
+    if (lock->is<Pending>()) {
+      cancelWith = lock->as<Pending>().mWorkerPrivate;
+      if (!cancelWith) {
+        // The worker wasn't actually created, so we should synthetically
+        // transition to canceled and onward.  Since we have the lock,
+        // perform the transition now for clarity, but we'll handle the rest of
+        // this case after dropping the lock.
+        TransitionStateFromPendingToCanceled(lock.ref());
+      }
+    }
+  }
+
+  if (cancelWith) {
+    cancelWith->Cancel();
+  } else {
+    TransitionStateFromCanceledToKilled();
+    CreationFailedOnAnyThread();
+  }
+}
+
+/**
+ * Operation execution classes/methods
+ */
+class RemoteWorkerChild::SharedWorkerOp : public RemoteWorkerChild::Op {
+ public:
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(SharedWorkerOp, override)
+
+  explicit SharedWorkerOp(RemoteWorkerOp&& aOp) : mOp(std::move(aOp)) {}
+
+  bool MaybeStart(RemoteWorkerChild* aOwner,
+                  RemoteWorkerChild::State& aState) override {
+    MOZ_ASSERT(!mStarted);
+    MOZ_ASSERT(aOwner);
+    // Thread: We are on the Worker Launcher thread.
+
+    // Return false, indicating we should queue this op if our current state is
+    // pending and this isn't a termination op (which should skip the line).
+    if (aState.is<Pending>() && !IsTerminationOp()) {
+      return false;
+    }
+
+    // If the worker is already shutting down (which should be unexpected
+    // because we should be told new operations after a termination op), just
+    // return true to indicate the op should be discarded.
+    if (aState.is<Canceled>() || aState.is<Killed>()) {
+#ifdef DEBUG
+      mStarted = true;
+#endif
+      if (mOp.type() == RemoteWorkerOp::TRemoteWorkerPortIdentifierOp) {
+        MessagePort::ForceClose(
+            mOp.get_RemoteWorkerPortIdentifierOp().portIdentifier());
+      }
+      return true;
+    }
+
+    MOZ_ASSERT(aState.is<Running>() || IsTerminationOp());
+
+    RefPtr<SharedWorkerOp> self = this;
+    RefPtr<RemoteWorkerChild> owner = aOwner;
+
+    nsCOMPtr<nsIRunnable> r = NS_NewRunnableFunction(
+        __func__, [self = std::move(self), owner = std::move(owner)]() mutable {
+          {
+            auto lock = owner->mState.Lock();
+
+            if (NS_WARN_IF(lock->is<Canceled>() || lock->is<Killed>())) {
+              self->Cancel();
+              // Worker has already canceled, force close the MessagePort.
+              if (self->mOp.type() ==
+                  RemoteWorkerOp::TRemoteWorkerPortIdentifierOp) {
+                MessagePort::ForceClose(
+                    self->mOp.get_RemoteWorkerPortIdentifierOp()
+                        .portIdentifier());
+              }
+              return;
+            }
+          }
+
+          self->StartOnMainThread(owner);
+        });
+
+    MOZ_ALWAYS_SUCCEEDS(SchedulerGroup::Dispatch(r.forget()));
+
+#ifdef DEBUG
+    mStarted = true;
+#endif
+
+    return true;
+  }
+
+  void StartOnMainThread(RefPtr<RemoteWorkerChild>& aOwner) final {
+    using Running = RemoteWorkerChild::Running;
+
+    AssertIsOnMainThread();
+
+    if (IsTerminationOp()) {
+      aOwner->CloseWorkerOnMainThread();
+      return;
+    }
+
+    auto lock = aOwner->mState.Lock();
+    MOZ_ASSERT(lock->is<Running>());
+    if (!lock->is<Running>()) {
+      aOwner->ErrorPropagationDispatch(NS_ERROR_DOM_INVALID_STATE_ERR);
+      return;
+    }
+
+    RefPtr<WorkerPrivate> workerPrivate = lock->as<Running>().mWorkerPrivate;
+
+    MOZ_ASSERT(workerPrivate);
+
+    if (mOp.type() == RemoteWorkerOp::TRemoteWorkerSuspendOp) {
+      workerPrivate->ParentWindowPaused();
+    } else if (mOp.type() == RemoteWorkerOp::TRemoteWorkerResumeOp) {
+      workerPrivate->ParentWindowResumed();
+    } else if (mOp.type() == RemoteWorkerOp::TRemoteWorkerFreezeOp) {
+      workerPrivate->Freeze(nullptr);
+    } else if (mOp.type() == RemoteWorkerOp::TRemoteWorkerThawOp) {
+      workerPrivate->Thaw(nullptr);
+    } else if (mOp.type() == RemoteWorkerOp::TRemoteWorkerPortIdentifierOp) {
+      RefPtr<MessagePortIdentifierRunnable> r =
+          new MessagePortIdentifierRunnable(
+              workerPrivate, aOwner,
+              mOp.get_RemoteWorkerPortIdentifierOp().portIdentifier());
+      if (NS_WARN_IF(!r->Dispatch())) {
+        aOwner->ErrorPropagationDispatch(NS_ERROR_FAILURE);
+      }
+    } else if (mOp.type() == RemoteWorkerOp::TRemoteWorkerAddWindowIDOp) {
+      aOwner->mWindowIDs.AppendElement(
+          mOp.get_RemoteWorkerAddWindowIDOp().windowID());
+    } else if (mOp.type() == RemoteWorkerOp::TRemoteWorkerRemoveWindowIDOp) {
+      aOwner->mWindowIDs.RemoveElement(
+          mOp.get_RemoteWorkerRemoveWindowIDOp().windowID());
+    } else {
+      MOZ_CRASH("Unknown RemoteWorkerOp type!");
+    }
+  }
+
+  void Cancel() override {
+#ifdef DEBUG
+    mStarted = true;
+#endif
+  }
+
+ private:
+  ~SharedWorkerOp() { MOZ_ASSERT(mStarted); }
+
+  bool IsTerminationOp() const {
+    return mOp.type() == RemoteWorkerOp::TRemoteWorkerTerminateOp;
+  }
+
+  RemoteWorkerOp mOp;
+
+#ifdef DEBUG
+  bool mStarted = false;
+#endif
+};
+
+void RemoteWorkerChild::AddPortIdentifier(
+    JSContext* aCx, WorkerPrivate* aWorkerPrivate,
+    UniqueMessagePortId& aPortIdentifier) {
+  if (NS_WARN_IF(!aWorkerPrivate->ConnectMessagePort(aCx, aPortIdentifier))) {
+    ErrorPropagationDispatch(NS_ERROR_FAILURE);
+  }
+}
+
+void RemoteWorkerChild::CancelAllPendingOps(State& aState) {
+  MOZ_ASSERT(aState.is<Pending>());
+
+  auto pendingOps = std::move(aState.as<Pending>().mPendingOps);
+
+  for (auto& op : pendingOps) {
+    op->Cancel();
+  }
+}
+
+void RemoteWorkerChild::MaybeStartOp(RefPtr<Op>&& aOp) {
+  MOZ_ASSERT(aOp);
+
+  auto lock = mState.Lock();
+
+  if (!aOp->MaybeStart(this, lock.ref())) {
+    // Maybestart returns false only if we are <Pending>.
+    lock->as<Pending>().mPendingOps.AppendElement(std::move(aOp));
+  }
+}
+
+IPCResult RemoteWorkerChild::RecvExecOp(RemoteWorkerOp&& aOp) {
+  MOZ_ASSERT(!mIsServiceWorker);
+
+  MaybeStartOp(new SharedWorkerOp(std::move(aOp)));
+
+  return IPC_OK();
+}
+
+IPCResult RemoteWorkerChild::RecvExecServiceWorkerOp(
+    ServiceWorkerOpArgs&& aArgs, ExecServiceWorkerOpResolver&& aResolve) {
+  MOZ_ASSERT(mIsServiceWorker);
+  MOZ_ASSERT(
+      aArgs.type() !=
+          ServiceWorkerOpArgs::TParentToChildServiceWorkerFetchEventOpArgs,
+      "FetchEvent operations should be sent via PFetchEventOp(Proxy) actors!");
+
+  MaybeReportServiceWorkerShutdownProgress(aArgs);
+
+  MaybeStartOp(ServiceWorkerOp::Create(std::move(aArgs), std::move(aResolve)));
+
+  return IPC_OK();
+}
+
+RefPtr<GenericPromise>
+RemoteWorkerChild::MaybeSendSetServiceWorkerSkipWaitingFlag() {
+  RefPtr<GenericPromise::Private> promise =
+      new GenericPromise::Private(__func__);
+
+  RefPtr<RemoteWorkerChild> self = this;
+
+  nsCOMPtr<nsIRunnable> r = NS_NewRunnableFunction(__func__, [self = std::move(
+                                                                  self),
+                                                              promise] {
+    if (!self->CanSend()) {
+      promise->Reject(NS_ERROR_DOM_ABORT_ERR, __func__);
+      return;
+    }
+
+    self->SendSetServiceWorkerSkipWaitingFlag()->Then(
+        GetCurrentSerialEventTarget(), __func__,
+        [promise](
+            const SetServiceWorkerSkipWaitingFlagPromise::ResolveOrRejectValue&
+                aResult) {
+          if (NS_WARN_IF(aResult.IsReject())) {
+            promise->Reject(NS_ERROR_DOM_ABORT_ERR, __func__);
+            return;
+          }
+
+          promise->Resolve(aResult.ResolveValue(), __func__);
+        });
+  });
+
+  GetActorEventTarget()->Dispatch(r.forget(), NS_DISPATCH_NORMAL);
+
+  return promise;
+}
+
+/**
+ * PFetchEventOpProxy methods
+ */
+already_AddRefed<PFetchEventOpProxyChild>
+RemoteWorkerChild::AllocPFetchEventOpProxyChild(
+    const ParentToChildServiceWorkerFetchEventOpArgs& aArgs) {
+  return RefPtr{new FetchEventOpProxyChild()}.forget();
+}
+
+IPCResult RemoteWorkerChild::RecvPFetchEventOpProxyConstructor(
+    PFetchEventOpProxyChild* aActor,
+    const ParentToChildServiceWorkerFetchEventOpArgs& aArgs) {
+  MOZ_ASSERT(aActor);
+
+  (static_cast<FetchEventOpProxyChild*>(aActor))->Initialize(aArgs);
+
+  return IPC_OK();
+}
+
+}  // namespace dom
+}  // namespace mozilla
diff --git a/dom/workers/remoteworkers/RemoteWorkerChild.h b/dom/workers/remoteworkers/RemoteWorkerChild.h
new file mode 100644
index 0000000000..cdb2fb32d7
--- /dev/null
+++ b/dom/workers/remoteworkers/RemoteWorkerChild.h
@@ -0,0 +1,239 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_RemoteWorkerChild_h
+#define mozilla_dom_RemoteWorkerChild_h
+
+#include "nsCOMPtr.h"
+#include "nsISupportsImpl.h"
+#include "nsTArray.h"
+
+#include "mozilla/DataMutex.h"
+#include "mozilla/MozPromise.h"
+#include "mozilla/RefPtr.h"
+#include "mozilla/ThreadBound.h"
+#include "mozilla/dom/PRemoteWorkerChild.h"
+#include "mozilla/dom/ServiceWorkerOpArgs.h"
+
+class nsISerialEventTarget;
+class nsIConsoleReportCollector;
+
+namespace mozilla::dom {
+
+class ErrorValue;
+class FetchEventOpProxyChild;
+class RemoteWorkerData;
+class RemoteWorkerServiceKeepAlive;
+class ServiceWorkerOp;
+class UniqueMessagePortId;
+class WeakWorkerRef;
+class WorkerErrorReport;
+class WorkerPrivate;
+
+/**
+ * Background-managed "Worker Launcher"-thread-resident created via the
+ * RemoteWorkerManager to actually spawn the worker. Currently, the worker will
+ * be spawned from the main thread due to nsIPrincipal not being able to be
+ * created on background threads and other ownership invariants, most of which
+ * can be relaxed in the future.
+ */
+class RemoteWorkerChild final : public PRemoteWorkerChild {
+  friend class FetchEventOpProxyChild;
+  friend class PRemoteWorkerChild;
+  friend class ServiceWorkerOp;
+
+  ~RemoteWorkerChild();
+
+ public:
+  // Note that all IPC-using methods must only be invoked on the
+  // RemoteWorkerService thread which the inherited
+  // IProtocol::GetActorEventTarget() will return for us.
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(RemoteWorkerChild, final)
+
+  explicit RemoteWorkerChild(const RemoteWorkerData& aData);
+
+  void ExecWorker(const RemoteWorkerData& aData);
+
+  void ErrorPropagationOnMainThread(const WorkerErrorReport* aReport,
+                                    bool aIsErrorEvent);
+
+  void CSPViolationPropagationOnMainThread(const nsAString& aJSON);
+
+  void NotifyLock(bool aCreated);
+
+  void NotifyWebTransport(bool aCreated);
+
+  void FlushReportsOnMainThread(nsIConsoleReportCollector* aReporter);
+
+  void AddPortIdentifier(JSContext* aCx, WorkerPrivate* aWorkerPrivate,
+                         UniqueMessagePortId& aPortIdentifier);
+
+  RefPtr<GenericNonExclusivePromise> GetTerminationPromise();
+
+  RefPtr<GenericPromise> MaybeSendSetServiceWorkerSkipWaitingFlag();
+
+  const nsTArray<uint64_t>& WindowIDs() const { return mWindowIDs; }
+
+ private:
+  class InitializeWorkerRunnable;
+
+  class Op;
+  class SharedWorkerOp;
+
+  struct WorkerPrivateAccessibleState {
+    ~WorkerPrivateAccessibleState();
+    RefPtr<WorkerPrivate> mWorkerPrivate;
+  };
+
+  // Initial state, mWorkerPrivate is initially null but will be initialized on
+  // the main thread by ExecWorkerOnMainThread when the WorkerPrivate is
+  // created.  The state will transition to Running or Canceled, also from the
+  // main thread.
+  struct Pending : WorkerPrivateAccessibleState {
+    nsTArray<RefPtr<Op>> mPendingOps;
+  };
+
+  // Running, with the state transition happening on the main thread as a result
+  // of the worker successfully processing our initialization runnable,
+  // indicating that top-level script execution successfully completed.  Because
+  // all of our state transitions happen on the main thread and are posed in
+  // terms of the main thread's perspective of the worker's state, it's very
+  // possible for us to skip directly from Pending to Canceled because we decide
+  // to cancel/terminate the worker prior to it finishing script loading or
+  // reporting back to us.
+  struct Running : WorkerPrivateAccessibleState {};
+
+  // Cancel() has been called on the WorkerPrivate on the main thread by a
+  // TerminationOp, top-level script evaluation has failed and canceled the
+  // worker, or in the case of a SharedWorker, close() has been called on
+  // the global scope by content code and the worker has advanced to the
+  // Canceling state.  (Dedicated Workers can also self close, but they will
+  // never be RemoteWorkers.  Although a SharedWorker can own DedicatedWorkers.)
+  // Browser shutdown will result in a TerminationOp thanks to use of a shutdown
+  // blocker in the parent, so the RuntimeService shouldn't get involved, but we
+  // would also handle that case acceptably too.
+  //
+  // Because worker self-closing is still handled by dispatching a runnable to
+  // the main thread to effectively call WorkerPrivate::Cancel(), there isn't
+  // a race between a worker deciding to self-close and our termination ops.
+  //
+  // In this state, we have dropped the reference to the WorkerPrivate and will
+  // no longer be dispatching runnables to the worker.  We wait in this state
+  // until the termination lambda is invoked letting us know that the worker has
+  // entirely shutdown and we can advanced to the Killed state.
+  struct Canceled {};
+
+  // The worker termination lambda has been invoked and we know the Worker is
+  // entirely shutdown.  (Inherently it is possible for us to advance to this
+  // state while the nsThread for the worker is still in the process of
+  // shutting down, but no more worker code will run on it.)
+  //
+  // This name is chosen to match the Worker's own state model.
+  struct Killed {};
+
+  using State = Variant<Pending, Running, Canceled, Killed>;
+
+  // The state of the WorkerPrivate as perceived by the owner on the main
+  // thread.  All state transitions now happen on the main thread, but the
+  // Worker Launcher thread will consult the state and will directly append ops
+  // to the Pending queue
+  DataMutex<State> mState;
+
+  const RefPtr<RemoteWorkerServiceKeepAlive> mServiceKeepAlive;
+
+  class Op {
+   public:
+    NS_INLINE_DECL_PURE_VIRTUAL_REFCOUNTING
+
+    virtual ~Op() = default;
+
+    virtual bool MaybeStart(RemoteWorkerChild* aOwner, State& aState) = 0;
+
+    virtual void StartOnMainThread(RefPtr<RemoteWorkerChild>& aOwner) = 0;
+
+    virtual void Cancel() = 0;
+  };
+
+  void ActorDestroy(ActorDestroyReason) override;
+
+  mozilla::ipc::IPCResult RecvExecOp(RemoteWorkerOp&& aOp);
+
+  mozilla::ipc::IPCResult RecvExecServiceWorkerOp(
+      ServiceWorkerOpArgs&& aArgs, ExecServiceWorkerOpResolver&& aResolve);
+
+  already_AddRefed<PFetchEventOpProxyChild> AllocPFetchEventOpProxyChild(
+      const ParentToChildServiceWorkerFetchEventOpArgs& aArgs);
+
+  mozilla::ipc::IPCResult RecvPFetchEventOpProxyConstructor(
+      PFetchEventOpProxyChild* aActor,
+      const ParentToChildServiceWorkerFetchEventOpArgs& aArgs) override;
+
+  nsresult ExecWorkerOnMainThread(RemoteWorkerData&& aData);
+
+  void ExceptionalErrorTransitionDuringExecWorker();
+
+  void RequestWorkerCancellation();
+
+  void InitializeOnWorker();
+
+  void CreationSucceededOnAnyThread();
+
+  void CreationFailedOnAnyThread();
+
+  void CreationSucceededOrFailedOnAnyThread(bool aDidCreationSucceed);
+
+  // Cancels the worker if it has been started and ensures that we transition
+  // to the Terminated state once the worker has been terminated or we have
+  // ensured that it will never start.
+  void CloseWorkerOnMainThread();
+
+  void ErrorPropagation(const ErrorValue& aValue);
+
+  void ErrorPropagationDispatch(nsresult aError);
+
+  // When the WorkerPrivate Cancellation lambda is invoked, it's possible that
+  // we have not yet advanced to running from pending, so we could be in either
+  // state.  This method is expected to be called by the Workers' cancellation
+  // lambda and will obtain the lock and call the
+  // TransitionStateFromPendingToCanceled if appropriate.  Otherwise it will
+  // directly move from the running state to the canceled state which does not
+  // require additional cleanup.
+  void OnWorkerCancellationTransitionStateFromPendingOrRunningToCanceled();
+  // A helper used by the above method by the worker cancellation lambda if the
+  // the worker hasn't started running, or in exceptional cases where we bail
+  // out of the ExecWorker method early.  The caller must be holding the lock
+  // (in order to pass in the state).
+  void TransitionStateFromPendingToCanceled(State& aState);
+  void TransitionStateFromCanceledToKilled();
+
+  void TransitionStateToRunning();
+
+  void TransitionStateToTerminated();
+
+  void TransitionStateToTerminated(State& aState);
+
+  void CancelAllPendingOps(State& aState);
+
+  void MaybeStartOp(RefPtr<Op>&& aOp);
+
+  const bool mIsServiceWorker;
+
+  // Touched on main-thread only.
+  nsTArray<uint64_t> mWindowIDs;
+
+  struct LauncherBoundData {
+    MozPromiseHolder<GenericNonExclusivePromise> mTerminationPromise;
+    // Flag to ensure we report creation at most once.  This could be cleaned up
+    // further.
+    bool mDidSendCreated = false;
+  };
+
+  ThreadBound<LauncherBoundData> mLauncherData;
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_RemoteWorkerChild_h
diff --git a/dom/workers/remoteworkers/RemoteWorkerController.cpp b/dom/workers/remoteworkers/RemoteWorkerController.cpp
new file mode 100644
index 0000000000..b0d56aa33d
--- /dev/null
+++ b/dom/workers/remoteworkers/RemoteWorkerController.cpp
@@ -0,0 +1,573 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "RemoteWorkerController.h"
+
+#include <utility>
+
+#include "nsDebug.h"
+
+#include "mozilla/Assertions.h"
+#include "mozilla/DebugOnly.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/RemoteLazyInputStreamStorage.h"
+#include "mozilla/dom/FetchEventOpParent.h"
+#include "mozilla/dom/FetchEventOpProxyParent.h"
+#include "mozilla/dom/MessagePortParent.h"
+#include "mozilla/dom/RemoteWorkerTypes.h"
+#include "mozilla/dom/ServiceWorkerCloneData.h"
+#include "mozilla/dom/ServiceWorkerShutdownState.h"
+#include "mozilla/ipc/BackgroundParent.h"
+#include "RemoteWorkerControllerParent.h"
+#include "RemoteWorkerManager.h"
+#include "RemoteWorkerParent.h"
+
+namespace mozilla {
+
+using namespace ipc;
+
+namespace dom {
+
+/* static */
+already_AddRefed<RemoteWorkerController> RemoteWorkerController::Create(
+    const RemoteWorkerData& aData, RemoteWorkerObserver* aObserver,
+    base::ProcessId aProcessId) {
+  AssertIsInMainProcess();
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(aObserver);
+
+  RefPtr<RemoteWorkerController> controller =
+      new RemoteWorkerController(aData, aObserver);
+
+  RefPtr<RemoteWorkerManager> manager = RemoteWorkerManager::GetOrCreate();
+  MOZ_ASSERT(manager);
+
+  // XXX: We do not check for failure here, should we?
+  manager->Launch(controller, aData, aProcessId);
+
+  return controller.forget();
+}
+
+RemoteWorkerController::RemoteWorkerController(const RemoteWorkerData& aData,
+                                               RemoteWorkerObserver* aObserver)
+    : mObserver(aObserver),
+      mState(ePending),
+      mIsServiceWorker(aData.serviceWorkerData().type() ==
+                       OptionalServiceWorkerData::TServiceWorkerData) {
+  AssertIsInMainProcess();
+  AssertIsOnBackgroundThread();
+}
+
+RemoteWorkerController::~RemoteWorkerController() {
+  AssertIsOnBackgroundThread();
+  MOZ_DIAGNOSTIC_ASSERT(mPendingOps.IsEmpty());
+}
+
+void RemoteWorkerController::SetWorkerActor(RemoteWorkerParent* aActor) {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(!mActor);
+  MOZ_ASSERT(aActor);
+
+  mActor = aActor;
+}
+
+void RemoteWorkerController::NoteDeadWorkerActor() {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(mActor);
+
+  // The actor has been destroyed without a proper close() notification. Let's
+  // inform the observer.
+  if (mState == eReady) {
+    mObserver->Terminated();
+  }
+
+  mActor = nullptr;
+
+  Shutdown();
+}
+
+void RemoteWorkerController::CreationFailed() {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(XRE_IsParentProcess());
+  MOZ_ASSERT(mState == ePending || mState == eTerminated);
+
+  if (mState == eTerminated) {
+    MOZ_ASSERT(!mActor);
+    MOZ_ASSERT(mPendingOps.IsEmpty());
+    // Nothing to do.
+    return;
+  }
+
+  NoteDeadWorker();
+
+  mObserver->CreationFailed();
+}
+
+void RemoteWorkerController::CreationSucceeded() {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(mState == ePending || mState == eTerminated);
+
+  if (mState == eTerminated) {
+    MOZ_ASSERT(!mActor);
+    MOZ_ASSERT(mPendingOps.IsEmpty());
+    // Nothing to do.
+    return;
+  }
+
+  MOZ_ASSERT(mActor);
+  mState = eReady;
+
+  mObserver->CreationSucceeded();
+
+  auto pendingOps = std::move(mPendingOps);
+
+  for (auto& op : pendingOps) {
+    DebugOnly<bool> started = op->MaybeStart(this);
+    MOZ_ASSERT(started);
+  }
+}
+
+void RemoteWorkerController::ErrorPropagation(const ErrorValue& aValue) {
+  AssertIsOnBackgroundThread();
+
+  mObserver->ErrorReceived(aValue);
+}
+
+void RemoteWorkerController::NotifyLock(bool aCreated) {
+  AssertIsOnBackgroundThread();
+
+  mObserver->LockNotified(aCreated);
+}
+
+void RemoteWorkerController::NotifyWebTransport(bool aCreated) {
+  AssertIsOnBackgroundThread();
+
+  mObserver->WebTransportNotified(aCreated);
+}
+
+void RemoteWorkerController::WorkerTerminated() {
+  AssertIsOnBackgroundThread();
+
+  NoteDeadWorker();
+
+  mObserver->Terminated();
+}
+
+void RemoteWorkerController::CancelAllPendingOps() {
+  AssertIsOnBackgroundThread();
+
+  auto pendingOps = std::move(mPendingOps);
+
+  for (auto& op : pendingOps) {
+    op->Cancel();
+  }
+}
+
+void RemoteWorkerController::Shutdown() {
+  AssertIsOnBackgroundThread();
+  Unused << NS_WARN_IF(mIsServiceWorker && !mPendingOps.IsEmpty());
+
+  if (mState == eTerminated) {
+    MOZ_ASSERT(mPendingOps.IsEmpty());
+    return;
+  }
+
+  mState = eTerminated;
+
+  CancelAllPendingOps();
+
+  if (!mActor) {
+    return;
+  }
+
+  mActor->SetController(nullptr);
+
+  /**
+   * The "non-remote-side" of the Service Worker will have ensured that the
+   * remote worker is terminated before calling `Shutdown().`
+   */
+  if (mIsServiceWorker) {
+    mActor->MaybeSendDelete();
+  } else {
+    Unused << mActor->SendExecOp(RemoteWorkerTerminateOp());
+  }
+
+  mActor = nullptr;
+}
+
+void RemoteWorkerController::NoteDeadWorker() {
+  AssertIsOnBackgroundThread();
+
+  CancelAllPendingOps();
+
+  /**
+   * The "non-remote-side" of the Service Worker will initiate `Shutdown()`
+   * once it's notified that all dispatched operations have either completed
+   * or canceled. That is, it'll explicitly call `Shutdown()` later.
+   */
+  if (!mIsServiceWorker) {
+    Shutdown();
+  }
+}
+
+template <typename... Args>
+void RemoteWorkerController::MaybeStartSharedWorkerOp(Args&&... aArgs) {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(!mIsServiceWorker);
+
+  UniquePtr<PendingSharedWorkerOp> op =
+      MakeUnique<PendingSharedWorkerOp>(std::forward<Args>(aArgs)...);
+
+  if (!op->MaybeStart(this)) {
+    mPendingOps.AppendElement(std::move(op));
+  }
+}
+
+void RemoteWorkerController::AddWindowID(uint64_t aWindowID) {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(aWindowID);
+
+  MaybeStartSharedWorkerOp(PendingSharedWorkerOp::eAddWindowID, aWindowID);
+}
+
+void RemoteWorkerController::RemoveWindowID(uint64_t aWindowID) {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(aWindowID);
+
+  MaybeStartSharedWorkerOp(PendingSharedWorkerOp::eRemoveWindowID, aWindowID);
+}
+
+void RemoteWorkerController::AddPortIdentifier(
+    const MessagePortIdentifier& aPortIdentifier) {
+  AssertIsOnBackgroundThread();
+
+  MaybeStartSharedWorkerOp(aPortIdentifier);
+}
+
+void RemoteWorkerController::Terminate() {
+  AssertIsOnBackgroundThread();
+
+  MaybeStartSharedWorkerOp(PendingSharedWorkerOp::eTerminate);
+}
+
+void RemoteWorkerController::Suspend() {
+  AssertIsOnBackgroundThread();
+
+  MaybeStartSharedWorkerOp(PendingSharedWorkerOp::eSuspend);
+}
+
+void RemoteWorkerController::Resume() {
+  AssertIsOnBackgroundThread();
+
+  MaybeStartSharedWorkerOp(PendingSharedWorkerOp::eResume);
+}
+
+void RemoteWorkerController::Freeze() {
+  AssertIsOnBackgroundThread();
+
+  MaybeStartSharedWorkerOp(PendingSharedWorkerOp::eFreeze);
+}
+
+void RemoteWorkerController::Thaw() {
+  AssertIsOnBackgroundThread();
+
+  MaybeStartSharedWorkerOp(PendingSharedWorkerOp::eThaw);
+}
+
+RefPtr<ServiceWorkerOpPromise> RemoteWorkerController::ExecServiceWorkerOp(
+    ServiceWorkerOpArgs&& aArgs) {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(mIsServiceWorker);
+
+  RefPtr<ServiceWorkerOpPromise::Private> promise =
+      new ServiceWorkerOpPromise::Private(__func__);
+
+  UniquePtr<PendingServiceWorkerOp> op =
+      MakeUnique<PendingServiceWorkerOp>(std::move(aArgs), promise);
+
+  if (!op->MaybeStart(this)) {
+    mPendingOps.AppendElement(std::move(op));
+  }
+
+  return promise;
+}
+
+RefPtr<ServiceWorkerFetchEventOpPromise>
+RemoteWorkerController::ExecServiceWorkerFetchEventOp(
+    const ParentToParentServiceWorkerFetchEventOpArgs& aArgs,
+    RefPtr<FetchEventOpParent> aReal) {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(mIsServiceWorker);
+
+  RefPtr<ServiceWorkerFetchEventOpPromise::Private> promise =
+      new ServiceWorkerFetchEventOpPromise::Private(__func__);
+
+  UniquePtr<PendingSWFetchEventOp> op =
+      MakeUnique<PendingSWFetchEventOp>(aArgs, promise, std::move(aReal));
+
+  if (!op->MaybeStart(this)) {
+    mPendingOps.AppendElement(std::move(op));
+  }
+
+  return promise;
+}
+
+RefPtr<GenericPromise> RemoteWorkerController::SetServiceWorkerSkipWaitingFlag()
+    const {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(mObserver);
+
+  RefPtr<GenericPromise::Private> promise =
+      new GenericPromise::Private(__func__);
+
+  static_cast<RemoteWorkerControllerParent*>(mObserver.get())
+      ->MaybeSendSetServiceWorkerSkipWaitingFlag(
+          [promise](bool aOk) { promise->Resolve(aOk, __func__); });
+
+  return promise;
+}
+
+bool RemoteWorkerController::IsTerminated() const {
+  return mState == eTerminated;
+}
+
+RemoteWorkerController::PendingSharedWorkerOp::PendingSharedWorkerOp(
+    Type aType, uint64_t aWindowID)
+    : mType(aType), mWindowID(aWindowID) {
+  AssertIsOnBackgroundThread();
+}
+
+RemoteWorkerController::PendingSharedWorkerOp::PendingSharedWorkerOp(
+    const MessagePortIdentifier& aPortIdentifier)
+    : mType(ePortIdentifier), mPortIdentifier(aPortIdentifier) {
+  AssertIsOnBackgroundThread();
+}
+
+RemoteWorkerController::PendingSharedWorkerOp::~PendingSharedWorkerOp() {
+  AssertIsOnBackgroundThread();
+  MOZ_DIAGNOSTIC_ASSERT(mCompleted);
+}
+
+bool RemoteWorkerController::PendingSharedWorkerOp::MaybeStart(
+    RemoteWorkerController* const aOwner) {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(!mCompleted);
+  MOZ_ASSERT(aOwner);
+
+  if (aOwner->mState == RemoteWorkerController::eTerminated) {
+    Cancel();
+    return true;
+  }
+
+  if (aOwner->mState == RemoteWorkerController::ePending &&
+      mType != eTerminate) {
+    return false;
+  }
+
+  switch (mType) {
+    case eTerminate:
+      aOwner->Shutdown();
+      break;
+    case eSuspend:
+      Unused << aOwner->mActor->SendExecOp(RemoteWorkerSuspendOp());
+      break;
+    case eResume:
+      Unused << aOwner->mActor->SendExecOp(RemoteWorkerResumeOp());
+      break;
+    case eFreeze:
+      Unused << aOwner->mActor->SendExecOp(RemoteWorkerFreezeOp());
+      break;
+    case eThaw:
+      Unused << aOwner->mActor->SendExecOp(RemoteWorkerThawOp());
+      break;
+    case ePortIdentifier:
+      Unused << aOwner->mActor->SendExecOp(
+          RemoteWorkerPortIdentifierOp(mPortIdentifier));
+      break;
+    case eAddWindowID:
+      Unused << aOwner->mActor->SendExecOp(
+          RemoteWorkerAddWindowIDOp(mWindowID));
+      break;
+    case eRemoveWindowID:
+      Unused << aOwner->mActor->SendExecOp(
+          RemoteWorkerRemoveWindowIDOp(mWindowID));
+      break;
+    default:
+      MOZ_CRASH("Unknown op.");
+  }
+
+  mCompleted = true;
+
+  return true;
+}
+
+void RemoteWorkerController::PendingSharedWorkerOp::Cancel() {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(!mCompleted);
+
+  // We don't want to leak the port if the operation has not been processed.
+  if (mType == ePortIdentifier) {
+    MessagePortParent::ForceClose(mPortIdentifier.uuid(),
+                                  mPortIdentifier.destinationUuid(),
+                                  mPortIdentifier.sequenceId());
+  }
+
+  mCompleted = true;
+}
+
+RemoteWorkerController::PendingServiceWorkerOp::PendingServiceWorkerOp(
+    ServiceWorkerOpArgs&& aArgs,
+    RefPtr<ServiceWorkerOpPromise::Private> aPromise)
+    : mArgs(std::move(aArgs)), mPromise(std::move(aPromise)) {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(mPromise);
+}
+
+RemoteWorkerController::PendingServiceWorkerOp::~PendingServiceWorkerOp() {
+  AssertIsOnBackgroundThread();
+  MOZ_DIAGNOSTIC_ASSERT(!mPromise);
+}
+
+bool RemoteWorkerController::PendingServiceWorkerOp::MaybeStart(
+    RemoteWorkerController* const aOwner) {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(mPromise);
+  MOZ_ASSERT(aOwner);
+
+  if (NS_WARN_IF(aOwner->mState == RemoteWorkerController::eTerminated)) {
+    mPromise->Reject(NS_ERROR_DOM_ABORT_ERR, __func__);
+    mPromise = nullptr;
+    return true;
+  }
+
+  // The target content process must still be starting up.
+  if (!aOwner->mActor) {
+    // We can avoid starting the worker at all if we know it should be
+    // terminated.
+    MOZ_ASSERT(aOwner->mState == RemoteWorkerController::ePending);
+    if (mArgs.type() ==
+        ServiceWorkerOpArgs::TServiceWorkerTerminateWorkerOpArgs) {
+      aOwner->CancelAllPendingOps();
+      Cancel();
+
+      aOwner->mState = RemoteWorkerController::eTerminated;
+
+      return true;
+    }
+
+    return false;
+  }
+
+  /**
+   * Allow termination operations to pass through while pending because the
+   * remote Service Worker can be terminated while still starting up.
+   */
+  if (aOwner->mState == RemoteWorkerController::ePending &&
+      mArgs.type() !=
+          ServiceWorkerOpArgs::TServiceWorkerTerminateWorkerOpArgs) {
+    return false;
+  }
+
+  MaybeReportServiceWorkerShutdownProgress(mArgs);
+
+  aOwner->mActor->SendExecServiceWorkerOp(mArgs)->Then(
+      GetCurrentSerialEventTarget(), __func__,
+      [promise = std::move(mPromise)](
+          PRemoteWorkerParent::ExecServiceWorkerOpPromise::
+              ResolveOrRejectValue&& aResult) {
+        if (NS_WARN_IF(aResult.IsReject())) {
+          promise->Reject(NS_ERROR_DOM_ABORT_ERR, __func__);
+          return;
+        }
+
+        promise->Resolve(std::move(aResult.ResolveValue()), __func__);
+      });
+
+  return true;
+}
+
+void RemoteWorkerController::PendingServiceWorkerOp::Cancel() {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(mPromise);
+
+  mPromise->Reject(NS_ERROR_DOM_ABORT_ERR, __func__);
+  mPromise = nullptr;
+}
+
+RemoteWorkerController::PendingSWFetchEventOp::PendingSWFetchEventOp(
+    const ParentToParentServiceWorkerFetchEventOpArgs& aArgs,
+    RefPtr<ServiceWorkerFetchEventOpPromise::Private> aPromise,
+    RefPtr<FetchEventOpParent>&& aReal)
+    : mArgs(aArgs), mPromise(std::move(aPromise)), mReal(aReal) {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(mPromise);
+
+  // If there is a TParentToParentStream in the request body, we need to
+  // save it to our stream.
+  IPCInternalRequest& req = mArgs.common().internalRequest();
+  if (req.body().isSome() &&
+      req.body().ref().type() == BodyStreamVariant::TParentToParentStream) {
+    nsCOMPtr<nsIInputStream> stream;
+    auto streamLength = req.bodySize();
+    const auto& uuid = req.body().ref().get_ParentToParentStream().uuid();
+
+    auto storage = RemoteLazyInputStreamStorage::Get().unwrapOr(nullptr);
+    MOZ_DIAGNOSTIC_ASSERT(storage);
+    storage->GetStream(uuid, 0, streamLength, getter_AddRefs(mBodyStream));
+    storage->ForgetStream(uuid);
+
+    MOZ_DIAGNOSTIC_ASSERT(mBodyStream);
+
+    req.body() = Nothing();
+  }
+}
+
+RemoteWorkerController::PendingSWFetchEventOp::~PendingSWFetchEventOp() {
+  AssertIsOnBackgroundThread();
+  MOZ_DIAGNOSTIC_ASSERT(!mPromise);
+}
+
+bool RemoteWorkerController::PendingSWFetchEventOp::MaybeStart(
+    RemoteWorkerController* const aOwner) {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(mPromise);
+  MOZ_ASSERT(aOwner);
+
+  if (NS_WARN_IF(aOwner->mState == RemoteWorkerController::eTerminated)) {
+    mPromise->Reject(NS_ERROR_DOM_ABORT_ERR, __func__);
+    mPromise = nullptr;
+    // Because the worker has transitioned to terminated, this operation is moot
+    // and so we should return true because there's no need to queue it.
+    return true;
+  }
+
+  // The target content process must still be starting up.
+  if (!aOwner->mActor) {
+    MOZ_ASSERT(aOwner->mState == RemoteWorkerController::ePending);
+    return false;
+  }
+
+  // At this point we are handing off responsibility for the promise to the
+  // actor.
+  FetchEventOpProxyParent::Create(aOwner->mActor.get(), std::move(mPromise),
+                                  mArgs, std::move(mReal),
+                                  std::move(mBodyStream));
+
+  return true;
+}
+
+void RemoteWorkerController::PendingSWFetchEventOp::Cancel() {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(mPromise);
+
+  if (mPromise) {
+    mPromise->Reject(NS_ERROR_DOM_ABORT_ERR, __func__);
+    mPromise = nullptr;
+  }
+}
+
+}  // namespace dom
+}  // namespace mozilla
diff --git a/dom/workers/remoteworkers/RemoteWorkerController.h b/dom/workers/remoteworkers/RemoteWorkerController.h
new file mode 100644
index 0000000000..af53634abd
--- /dev/null
+++ b/dom/workers/remoteworkers/RemoteWorkerController.h
@@ -0,0 +1,323 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_RemoteWorkerController_h
+#define mozilla_dom_RemoteWorkerController_h
+
+#include "nsISupportsImpl.h"
+#include "nsTArray.h"
+
+#include "mozilla/RefPtr.h"
+#include "mozilla/UniquePtr.h"
+#include "mozilla/dom/DOMTypes.h"
+#include "mozilla/dom/ServiceWorkerOpArgs.h"
+#include "mozilla/dom/ServiceWorkerOpPromise.h"
+
+namespace mozilla::dom {
+
+/* Here's a graph about this remote workers are spawned.
+ *
+ *  _________________________________    |   ________________________________
+ * |                                 |   |  |                                |
+ * |              Parent process     |  IPC |          Creation of Process X |
+ * |              PBackground thread |   |  |                                |
+ * |                                 |   |  | [RemoteWorkerService::Init()]  |
+ * |                                 |   |  |               |                |
+ * |                                 |   |  |               | (1)            |
+ * | [RemoteWorkerManager::  (2)     |   |  |               V                |
+ * |                RegisterActor()]<-------- [new RemoteWorkerServiceChild] |
+ * |                                 |   |  |                                |
+ * |  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~   |   |  |________________________________|
+ * |                                 |   |
+ * |  new SharedWorker/ServiceWorker |   |
+ * |      |     ^                    |  IPC
+ * |  (3) |  (4)|                    |
+ * |      V     |                    |   |
+ * | [RemoteWorkerController::       |   |
+ * |         |         Create(data)] |   |
+ * |         | (5)                   |   |
+ * |         V                       |   |
+ * | [RemoteWorkerManager::Launch()] |   |
+ * |         |                       |  IPC   _____________________________
+ * |         | (6)                   |   |   |                             |
+ * |         |                       |       | Selected content process    |
+ * |         V                       |  (7)  |                             |
+ * | [SendPRemoteWorkerConstructor()]--------->[new RemoteWorkerChild()]   |
+ * |         |                       |   |   |             |               |
+ * |         | (8)                   |   |   |             |               |
+ * |         V                       |   |   |             V               |
+ * | [RemoteWorkerController->       |   |   | RemoteWorkerChild->Exec()   |
+ * |         | SetControllerActor()] |   |   |_____________________________|
+ * |     (9) |                       |  IPC
+ * |         V                       |   |
+ * | [RemoteWorkerObserver->         |   |
+ * |           CreationCompleted()]  |   |
+ * |_________________________________|   |
+ *                                       |
+ *
+ * 1. When a new process starts, it creates a RemoteWorkerService singleton.
+ *    This service creates a new thread (Worker Launcher) and from there, it
+ *    starts a PBackground RemoteWorkerServiceChild actor.
+ * 2. On the parent process, PBackground thread, RemoteWorkerServiceParent
+ *    actors are registered into the RemoteWorkerManager service.
+ *
+ * 3. At some point, a SharedWorker or a ServiceWorker must be executed.
+ *    RemoteWorkerController::Create() is used to start the launching. This
+ *    method must be called on the parent process, on the PBackground thread.
+ * 4. RemoteWorkerController object is immediately returned to the caller. Any
+ *    operation done with this controller object will be stored in a queue,
+ *    until the launching is correctly executed.
+ * 5. RemoteWorkerManager has the list of active RemoteWorkerServiceParent
+ *    actors. From them, it picks one.
+ *    In case we don't have any content process to select, a new one is
+ *    spawned. If this happens, the operation is suspended until a new
+ *    RemoteWorkerServiceParent is registered.
+ * 6. RemoteWorkerServiceParent is used to create a RemoteWorkerParent.
+ * 7. RemoteWorkerChild is created on a selected process and it executes the
+ *    WorkerPrivate.
+ * 8. The RemoteWorkerParent actor is passed to the RemoteWorkerController.
+ * 9. RemoteWorkerController now is ready to continue and it called
+ *    RemoteWorkerObserver to inform that the operation is completed.
+ *    In case there were pending operations, they are now executed.
+ */
+
+class ErrorValue;
+class FetchEventOpParent;
+class RemoteWorkerControllerParent;
+class RemoteWorkerData;
+class RemoteWorkerManager;
+class RemoteWorkerParent;
+
+class RemoteWorkerObserver {
+ public:
+  NS_INLINE_DECL_PURE_VIRTUAL_REFCOUNTING
+
+  virtual void CreationFailed() = 0;
+
+  virtual void CreationSucceeded() = 0;
+
+  virtual void ErrorReceived(const ErrorValue& aValue) = 0;
+
+  virtual void LockNotified(bool aCreated) = 0;
+
+  virtual void WebTransportNotified(bool aCreated) = 0;
+
+  virtual void Terminated() = 0;
+};
+
+/**
+ * PBackground instance created by static RemoteWorkerController::Create that
+ * builds on RemoteWorkerManager. Interface to control the remote worker as well
+ * as receive events via the RemoteWorkerObserver interface that the owner
+ * (SharedWorkerManager in this case) must implement to hear about errors,
+ * termination, and whether the initial spawning succeeded/failed.
+ *
+ * Its methods may be called immediately after creation even though the worker
+ * is created asynchronously; an internal operation queue makes this work.
+ * Communicates with the remote worker via owned RemoteWorkerParent over
+ * PRemoteWorker protocol.
+ */
+class RemoteWorkerController final {
+  friend class RemoteWorkerControllerParent;
+  friend class RemoteWorkerManager;
+  friend class RemoteWorkerParent;
+
+ public:
+  NS_INLINE_DECL_REFCOUNTING(RemoteWorkerController)
+
+  static already_AddRefed<RemoteWorkerController> Create(
+      const RemoteWorkerData& aData, RemoteWorkerObserver* aObserver,
+      base::ProcessId = 0);
+
+  void AddWindowID(uint64_t aWindowID);
+
+  void RemoveWindowID(uint64_t aWindowID);
+
+  void AddPortIdentifier(const MessagePortIdentifier& aPortIdentifier);
+
+  void Terminate();
+
+  void Suspend();
+
+  void Resume();
+
+  void Freeze();
+
+  void Thaw();
+
+  RefPtr<ServiceWorkerOpPromise> ExecServiceWorkerOp(
+      ServiceWorkerOpArgs&& aArgs);
+
+  RefPtr<ServiceWorkerFetchEventOpPromise> ExecServiceWorkerFetchEventOp(
+      const ParentToParentServiceWorkerFetchEventOpArgs& aArgs,
+      RefPtr<FetchEventOpParent> aReal);
+
+  RefPtr<GenericPromise> SetServiceWorkerSkipWaitingFlag() const;
+
+  bool IsTerminated() const;
+
+  void NotifyWebTransport(bool aCreated);
+
+ private:
+  RemoteWorkerController(const RemoteWorkerData& aData,
+                         RemoteWorkerObserver* aObserver);
+
+  ~RemoteWorkerController();
+
+  void SetWorkerActor(RemoteWorkerParent* aActor);
+
+  void NoteDeadWorkerActor();
+
+  void ErrorPropagation(const ErrorValue& aValue);
+
+  void NotifyLock(bool aCreated);
+
+  void WorkerTerminated();
+
+  void Shutdown();
+
+  void CreationFailed();
+
+  void CreationSucceeded();
+
+  void CancelAllPendingOps();
+
+  template <typename... Args>
+  void MaybeStartSharedWorkerOp(Args&&... aArgs);
+
+  void NoteDeadWorker();
+
+  RefPtr<RemoteWorkerObserver> mObserver;
+  RefPtr<RemoteWorkerParent> mActor;
+
+  enum {
+    ePending,
+    eReady,
+    eTerminated,
+  } mState;
+
+  const bool mIsServiceWorker;
+
+  /**
+   * `PendingOp` is responsible for encapsulating logic for starting and
+   * canceling pending remote worker operations, as this logic may vary
+   * depending on the type of the remote worker and the type of the operation.
+   */
+  class PendingOp {
+   public:
+    PendingOp() = default;
+
+    PendingOp(const PendingOp&) = delete;
+
+    PendingOp& operator=(const PendingOp&) = delete;
+
+    virtual ~PendingOp() = default;
+
+    /**
+     * Returns `true` if execution has started or the operation is moot and
+     * doesn't need to be queued, `false` if execution hasn't started and the
+     * operation should be queued.  In general, operations should only return
+     * false when a remote worker is first starting up.  Operations may also
+     * somewhat non-intuitively return true without doing anything if the worker
+     * has already been told to shutdown.
+     *
+     * Starting execution may depend the state of `aOwner.`
+     */
+    virtual bool MaybeStart(RemoteWorkerController* const aOwner) = 0;
+
+    /**
+     * Invoked if the operation will never have MaybeStart() called again
+     * because the RemoteWorkerController has terminated (or will never start).
+     * This should be used by PendingOps to clean up any resources they own and
+     * may also be called internally by their MaybeStart() methods if they
+     * determine the worker has been terminated.  This should be idempotent.
+     */
+    virtual void Cancel() = 0;
+  };
+
+  class PendingSharedWorkerOp final : public PendingOp {
+   public:
+    enum Type {
+      eTerminate,
+      eSuspend,
+      eResume,
+      eFreeze,
+      eThaw,
+      ePortIdentifier,
+      eAddWindowID,
+      eRemoveWindowID,
+    };
+
+    explicit PendingSharedWorkerOp(Type aType, uint64_t aWindowID = 0);
+
+    explicit PendingSharedWorkerOp(
+        const MessagePortIdentifier& aPortIdentifier);
+
+    ~PendingSharedWorkerOp();
+
+    bool MaybeStart(RemoteWorkerController* const aOwner) override;
+
+    void Cancel() override;
+
+   private:
+    const Type mType;
+    const MessagePortIdentifier mPortIdentifier;
+    const uint64_t mWindowID = 0;
+    bool mCompleted = false;
+  };
+
+  class PendingServiceWorkerOp final : public PendingOp {
+   public:
+    PendingServiceWorkerOp(ServiceWorkerOpArgs&& aArgs,
+                           RefPtr<ServiceWorkerOpPromise::Private> aPromise);
+
+    ~PendingServiceWorkerOp();
+
+    bool MaybeStart(RemoteWorkerController* const aOwner) override;
+
+    void Cancel() override;
+
+   private:
+    ServiceWorkerOpArgs mArgs;
+    RefPtr<ServiceWorkerOpPromise::Private> mPromise;
+  };
+
+  /**
+   * Custom pending op type to deal with the complexities of FetchEvents having
+   * their own actor.
+   *
+   * FetchEvent Ops have their own actor type because their lifecycle is more
+   * complex than IPDL's async return value mechanism allows.  Additionally,
+   * its IPC struct potentially has to serialize RemoteLazyStreams which
+   * requires us to hold an nsIInputStream when at rest and serialize it when
+   * eventually sending.
+   */
+  class PendingSWFetchEventOp final : public PendingOp {
+   public:
+    PendingSWFetchEventOp(
+        const ParentToParentServiceWorkerFetchEventOpArgs& aArgs,
+        RefPtr<ServiceWorkerFetchEventOpPromise::Private> aPromise,
+        RefPtr<FetchEventOpParent>&& aReal);
+
+    ~PendingSWFetchEventOp();
+
+    bool MaybeStart(RemoteWorkerController* const aOwner) override;
+
+    void Cancel() override;
+
+   private:
+    ParentToParentServiceWorkerFetchEventOpArgs mArgs;
+    RefPtr<ServiceWorkerFetchEventOpPromise::Private> mPromise;
+    RefPtr<FetchEventOpParent> mReal;
+    nsCOMPtr<nsIInputStream> mBodyStream;
+  };
+
+  nsTArray<UniquePtr<PendingOp>> mPendingOps;
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_RemoteWorkerController_h
diff --git a/dom/workers/remoteworkers/RemoteWorkerControllerChild.cpp b/dom/workers/remoteworkers/RemoteWorkerControllerChild.cpp
new file mode 100644
index 0000000000..5a1db77cf0
--- /dev/null
+++ b/dom/workers/remoteworkers/RemoteWorkerControllerChild.cpp
@@ -0,0 +1,162 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "RemoteWorkerControllerChild.h"
+
+#include <utility>
+
+#include "MainThreadUtils.h"
+#include "nsError.h"
+#include "nsThreadUtils.h"
+
+#include "ServiceWorkerPrivate.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/RefPtr.h"
+#include "mozilla/Unused.h"
+#include "mozilla/dom/PFetchEventOpChild.h"
+
+namespace mozilla {
+
+using ipc::IPCResult;
+
+namespace dom {
+
+RemoteWorkerControllerChild::RemoteWorkerControllerChild(
+    RefPtr<RemoteWorkerObserver> aObserver)
+    : mObserver(std::move(aObserver)) {
+  AssertIsOnMainThread();
+  mRemoteWorkerLaunchStart = TimeStamp::Now();
+  MOZ_ASSERT(mObserver);
+}
+
+PFetchEventOpChild* RemoteWorkerControllerChild::AllocPFetchEventOpChild(
+    const ParentToParentServiceWorkerFetchEventOpArgs& aArgs) {
+  MOZ_CRASH("PFetchEventOpChild actors must be manually constructed!");
+  return nullptr;
+}
+
+TimeStamp RemoteWorkerControllerChild::GetRemoteWorkerLaunchStart() {
+  MOZ_ASSERT(mRemoteWorkerLaunchStart);
+  return mRemoteWorkerLaunchStart;
+}
+
+TimeStamp RemoteWorkerControllerChild::GetRemoteWorkerLaunchEnd() {
+  MOZ_ASSERT(mRemoteWorkerLaunchEnd);
+  return mRemoteWorkerLaunchEnd;
+}
+
+bool RemoteWorkerControllerChild::DeallocPFetchEventOpChild(
+    PFetchEventOpChild* aActor) {
+  AssertIsOnMainThread();
+  MOZ_ASSERT(aActor);
+
+  delete aActor;
+  return true;
+}
+
+void RemoteWorkerControllerChild::ActorDestroy(ActorDestroyReason aReason) {
+  AssertIsOnMainThread();
+
+  mIPCActive = false;
+
+  if (NS_WARN_IF(mObserver)) {
+    mObserver->ErrorReceived(NS_ERROR_DOM_ABORT_ERR);
+  }
+}
+
+IPCResult RemoteWorkerControllerChild::RecvCreationFailed() {
+  AssertIsOnMainThread();
+
+  if (mObserver) {
+    mObserver->CreationFailed();
+  }
+
+  return IPC_OK();
+}
+
+IPCResult RemoteWorkerControllerChild::RecvCreationSucceeded() {
+  AssertIsOnMainThread();
+  mRemoteWorkerLaunchEnd = TimeStamp::Now();
+
+  if (mObserver) {
+    mObserver->CreationSucceeded();
+  }
+
+  return IPC_OK();
+}
+
+IPCResult RemoteWorkerControllerChild::RecvErrorReceived(
+    const ErrorValue& aError) {
+  AssertIsOnMainThread();
+  mRemoteWorkerLaunchEnd = TimeStamp::Now();
+
+  if (mObserver) {
+    mObserver->ErrorReceived(aError);
+  }
+
+  return IPC_OK();
+}
+
+IPCResult RemoteWorkerControllerChild::RecvTerminated() {
+  AssertIsOnMainThread();
+
+  if (mObserver) {
+    mObserver->Terminated();
+  }
+
+  return IPC_OK();
+}
+
+IPCResult RemoteWorkerControllerChild::RecvSetServiceWorkerSkipWaitingFlag(
+    SetServiceWorkerSkipWaitingFlagResolver&& aResolve) {
+  AssertIsOnMainThread();
+
+  if (mObserver) {
+    static_cast<ServiceWorkerPrivate*>(mObserver.get())
+        ->SetSkipWaitingFlag()
+        ->Then(GetCurrentSerialEventTarget(), __func__,
+               [resolve = std::move(aResolve)](
+                   const GenericPromise::ResolveOrRejectValue& aResult) {
+                 resolve(aResult.IsResolve() ? aResult.ResolveValue() : false);
+               });
+
+    return IPC_OK();
+  }
+
+  aResolve(false);
+
+  return IPC_OK();
+}
+
+void RemoteWorkerControllerChild::RevokeObserver(
+    RemoteWorkerObserver* aObserver) {
+  AssertIsOnMainThread();
+  MOZ_ASSERT(aObserver);
+  MOZ_ASSERT(aObserver == mObserver);
+
+  mObserver = nullptr;
+}
+
+void RemoteWorkerControllerChild::MaybeSendDelete() {
+  AssertIsOnMainThread();
+
+  if (!mIPCActive) {
+    return;
+  }
+
+  RefPtr<RemoteWorkerControllerChild> self = this;
+
+  SendShutdown()->Then(
+      GetCurrentSerialEventTarget(), __func__,
+      [self = std::move(self)](const ShutdownPromise::ResolveOrRejectValue&) {
+        if (self->mIPCActive) {
+          Unused << self->Send__delete__(self);
+        }
+      });
+}
+
+}  // namespace dom
+}  // namespace mozilla
diff --git a/dom/workers/remoteworkers/RemoteWorkerControllerChild.h b/dom/workers/remoteworkers/RemoteWorkerControllerChild.h
new file mode 100644
index 0000000000..283fff3916
--- /dev/null
+++ b/dom/workers/remoteworkers/RemoteWorkerControllerChild.h
@@ -0,0 +1,70 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_remoteworkercontrollerchild_h__
+#define mozilla_dom_remoteworkercontrollerchild_h__
+
+#include "nsISupportsImpl.h"
+
+#include "RemoteWorkerController.h"
+#include "mozilla/RefPtr.h"
+#include "mozilla/dom/PRemoteWorkerControllerChild.h"
+
+namespace mozilla::dom {
+
+/**
+ * Parent-process main-thread proxy used by ServiceWorkerManager to control
+ * RemoteWorkerController instances on the parent-process PBackground thread.
+ */
+class RemoteWorkerControllerChild final : public PRemoteWorkerControllerChild {
+  friend class PRemoteWorkerControllerChild;
+
+ public:
+  NS_INLINE_DECL_REFCOUNTING(RemoteWorkerControllerChild, override)
+
+  explicit RemoteWorkerControllerChild(RefPtr<RemoteWorkerObserver> aObserver);
+
+  void Initialize();
+
+  void RevokeObserver(RemoteWorkerObserver* aObserver);
+
+  void MaybeSendDelete();
+
+  TimeStamp GetRemoteWorkerLaunchStart();
+  TimeStamp GetRemoteWorkerLaunchEnd();
+
+ private:
+  ~RemoteWorkerControllerChild() = default;
+
+  PFetchEventOpChild* AllocPFetchEventOpChild(
+      const ParentToParentServiceWorkerFetchEventOpArgs& aArgs);
+
+  bool DeallocPFetchEventOpChild(PFetchEventOpChild* aActor);
+
+  void ActorDestroy(ActorDestroyReason aReason) override;
+
+  mozilla::ipc::IPCResult RecvCreationFailed();
+
+  mozilla::ipc::IPCResult RecvCreationSucceeded();
+
+  mozilla::ipc::IPCResult RecvErrorReceived(const ErrorValue& aError);
+
+  mozilla::ipc::IPCResult RecvTerminated();
+
+  mozilla::ipc::IPCResult RecvSetServiceWorkerSkipWaitingFlag(
+      SetServiceWorkerSkipWaitingFlagResolver&& aResolve);
+
+  RefPtr<RemoteWorkerObserver> mObserver;
+
+  bool mIPCActive = true;
+
+  TimeStamp mRemoteWorkerLaunchStart;
+  TimeStamp mRemoteWorkerLaunchEnd;
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_remoteworkercontrollerchild_h__
diff --git a/dom/workers/remoteworkers/RemoteWorkerControllerParent.cpp b/dom/workers/remoteworkers/RemoteWorkerControllerParent.cpp
new file mode 100644
index 0000000000..7ac901f655
--- /dev/null
+++ b/dom/workers/remoteworkers/RemoteWorkerControllerParent.cpp
@@ -0,0 +1,215 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "RemoteWorkerControllerParent.h"
+
+#include <utility>
+
+#include "nsCOMPtr.h"
+#include "nsDebug.h"
+#include "nsError.h"
+#include "nsThreadUtils.h"
+
+#include "mozilla/Assertions.h"
+#include "mozilla/Unused.h"
+#include "mozilla/dom/FetchEventOpParent.h"
+#include "mozilla/dom/RemoteWorkerParent.h"
+#include "mozilla/dom/ServiceWorkerOpPromise.h"
+#include "mozilla/ipc/BackgroundParent.h"
+
+namespace mozilla {
+
+using namespace ipc;
+
+namespace dom {
+
+RemoteWorkerControllerParent::RemoteWorkerControllerParent(
+    const RemoteWorkerData& aRemoteWorkerData)
+    : mRemoteWorkerController(RemoteWorkerController::Create(
+          aRemoteWorkerData, this, 0 /* random process ID */)) {
+  AssertIsInMainProcess();
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(mRemoteWorkerController);
+}
+
+RefPtr<RemoteWorkerParent> RemoteWorkerControllerParent::GetRemoteWorkerParent()
+    const {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(mRemoteWorkerController);
+
+  return mRemoteWorkerController->mActor;
+}
+
+void RemoteWorkerControllerParent::MaybeSendSetServiceWorkerSkipWaitingFlag(
+    std::function<void(bool)>&& aCallback) {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(aCallback);
+
+  if (!mIPCActive) {
+    aCallback(false);
+    return;
+  }
+
+  SendSetServiceWorkerSkipWaitingFlag()->Then(
+      GetCurrentSerialEventTarget(), __func__,
+      [callback = std::move(aCallback)](
+          const SetServiceWorkerSkipWaitingFlagPromise::ResolveOrRejectValue&
+              aResult) {
+        callback(aResult.IsResolve() ? aResult.ResolveValue() : false);
+      });
+}
+
+RemoteWorkerControllerParent::~RemoteWorkerControllerParent() {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(!mIPCActive);
+  MOZ_ASSERT(!mRemoteWorkerController);
+}
+
+PFetchEventOpParent* RemoteWorkerControllerParent::AllocPFetchEventOpParent(
+    const ParentToParentServiceWorkerFetchEventOpArgs& aArgs) {
+  AssertIsOnBackgroundThread();
+
+  RefPtr<FetchEventOpParent> actor = new FetchEventOpParent();
+  return actor.forget().take();
+}
+
+IPCResult RemoteWorkerControllerParent::RecvPFetchEventOpConstructor(
+    PFetchEventOpParent* aActor,
+    const ParentToParentServiceWorkerFetchEventOpArgs& aArgs) {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(aActor);
+
+  RefPtr<FetchEventOpParent> realFetchOp =
+      static_cast<FetchEventOpParent*>(aActor);
+  mRemoteWorkerController->ExecServiceWorkerFetchEventOp(aArgs, realFetchOp)
+      ->Then(
+          GetCurrentSerialEventTarget(), __func__,
+          [fetchOp = std::move(realFetchOp)](
+              ServiceWorkerFetchEventOpPromise::ResolveOrRejectValue&&
+                  aResult) {
+            if (NS_WARN_IF(aResult.IsReject())) {
+              MOZ_ASSERT(NS_FAILED(aResult.RejectValue()));
+              Unused << fetchOp->Send__delete__(fetchOp, aResult.RejectValue());
+              return;
+            }
+
+            Unused << fetchOp->Send__delete__(fetchOp, aResult.ResolveValue());
+          });
+
+  return IPC_OK();
+}
+
+bool RemoteWorkerControllerParent::DeallocPFetchEventOpParent(
+    PFetchEventOpParent* aActor) {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(aActor);
+
+  RefPtr<FetchEventOpParent> actor =
+      dont_AddRef(static_cast<FetchEventOpParent*>(aActor));
+  return true;
+}
+
+IPCResult RemoteWorkerControllerParent::RecvExecServiceWorkerOp(
+    ServiceWorkerOpArgs&& aArgs, ExecServiceWorkerOpResolver&& aResolve) {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(mIPCActive);
+  MOZ_ASSERT(mRemoteWorkerController);
+
+  mRemoteWorkerController->ExecServiceWorkerOp(std::move(aArgs))
+      ->Then(GetCurrentSerialEventTarget(), __func__,
+             [resolve = std::move(aResolve)](
+                 ServiceWorkerOpPromise::ResolveOrRejectValue&& aResult) {
+               if (NS_WARN_IF(aResult.IsReject())) {
+                 MOZ_ASSERT(NS_FAILED(aResult.RejectValue()));
+                 resolve(aResult.RejectValue());
+                 return;
+               }
+
+               resolve(aResult.ResolveValue());
+             });
+
+  return IPC_OK();
+}
+
+IPCResult RemoteWorkerControllerParent::RecvShutdown(
+    ShutdownResolver&& aResolve) {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(mIPCActive);
+  MOZ_ASSERT(mRemoteWorkerController);
+
+  mIPCActive = false;
+
+  mRemoteWorkerController->Shutdown();
+  mRemoteWorkerController = nullptr;
+
+  aResolve(true);
+
+  return IPC_OK();
+}
+
+IPCResult RemoteWorkerControllerParent::Recv__delete__() {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(!mIPCActive);
+  MOZ_ASSERT(!mRemoteWorkerController);
+
+  return IPC_OK();
+}
+
+void RemoteWorkerControllerParent::ActorDestroy(ActorDestroyReason aReason) {
+  AssertIsOnBackgroundThread();
+
+  if (NS_WARN_IF(mIPCActive)) {
+    mIPCActive = false;
+  }
+
+  if (NS_WARN_IF(mRemoteWorkerController)) {
+    mRemoteWorkerController->Shutdown();
+    mRemoteWorkerController = nullptr;
+  }
+}
+
+void RemoteWorkerControllerParent::CreationFailed() {
+  AssertIsOnBackgroundThread();
+
+  if (!mIPCActive) {
+    return;
+  }
+
+  Unused << SendCreationFailed();
+}
+
+void RemoteWorkerControllerParent::CreationSucceeded() {
+  AssertIsOnBackgroundThread();
+
+  if (!mIPCActive) {
+    return;
+  }
+
+  Unused << SendCreationSucceeded();
+}
+
+void RemoteWorkerControllerParent::ErrorReceived(const ErrorValue& aValue) {
+  AssertIsOnBackgroundThread();
+
+  if (!mIPCActive) {
+    return;
+  }
+
+  Unused << SendErrorReceived(aValue);
+}
+
+void RemoteWorkerControllerParent::Terminated() {
+  AssertIsOnBackgroundThread();
+
+  if (!mIPCActive) {
+    return;
+  }
+
+  Unused << SendTerminated();
+}
+
+}  // namespace dom
+}  // namespace mozilla
diff --git a/dom/workers/remoteworkers/RemoteWorkerControllerParent.h b/dom/workers/remoteworkers/RemoteWorkerControllerParent.h
new file mode 100644
index 0000000000..618fbf9506
--- /dev/null
+++ b/dom/workers/remoteworkers/RemoteWorkerControllerParent.h
@@ -0,0 +1,86 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_remoteworkercontrollerparent_h__
+#define mozilla_dom_remoteworkercontrollerparent_h__
+
+#include <functional>
+
+#include "nsISupportsImpl.h"
+
+#include "RemoteWorkerController.h"
+#include "mozilla/RefPtr.h"
+#include "mozilla/dom/PRemoteWorkerControllerParent.h"
+
+namespace mozilla::dom {
+
+/**
+ * PBackground-resident proxy used by ServiceWorkerManager because canonical
+ * ServiceWorkerManager state exists on the parent process main thread but the
+ * RemoteWorkerController API is used from the parent process PBackground
+ * thread.
+ */
+class RemoteWorkerControllerParent final : public PRemoteWorkerControllerParent,
+                                           public RemoteWorkerObserver {
+  friend class PRemoteWorkerControllerParent;
+
+ public:
+  NS_INLINE_DECL_REFCOUNTING(RemoteWorkerControllerParent, override)
+
+  explicit RemoteWorkerControllerParent(
+      const RemoteWorkerData& aRemoteWorkerData);
+
+  // Returns the corresponding RemoteWorkerParent (if any).
+  RefPtr<RemoteWorkerParent> GetRemoteWorkerParent() const;
+
+  void MaybeSendSetServiceWorkerSkipWaitingFlag(
+      std::function<void(bool)>&& aCallback);
+
+ private:
+  ~RemoteWorkerControllerParent();
+
+  PFetchEventOpParent* AllocPFetchEventOpParent(
+      const ParentToParentServiceWorkerFetchEventOpArgs& aArgs);
+
+  mozilla::ipc::IPCResult RecvPFetchEventOpConstructor(
+      PFetchEventOpParent* aActor,
+      const ParentToParentServiceWorkerFetchEventOpArgs& aArgs) override;
+
+  bool DeallocPFetchEventOpParent(PFetchEventOpParent* aActor);
+
+  mozilla::ipc::IPCResult RecvExecServiceWorkerOp(
+      ServiceWorkerOpArgs&& aArgs, ExecServiceWorkerOpResolver&& aResolve);
+
+  mozilla::ipc::IPCResult RecvShutdown(ShutdownResolver&& aResolve);
+
+  mozilla::ipc::IPCResult Recv__delete__() override;
+
+  void ActorDestroy(ActorDestroyReason aReason) override;
+
+  void CreationFailed() override;
+
+  void CreationSucceeded() override;
+
+  void ErrorReceived(const ErrorValue& aValue) override;
+
+  void LockNotified(bool aCreated) final {
+    // no-op for service workers
+  }
+
+  void WebTransportNotified(bool aCreated) final {
+    // no-op for service workers
+  }
+
+  void Terminated() override;
+
+  RefPtr<RemoteWorkerController> mRemoteWorkerController;
+
+  bool mIPCActive = true;
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_remoteworkercontrollerparent_h__
diff --git a/dom/workers/remoteworkers/RemoteWorkerManager.cpp b/dom/workers/remoteworkers/RemoteWorkerManager.cpp
new file mode 100644
index 0000000000..29577f0a34
--- /dev/null
+++ b/dom/workers/remoteworkers/RemoteWorkerManager.cpp
@@ -0,0 +1,627 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "RemoteWorkerManager.h"
+
+#include <utility>
+
+#include "mozilla/SchedulerGroup.h"
+#include "mozilla/ScopeExit.h"
+#include "mozilla/dom/ContentChild.h"  // ContentChild::GetSingleton
+#include "mozilla/dom/ProcessIsolation.h"
+#include "mozilla/dom/RemoteWorkerController.h"
+#include "mozilla/dom/RemoteWorkerParent.h"
+#include "mozilla/ipc/BackgroundParent.h"
+#include "mozilla/ipc/BackgroundUtils.h"
+#include "mozilla/ipc/PBackgroundParent.h"
+#include "mozilla/StaticPrefs_extensions.h"
+#include "nsCOMPtr.h"
+#include "nsImportModule.h"
+#include "nsIXULRuntime.h"
+#include "nsTArray.h"
+#include "nsThreadUtils.h"
+#include "RemoteWorkerServiceParent.h"
+
+mozilla::LazyLogModule gRemoteWorkerManagerLog("RemoteWorkerManager");
+
+#ifdef LOG
+#  undef LOG
+#endif
+#define LOG(fmt) \
+  MOZ_LOG(gRemoteWorkerManagerLog, mozilla::LogLevel::Verbose, fmt)
+
+namespace mozilla {
+
+using namespace ipc;
+
+namespace dom {
+
+namespace {
+
+// Raw pointer because this object is kept alive by RemoteWorkerServiceParent
+// actors.
+RemoteWorkerManager* sRemoteWorkerManager;
+
+bool IsServiceWorker(const RemoteWorkerData& aData) {
+  return aData.serviceWorkerData().type() ==
+         OptionalServiceWorkerData::TServiceWorkerData;
+}
+
+void TransmitPermissionsAndBlobURLsForPrincipalInfo(
+    ContentParent* aContentParent, const PrincipalInfo& aPrincipalInfo) {
+  AssertIsOnMainThread();
+  MOZ_ASSERT(aContentParent);
+
+  auto principalOrErr = PrincipalInfoToPrincipal(aPrincipalInfo);
+
+  if (NS_WARN_IF(principalOrErr.isErr())) {
+    return;
+  }
+
+  nsCOMPtr<nsIPrincipal> principal = principalOrErr.unwrap();
+
+  aContentParent->TransmitBlobURLsForPrincipal(principal);
+
+  MOZ_ALWAYS_SUCCEEDS(
+      aContentParent->TransmitPermissionsForPrincipal(principal));
+}
+
+}  // namespace
+
+// static
+bool RemoteWorkerManager::MatchRemoteType(const nsACString& processRemoteType,
+                                          const nsACString& workerRemoteType) {
+  LOG(("MatchRemoteType [processRemoteType=%s, workerRemoteType=%s]",
+       PromiseFlatCString(processRemoteType).get(),
+       PromiseFlatCString(workerRemoteType).get()));
+
+  // Respecting COOP and COEP requires processing headers in the parent
+  // process in order to choose an appropriate content process, but the
+  // workers' ScriptLoader processes headers in content processes. An
+  // intermediary step that provides security guarantees is to simply never
+  // allow SharedWorkers and ServiceWorkers to exist in a COOP+COEP process.
+  // The ultimate goal is to allow these worker types to be put in such
+  // processes based on their script response headers.
+  // https://bugzilla.mozilla.org/show_bug.cgi?id=1595206
+  //
+  // RemoteWorkerManager::GetRemoteType should not select this remoteType
+  // and so workerRemoteType is not expected to be set to a coop+coep
+  // remoteType and here we can just assert that it is not happening.
+  MOZ_ASSERT(!IsWebCoopCoepRemoteType(workerRemoteType));
+
+  return processRemoteType.Equals(workerRemoteType);
+}
+
+// static
+Result<nsCString, nsresult> RemoteWorkerManager::GetRemoteType(
+    const nsCOMPtr<nsIPrincipal>& aPrincipal, WorkerKind aWorkerKind) {
+  AssertIsOnMainThread();
+
+  MOZ_ASSERT_IF(aWorkerKind == WorkerKind::WorkerKindService,
+                aPrincipal->GetIsContentPrincipal());
+
+  // If E10S is fully disabled, there are no decisions to be made, and we need
+  // to finish the load in the parent process.
+  if (!BrowserTabsRemoteAutostart()) {
+    LOG(("GetRemoteType: Loading in parent process as e10s is disabled"));
+    return NOT_REMOTE_TYPE;
+  }
+
+  nsCString preferredRemoteType = DEFAULT_REMOTE_TYPE;
+  if (aWorkerKind == WorkerKind::WorkerKindShared) {
+    if (auto* contentChild = ContentChild::GetSingleton()) {
+      // For a shared worker set the preferred remote type to the content
+      // child process remote type.
+      preferredRemoteType = contentChild->GetRemoteType();
+    } else if (aPrincipal->IsSystemPrincipal()) {
+      preferredRemoteType = NOT_REMOTE_TYPE;
+    }
+  }
+
+  auto result = IsolationOptionsForWorker(
+      aPrincipal, aWorkerKind, preferredRemoteType, FissionAutostart());
+  if (NS_WARN_IF(result.isErr())) {
+    LOG(("GetRemoteType Abort: IsolationOptionsForWorker failed"));
+    return Err(NS_ERROR_DOM_ABORT_ERR);
+  }
+  auto options = result.unwrap();
+
+  if (MOZ_LOG_TEST(gRemoteWorkerManagerLog, LogLevel::Verbose)) {
+    nsCString principalOrigin;
+    aPrincipal->GetOrigin(principalOrigin);
+
+    LOG(
+        ("GetRemoteType workerType=%s, principal=%s, "
+         "preferredRemoteType=%s, selectedRemoteType=%s",
+         aWorkerKind == WorkerKind::WorkerKindService ? "service" : "shared",
+         principalOrigin.get(), preferredRemoteType.get(),
+         options.mRemoteType.get()));
+  }
+
+  return options.mRemoteType;
+}
+
+// static
+bool RemoteWorkerManager::HasExtensionPrincipal(const RemoteWorkerData& aData) {
+  auto principalInfo = aData.principalInfo();
+  return principalInfo.type() == PrincipalInfo::TContentPrincipalInfo &&
+         // This helper method is also called from the background thread and so
+         // we can't check if the principal does have an addonPolicy object
+         // associated and we have to resort to check the url scheme instead.
+         StringBeginsWith(principalInfo.get_ContentPrincipalInfo().spec(),
+                          "moz-extension://"_ns);
+}
+
+// static
+bool RemoteWorkerManager::IsRemoteTypeAllowed(const RemoteWorkerData& aData) {
+  AssertIsOnMainThread();
+
+  // If Gecko is running in single process mode, there is no child process
+  // to select and we have to just consider it valid (if it should haven't
+  // been launched it should have been already prevented before reaching
+  // a RemoteWorkerChild instance).
+  if (!BrowserTabsRemoteAutostart()) {
+    return true;
+  }
+
+  const auto& principalInfo = aData.principalInfo();
+
+  auto* contentChild = ContentChild::GetSingleton();
+  if (!contentChild) {
+    // If e10s isn't disabled, only workers related to the system principal
+    // should be allowed to run in the parent process, and extension principals
+    // if extensions.webextensions.remote is false.
+    return principalInfo.type() == PrincipalInfo::TSystemPrincipalInfo ||
+           (!StaticPrefs::extensions_webextensions_remote() &&
+            aData.remoteType().Equals(NOT_REMOTE_TYPE) &&
+            HasExtensionPrincipal(aData));
+  }
+
+  auto principalOrErr = PrincipalInfoToPrincipal(principalInfo);
+  if (NS_WARN_IF(principalOrErr.isErr())) {
+    return false;
+  }
+  nsCOMPtr<nsIPrincipal> principal = principalOrErr.unwrap();
+
+  // Recompute the remoteType based on the principal, to double-check that it
+  // has not been tempered to select a different child process than the one
+  // expected.
+  bool isServiceWorker = aData.serviceWorkerData().type() ==
+                         OptionalServiceWorkerData::TServiceWorkerData;
+  auto remoteType = GetRemoteType(
+      principal, isServiceWorker ? WorkerKindService : WorkerKindShared);
+  if (NS_WARN_IF(remoteType.isErr())) {
+    LOG(("IsRemoteTypeAllowed: Error to retrieve remote type"));
+    return false;
+  }
+
+  return MatchRemoteType(remoteType.unwrap(), contentChild->GetRemoteType());
+}
+
+/* static */
+already_AddRefed<RemoteWorkerManager> RemoteWorkerManager::GetOrCreate() {
+  AssertIsInMainProcess();
+  AssertIsOnBackgroundThread();
+
+  if (!sRemoteWorkerManager) {
+    sRemoteWorkerManager = new RemoteWorkerManager();
+  }
+
+  RefPtr<RemoteWorkerManager> rwm = sRemoteWorkerManager;
+  return rwm.forget();
+}
+
+RemoteWorkerManager::RemoteWorkerManager() : mParentActor(nullptr) {
+  AssertIsInMainProcess();
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(!sRemoteWorkerManager);
+}
+
+RemoteWorkerManager::~RemoteWorkerManager() {
+  AssertIsInMainProcess();
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(sRemoteWorkerManager == this);
+  sRemoteWorkerManager = nullptr;
+}
+
+void RemoteWorkerManager::RegisterActor(RemoteWorkerServiceParent* aActor) {
+  AssertIsInMainProcess();
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(aActor);
+
+  if (!BackgroundParent::IsOtherProcessActor(aActor->Manager())) {
+    MOZ_ASSERT(!mParentActor);
+    mParentActor = aActor;
+    MOZ_ASSERT(mPendings.IsEmpty());
+    return;
+  }
+
+  MOZ_ASSERT(!mChildActors.Contains(aActor));
+  mChildActors.AppendElement(aActor);
+
+  if (!mPendings.IsEmpty()) {
+    const auto& processRemoteType = aActor->GetRemoteType();
+    nsTArray<Pending> unlaunched;
+
+    // Flush pending launching.
+    for (Pending& p : mPendings) {
+      if (p.mController->IsTerminated()) {
+        continue;
+      }
+
+      const auto& workerRemoteType = p.mData.remoteType();
+
+      if (MatchRemoteType(processRemoteType, workerRemoteType)) {
+        LOG(("RegisterActor - Launch Pending, workerRemoteType=%s",
+             workerRemoteType.get()));
+        LaunchInternal(p.mController, aActor, p.mData);
+      } else {
+        unlaunched.AppendElement(std::move(p));
+        continue;
+      }
+    }
+
+    std::swap(mPendings, unlaunched);
+
+    // AddRef is called when the first Pending object is added to mPendings, so
+    // the balancing Release is called when the last Pending object is removed.
+    // RemoteWorkerServiceParents will hold strong references to
+    // RemoteWorkerManager.
+    if (mPendings.IsEmpty()) {
+      Release();
+    }
+
+    LOG(("RegisterActor - mPendings length: %zu", mPendings.Length()));
+  }
+}
+
+void RemoteWorkerManager::UnregisterActor(RemoteWorkerServiceParent* aActor) {
+  AssertIsInMainProcess();
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(aActor);
+
+  if (aActor == mParentActor) {
+    mParentActor = nullptr;
+  } else {
+    MOZ_ASSERT(mChildActors.Contains(aActor));
+    mChildActors.RemoveElement(aActor);
+  }
+}
+
+void RemoteWorkerManager::Launch(RemoteWorkerController* aController,
+                                 const RemoteWorkerData& aData,
+                                 base::ProcessId aProcessId) {
+  AssertIsInMainProcess();
+  AssertIsOnBackgroundThread();
+
+  RemoteWorkerServiceParent* targetActor = SelectTargetActor(aData, aProcessId);
+
+  // If there is not an available actor, let's store the data, and let's spawn a
+  // new process.
+  if (!targetActor) {
+    // If this is the first time we have a pending launching, we must keep alive
+    // the manager.
+    if (mPendings.IsEmpty()) {
+      AddRef();
+    }
+
+    Pending* pending = mPendings.AppendElement();
+    pending->mController = aController;
+    pending->mData = aData;
+
+    // Launching is async, so we cannot check for failures right here.
+    LaunchNewContentProcess(aData);
+    return;
+  }
+
+  /**
+   * If a target actor for the remote worker has been selected, the actor has
+   * already been registered with the corresponding `ContentParent` and we
+   * should not increment the `mRemoteWorkerActorData`'s `mCount` again (see
+   * `SelectTargetActorForServiceWorker()` /
+   * `SelectTargetActorForSharedWorker()`).
+   */
+  LaunchInternal(aController, targetActor, aData, true);
+}
+
+void RemoteWorkerManager::LaunchInternal(
+    RemoteWorkerController* aController,
+    RemoteWorkerServiceParent* aTargetActor, const RemoteWorkerData& aData,
+    bool aRemoteWorkerAlreadyRegistered) {
+  AssertIsInMainProcess();
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(aController);
+  MOZ_ASSERT(aTargetActor);
+  MOZ_ASSERT(aTargetActor == mParentActor ||
+             mChildActors.Contains(aTargetActor));
+
+  // We need to send permissions to content processes, but not if we're spawning
+  // the worker here in the parent process.
+  if (aTargetActor != mParentActor) {
+    RefPtr<ThreadsafeContentParentHandle> contentHandle =
+        BackgroundParent::GetContentParentHandle(aTargetActor->Manager());
+
+    // This won't cause any race conditions because the content process
+    // should wait for the permissions to be received before executing the
+    // Service Worker.
+    nsCOMPtr<nsIRunnable> r = NS_NewRunnableFunction(
+        __func__, [contentHandle = std::move(contentHandle),
+                   principalInfo = aData.principalInfo()] {
+          AssertIsOnMainThread();
+          if (RefPtr<ContentParent> contentParent =
+                  contentHandle->GetContentParent()) {
+            TransmitPermissionsAndBlobURLsForPrincipalInfo(contentParent,
+                                                           principalInfo);
+          }
+        });
+
+    MOZ_ALWAYS_SUCCEEDS(SchedulerGroup::Dispatch(r.forget()));
+  }
+
+  RefPtr<RemoteWorkerParent> workerActor = MakeAndAddRef<RemoteWorkerParent>();
+  if (!aTargetActor->Manager()->SendPRemoteWorkerConstructor(workerActor,
+                                                             aData)) {
+    AsyncCreationFailed(aController);
+    return;
+  }
+
+  workerActor->Initialize(aRemoteWorkerAlreadyRegistered);
+
+  // This makes the link better the 2 actors.
+  aController->SetWorkerActor(workerActor);
+  workerActor->SetController(aController);
+}
+
+void RemoteWorkerManager::AsyncCreationFailed(
+    RemoteWorkerController* aController) {
+  RefPtr<RemoteWorkerController> controller = aController;
+  nsCOMPtr<nsIRunnable> r =
+      NS_NewRunnableFunction("RemoteWorkerManager::AsyncCreationFailed",
+                             [controller]() { controller->CreationFailed(); });
+
+  NS_DispatchToCurrentThread(r.forget());
+}
+
+template <typename Callback>
+void RemoteWorkerManager::ForEachActor(
+    Callback&& aCallback, const nsACString& aRemoteType,
+    Maybe<base::ProcessId> aProcessId) const {
+  AssertIsOnBackgroundThread();
+
+  const auto length = mChildActors.Length();
+
+  auto end = static_cast<uint32_t>(rand()) % length;
+  if (aProcessId) {
+    // Start from the actor with the given processId instead of starting from
+    // a random index.
+    for (auto j = length - 1; j > 0; j--) {
+      if (mChildActors[j]->OtherPid() == *aProcessId) {
+        end = j;
+        break;
+      }
+    }
+  }
+
+  uint32_t i = end;
+
+  do {
+    MOZ_ASSERT(i < mChildActors.Length());
+    RemoteWorkerServiceParent* actor = mChildActors[i];
+
+    if (MatchRemoteType(actor->GetRemoteType(), aRemoteType)) {
+      ThreadsafeContentParentHandle* contentHandle =
+          BackgroundParent::GetContentParentHandle(actor->Manager());
+
+      if (!aCallback(actor, contentHandle)) {
+        break;
+      }
+    }
+
+    i = (i + 1) % length;
+  } while (i != end);
+}
+
+/**
+ * When selecting a target actor for a given remote worker, we have to consider
+ * that:
+ *
+ * - Service Workers can spawn even when their registering page/script isn't
+ *   active (e.g. push notifications), so we don't attempt to spawn the worker
+ *   in its registering script's process. We search linearly and choose the
+ *   search's starting position randomly.
+ *
+ * - When Fission is enabled, Shared Workers may have to be spawned into
+ * different child process from the one where it has been registered from, and
+ * that child process may be going to be marked as dead and shutdown.
+ *
+ * Spawning the workers in a random process makes the process selection criteria
+ * a little tricky, as a candidate process may imminently shutdown due to a
+ * remove worker actor unregistering
+ * (see `ContentParent::UnregisterRemoveWorkerActor`).
+ *
+ * In `ContentParent::MaybeBeginShutdown` we only dispatch a runnable
+ * to call `ContentParent::ShutDownProcess` if there are no registered remote
+ * worker actors, and we ensure that the check for the number of registered
+ * actors and the dispatching of the runnable are atomic. That happens on the
+ * main thread, so here on the background thread,  while
+ * `ContentParent::mRemoteWorkerActorData` is locked, if `mCount` > 0, we can
+ * register a remote worker actor "early" and guarantee that the corresponding
+ * content process will not shutdown.
+ */
+RemoteWorkerServiceParent* RemoteWorkerManager::SelectTargetActorInternal(
+    const RemoteWorkerData& aData, base::ProcessId aProcessId) const {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(!mChildActors.IsEmpty());
+
+  RemoteWorkerServiceParent* actor = nullptr;
+
+  const auto& workerRemoteType = aData.remoteType();
+
+  ForEachActor(
+      [&](RemoteWorkerServiceParent* aActor,
+          ThreadsafeContentParentHandle* aContentHandle) {
+        // Make sure to choose an actor related to a child process that is not
+        // going to shutdown while we are still in the process of launching the
+        // remote worker.
+        //
+        // ForEachActor will start from the child actor coming from the child
+        // process with a pid equal to aProcessId if any, otherwise it would
+        // start from a random actor in the mChildActors array, this guarantees
+        // that we will choose that actor if it does also match the remote type.
+        if (aContentHandle->MaybeRegisterRemoteWorkerActor(
+                [&](uint32_t count, bool shutdownStarted) -> bool {
+                  return (count || !shutdownStarted) &&
+                         (aActor->OtherPid() == aProcessId || !actor);
+                })) {
+          actor = aActor;
+          return false;
+        }
+        MOZ_ASSERT(!actor);
+        return true;
+      },
+      workerRemoteType, IsServiceWorker(aData) ? Nothing() : Some(aProcessId));
+
+  return actor;
+}
+
+RemoteWorkerServiceParent* RemoteWorkerManager::SelectTargetActor(
+    const RemoteWorkerData& aData, base::ProcessId aProcessId) {
+  AssertIsInMainProcess();
+  AssertIsOnBackgroundThread();
+
+  // System principal workers should run on the parent process.
+  if (aData.principalInfo().type() == PrincipalInfo::TSystemPrincipalInfo) {
+    MOZ_ASSERT(mParentActor);
+    return mParentActor;
+  }
+
+  // Extension principal workers are allowed to run on the parent process
+  // when "extensions.webextensions.remote" pref is false.
+  if (aProcessId == base::GetCurrentProcId() &&
+      aData.remoteType().Equals(NOT_REMOTE_TYPE) &&
+      !StaticPrefs::extensions_webextensions_remote() &&
+      HasExtensionPrincipal(aData)) {
+    MOZ_ASSERT(mParentActor);
+    return mParentActor;
+  }
+
+  // If e10s is off, use the parent process.
+  if (!BrowserTabsRemoteAutostart()) {
+    MOZ_ASSERT(mParentActor);
+    return mParentActor;
+  }
+
+  // We shouldn't have to worry about content-principal parent-process workers.
+  MOZ_ASSERT(aProcessId != base::GetCurrentProcId());
+
+  if (mChildActors.IsEmpty()) {
+    return nullptr;
+  }
+
+  return SelectTargetActorInternal(aData, aProcessId);
+}
+
+void RemoteWorkerManager::LaunchNewContentProcess(
+    const RemoteWorkerData& aData) {
+  AssertIsInMainProcess();
+  AssertIsOnBackgroundThread();
+
+  nsCOMPtr<nsISerialEventTarget> bgEventTarget = GetCurrentSerialEventTarget();
+
+  using LaunchPromiseType = ContentParent::LaunchPromise;
+  using CallbackParamType = LaunchPromiseType::ResolveOrRejectValue;
+
+  // A new content process must be requested on the main thread. On success,
+  // the success callback will also run on the main thread. On failure, however,
+  // the failure callback must be run on the background thread - it uses
+  // RemoteWorkerManager, and RemoteWorkerManager isn't threadsafe, so the
+  // promise callback will just dispatch the "real" failure callback to the
+  // background thread.
+  auto processLaunchCallback = [principalInfo = aData.principalInfo(),
+                                bgEventTarget = std::move(bgEventTarget),
+                                self = RefPtr<RemoteWorkerManager>(this)](
+                                   const CallbackParamType& aValue,
+                                   const nsCString& remoteType) mutable {
+    if (aValue.IsResolve()) {
+      LOG(("LaunchNewContentProcess: successfully got child process"));
+
+      // The failure callback won't run, and we're on the main thread, so
+      // we need to properly release the thread-unsafe RemoteWorkerManager.
+      NS_ProxyRelease(__func__, bgEventTarget, self.forget());
+    } else {
+      // The "real" failure callback.
+      nsCOMPtr<nsIRunnable> r = NS_NewRunnableFunction(
+          __func__, [self = std::move(self), remoteType] {
+            nsTArray<Pending> uncancelled;
+            auto pendings = std::move(self->mPendings);
+
+            for (const auto& pending : pendings) {
+              const auto& workerRemoteType = pending.mData.remoteType();
+              if (self->MatchRemoteType(remoteType, workerRemoteType)) {
+                LOG(
+                    ("LaunchNewContentProcess: Cancel pending with "
+                     "workerRemoteType=%s",
+                     workerRemoteType.get()));
+                pending.mController->CreationFailed();
+              } else {
+                uncancelled.AppendElement(pending);
+              }
+            }
+
+            std::swap(self->mPendings, uncancelled);
+          });
+
+      bgEventTarget->Dispatch(r.forget(), NS_DISPATCH_NORMAL);
+    }
+  };
+
+  LOG(("LaunchNewContentProcess: remoteType=%s", aData.remoteType().get()));
+
+  nsCOMPtr<nsIRunnable> r = NS_NewRunnableFunction(
+      __func__, [callback = std::move(processLaunchCallback),
+                 workerRemoteType = aData.remoteType()]() mutable {
+        auto remoteType =
+            workerRemoteType.IsEmpty() ? DEFAULT_REMOTE_TYPE : workerRemoteType;
+
+        RefPtr<LaunchPromiseType> onFinished;
+        if (!AppShutdown::IsInOrBeyond(ShutdownPhase::AppShutdownConfirmed)) {
+          // Request a process making sure to specify aPreferUsed=true.  For a
+          // given remoteType there's a pool size limit.  If we pass aPreferUsed
+          // here, then if there's any process in the pool already, we will use
+          // that.  If we pass false (which is the default if omitted), then
+          // this call will spawn a new process if the pool isn't at its limit
+          // yet.
+          //
+          // (Our intent is never to grow the pool size here.  Our logic gets
+          // here because our current logic on PBackground is only aware of
+          // RemoteWorkerServiceParent actors that have registered themselves,
+          // which is fundamentally unaware of processes that will match in the
+          // future when they register.  So we absolutely are fine with and want
+          // any existing processes.)
+          onFinished = ContentParent::GetNewOrUsedBrowserProcessAsync(
+              /* aRemoteType = */ remoteType,
+              /* aGroup */ nullptr,
+              hal::ProcessPriority::PROCESS_PRIORITY_FOREGROUND,
+              /* aPreferUsed */ true);
+        } else {
+          // We can find this event still in flight after having been asked to
+          // shutdown. Let's fake a failure to ensure our callback is called
+          // such that we clean up everything properly.
+          onFinished = LaunchPromiseType::CreateAndReject(
+              NS_ERROR_ILLEGAL_DURING_SHUTDOWN, __func__);
+        }
+        onFinished->Then(GetCurrentSerialEventTarget(), __func__,
+                         [callback = std::move(callback),
+                          remoteType](const CallbackParamType& aValue) mutable {
+                           callback(aValue, remoteType);
+                         });
+      });
+
+  SchedulerGroup::Dispatch(r.forget());
+}
+
+}  // namespace dom
+}  // namespace mozilla
diff --git a/dom/workers/remoteworkers/RemoteWorkerManager.h b/dom/workers/remoteworkers/RemoteWorkerManager.h
new file mode 100644
index 0000000000..5ff11ee6e6
--- /dev/null
+++ b/dom/workers/remoteworkers/RemoteWorkerManager.h
@@ -0,0 +1,118 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_RemoteWorkerManager_h
+#define mozilla_dom_RemoteWorkerManager_h
+
+#include "base/process.h"
+#include "mozilla/RefPtr.h"
+#include "mozilla/dom/ContentParent.h"
+#include "mozilla/dom/RemoteWorkerTypes.h"
+#include "mozilla/dom/WorkerPrivate.h"  // WorkerKind enum
+#include "nsISupportsImpl.h"
+#include "nsTArray.h"
+
+namespace mozilla::dom {
+
+class RemoteWorkerController;
+class RemoteWorkerServiceParent;
+
+/**
+ * PBackground instance that keeps tracks of RemoteWorkerServiceParent actors
+ * (1 per process, including the main process) and pending
+ * RemoteWorkerController requests to spawn remote workers if the spawn request
+ * can't be immediately fulfilled. Decides which RemoteWorkerServerParent to use
+ * internally via SelectTargetActor in order to select a BackgroundParent
+ * manager on which to create a RemoteWorkerParent.
+ */
+class RemoteWorkerManager final {
+ public:
+  NS_INLINE_DECL_REFCOUNTING(RemoteWorkerManager)
+
+  static already_AddRefed<RemoteWorkerManager> GetOrCreate();
+
+  void RegisterActor(RemoteWorkerServiceParent* aActor);
+
+  void UnregisterActor(RemoteWorkerServiceParent* aActor);
+
+  void Launch(RemoteWorkerController* aController,
+              const RemoteWorkerData& aData, base::ProcessId aProcessId);
+
+  static bool MatchRemoteType(const nsACString& processRemoteType,
+                              const nsACString& workerRemoteType);
+
+  /**
+   * Get the child process RemoteType where a RemoteWorker should be
+   * launched.
+   */
+  static Result<nsCString, nsresult> GetRemoteType(
+      const nsCOMPtr<nsIPrincipal>& aPrincipal, WorkerKind aWorkerKind);
+
+  /**
+   * Verify if a remote worker should be allowed to run in the current
+   * child process remoteType.
+   */
+  static bool IsRemoteTypeAllowed(const RemoteWorkerData& aData);
+
+  static bool HasExtensionPrincipal(const RemoteWorkerData& aData);
+
+ private:
+  RemoteWorkerManager();
+  ~RemoteWorkerManager();
+
+  RemoteWorkerServiceParent* SelectTargetActor(const RemoteWorkerData& aData,
+                                               base::ProcessId aProcessId);
+
+  RemoteWorkerServiceParent* SelectTargetActorInternal(
+      const RemoteWorkerData& aData, base::ProcessId aProcessId) const;
+
+  void LaunchInternal(RemoteWorkerController* aController,
+                      RemoteWorkerServiceParent* aTargetActor,
+                      const RemoteWorkerData& aData,
+                      bool aRemoteWorkerAlreadyRegistered = false);
+
+  void LaunchNewContentProcess(const RemoteWorkerData& aData);
+
+  void AsyncCreationFailed(RemoteWorkerController* aController);
+
+  // Iterate through all RemoteWorkerServiceParent actors with the given
+  // remoteType, starting from the actor related to a child process with pid
+  // aProcessId if needed and available or from a random index otherwise (as if
+  // iterating through a circular array).
+  //
+  // aCallback should be a invokable object with a function signature of
+  //   bool (RemoteWorkerServiceParent*, RefPtr<ContentParent>&&)
+  //
+  // aCallback is called with the actor and corresponding ContentParent, should
+  // return false to abort iteration before all actors have been traversed (e.g.
+  // if the desired actor is found), and must not mutate mChildActors (which
+  // shouldn't be an issue because this function is const). aCallback also
+  // doesn't need to worry about proxy-releasing the ContentParent if it isn't
+  // moved out of the parameter.
+  template <typename Callback>
+  void ForEachActor(Callback&& aCallback, const nsACString& aRemoteType,
+                    Maybe<base::ProcessId> aProcessId = Nothing()) const;
+
+  // The list of existing RemoteWorkerServiceParent actors for child processes.
+  // Raw pointers because RemoteWorkerServiceParent actors unregister themselves
+  // when destroyed.
+  // XXX For Fission, where we could have a lot of child actors, should we maybe
+  // instead keep either a hash table (PID->actor) or perhaps store the actors
+  // in order, sorted by PID, to avoid linear lookup times?
+  nsTArray<RemoteWorkerServiceParent*> mChildActors;
+  RemoteWorkerServiceParent* mParentActor;
+
+  struct Pending {
+    RefPtr<RemoteWorkerController> mController;
+    RemoteWorkerData mData;
+  };
+
+  nsTArray<Pending> mPendings;
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_RemoteWorkerManager_h
diff --git a/dom/workers/remoteworkers/RemoteWorkerParent.cpp b/dom/workers/remoteworkers/RemoteWorkerParent.cpp
new file mode 100644
index 0000000000..1a9613b799
--- /dev/null
+++ b/dom/workers/remoteworkers/RemoteWorkerParent.cpp
@@ -0,0 +1,200 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "RemoteWorkerParent.h"
+#include "RemoteWorkerController.h"
+#include "mozilla/dom/ContentParent.h"
+#include "mozilla/dom/PFetchEventOpProxyParent.h"
+#include "mozilla/ipc/BackgroundParent.h"
+#include "mozilla/SchedulerGroup.h"
+#include "mozilla/Unused.h"
+#include "nsProxyRelease.h"
+
+namespace mozilla {
+
+using namespace ipc;
+
+namespace dom {
+
+namespace {
+
+class UnregisterActorRunnable final : public Runnable {
+ public:
+  explicit UnregisterActorRunnable(
+      already_AddRefed<ThreadsafeContentParentHandle> aParent)
+      : Runnable("UnregisterActorRunnable"), mContentHandle(aParent) {
+    AssertIsOnBackgroundThread();
+  }
+
+  NS_IMETHOD
+  Run() override {
+    AssertIsOnMainThread();
+    if (RefPtr<ContentParent> contentParent =
+            mContentHandle->GetContentParent()) {
+      contentParent->UnregisterRemoveWorkerActor();
+    }
+
+    return NS_OK;
+  }
+
+ private:
+  RefPtr<ThreadsafeContentParentHandle> mContentHandle;
+};
+
+}  // namespace
+
+RemoteWorkerParent::RemoteWorkerParent() {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(XRE_IsParentProcess());
+}
+
+RemoteWorkerParent::~RemoteWorkerParent() {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(XRE_IsParentProcess());
+}
+
+void RemoteWorkerParent::Initialize(bool aAlreadyRegistered) {
+  RefPtr<ThreadsafeContentParentHandle> parent =
+      BackgroundParent::GetContentParentHandle(Manager());
+
+  // Parent is null if the child actor runs on the parent process.
+  if (parent) {
+    if (!aAlreadyRegistered) {
+      parent->RegisterRemoteWorkerActor();
+    }
+
+    NS_ReleaseOnMainThread("RemoteWorkerParent::Initialize ContentParent",
+                           parent.forget());
+  }
+}
+
+already_AddRefed<PFetchEventOpProxyParent>
+RemoteWorkerParent::AllocPFetchEventOpProxyParent(
+    const ParentToChildServiceWorkerFetchEventOpArgs& aArgs) {
+  MOZ_CRASH("PFetchEventOpProxyParent actors must be manually constructed!");
+  return nullptr;
+}
+
+void RemoteWorkerParent::ActorDestroy(IProtocol::ActorDestroyReason) {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(XRE_IsParentProcess());
+
+  RefPtr<ThreadsafeContentParentHandle> parent =
+      BackgroundParent::GetContentParentHandle(Manager());
+
+  // Parent is null if the child actor runs on the parent process.
+  if (parent) {
+    RefPtr<UnregisterActorRunnable> r =
+        new UnregisterActorRunnable(parent.forget());
+    SchedulerGroup::Dispatch(r.forget());
+  }
+
+  if (mController) {
+    mController->NoteDeadWorkerActor();
+    mController = nullptr;
+  }
+}
+
+IPCResult RemoteWorkerParent::RecvCreated(const bool& aStatus) {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(XRE_IsParentProcess());
+
+  if (!mController) {
+    return IPC_OK();
+  }
+
+  if (aStatus) {
+    mController->CreationSucceeded();
+  } else {
+    mController->CreationFailed();
+  }
+
+  return IPC_OK();
+}
+
+IPCResult RemoteWorkerParent::RecvError(const ErrorValue& aValue) {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(XRE_IsParentProcess());
+
+  if (mController) {
+    mController->ErrorPropagation(aValue);
+  }
+
+  return IPC_OK();
+}
+
+IPCResult RemoteWorkerParent::RecvNotifyLock(const bool& aCreated) {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(XRE_IsParentProcess());
+
+  if (mController) {
+    mController->NotifyLock(aCreated);
+  }
+
+  return IPC_OK();
+}
+
+IPCResult RemoteWorkerParent::RecvNotifyWebTransport(const bool& aCreated) {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(XRE_IsParentProcess());
+
+  if (mController) {
+    mController->NotifyWebTransport(aCreated);
+  }
+
+  return IPC_OK();
+}
+
+void RemoteWorkerParent::MaybeSendDelete() {
+  if (mDeleteSent) {
+    return;
+  }
+
+  // For some reason, if the following two lines are swapped, ASan says there's
+  // a UAF...
+  mDeleteSent = true;
+  Unused << Send__delete__(this);
+}
+
+IPCResult RemoteWorkerParent::RecvClose() {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(XRE_IsParentProcess());
+
+  if (mController) {
+    mController->WorkerTerminated();
+  }
+
+  MaybeSendDelete();
+
+  return IPC_OK();
+}
+
+void RemoteWorkerParent::SetController(RemoteWorkerController* aController) {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(XRE_IsParentProcess());
+
+  mController = aController;
+}
+
+IPCResult RemoteWorkerParent::RecvSetServiceWorkerSkipWaitingFlag(
+    SetServiceWorkerSkipWaitingFlagResolver&& aResolve) {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(XRE_IsParentProcess());
+
+  if (mController) {
+    mController->SetServiceWorkerSkipWaitingFlag()->Then(
+        GetCurrentSerialEventTarget(), __func__,
+        [resolve = aResolve](bool /* unused */) { resolve(true); },
+        [resolve = aResolve](nsresult /* unused */) { resolve(false); });
+  } else {
+    aResolve(false);
+  }
+
+  return IPC_OK();
+}
+
+}  // namespace dom
+}  // namespace mozilla
diff --git a/dom/workers/remoteworkers/RemoteWorkerParent.h b/dom/workers/remoteworkers/RemoteWorkerParent.h
new file mode 100644
index 0000000000..811206eb91
--- /dev/null
+++ b/dom/workers/remoteworkers/RemoteWorkerParent.h
@@ -0,0 +1,62 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_RemoteWorkerParent_h
+#define mozilla_dom_RemoteWorkerParent_h
+
+#include "mozilla/dom/PRemoteWorkerParent.h"
+
+namespace mozilla::dom {
+
+class RemoteWorkerController;
+
+/**
+ * PBackground-managed parent actor that is mutually associated with a single
+ * RemoteWorkerController.  Relays error/close events to the controller and in
+ * turns is told life-cycle events.
+ */
+class RemoteWorkerParent final : public PRemoteWorkerParent {
+  friend class PRemoteWorkerParent;
+
+ public:
+  NS_INLINE_DECL_REFCOUNTING(RemoteWorkerParent, override);
+
+  RemoteWorkerParent();
+
+  void Initialize(bool aAlreadyRegistered = false);
+
+  void SetController(RemoteWorkerController* aController);
+
+  void MaybeSendDelete();
+
+ private:
+  ~RemoteWorkerParent();
+
+  already_AddRefed<PFetchEventOpProxyParent> AllocPFetchEventOpProxyParent(
+      const ParentToChildServiceWorkerFetchEventOpArgs& aArgs);
+
+  void ActorDestroy(mozilla::ipc::IProtocol::ActorDestroyReason) override;
+
+  mozilla::ipc::IPCResult RecvError(const ErrorValue& aValue);
+
+  mozilla::ipc::IPCResult RecvNotifyLock(const bool& aCreated);
+
+  mozilla::ipc::IPCResult RecvNotifyWebTransport(const bool& aCreated);
+
+  mozilla::ipc::IPCResult RecvClose();
+
+  mozilla::ipc::IPCResult RecvCreated(const bool& aStatus);
+
+  mozilla::ipc::IPCResult RecvSetServiceWorkerSkipWaitingFlag(
+      SetServiceWorkerSkipWaitingFlagResolver&& aResolve);
+
+  bool mDeleteSent = false;
+  RefPtr<RemoteWorkerController> mController;
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_RemoteWorkerParent_h
diff --git a/dom/workers/remoteworkers/RemoteWorkerService.cpp b/dom/workers/remoteworkers/RemoteWorkerService.cpp
new file mode 100644
index 0000000000..5a33160c04
--- /dev/null
+++ b/dom/workers/remoteworkers/RemoteWorkerService.cpp
@@ -0,0 +1,345 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "RemoteWorkerService.h"
+
+#include "mozilla/dom/PRemoteWorkerParent.h"
+#include "mozilla/ipc/BackgroundChild.h"
+#include "mozilla/ipc/BackgroundParent.h"
+#include "mozilla/ipc/PBackgroundChild.h"
+#include "mozilla/ipc/PBackgroundParent.h"
+#include "mozilla/SchedulerGroup.h"
+#include "mozilla/Services.h"
+#include "mozilla/SpinEventLoopUntil.h"
+#include "mozilla/StaticMutex.h"
+#include "mozilla/StaticPtr.h"
+#include "nsIObserverService.h"
+#include "nsIThread.h"
+#include "nsThreadUtils.h"
+#include "nsXPCOMPrivate.h"
+#include "RemoteWorkerController.h"
+#include "RemoteWorkerServiceChild.h"
+#include "RemoteWorkerServiceParent.h"
+
+namespace mozilla {
+
+using namespace ipc;
+
+namespace dom {
+
+namespace {
+
+StaticMutex sRemoteWorkerServiceMutex;
+StaticRefPtr<RemoteWorkerService> sRemoteWorkerService;
+
+}  // namespace
+
+/**
+ * Block shutdown until the RemoteWorkers have shutdown so that we do not try
+ * and shutdown the RemoteWorkerService "Worker Launcher" thread until they have
+ * cleanly shutdown.
+ *
+ * Note that this shutdown blocker is not used to initiate shutdown of any of
+ * the workers directly; their shutdown is initiated from PBackground in the
+ * parent process.  The shutdown blocker just exists to avoid races around
+ * shutting down the worker launcher thread after all of the workers have
+ * shutdown and torn down their actors.
+ *
+ * Currently, it should be the case that the ContentParent should want to keep
+ * the content processes alive until the RemoteWorkers have all reported their
+ * shutdown over IPC (on the "Worker Launcher" thread).  So for an orderly
+ * content process shutdown that is waiting for there to no longer be a reason
+ * to keep the content process alive, this blocker should only hang around for
+ * a brief period of time, helping smooth out lifecycle edge cases.
+ *
+ * In the event the content process is trying to shutdown while the
+ * RemoteWorkers think they should still be alive, it's possible that this
+ * blocker could expose the relevant logic error in the parent process if no
+ * attempt is made to shutdown the RemoteWorker.
+ *
+ * ## Major Implementation Note: This is not actually an nsIAsyncShutdownClient
+ *
+ * Until https://bugzilla.mozilla.org/show_bug.cgi?id=1760855 provides us with a
+ * non-JS implementation of nsIAsyncShutdownService, this implementation
+ * actually uses event loop spinning.  The patch on
+ * https://bugzilla.mozilla.org/show_bug.cgi?id=1775784 that changed us to use
+ * this hack can be reverted when the time is right.
+ *
+ * Event loop spinning is handled by `RemoteWorkerService::Observe` and it calls
+ * our exposed `ShouldBlockShutdown()` to know when to stop spinning.
+ */
+class RemoteWorkerServiceShutdownBlocker final {
+  ~RemoteWorkerServiceShutdownBlocker() = default;
+
+ public:
+  explicit RemoteWorkerServiceShutdownBlocker(RemoteWorkerService* aService)
+      : mService(aService), mBlockShutdown(true) {}
+
+  void RemoteWorkersAllGoneAllowShutdown() {
+    mService->FinishShutdown();
+    mService = nullptr;
+
+    mBlockShutdown = false;
+  }
+
+  bool ShouldBlockShutdown() { return mBlockShutdown; }
+
+  NS_INLINE_DECL_REFCOUNTING(RemoteWorkerServiceShutdownBlocker);
+
+  RefPtr<RemoteWorkerService> mService;
+  bool mBlockShutdown;
+};
+
+RemoteWorkerServiceKeepAlive::RemoteWorkerServiceKeepAlive(
+    RemoteWorkerServiceShutdownBlocker* aBlocker)
+    : mBlocker(aBlocker) {
+  MOZ_ASSERT(NS_IsMainThread());
+}
+
+RemoteWorkerServiceKeepAlive::~RemoteWorkerServiceKeepAlive() {
+  // Dispatch a runnable to the main thread to tell the Shutdown Blocker to
+  // remove itself and notify the RemoteWorkerService it can finish its
+  // shutdown.  We dispatch this to the main thread even if we are already on
+  // the main thread.
+  nsCOMPtr<nsIRunnable> r =
+      NS_NewRunnableFunction(__func__, [blocker = std::move(mBlocker)] {
+        blocker->RemoteWorkersAllGoneAllowShutdown();
+      });
+  MOZ_ALWAYS_SUCCEEDS(SchedulerGroup::Dispatch(r.forget()));
+}
+
+/* static */
+void RemoteWorkerService::Initialize() {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  StaticMutexAutoLock lock(sRemoteWorkerServiceMutex);
+  MOZ_ASSERT(!sRemoteWorkerService);
+
+  RefPtr<RemoteWorkerService> service = new RemoteWorkerService();
+
+  // ## Content Process Initialization Case
+  //
+  // We are being told to initialize now that we know what our remote type is.
+  // Now is a fine time to call InitializeOnMainThread.
+  if (!XRE_IsParentProcess()) {
+    nsresult rv = service->InitializeOnMainThread();
+    if (NS_WARN_IF(NS_FAILED(rv))) {
+      return;
+    }
+
+    sRemoteWorkerService = service;
+    return;
+  }
+  // ## Parent Process Initialization Case
+  //
+  // Otherwise we are in the parent process and were invoked by
+  // nsLayoutStatics::Initialize.  We wait until profile-after-change to kick
+  // off the Worker Launcher thread and have it connect to PBackground.  This is
+  // an appropriate time for remote worker APIs to come online, especially
+  // because the PRemoteWorkerService mechanism needs processes to eagerly
+  // register themselves with PBackground since the design explicitly intends to
+  // avoid blocking on the main threads.  (Disclaimer: Currently, things block
+  // on the main thread.)
+
+  nsCOMPtr<nsIObserverService> obs = services::GetObserverService();
+  if (NS_WARN_IF(!obs)) {
+    return;
+  }
+
+  nsresult rv = obs->AddObserver(service, "profile-after-change", false);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return;
+  }
+
+  sRemoteWorkerService = service;
+}
+
+/* static */
+nsIThread* RemoteWorkerService::Thread() {
+  StaticMutexAutoLock lock(sRemoteWorkerServiceMutex);
+  MOZ_ASSERT(sRemoteWorkerService);
+  MOZ_ASSERT(sRemoteWorkerService->mThread);
+  return sRemoteWorkerService->mThread;
+}
+
+/* static */
+already_AddRefed<RemoteWorkerServiceKeepAlive>
+RemoteWorkerService::MaybeGetKeepAlive() {
+  StaticMutexAutoLock lock(sRemoteWorkerServiceMutex);
+  // In normal operation no one should be calling this without a service
+  // existing, so assert, but we'll also handle this being null as it is a
+  // plausible shutdown race.
+  MOZ_ASSERT(sRemoteWorkerService);
+  if (!sRemoteWorkerService) {
+    return nullptr;
+  }
+
+  // Note that this value can be null, but this all handles that.
+  auto lockedKeepAlive = sRemoteWorkerService->mKeepAlive.Lock();
+  RefPtr<RemoteWorkerServiceKeepAlive> extraRef = *lockedKeepAlive;
+  return extraRef.forget();
+}
+
+nsresult RemoteWorkerService::InitializeOnMainThread() {
+  // I would like to call this thread "DOM Remote Worker Launcher", but the max
+  // length is 16 chars.
+  nsresult rv = NS_NewNamedThread("Worker Launcher", getter_AddRefs(mThread));
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  nsCOMPtr<nsIObserverService> obs = services::GetObserverService();
+  if (NS_WARN_IF(!obs)) {
+    return NS_ERROR_FAILURE;
+  }
+
+  rv = obs->AddObserver(this, NS_XPCOM_SHUTDOWN_OBSERVER_ID, false);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  mShutdownBlocker = new RemoteWorkerServiceShutdownBlocker(this);
+
+  {
+    RefPtr<RemoteWorkerServiceKeepAlive> keepAlive =
+        new RemoteWorkerServiceKeepAlive(mShutdownBlocker);
+
+    auto lockedKeepAlive = mKeepAlive.Lock();
+    *lockedKeepAlive = std::move(keepAlive);
+  }
+
+  RefPtr<RemoteWorkerService> self = this;
+  nsCOMPtr<nsIRunnable> r = NS_NewRunnableFunction(
+      "InitializeThread", [self]() { self->InitializeOnTargetThread(); });
+
+  rv = mThread->Dispatch(r.forget(), NS_DISPATCH_NORMAL);
+  if (NS_WARN_IF(NS_FAILED(rv))) {
+    return rv;
+  }
+
+  return NS_OK;
+}
+
+RemoteWorkerService::RemoteWorkerService()
+    : mKeepAlive(nullptr, "RemoteWorkerService::mKeepAlive") {
+  MOZ_ASSERT(NS_IsMainThread());
+}
+
+RemoteWorkerService::~RemoteWorkerService() = default;
+
+void RemoteWorkerService::InitializeOnTargetThread() {
+  MOZ_ASSERT(mThread);
+  MOZ_ASSERT(mThread->IsOnCurrentThread());
+
+  PBackgroundChild* backgroundActor =
+      BackgroundChild::GetOrCreateForCurrentThread();
+  if (NS_WARN_IF(!backgroundActor)) {
+    return;
+  }
+
+  RefPtr<RemoteWorkerServiceChild> serviceActor =
+      MakeAndAddRef<RemoteWorkerServiceChild>();
+  if (NS_WARN_IF(!backgroundActor->SendPRemoteWorkerServiceConstructor(
+          serviceActor))) {
+    return;
+  }
+
+  // Now we are ready!
+  mActor = serviceActor;
+}
+
+void RemoteWorkerService::CloseActorOnTargetThread() {
+  MOZ_ASSERT(mThread);
+  MOZ_ASSERT(mThread->IsOnCurrentThread());
+
+  // If mActor is nullptr it means that initialization failed.
+  if (mActor) {
+    // Here we need to shutdown the IPC protocol.
+    mActor->Send__delete__(mActor);
+    mActor = nullptr;
+  }
+}
+
+NS_IMETHODIMP
+RemoteWorkerService::Observe(nsISupports* aSubject, const char* aTopic,
+                             const char16_t* aData) {
+  if (!strcmp(aTopic, NS_XPCOM_SHUTDOWN_OBSERVER_ID)) {
+    MOZ_ASSERT(mThread);
+
+    nsCOMPtr<nsIObserverService> obs = services::GetObserverService();
+    if (obs) {
+      obs->RemoveObserver(this, NS_XPCOM_SHUTDOWN_OBSERVER_ID);
+    }
+
+    // Note that nsObserverList::NotifyObservers will hold a strong reference to
+    // our instance throughout the entire duration of this call, so it is not
+    // necessary for us to hold a kungFuDeathGrip here.
+
+    // Drop our keep-alive.  This could immediately result in our blocker saying
+    // it's okay for us to shutdown.  SpinEventLoopUntil checks the predicate
+    // before spinning, so in the ideal case we will not spin the loop at all.
+    BeginShutdown();
+
+    MOZ_ALWAYS_TRUE(SpinEventLoopUntil(
+        "RemoteWorkerService::Observe"_ns,
+        [&]() { return !mShutdownBlocker->ShouldBlockShutdown(); }));
+
+    mShutdownBlocker = nullptr;
+
+    return NS_OK;
+  }
+
+  MOZ_ASSERT(!strcmp(aTopic, "profile-after-change"));
+  MOZ_ASSERT(XRE_IsParentProcess());
+
+  nsCOMPtr<nsIObserverService> obs = services::GetObserverService();
+  if (obs) {
+    obs->RemoveObserver(this, "profile-after-change");
+  }
+
+  return InitializeOnMainThread();
+}
+
+void RemoteWorkerService::BeginShutdown() {
+  // Drop our keepalive reference which may allow near-immediate removal of the
+  // blocker.
+  auto lockedKeepAlive = mKeepAlive.Lock();
+  *lockedKeepAlive = nullptr;
+}
+
+void RemoteWorkerService::FinishShutdown() {
+  // Clear the singleton before spinning the event loop when shutting down the
+  // thread so that MaybeGetKeepAlive() can assert if there are any late calls
+  // and to better reflect the actual state.
+  //
+  // Our caller, the RemoteWorkerServiceShutdownBlocker, will continue to hold a
+  // strong reference to us until we return from this call, so there are no
+  // lifecycle implications to dropping this reference.
+  {
+    StaticMutexAutoLock lock(sRemoteWorkerServiceMutex);
+    sRemoteWorkerService = nullptr;
+  }
+
+  RefPtr<RemoteWorkerService> self = this;
+  nsCOMPtr<nsIRunnable> r =
+      NS_NewRunnableFunction("RemoteWorkerService::CloseActorOnTargetThread",
+                             [self]() { self->CloseActorOnTargetThread(); });
+
+  mThread->Dispatch(r.forget(), NS_DISPATCH_NORMAL);
+
+  // We've posted a shutdown message; now shutdown the thread.  This will spin
+  // a nested event loop waiting for the thread to process all pending events
+  // (including the just dispatched CloseActorOnTargetThread which will close
+  // the actor), ensuring to block main thread shutdown long enough to avoid
+  // races.
+  mThread->Shutdown();
+  mThread = nullptr;
+}
+
+NS_IMPL_ISUPPORTS(RemoteWorkerService, nsIObserver)
+
+}  // namespace dom
+}  // namespace mozilla
diff --git a/dom/workers/remoteworkers/RemoteWorkerService.h b/dom/workers/remoteworkers/RemoteWorkerService.h
new file mode 100644
index 0000000000..9e05e3958b
--- /dev/null
+++ b/dom/workers/remoteworkers/RemoteWorkerService.h
@@ -0,0 +1,123 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_RemoteWorkerService_h
+#define mozilla_dom_RemoteWorkerService_h
+
+#include "mozilla/AlreadyAddRefed.h"
+#include "mozilla/DataMutex.h"
+#include "nsCOMPtr.h"
+#include "nsIObserver.h"
+#include "nsISupportsImpl.h"
+
+class nsIThread;
+
+namespace mozilla::dom {
+
+class RemoteWorkerService;
+class RemoteWorkerServiceChild;
+class RemoteWorkerServiceShutdownBlocker;
+
+/**
+ * Refcounted lifecycle helper; when its refcount goes to zero its destructor
+ * will call RemoteWorkerService::Shutdown() which will remove the shutdown
+ * blocker and shutdown the "Worker Launcher" thread.
+ *
+ * The RemoteWorkerService itself will hold a reference to this singleton which
+ * it will use to hand out additional refcounts to RemoteWorkerChild instances.
+ * When the shutdown blocker is notified that it's time to shutdown, the
+ * RemoteWorkerService's reference will be dropped.
+ */
+class RemoteWorkerServiceKeepAlive {
+ public:
+  explicit RemoteWorkerServiceKeepAlive(
+      RemoteWorkerServiceShutdownBlocker* aBlocker);
+
+ private:
+  ~RemoteWorkerServiceKeepAlive();
+
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(RemoteWorkerServiceKeepAlive);
+
+  RefPtr<RemoteWorkerServiceShutdownBlocker> mBlocker;
+};
+
+/**
+ * Every process has a RemoteWorkerService which does the actual spawning of
+ * RemoteWorkerChild instances. The RemoteWorkerService creates a "Worker
+ * Launcher" thread at initialization on which it creates a
+ * RemoteWorkerServiceChild to service spawn requests. The thread is exposed as
+ * RemoteWorkerService::Thread(). A new/distinct thread is used because we
+ * (eventually) don't want to deal with main-thread contention, content
+ * processes have no equivalent of a PBackground thread, and actors are bound to
+ * specific threads.
+ *
+ * (Disclaimer: currently most RemoteWorkerOps need to happen on the main thread
+ * because the main-thread ends up as the owner of the worker and all
+ * manipulation of the worker must happen from the owning thread.)
+ */
+class RemoteWorkerService final : public nsIObserver {
+  friend class RemoteWorkerServiceShutdownBlocker;
+  friend class RemoteWorkerServiceKeepAlive;
+
+ public:
+  NS_DECL_THREADSAFE_ISUPPORTS
+  NS_DECL_NSIOBSERVER
+
+  // To be called when a process is initialized on main-thread.
+  static void Initialize();
+
+  static nsIThread* Thread();
+
+  // Called by RemoteWorkerChild instances on the "Worker Launcher" thread at
+  // their creation to assist in tracking when it's safe to shutdown the
+  // RemoteWorkerService and "Worker Launcher" thread.  This method will return
+  // a null pointer if the RemoteWorkerService has already begun shutdown.
+  //
+  // This is somewhat awkwardly a static method because the RemoteWorkerChild
+  // instances are not managed by RemoteWorkerServiceChild, but instead are
+  // managed by PBackground(Child).  So we either need to find the
+  // RemoteWorkerService via the hidden singleton or by having the
+  // RemoteWorkerChild use PBackgroundChild::ManagedPRemoteWorkerServiceChild()
+  // to locate the instance.  We are choosing to use the singleton because we
+  // already need to acquire a mutex in the call regardless and the upcoming
+  // refactorings may want to start using new toplevel protocols and this will
+  // avoid requiring a change when that happens.
+  static already_AddRefed<RemoteWorkerServiceKeepAlive> MaybeGetKeepAlive();
+
+ private:
+  RemoteWorkerService();
+  ~RemoteWorkerService();
+
+  nsresult InitializeOnMainThread();
+
+  void InitializeOnTargetThread();
+
+  void CloseActorOnTargetThread();
+
+  // Called by RemoteWorkerServiceShutdownBlocker when it's time to drop the
+  // RemoteWorkerServiceKeepAlive reference.
+  void BeginShutdown();
+
+  // Called by RemoteWorkerServiceShutdownBlocker when the blocker has been
+  // removed and it's safe to shutdown the "Worker Launcher" thread.
+  void FinishShutdown();
+
+  nsCOMPtr<nsIThread> mThread;
+  RefPtr<RemoteWorkerServiceChild> mActor;
+  // The keep-alive is set and cleared on the main thread but we will hand out
+  // additional references to it from the "Worker Launcher" thread, so it's
+  // appropriate to use a mutex.  (Alternately we could have used a ThreadBound
+  // and set and cleared on the "Worker Launcher" thread, but that would
+  // involve more moving parts and could have complicated edge cases.)
+  DataMutex<RefPtr<RemoteWorkerServiceKeepAlive>> mKeepAlive;
+  // In order to poll the blocker to know when we can stop spinning the event
+  // loop at shutdown, we retain a reference to the blocker.
+  RefPtr<RemoteWorkerServiceShutdownBlocker> mShutdownBlocker;
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_RemoteWorkerService_h
diff --git a/dom/workers/remoteworkers/RemoteWorkerServiceChild.cpp b/dom/workers/remoteworkers/RemoteWorkerServiceChild.cpp
new file mode 100644
index 0000000000..100908064e
--- /dev/null
+++ b/dom/workers/remoteworkers/RemoteWorkerServiceChild.cpp
@@ -0,0 +1,16 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "RemoteWorkerServiceChild.h"
+#include "RemoteWorkerController.h"
+
+namespace mozilla::dom {
+
+RemoteWorkerServiceChild::RemoteWorkerServiceChild() = default;
+
+RemoteWorkerServiceChild::~RemoteWorkerServiceChild() = default;
+
+}  // namespace mozilla::dom
diff --git a/dom/workers/remoteworkers/RemoteWorkerServiceChild.h b/dom/workers/remoteworkers/RemoteWorkerServiceChild.h
new file mode 100644
index 0000000000..41ae879b29
--- /dev/null
+++ b/dom/workers/remoteworkers/RemoteWorkerServiceChild.h
@@ -0,0 +1,34 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_RemoteWorkerServiceChild_h
+#define mozilla_dom_RemoteWorkerServiceChild_h
+
+#include "mozilla/dom/PRemoteWorkerServiceChild.h"
+#include "nsISupportsImpl.h"
+
+namespace mozilla::dom {
+
+class RemoteWorkerController;
+class RemoteWorkerData;
+
+/**
+ * "Worker Launcher"-thread child actor created by the RemoteWorkerService to
+ * register itself with the PBackground RemoteWorkerManager in the parent.
+ */
+class RemoteWorkerServiceChild final : public PRemoteWorkerServiceChild {
+ public:
+  NS_INLINE_DECL_REFCOUNTING(RemoteWorkerServiceChild, final)
+
+  RemoteWorkerServiceChild();
+
+ private:
+  ~RemoteWorkerServiceChild();
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_RemoteWorkerServiceChild_h
diff --git a/dom/workers/remoteworkers/RemoteWorkerServiceParent.cpp b/dom/workers/remoteworkers/RemoteWorkerServiceParent.cpp
new file mode 100644
index 0000000000..c7fd5ea6c8
--- /dev/null
+++ b/dom/workers/remoteworkers/RemoteWorkerServiceParent.cpp
@@ -0,0 +1,34 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "RemoteWorkerServiceParent.h"
+#include "RemoteWorkerManager.h"
+#include "mozilla/ipc/BackgroundParent.h"
+
+namespace mozilla {
+
+using namespace ipc;
+
+namespace dom {
+
+RemoteWorkerServiceParent::RemoteWorkerServiceParent()
+    : mManager(RemoteWorkerManager::GetOrCreate()) {}
+
+RemoteWorkerServiceParent::~RemoteWorkerServiceParent() = default;
+
+void RemoteWorkerServiceParent::Initialize(const nsACString& aRemoteType) {
+  AssertIsOnBackgroundThread();
+  mRemoteType = aRemoteType;
+  mManager->RegisterActor(this);
+}
+
+void RemoteWorkerServiceParent::ActorDestroy(IProtocol::ActorDestroyReason) {
+  AssertIsOnBackgroundThread();
+  mManager->UnregisterActor(this);
+}
+
+}  // namespace dom
+}  // namespace mozilla
diff --git a/dom/workers/remoteworkers/RemoteWorkerServiceParent.h b/dom/workers/remoteworkers/RemoteWorkerServiceParent.h
new file mode 100644
index 0000000000..31ed29a78c
--- /dev/null
+++ b/dom/workers/remoteworkers/RemoteWorkerServiceParent.h
@@ -0,0 +1,41 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_RemoteWorkerServiceParent_h
+#define mozilla_dom_RemoteWorkerServiceParent_h
+
+#include "mozilla/dom/PRemoteWorkerServiceParent.h"
+#include "mozilla/dom/RemoteType.h"
+
+namespace mozilla::dom {
+
+class RemoteWorkerManager;
+
+/**
+ * PBackground parent actor that registers with the PBackground
+ * RemoteWorkerManager and used to relay spawn requests.
+ */
+class RemoteWorkerServiceParent final : public PRemoteWorkerServiceParent {
+ public:
+  RemoteWorkerServiceParent();
+  NS_INLINE_DECL_REFCOUNTING(RemoteWorkerServiceParent, override);
+
+  void ActorDestroy(mozilla::ipc::IProtocol::ActorDestroyReason) override;
+
+  void Initialize(const nsACString& aRemoteType);
+
+  nsCString GetRemoteType() const { return mRemoteType; }
+
+ private:
+  ~RemoteWorkerServiceParent();
+
+  RefPtr<RemoteWorkerManager> mManager;
+  nsCString mRemoteType = NOT_REMOTE_TYPE;
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_RemoteWorkerServiceParent_h
diff --git a/dom/workers/remoteworkers/RemoteWorkerTypes.ipdlh b/dom/workers/remoteworkers/RemoteWorkerTypes.ipdlh
new file mode 100644
index 0000000000..8894450b72
--- /dev/null
+++ b/dom/workers/remoteworkers/RemoteWorkerTypes.ipdlh
@@ -0,0 +1,130 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+include ClientIPCTypes;
+include IPCServiceWorkerDescriptor;
+include IPCServiceWorkerRegistrationDescriptor;
+include PBackgroundSharedTypes;
+include URIParams;
+include DOMTypes;
+include NeckoChannelParams;
+include ProtocolTypes;
+
+include "mozilla/dom/ClientIPCUtils.h";
+include "mozilla/dom/ReferrerInfoUtils.h";
+include "mozilla/dom/WorkerIPCUtils.h";
+
+using struct mozilla::void_t from "mozilla/ipc/IPCCore.h";
+using mozilla::dom::RequestCredentials from "mozilla/dom/RequestBinding.h";
+using mozilla::StorageAccess from "mozilla/StorageAccess.h";
+using mozilla::OriginTrials from "mozilla/OriginTrialsIPCUtils.h";
+using mozilla::dom::WorkerType from "mozilla/dom/WorkerBinding.h";
+
+namespace mozilla {
+namespace dom {
+
+struct ServiceWorkerData {
+  IPCServiceWorkerDescriptor descriptor;
+  IPCServiceWorkerRegistrationDescriptor registrationDescriptor;
+  nsString cacheName;
+  uint32_t loadFlags;
+  nsString id;
+};
+
+union OptionalServiceWorkerData {
+  void_t;
+  ServiceWorkerData;
+};
+
+struct RemoteWorkerData
+{
+  // This should only be used for devtools.
+  nsString originalScriptURL;
+
+  // It is important to pass these as URIParams instead of strings for blob
+  // URLs: they carry an additional bit of state with them (mIsRevoked) that
+  // gives us a chance to use them, even after they've been revoked. Because
+  // we're asynchronously calling into the parent process before potentially
+  // loading the worker, it is important to keep this state. Note that this
+  // isn't a panacea: once the URL has been revoked, it'll give the worker 5
+  // seconds to actually load it; so it's possible to still fail to load the
+  // blob URL if it takes too long to do the round trip.
+  URIParams baseScriptURL;
+  URIParams resolvedScriptURL;
+
+  nsString name;
+  WorkerType type;
+  RequestCredentials credentials;
+
+  PrincipalInfo loadingPrincipalInfo;
+  PrincipalInfo principalInfo;
+  PrincipalInfo partitionedPrincipalInfo;
+
+  bool useRegularPrincipal;
+  bool usingStorageAccess;
+
+  CookieJarSettingsArgs cookieJarSettings;
+
+  nsCString domain;
+
+  bool isSecureContext;
+
+  IPCClientInfo? clientInfo;
+
+  nullable nsIReferrerInfo referrerInfo;
+
+  StorageAccess storageAccess;
+
+  bool isThirdPartyContextToTopWindow;
+
+  bool shouldResistFingerprinting;
+
+  uint64_t? overriddenFingerprintingSettings;
+
+  OriginTrials originTrials;
+
+  OptionalServiceWorkerData serviceWorkerData;
+
+  nsID agentClusterId;
+
+  // Child process remote type where the worker should only run on.
+  nsCString remoteType;
+};
+
+// ErrorData/ErrorDataNote correspond to WorkerErrorReport/WorkerErrorNote
+// which in turn correspond to JSErrorReport/JSErrorNotes which allows JS to
+// report complicated errors such as redeclarations that involve multiple
+// distinct lines.  For more generic error-propagation IPC structures, see bug
+// 1357463 on making ErrorResult usable over IPC.
+
+struct ErrorDataNote {
+  uint32_t lineNumber;
+  uint32_t columnNumber;
+  nsString message;
+  nsString filename;
+};
+
+struct ErrorData {
+  bool isWarning;
+  uint32_t lineNumber;
+  uint32_t columnNumber;
+  nsString message;
+  nsString filename;
+  nsString line;
+  ErrorDataNote[] notes;
+};
+
+struct CSPViolation {
+  nsString json;
+};
+
+union ErrorValue {
+  nsresult;
+  ErrorData;
+  CSPViolation;
+  void_t;
+};
+
+} // namespace dom
+} // namespace mozilla
diff --git a/dom/workers/remoteworkers/moz.build b/dom/workers/remoteworkers/moz.build
new file mode 100644
index 0000000000..9983b7dd10
--- /dev/null
+++ b/dom/workers/remoteworkers/moz.build
@@ -0,0 +1,45 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+EXPORTS.mozilla.dom += [
+    "RemoteWorkerChild.h",
+    "RemoteWorkerController.h",
+    "RemoteWorkerControllerChild.h",
+    "RemoteWorkerControllerParent.h",
+    "RemoteWorkerManager.h",
+    "RemoteWorkerParent.h",
+    "RemoteWorkerService.h",
+    "RemoteWorkerServiceChild.h",
+    "RemoteWorkerServiceParent.h",
+]
+
+UNIFIED_SOURCES += [
+    "RemoteWorkerChild.cpp",
+    "RemoteWorkerController.cpp",
+    "RemoteWorkerControllerChild.cpp",
+    "RemoteWorkerControllerParent.cpp",
+    "RemoteWorkerManager.cpp",
+    "RemoteWorkerParent.cpp",
+    "RemoteWorkerService.cpp",
+    "RemoteWorkerServiceChild.cpp",
+    "RemoteWorkerServiceParent.cpp",
+]
+
+LOCAL_INCLUDES += [
+    "/dom/serviceworkers",
+    "/xpcom/build",
+]
+
+IPDL_SOURCES += [
+    "PRemoteWorker.ipdl",
+    "PRemoteWorkerController.ipdl",
+    "PRemoteWorkerService.ipdl",
+    "RemoteWorkerTypes.ipdlh",
+]
+
+include("/ipc/chromium/chromium-config.mozbuild")
+
+FINAL_LIBRARY = "xul"
diff --git a/dom/workers/sharedworkers/PSharedWorker.ipdl b/dom/workers/sharedworkers/PSharedWorker.ipdl
new file mode 100644
index 0000000000..2406a731da
--- /dev/null
+++ b/dom/workers/sharedworkers/PSharedWorker.ipdl
@@ -0,0 +1,40 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+include protocol PBackground;
+
+include RemoteWorkerTypes;
+
+namespace mozilla {
+namespace dom {
+
+/**
+ * Protocol for SharedWorker bindings to communicate with per-worker
+ * SharedWorkerManager instances in the parent via SharedWorkerChild /
+ * SharedWorkerParent and SharedWorkerService getting/creating the
+ * SharedWorkerManager if it doesn't already exist. Main-thread to PBackground.
+ */
+[ManualDealloc]
+protocol PSharedWorker
+{
+  manager PBackground;
+
+parent:
+  async Close();
+  async Suspend();
+  async Resume();
+  async Freeze();
+  async Thaw();
+
+child:
+  async Error(ErrorValue value);
+  async NotifyLock(bool aCreated);
+  async NotifyWebTransport(bool aCreated);
+  async Terminate();
+
+  async __delete__();
+};
+
+} // namespace dom
+} // namespace mozilla
diff --git a/dom/workers/sharedworkers/SharedWorker.cpp b/dom/workers/sharedworkers/SharedWorker.cpp
new file mode 100644
index 0000000000..d3bb3bfcaa
--- /dev/null
+++ b/dom/workers/sharedworkers/SharedWorker.cpp
@@ -0,0 +1,445 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "SharedWorker.h"
+
+#include "mozilla/AntiTrackingUtils.h"
+#include "mozilla/AsyncEventDispatcher.h"
+#include "mozilla/BasePrincipal.h"
+#include "mozilla/EventDispatcher.h"
+#include "mozilla/dom/ClientInfo.h"
+#include "mozilla/dom/Event.h"
+#include "mozilla/dom/MessageChannel.h"
+#include "mozilla/dom/MessagePort.h"
+#include "mozilla/dom/PMessagePort.h"
+#include "mozilla/dom/RemoteWorkerManager.h"  // RemoteWorkerManager::GetRemoteType
+#include "mozilla/dom/RemoteWorkerTypes.h"
+#include "mozilla/dom/SharedWorkerBinding.h"
+#include "mozilla/dom/SharedWorkerChild.h"
+#include "mozilla/dom/WorkerBinding.h"
+#include "mozilla/dom/WorkerLoadInfo.h"
+#include "mozilla/dom/WorkerPrivate.h"
+#include "mozilla/ipc/BackgroundChild.h"
+#include "mozilla/ipc/BackgroundUtils.h"
+#include "mozilla/ipc/PBackgroundChild.h"
+#include "mozilla/ipc/URIUtils.h"
+#include "mozilla/net/CookieJarSettings.h"
+#include "mozilla/StorageAccess.h"
+#include "nsGlobalWindowInner.h"
+#include "nsPIDOMWindow.h"
+
+#ifdef XP_WIN
+#  undef PostMessage
+#endif
+
+using namespace mozilla;
+using namespace mozilla::dom;
+using namespace mozilla::ipc;
+
+SharedWorker::SharedWorker(nsPIDOMWindowInner* aWindow,
+                           SharedWorkerChild* aActor, MessagePort* aMessagePort)
+    : DOMEventTargetHelper(aWindow),
+      mWindow(aWindow),
+      mActor(aActor),
+      mMessagePort(aMessagePort),
+      mFrozen(false) {
+  AssertIsOnMainThread();
+  MOZ_ASSERT(aActor);
+  MOZ_ASSERT(aMessagePort);
+}
+
+SharedWorker::~SharedWorker() {
+  AssertIsOnMainThread();
+  Close();
+}
+
+// static
+already_AddRefed<SharedWorker> SharedWorker::Constructor(
+    const GlobalObject& aGlobal, const nsAString& aScriptURL,
+    const StringOrWorkerOptions& aOptions, ErrorResult& aRv) {
+  AssertIsOnMainThread();
+
+  nsCOMPtr<nsPIDOMWindowInner> window =
+      do_QueryInterface(aGlobal.GetAsSupports());
+  MOZ_ASSERT(window);
+
+  // Our current idiom is that storage-related APIs specialize for the system
+  // principal themselves, which is consistent with StorageAllowedForwindow not
+  // specializing for the system principal.  Without this specialization we
+  // would end up with ePrivateBrowsing for system principaled private browsing
+  // windows which is explicitly not what we want.  System Principal code always
+  // should have access to storage.  It may make sense to enhance
+  // StorageAllowedForWindow in the future to handle this after comprehensive
+  // auditing.
+  nsCOMPtr<nsIPrincipal> principal = aGlobal.GetSubjectPrincipal();
+  StorageAccess storageAllowed;
+  if (principal && principal->IsSystemPrincipal()) {
+    storageAllowed = StorageAccess::eAllow;
+  } else {
+    storageAllowed = StorageAllowedForWindow(window);
+  }
+
+  if (storageAllowed == StorageAccess::eDeny) {
+    aRv.ThrowSecurityError("StorageAccess denied.");
+    return nullptr;
+  }
+
+  if (ShouldPartitionStorage(storageAllowed) &&
+      !StoragePartitioningEnabled(
+          storageAllowed, window->GetExtantDoc()->CookieJarSettings())) {
+    aRv.ThrowSecurityError("StoragePartitioning not enabled.");
+    return nullptr;
+  }
+
+  // Assert that the principal private browsing state matches the
+  // StorageAccess value.
+#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
+  if (storageAllowed == StorageAccess::ePrivateBrowsing) {
+    uint32_t privateBrowsingId = 0;
+    if (principal) {
+      MOZ_ALWAYS_SUCCEEDS(principal->GetPrivateBrowsingId(&privateBrowsingId));
+    }
+    MOZ_DIAGNOSTIC_ASSERT(privateBrowsingId != 0);
+  }
+#endif  // MOZ_DIAGNOSTIC_ASSERT_ENABLED
+
+  PBackgroundChild* actorChild = BackgroundChild::GetOrCreateForCurrentThread();
+  if (!actorChild || !actorChild->CanSend()) {
+    aRv.ThrowSecurityError("PBackground not available.");
+    return nullptr;
+  }
+
+  nsAutoString name;
+  WorkerType workerType = WorkerType::Classic;
+  RequestCredentials credentials = RequestCredentials::Omit;
+  if (aOptions.IsString()) {
+    name = aOptions.GetAsString();
+  } else {
+    MOZ_ASSERT(aOptions.IsWorkerOptions());
+    name = aOptions.GetAsWorkerOptions().mName;
+    workerType = aOptions.GetAsWorkerOptions().mType;
+    credentials = aOptions.GetAsWorkerOptions().mCredentials;
+  }
+
+  JSContext* cx = aGlobal.Context();
+
+  WorkerLoadInfo loadInfo;
+  aRv = WorkerPrivate::GetLoadInfo(
+      cx, window, nullptr, aScriptURL, workerType, credentials, false,
+      WorkerPrivate::OverrideLoadGroup, WorkerKindShared, &loadInfo);
+  if (NS_WARN_IF(aRv.Failed())) {
+    return nullptr;
+  }
+
+  PrincipalInfo principalInfo;
+  aRv = PrincipalToPrincipalInfo(loadInfo.mPrincipal, &principalInfo);
+  if (NS_WARN_IF(aRv.Failed())) {
+    return nullptr;
+  }
+
+  PrincipalInfo loadingPrincipalInfo;
+  aRv = PrincipalToPrincipalInfo(loadInfo.mLoadingPrincipal,
+                                 &loadingPrincipalInfo);
+  if (NS_WARN_IF(aRv.Failed())) {
+    return nullptr;
+  }
+
+  // Here, the PartitionedPrincipal is always equal to the SharedWorker's
+  // principal because the channel is not opened yet, and, because of this, it's
+  // not classified. We need to force the correct originAttributes.
+  //
+  // The sharedWorker's principal could be a null principal, e.g. loading a
+  // data url. In this case, we don't need to force the OAs for the partitioned
+  // principal because creating storage from a null principal will fail anyway.
+  // We should only do this for content principals.
+  //
+  // You can find more details in StoragePrincipalHelper.h
+  if (ShouldPartitionStorage(storageAllowed) &&
+      BasePrincipal::Cast(loadInfo.mPrincipal)->IsContentPrincipal()) {
+    nsCOMPtr<nsIScriptObjectPrincipal> sop = do_QueryInterface(window);
+    if (!sop) {
+      aRv.ThrowSecurityError("ScriptObjectPrincipal not available.");
+      return nullptr;
+    }
+
+    nsIPrincipal* windowPrincipal = sop->GetPrincipal();
+    if (!windowPrincipal) {
+      aRv.ThrowSecurityError("WindowPrincipal not available.");
+      return nullptr;
+    }
+
+    nsIPrincipal* windowPartitionedPrincipal = sop->PartitionedPrincipal();
+    if (!windowPartitionedPrincipal) {
+      aRv.ThrowSecurityError("WindowPartitionedPrincipal not available.");
+      return nullptr;
+    }
+
+    if (!windowPrincipal->Equals(windowPartitionedPrincipal)) {
+      loadInfo.mPartitionedPrincipal =
+          BasePrincipal::Cast(loadInfo.mPrincipal)
+              ->CloneForcingOriginAttributes(
+                  BasePrincipal::Cast(windowPartitionedPrincipal)
+                      ->OriginAttributesRef());
+    }
+  }
+
+  PrincipalInfo partitionedPrincipalInfo;
+  if (loadInfo.mPrincipal->Equals(loadInfo.mPartitionedPrincipal)) {
+    partitionedPrincipalInfo = principalInfo;
+  } else {
+    aRv = PrincipalToPrincipalInfo(loadInfo.mPartitionedPrincipal,
+                                   &partitionedPrincipalInfo);
+    if (NS_WARN_IF(aRv.Failed())) {
+      return nullptr;
+    }
+  }
+
+  // We don't actually care about this MessageChannel, but we use it to 'steal'
+  // its 2 connected ports.
+  nsCOMPtr<nsIGlobalObject> global = do_QueryInterface(window);
+  RefPtr<MessageChannel> channel = MessageChannel::Constructor(global, aRv);
+  if (NS_WARN_IF(aRv.Failed())) {
+    return nullptr;
+  }
+
+  UniqueMessagePortId portIdentifier;
+  channel->Port1()->CloneAndDisentangle(portIdentifier);
+
+  URIParams resolvedScriptURL;
+  SerializeURI(loadInfo.mResolvedScriptURI, resolvedScriptURL);
+
+  URIParams baseURL;
+  SerializeURI(loadInfo.mBaseURI, baseURL);
+
+  // Register this component to PBackground.
+  bool isSecureContext = JS::GetIsSecureContext(js::GetContextRealm(cx));
+
+  Maybe<IPCClientInfo> ipcClientInfo;
+  Maybe<ClientInfo> clientInfo = window->GetClientInfo();
+  if (clientInfo.isSome()) {
+    ipcClientInfo.emplace(clientInfo.value().ToIPC());
+  }
+
+  nsID agentClusterId = nsID::GenerateUUID();
+
+  net::CookieJarSettingsArgs cjsData;
+  MOZ_ASSERT(loadInfo.mCookieJarSettings);
+  net::CookieJarSettings::Cast(loadInfo.mCookieJarSettings)->Serialize(cjsData);
+
+  auto remoteType = RemoteWorkerManager::GetRemoteType(
+      loadInfo.mPrincipal, WorkerKind::WorkerKindShared);
+  if (NS_WARN_IF(remoteType.isErr())) {
+    aRv.Throw(remoteType.unwrapErr());
+    return nullptr;
+  }
+
+  Maybe<uint64_t> overriddenFingerprintingSettingsArg;
+  if (loadInfo.mOverriddenFingerprintingSettings.isSome()) {
+    overriddenFingerprintingSettingsArg.emplace(
+        uint64_t(loadInfo.mOverriddenFingerprintingSettings.ref()));
+  }
+
+  RemoteWorkerData remoteWorkerData(
+      nsString(aScriptURL), baseURL, resolvedScriptURL, name, workerType,
+      credentials, loadingPrincipalInfo, principalInfo,
+      partitionedPrincipalInfo, loadInfo.mUseRegularPrincipal,
+      loadInfo.mUsingStorageAccess, cjsData, loadInfo.mDomain, isSecureContext,
+      ipcClientInfo, loadInfo.mReferrerInfo, storageAllowed,
+      AntiTrackingUtils::IsThirdPartyWindow(window, nullptr),
+      loadInfo.mShouldResistFingerprinting, overriddenFingerprintingSettingsArg,
+      OriginTrials::FromWindow(nsGlobalWindowInner::Cast(window)),
+      void_t() /* OptionalServiceWorkerData */, agentClusterId,
+      remoteType.unwrap());
+
+  PSharedWorkerChild* pActor = actorChild->SendPSharedWorkerConstructor(
+      remoteWorkerData, loadInfo.mWindowID, portIdentifier.release());
+  if (!pActor) {
+    MOZ_ASSERT_UNREACHABLE("We already checked PBackground above.");
+    aRv.ThrowSecurityError("PBackground not available.");
+    return nullptr;
+  }
+
+  RefPtr<SharedWorkerChild> actor = static_cast<SharedWorkerChild*>(pActor);
+
+  RefPtr<SharedWorker> sharedWorker =
+      new SharedWorker(window, actor, channel->Port2());
+
+  // Let's inform the window about this SharedWorker.
+  nsGlobalWindowInner::Cast(window)->StoreSharedWorker(sharedWorker);
+  actor->SetParent(sharedWorker);
+
+  if (nsGlobalWindowInner::Cast(window)->IsSuspended()) {
+    sharedWorker->Suspend();
+  }
+
+  return sharedWorker.forget();
+}
+
+MessagePort* SharedWorker::Port() {
+  AssertIsOnMainThread();
+  return mMessagePort;
+}
+
+void SharedWorker::Freeze() {
+  AssertIsOnMainThread();
+  MOZ_ASSERT(!IsFrozen());
+
+  if (mFrozen) {
+    return;
+  }
+
+  mFrozen = true;
+
+  if (mActor) {
+    mActor->SendFreeze();
+  }
+}
+
+void SharedWorker::Thaw() {
+  AssertIsOnMainThread();
+  MOZ_ASSERT(IsFrozen());
+
+  if (!mFrozen) {
+    return;
+  }
+
+  mFrozen = false;
+
+  if (mActor) {
+    mActor->SendThaw();
+  }
+
+  if (!mFrozenEvents.IsEmpty()) {
+    nsTArray<RefPtr<Event>> events = std::move(mFrozenEvents);
+
+    for (uint32_t index = 0; index < events.Length(); index++) {
+      RefPtr<Event>& event = events[index];
+      MOZ_ASSERT(event);
+
+      RefPtr<EventTarget> target = event->GetTarget();
+      ErrorResult rv;
+      target->DispatchEvent(*event, rv);
+      if (rv.Failed()) {
+        NS_WARNING("Failed to dispatch event!");
+      }
+    }
+  }
+}
+
+void SharedWorker::QueueEvent(Event* aEvent) {
+  AssertIsOnMainThread();
+  MOZ_ASSERT(aEvent);
+  MOZ_ASSERT(IsFrozen());
+
+  mFrozenEvents.AppendElement(aEvent);
+}
+
+void SharedWorker::Close() {
+  AssertIsOnMainThread();
+
+  if (mWindow) {
+    nsGlobalWindowInner::Cast(mWindow)->ForgetSharedWorker(this);
+    mWindow = nullptr;
+  }
+
+  if (mActor) {
+    mActor->SendClose();
+    mActor->SetParent(nullptr);
+    mActor = nullptr;
+  }
+
+  if (mMessagePort) {
+    mMessagePort->Close();
+  }
+}
+
+void SharedWorker::Suspend() {
+  if (mActor) {
+    mActor->SendSuspend();
+  }
+}
+
+void SharedWorker::Resume() {
+  if (mActor) {
+    mActor->SendResume();
+  }
+}
+
+void SharedWorker::PostMessage(JSContext* aCx, JS::Handle<JS::Value> aMessage,
+                               const Sequence<JSObject*>& aTransferable,
+                               ErrorResult& aRv) {
+  AssertIsOnMainThread();
+  MOZ_ASSERT(mMessagePort);
+
+  mMessagePort->PostMessage(aCx, aMessage, aTransferable, aRv);
+}
+
+NS_IMPL_ADDREF_INHERITED(SharedWorker, DOMEventTargetHelper)
+NS_IMPL_RELEASE_INHERITED(SharedWorker, DOMEventTargetHelper)
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(SharedWorker)
+NS_INTERFACE_MAP_END_INHERITING(DOMEventTargetHelper)
+
+NS_IMPL_CYCLE_COLLECTION_CLASS(SharedWorker)
+
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(SharedWorker,
+                                                  DOMEventTargetHelper)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mWindow)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mMessagePort)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mFrozenEvents)
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED(SharedWorker,
+                                                DOMEventTargetHelper)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mWindow)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mMessagePort)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mFrozenEvents)
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+
+JSObject* SharedWorker::WrapObject(JSContext* aCx,
+                                   JS::Handle<JSObject*> aGivenProto) {
+  AssertIsOnMainThread();
+
+  return SharedWorker_Binding::Wrap(aCx, this, aGivenProto);
+}
+
+void SharedWorker::GetEventTargetParent(EventChainPreVisitor& aVisitor) {
+  AssertIsOnMainThread();
+
+  if (IsFrozen()) {
+    RefPtr<Event> event = aVisitor.mDOMEvent;
+    if (!event) {
+      event = EventDispatcher::CreateEvent(aVisitor.mEvent->mOriginalTarget,
+                                           aVisitor.mPresContext,
+                                           aVisitor.mEvent, u""_ns);
+    }
+
+    QueueEvent(event);
+
+    aVisitor.mCanHandle = false;
+    aVisitor.SetParentTarget(nullptr, false);
+    return;
+  }
+
+  DOMEventTargetHelper::GetEventTargetParent(aVisitor);
+}
+
+void SharedWorker::DisconnectFromOwner() {
+  Close();
+  DOMEventTargetHelper::DisconnectFromOwner();
+}
+
+void SharedWorker::ErrorPropagation(nsresult aError) {
+  AssertIsOnMainThread();
+  MOZ_ASSERT(mActor);
+  MOZ_ASSERT(NS_FAILED(aError));
+
+  RefPtr<AsyncEventDispatcher> errorEvent =
+      new AsyncEventDispatcher(this, u"error"_ns, CanBubble::eNo);
+  errorEvent->PostDOMEvent();
+
+  Close();
+}
diff --git a/dom/workers/sharedworkers/SharedWorker.h b/dom/workers/sharedworkers/SharedWorker.h
new file mode 100644
index 0000000000..be61de8889
--- /dev/null
+++ b/dom/workers/sharedworkers/SharedWorker.h
@@ -0,0 +1,96 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_workers_sharedworker_h__
+#define mozilla_dom_workers_sharedworker_h__
+
+#include "mozilla/dom/WorkerCommon.h"
+#include "mozilla/dom/BindingDeclarations.h"
+#include "mozilla/DOMEventTargetHelper.h"
+
+#ifdef XP_WIN
+#  undef PostMessage
+#endif
+
+class nsPIDOMWindowInner;
+
+namespace mozilla {
+class EventChainPreVisitor;
+
+namespace dom {
+class MessagePort;
+class StringOrWorkerOptions;
+class Event;
+
+class SharedWorkerChild;
+
+/**
+ * DOM binding. Holds a SharedWorkerChild. Must exist on the main thread because
+ * we only allow top-level windows to create SharedWorkers.
+ */
+class SharedWorker final : public DOMEventTargetHelper {
+  using ErrorResult = mozilla::ErrorResult;
+  using GlobalObject = mozilla::dom::GlobalObject;
+
+  RefPtr<nsPIDOMWindowInner> mWindow;
+  RefPtr<SharedWorkerChild> mActor;
+  RefPtr<MessagePort> mMessagePort;
+  nsTArray<RefPtr<Event>> mFrozenEvents;
+  bool mFrozen;
+
+ public:
+  static already_AddRefed<SharedWorker> Constructor(
+      const GlobalObject& aGlobal, const nsAString& aScriptURL,
+      const StringOrWorkerOptions& aOptions, ErrorResult& aRv);
+
+  MessagePort* Port();
+
+  bool IsFrozen() const { return mFrozen; }
+
+  void QueueEvent(Event* aEvent);
+
+  NS_DECL_ISUPPORTS_INHERITED
+  NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(SharedWorker, DOMEventTargetHelper)
+
+  IMPL_EVENT_HANDLER(error)
+
+  virtual JSObject* WrapObject(JSContext* aCx,
+                               JS::Handle<JSObject*> aGivenProto) override;
+
+  void GetEventTargetParent(EventChainPreVisitor& aVisitor) override;
+
+  void DisconnectFromOwner() override;
+
+  void ErrorPropagation(nsresult aError);
+
+  // Methods called from the window.
+
+  void Close();
+
+  void Suspend();
+
+  void Resume();
+
+  void Freeze();
+
+  void Thaw();
+
+ private:
+  SharedWorker(nsPIDOMWindowInner* aWindow, SharedWorkerChild* aActor,
+               MessagePort* aMessagePort);
+
+  // This class is reference-counted and will be destroyed from Release().
+  ~SharedWorker();
+
+  // Only called by MessagePort.
+  void PostMessage(JSContext* aCx, JS::Handle<JS::Value> aMessage,
+                   const Sequence<JSObject*>& aTransferable, ErrorResult& aRv);
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_workers_sharedworker_h__
diff --git a/dom/workers/sharedworkers/SharedWorkerChild.cpp b/dom/workers/sharedworkers/SharedWorkerChild.cpp
new file mode 100644
index 0000000000..21ae74681b
--- /dev/null
+++ b/dom/workers/sharedworkers/SharedWorkerChild.cpp
@@ -0,0 +1,181 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "SharedWorkerChild.h"
+#include "mozilla/dom/ErrorEvent.h"
+#include "mozilla/dom/ErrorEventBinding.h"
+#include "mozilla/dom/Exceptions.h"
+#include "mozilla/dom/RootedDictionary.h"
+#include "mozilla/dom/SecurityPolicyViolationEvent.h"
+#include "mozilla/dom/SecurityPolicyViolationEventBinding.h"
+#include "mozilla/dom/ScriptSettings.h"
+#include "mozilla/dom/SharedWorker.h"
+#include "mozilla/dom/WebTransport.h"
+#include "mozilla/dom/WindowGlobalChild.h"
+#include "mozilla/dom/WorkerError.h"
+#include "mozilla/dom/locks/LockManagerChild.h"
+
+namespace mozilla {
+
+using namespace ipc;
+
+namespace dom {
+
+SharedWorkerChild::SharedWorkerChild() : mParent(nullptr), mActive(true) {}
+
+SharedWorkerChild::~SharedWorkerChild() = default;
+
+void SharedWorkerChild::ActorDestroy(ActorDestroyReason aWhy) {
+  mActive = false;
+}
+
+void SharedWorkerChild::SendClose() {
+  if (mActive) {
+    // This is the last message.
+    mActive = false;
+    PSharedWorkerChild::SendClose();
+  }
+}
+
+void SharedWorkerChild::SendSuspend() {
+  if (mActive) {
+    PSharedWorkerChild::SendSuspend();
+  }
+}
+
+void SharedWorkerChild::SendResume() {
+  if (mActive) {
+    PSharedWorkerChild::SendResume();
+  }
+}
+
+void SharedWorkerChild::SendFreeze() {
+  if (mActive) {
+    PSharedWorkerChild::SendFreeze();
+  }
+}
+
+void SharedWorkerChild::SendThaw() {
+  if (mActive) {
+    PSharedWorkerChild::SendThaw();
+  }
+}
+
+IPCResult SharedWorkerChild::RecvError(const ErrorValue& aValue) {
+  if (!mParent) {
+    return IPC_OK();
+  }
+
+  if (aValue.type() == ErrorValue::Tnsresult) {
+    mParent->ErrorPropagation(aValue.get_nsresult());
+    return IPC_OK();
+  }
+
+  nsPIDOMWindowInner* window = mParent->GetOwner();
+  uint64_t innerWindowId = window ? window->WindowID() : 0;
+
+  if (aValue.type() == ErrorValue::TCSPViolation) {
+    SecurityPolicyViolationEventInit violationEventInit;
+    if (NS_WARN_IF(
+            !violationEventInit.Init(aValue.get_CSPViolation().json()))) {
+      return IPC_OK();
+    }
+
+    if (NS_WARN_IF(!window)) {
+      return IPC_OK();
+    }
+
+    RefPtr<EventTarget> eventTarget = window->GetExtantDoc();
+    if (NS_WARN_IF(!eventTarget)) {
+      return IPC_OK();
+    }
+
+    RefPtr<Event> event = SecurityPolicyViolationEvent::Constructor(
+        eventTarget, u"securitypolicyviolation"_ns, violationEventInit);
+    event->SetTrusted(true);
+
+    eventTarget->DispatchEvent(*event);
+    return IPC_OK();
+  }
+
+  if (aValue.type() == ErrorValue::TErrorData &&
+      aValue.get_ErrorData().isWarning()) {
+    // Don't fire any events for warnings. Just log to console.
+    WorkerErrorReport::LogErrorToConsole(aValue.get_ErrorData(), innerWindowId);
+    return IPC_OK();
+  }
+
+  AutoJSAPI jsapi;
+  jsapi.Init();
+
+  RefPtr<Event> event;
+  if (aValue.type() == ErrorValue::TErrorData) {
+    const ErrorData& errorData = aValue.get_ErrorData();
+    RootedDictionary<ErrorEventInit> errorInit(jsapi.cx());
+    errorInit.mBubbles = false;
+    errorInit.mCancelable = true;
+    errorInit.mMessage = errorData.message();
+    errorInit.mFilename = errorData.filename();
+    errorInit.mLineno = errorData.lineNumber();
+    errorInit.mColno = errorData.columnNumber();
+
+    event = ErrorEvent::Constructor(mParent, u"error"_ns, errorInit);
+  } else {
+    event = Event::Constructor(mParent, u"error"_ns, EventInit());
+  }
+  event->SetTrusted(true);
+
+  ErrorResult res;
+  bool defaultActionEnabled =
+      mParent->DispatchEvent(*event, CallerType::System, res);
+  if (res.Failed()) {
+    ThrowAndReport(window, res.StealNSResult());
+    return IPC_OK();
+  }
+
+  if (aValue.type() != ErrorValue::TErrorData) {
+    MOZ_ASSERT(aValue.type() == ErrorValue::Tvoid_t);
+    return IPC_OK();
+  }
+
+  if (defaultActionEnabled) {
+    WorkerErrorReport::LogErrorToConsole(aValue.get_ErrorData(), innerWindowId);
+  }
+
+  return IPC_OK();
+}
+
+IPCResult SharedWorkerChild::RecvNotifyLock(bool aCreated) {
+  if (!mParent) {
+    return IPC_OK();
+  }
+
+  locks::LockManagerChild::NotifyBFCacheOnMainThread(mParent->GetOwner(),
+                                                     aCreated);
+
+  return IPC_OK();
+}
+
+IPCResult SharedWorkerChild::RecvNotifyWebTransport(bool aCreated) {
+  if (!mParent) {
+    return IPC_OK();
+  }
+
+  WebTransport::NotifyBFCacheOnMainThread(mParent->GetOwner(), aCreated);
+
+  return IPC_OK();
+}
+
+IPCResult SharedWorkerChild::RecvTerminate() {
+  if (mParent) {
+    mParent->Close();
+  }
+
+  return IPC_OK();
+}
+
+}  // namespace dom
+}  // namespace mozilla
diff --git a/dom/workers/sharedworkers/SharedWorkerChild.h b/dom/workers/sharedworkers/SharedWorkerChild.h
new file mode 100644
index 0000000000..c899589320
--- /dev/null
+++ b/dom/workers/sharedworkers/SharedWorkerChild.h
@@ -0,0 +1,61 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_dom_SharedWorkerChild_h
+#define mozilla_dom_dom_SharedWorkerChild_h
+
+#include "mozilla/dom/PSharedWorkerChild.h"
+#include "nsISupportsImpl.h"
+
+namespace mozilla::dom {
+
+class SharedWorker;
+
+/**
+ * Held by SharedWorker bindings to remotely control sharedworker lifecycle and
+ * receive error and termination reports.
+ */
+class SharedWorkerChild final : public mozilla::dom::PSharedWorkerChild {
+  friend class PSharedWorkerChild;
+
+ public:
+  NS_INLINE_DECL_REFCOUNTING(SharedWorkerChild)
+
+  SharedWorkerChild();
+
+  void SetParent(SharedWorker* aSharedWorker) { mParent = aSharedWorker; }
+
+  void SendClose();
+
+  void SendSuspend();
+
+  void SendResume();
+
+  void SendFreeze();
+
+  void SendThaw();
+
+ private:
+  ~SharedWorkerChild();
+
+  mozilla::ipc::IPCResult RecvError(const ErrorValue& aValue);
+
+  mozilla::ipc::IPCResult RecvNotifyLock(bool aCreated);
+
+  mozilla::ipc::IPCResult RecvNotifyWebTransport(bool aCreated);
+
+  mozilla::ipc::IPCResult RecvTerminate();
+
+  void ActorDestroy(ActorDestroyReason aWhy) override;
+
+  // Raw pointer because mParent is set to null when released.
+  SharedWorker* MOZ_NON_OWNING_REF mParent;
+  bool mActive;
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_dom_SharedWorkerChild_h
diff --git a/dom/workers/sharedworkers/SharedWorkerManager.cpp b/dom/workers/sharedworkers/SharedWorkerManager.cpp
new file mode 100644
index 0000000000..37dbc700d9
--- /dev/null
+++ b/dom/workers/sharedworkers/SharedWorkerManager.cpp
@@ -0,0 +1,348 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "SharedWorkerManager.h"
+#include "SharedWorkerParent.h"
+#include "SharedWorkerService.h"
+#include "mozilla/dom/MessagePort.h"
+#include "mozilla/dom/PSharedWorker.h"
+#include "mozilla/ipc/BackgroundParent.h"
+#include "mozilla/ipc/URIUtils.h"
+#include "mozilla/dom/RemoteWorkerController.h"
+#include "nsIConsoleReportCollector.h"
+#include "nsIPrincipal.h"
+#include "nsProxyRelease.h"
+
+namespace mozilla::dom {
+
+// static
+already_AddRefed<SharedWorkerManagerHolder> SharedWorkerManager::Create(
+    SharedWorkerService* aService, nsIEventTarget* aPBackgroundEventTarget,
+    const RemoteWorkerData& aData, nsIPrincipal* aLoadingPrincipal,
+    const OriginAttributes& aEffectiveStoragePrincipalAttrs) {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  RefPtr<SharedWorkerManager> manager =
+      new SharedWorkerManager(aPBackgroundEventTarget, aData, aLoadingPrincipal,
+                              aEffectiveStoragePrincipalAttrs);
+
+  RefPtr<SharedWorkerManagerHolder> holder =
+      new SharedWorkerManagerHolder(manager, aService);
+  return holder.forget();
+}
+
+SharedWorkerManager::SharedWorkerManager(
+    nsIEventTarget* aPBackgroundEventTarget, const RemoteWorkerData& aData,
+    nsIPrincipal* aLoadingPrincipal,
+    const OriginAttributes& aEffectiveStoragePrincipalAttrs)
+    : mPBackgroundEventTarget(aPBackgroundEventTarget),
+      mLoadingPrincipal(aLoadingPrincipal),
+      mDomain(aData.domain()),
+      mEffectiveStoragePrincipalAttrs(aEffectiveStoragePrincipalAttrs),
+      mResolvedScriptURL(DeserializeURI(aData.resolvedScriptURL())),
+      mName(aData.name()),
+      mIsSecureContext(aData.isSecureContext()),
+      mSuspended(false),
+      mFrozen(false) {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(aLoadingPrincipal);
+}
+
+SharedWorkerManager::~SharedWorkerManager() {
+  NS_ReleaseOnMainThread("SharedWorkerManager::mLoadingPrincipal",
+                         mLoadingPrincipal.forget());
+  NS_ProxyRelease("SharedWorkerManager::mRemoteWorkerController",
+                  mPBackgroundEventTarget, mRemoteWorkerController.forget());
+}
+
+bool SharedWorkerManager::MaybeCreateRemoteWorker(
+    const RemoteWorkerData& aData, uint64_t aWindowID,
+    UniqueMessagePortId& aPortIdentifier, base::ProcessId aProcessId) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+
+  // Creating remote workers may result in creating new processes, but during
+  // parent shutdown that would add just noise, so better bail out.
+  if (AppShutdown::IsInOrBeyond(ShutdownPhase::AppShutdownConfirmed)) {
+    return false;
+  }
+
+  if (!mRemoteWorkerController) {
+    mRemoteWorkerController =
+        RemoteWorkerController::Create(aData, this, aProcessId);
+    if (NS_WARN_IF(!mRemoteWorkerController)) {
+      return false;
+    }
+  }
+
+  if (aWindowID) {
+    mRemoteWorkerController->AddWindowID(aWindowID);
+  }
+
+  mRemoteWorkerController->AddPortIdentifier(aPortIdentifier.release());
+  return true;
+}
+
+already_AddRefed<SharedWorkerManagerHolder>
+SharedWorkerManager::MatchOnMainThread(
+    SharedWorkerService* aService, const nsACString& aDomain,
+    nsIURI* aScriptURL, const nsAString& aName, nsIPrincipal* aLoadingPrincipal,
+    const OriginAttributes& aEffectiveStoragePrincipalAttrs) {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  bool urlEquals;
+  if (NS_FAILED(aScriptURL->Equals(mResolvedScriptURL, &urlEquals))) {
+    return nullptr;
+  }
+
+  bool match =
+      aDomain == mDomain && urlEquals && aName == mName &&
+      // We want to be sure that the window's principal subsumes the
+      // SharedWorker's loading principal and vice versa.
+      mLoadingPrincipal->Subsumes(aLoadingPrincipal) &&
+      aLoadingPrincipal->Subsumes(mLoadingPrincipal) &&
+      mEffectiveStoragePrincipalAttrs == aEffectiveStoragePrincipalAttrs;
+  if (!match) {
+    return nullptr;
+  }
+
+  RefPtr<SharedWorkerManagerHolder> holder =
+      new SharedWorkerManagerHolder(this, aService);
+  return holder.forget();
+}
+
+void SharedWorkerManager::AddActor(SharedWorkerParent* aParent) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  MOZ_ASSERT(aParent);
+  MOZ_ASSERT(!mActors.Contains(aParent));
+
+  mActors.AppendElement(aParent);
+
+  if (mLockCount) {
+    Unused << aParent->SendNotifyLock(true);
+  }
+
+  if (mWebTransportCount) {
+    Unused << aParent->SendNotifyWebTransport(true);
+  }
+
+  // NB: We don't update our Suspended/Frozen state here, yet. The aParent is
+  // responsible for doing so from SharedWorkerParent::ManagerCreated.
+  // XXX But we could avoid iterating all of our actors because if aParent is
+  // not frozen and we are, we would just need to thaw ourselves.
+}
+
+void SharedWorkerManager::RemoveActor(SharedWorkerParent* aParent) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  MOZ_ASSERT(aParent);
+  MOZ_ASSERT(mActors.Contains(aParent));
+
+  uint64_t windowID = aParent->WindowID();
+  if (windowID) {
+    mRemoteWorkerController->RemoveWindowID(windowID);
+  }
+
+  mActors.RemoveElement(aParent);
+
+  if (!mActors.IsEmpty()) {
+    // Our remaining actors could be all suspended or frozen.
+    UpdateSuspend();
+    UpdateFrozen();
+    return;
+  }
+}
+
+void SharedWorkerManager::Terminate() {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  MOZ_ASSERT(mActors.IsEmpty());
+  MOZ_ASSERT(mHolders.IsEmpty());
+
+  // mRemoteWorkerController creation can fail. If the creation fails
+  // mRemoteWorkerController is nullptr and we should stop termination here.
+  if (!mRemoteWorkerController) {
+    return;
+  }
+
+  mRemoteWorkerController->Terminate();
+  mRemoteWorkerController = nullptr;
+}
+
+void SharedWorkerManager::UpdateSuspend() {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  MOZ_ASSERT(mRemoteWorkerController);
+
+  uint32_t suspended = 0;
+
+  for (SharedWorkerParent* actor : mActors) {
+    if (actor->IsSuspended()) {
+      ++suspended;
+    }
+  }
+
+  // Call Suspend only when all of our actors' windows are suspended and call
+  // Resume only when one of them resumes.
+  if ((mSuspended && suspended == mActors.Length()) ||
+      (!mSuspended && suspended != mActors.Length())) {
+    return;
+  }
+
+  if (!mSuspended) {
+    mSuspended = true;
+    mRemoteWorkerController->Suspend();
+  } else {
+    mSuspended = false;
+    mRemoteWorkerController->Resume();
+  }
+}
+
+void SharedWorkerManager::UpdateFrozen() {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  MOZ_ASSERT(mRemoteWorkerController);
+
+  uint32_t frozen = 0;
+
+  for (SharedWorkerParent* actor : mActors) {
+    if (actor->IsFrozen()) {
+      ++frozen;
+    }
+  }
+
+  // Similar to UpdateSuspend, above, we only want to be frozen when all of our
+  // actors are frozen.
+  if ((mFrozen && frozen == mActors.Length()) ||
+      (!mFrozen && frozen != mActors.Length())) {
+    return;
+  }
+
+  if (!mFrozen) {
+    mFrozen = true;
+    mRemoteWorkerController->Freeze();
+  } else {
+    mFrozen = false;
+    mRemoteWorkerController->Thaw();
+  }
+}
+
+bool SharedWorkerManager::IsSecureContext() const { return mIsSecureContext; }
+
+void SharedWorkerManager::CreationFailed() {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+
+  for (SharedWorkerParent* actor : mActors) {
+    Unused << actor->SendError(NS_ERROR_FAILURE);
+  }
+}
+
+void SharedWorkerManager::CreationSucceeded() {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  // Nothing to do here.
+}
+
+void SharedWorkerManager::ErrorReceived(const ErrorValue& aValue) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+
+  for (SharedWorkerParent* actor : mActors) {
+    Unused << actor->SendError(aValue);
+  }
+}
+
+void SharedWorkerManager::LockNotified(bool aCreated) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  MOZ_ASSERT_IF(!aCreated, mLockCount > 0);
+
+  mLockCount += aCreated ? 1 : -1;
+
+  // Notify only when we either:
+  // 1. Got a new lock when nothing were there
+  // 2. Lost all locks
+  if ((aCreated && mLockCount == 1) || !mLockCount) {
+    for (SharedWorkerParent* actor : mActors) {
+      Unused << actor->SendNotifyLock(aCreated);
+    }
+  }
+};
+
+void SharedWorkerManager::WebTransportNotified(bool aCreated) {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+  MOZ_ASSERT_IF(!aCreated, mWebTransportCount > 0);
+
+  mWebTransportCount += aCreated ? 1 : -1;
+
+  // Notify only when we either:
+  // 1. Got a first WebTransport
+  // 2. The last WebTransport goes away
+  if ((aCreated && mWebTransportCount == 1) || mWebTransportCount == 0) {
+    for (SharedWorkerParent* actor : mActors) {
+      Unused << actor->SendNotifyWebTransport(aCreated);
+    }
+  }
+};
+
+void SharedWorkerManager::Terminated() {
+  ::mozilla::ipc::AssertIsOnBackgroundThread();
+
+  for (SharedWorkerParent* actor : mActors) {
+    Unused << actor->SendTerminate();
+  }
+}
+
+void SharedWorkerManager::RegisterHolder(SharedWorkerManagerHolder* aHolder) {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(aHolder);
+  MOZ_ASSERT(!mHolders.Contains(aHolder));
+
+  mHolders.AppendElement(aHolder);
+}
+
+void SharedWorkerManager::UnregisterHolder(SharedWorkerManagerHolder* aHolder) {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(aHolder);
+  MOZ_ASSERT(mHolders.Contains(aHolder));
+
+  mHolders.RemoveElement(aHolder);
+
+  if (!mHolders.IsEmpty()) {
+    return;
+  }
+
+  // Time to go.
+
+  aHolder->Service()->RemoveWorkerManagerOnMainThread(this);
+
+  RefPtr<SharedWorkerManager> self = this;
+  mPBackgroundEventTarget->Dispatch(
+      NS_NewRunnableFunction(
+          "SharedWorkerService::RemoveWorkerManagerOnMainThread",
+          [self]() { self->Terminate(); }),
+      NS_DISPATCH_NORMAL);
+}
+
+SharedWorkerManagerHolder::SharedWorkerManagerHolder(
+    SharedWorkerManager* aManager, SharedWorkerService* aService)
+    : mManager(aManager), mService(aService) {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(aManager);
+  MOZ_ASSERT(aService);
+
+  aManager->RegisterHolder(this);
+}
+
+SharedWorkerManagerHolder::~SharedWorkerManagerHolder() {
+  MOZ_ASSERT(NS_IsMainThread());
+  mManager->UnregisterHolder(this);
+}
+
+SharedWorkerManagerWrapper::SharedWorkerManagerWrapper(
+    already_AddRefed<SharedWorkerManagerHolder> aHolder)
+    : mHolder(aHolder) {
+  MOZ_ASSERT(NS_IsMainThread());
+}
+
+SharedWorkerManagerWrapper::~SharedWorkerManagerWrapper() {
+  NS_ReleaseOnMainThread("SharedWorkerManagerWrapper::mHolder",
+                         mHolder.forget());
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/workers/sharedworkers/SharedWorkerManager.h b/dom/workers/sharedworkers/SharedWorkerManager.h
new file mode 100644
index 0000000000..fceabca4d4
--- /dev/null
+++ b/dom/workers/sharedworkers/SharedWorkerManager.h
@@ -0,0 +1,164 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_SharedWorkerManager_h
+#define mozilla_dom_SharedWorkerManager_h
+
+#include "SharedWorkerParent.h"
+#include "mozilla/dom/RemoteWorkerController.h"
+#include "mozilla/dom/quota/CheckedUnsafePtr.h"
+#include "nsISupportsImpl.h"
+#include "nsTArray.h"
+
+class nsIPrincipal;
+
+namespace mozilla::dom {
+
+class UniqueMessagePortId;
+class RemoteWorkerData;
+class SharedWorkerManager;
+class SharedWorkerService;
+
+// Main-thread only object that keeps a manager and the service alive.
+// When the last SharedWorkerManagerHolder is released, the corresponding
+// manager unregisters itself from the service and terminates the worker.
+class SharedWorkerManagerHolder final
+    : public SupportsCheckedUnsafePtr<CheckIf<DiagnosticAssertEnabled>> {
+ public:
+  NS_INLINE_DECL_REFCOUNTING(SharedWorkerManagerHolder);
+
+  SharedWorkerManagerHolder(SharedWorkerManager* aManager,
+                            SharedWorkerService* aService);
+
+  SharedWorkerManager* Manager() const { return mManager; }
+
+  SharedWorkerService* Service() const { return mService; }
+
+ private:
+  ~SharedWorkerManagerHolder();
+
+  const RefPtr<SharedWorkerManager> mManager;
+  const RefPtr<SharedWorkerService> mService;
+};
+
+// Thread-safe wrapper for SharedWorkerManagerHolder.
+class SharedWorkerManagerWrapper final {
+ public:
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(SharedWorkerManagerWrapper);
+
+  explicit SharedWorkerManagerWrapper(
+      already_AddRefed<SharedWorkerManagerHolder> aHolder);
+
+  SharedWorkerManager* Manager() const { return mHolder->Manager(); }
+
+ private:
+  ~SharedWorkerManagerWrapper();
+
+  RefPtr<SharedWorkerManagerHolder> mHolder;
+};
+
+/**
+ * PBackground instance that corresponds to a single logical Shared Worker that
+ * exists somewhere in the process tree. Referenced/owned by multiple
+ * SharedWorkerParent instances on the PBackground thread. Holds/owns a single
+ * RemoteWorkerController to interact with the actual shared worker thread,
+ * wherever it is located. Creates the RemoteWorkerController via
+ * RemoteWorkerController::Create which uses RemoteWorkerManager::Launch under
+ * the hood.
+ */
+class SharedWorkerManager final : public RemoteWorkerObserver {
+ public:
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(SharedWorkerManager, override);
+
+  // Called on main-thread thread methods
+
+  static already_AddRefed<SharedWorkerManagerHolder> Create(
+      SharedWorkerService* aService, nsIEventTarget* aPBackgroundEventTarget,
+      const RemoteWorkerData& aData, nsIPrincipal* aLoadingPrincipal,
+      const OriginAttributes& aEffectiveStoragePrincipalAttrs);
+
+  // Returns a holder if this manager matches. The holder blocks the shutdown of
+  // the manager.
+  already_AddRefed<SharedWorkerManagerHolder> MatchOnMainThread(
+      SharedWorkerService* aService, const nsACString& aDomain,
+      nsIURI* aScriptURL, const nsAString& aName,
+      nsIPrincipal* aLoadingPrincipal,
+      const OriginAttributes& aEffectiveStoragePrincipalAttrs);
+
+  // RemoteWorkerObserver
+
+  void CreationFailed() override;
+
+  void CreationSucceeded() override;
+
+  void ErrorReceived(const ErrorValue& aValue) override;
+
+  void LockNotified(bool aCreated) final;
+
+  void WebTransportNotified(bool aCreated) final;
+
+  void Terminated() override;
+
+  // Called on PBackground thread methods
+
+  bool MaybeCreateRemoteWorker(const RemoteWorkerData& aData,
+                               uint64_t aWindowID,
+                               UniqueMessagePortId& aPortIdentifier,
+                               base::ProcessId aProcessId);
+
+  void AddActor(SharedWorkerParent* aParent);
+
+  void RemoveActor(SharedWorkerParent* aParent);
+
+  void UpdateSuspend();
+
+  void UpdateFrozen();
+
+  bool IsSecureContext() const;
+
+  void Terminate();
+
+  // Called on main-thread only.
+
+  void RegisterHolder(SharedWorkerManagerHolder* aHolder);
+
+  void UnregisterHolder(SharedWorkerManagerHolder* aHolder);
+
+ private:
+  SharedWorkerManager(nsIEventTarget* aPBackgroundEventTarget,
+                      const RemoteWorkerData& aData,
+                      nsIPrincipal* aLoadingPrincipal,
+                      const OriginAttributes& aEffectiveStoragePrincipalAttrs);
+
+  ~SharedWorkerManager();
+
+  nsCOMPtr<nsIEventTarget> mPBackgroundEventTarget;
+
+  nsCOMPtr<nsIPrincipal> mLoadingPrincipal;
+  const nsCString mDomain;
+  const OriginAttributes mEffectiveStoragePrincipalAttrs;
+  const nsCOMPtr<nsIURI> mResolvedScriptURL;
+  const nsString mName;
+  const bool mIsSecureContext;
+  bool mSuspended;
+  bool mFrozen;
+  uint32_t mLockCount = 0;
+  uint32_t mWebTransportCount = 0;
+
+  // Raw pointers because SharedWorkerParent unregisters itself in
+  // ActorDestroy().
+  nsTArray<CheckedUnsafePtr<SharedWorkerParent>> mActors;
+
+  RefPtr<RemoteWorkerController> mRemoteWorkerController;
+
+  // Main-thread only. Raw Pointers because holders keep the manager alive and
+  // they unregister themselves in their DTOR.
+  nsTArray<CheckedUnsafePtr<SharedWorkerManagerHolder>> mHolders;
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_SharedWorkerManager_h
diff --git a/dom/workers/sharedworkers/SharedWorkerParent.cpp b/dom/workers/sharedworkers/SharedWorkerParent.cpp
new file mode 100644
index 0000000000..38e56f5100
--- /dev/null
+++ b/dom/workers/sharedworkers/SharedWorkerParent.cpp
@@ -0,0 +1,165 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "SharedWorkerParent.h"
+#include "SharedWorkerManager.h"
+#include "SharedWorkerService.h"
+#include "mozilla/dom/RemoteWorkerTypes.h"
+#include "mozilla/ipc/BackgroundParent.h"
+#include "mozilla/ipc/BackgroundUtils.h"
+#include "mozilla/Unused.h"
+
+namespace mozilla {
+
+using namespace ipc;
+
+namespace dom {
+
+SharedWorkerParent::SharedWorkerParent()
+    : mBackgroundEventTarget(GetCurrentSerialEventTarget()),
+      mStatus(eInit),
+      mSuspended(false),
+      mFrozen(false) {
+  AssertIsOnBackgroundThread();
+}
+
+SharedWorkerParent::~SharedWorkerParent() = default;
+
+void SharedWorkerParent::ActorDestroy(IProtocol::ActorDestroyReason aReason) {
+  AssertIsOnBackgroundThread();
+
+  if (mWorkerManagerWrapper) {
+    mWorkerManagerWrapper->Manager()->RemoveActor(this);
+    mWorkerManagerWrapper = nullptr;
+  }
+}
+
+void SharedWorkerParent::Initialize(
+    const RemoteWorkerData& aData, uint64_t aWindowID,
+    const MessagePortIdentifier& aPortIdentifier) {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(mStatus == eInit);
+
+  mWindowID = aWindowID;
+
+  mStatus = ePending;
+
+  RefPtr<SharedWorkerService> service = SharedWorkerService::GetOrCreate();
+  MOZ_ASSERT(service);
+  service->GetOrCreateWorkerManager(this, aData, aWindowID, aPortIdentifier);
+}
+
+IPCResult SharedWorkerParent::RecvClose() {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(mStatus == ePending || mStatus == eActive);
+
+  mStatus = eClosed;
+
+  if (mWorkerManagerWrapper) {
+    mWorkerManagerWrapper->Manager()->RemoveActor(this);
+    mWorkerManagerWrapper = nullptr;
+  }
+
+  Unused << Send__delete__(this);
+  return IPC_OK();
+}
+
+IPCResult SharedWorkerParent::RecvSuspend() {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(!mSuspended);
+  MOZ_ASSERT(mStatus == ePending || mStatus == eActive);
+
+  mSuspended = true;
+
+  if (mStatus == eActive) {
+    MOZ_ASSERT(mWorkerManagerWrapper);
+    mWorkerManagerWrapper->Manager()->UpdateSuspend();
+  }
+
+  return IPC_OK();
+}
+
+IPCResult SharedWorkerParent::RecvResume() {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(mSuspended);
+  MOZ_ASSERT(mStatus == ePending || mStatus == eActive);
+
+  mSuspended = false;
+
+  if (mStatus == eActive) {
+    MOZ_ASSERT(mWorkerManagerWrapper);
+    mWorkerManagerWrapper->Manager()->UpdateSuspend();
+  }
+
+  return IPC_OK();
+}
+
+IPCResult SharedWorkerParent::RecvFreeze() {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(!mFrozen);
+  MOZ_ASSERT(mStatus == ePending || mStatus == eActive);
+
+  mFrozen = true;
+
+  if (mStatus == eActive) {
+    MOZ_ASSERT(mWorkerManagerWrapper);
+    mWorkerManagerWrapper->Manager()->UpdateFrozen();
+  }
+
+  return IPC_OK();
+}
+
+IPCResult SharedWorkerParent::RecvThaw() {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(mFrozen);
+  MOZ_ASSERT(mStatus == ePending || mStatus == eActive);
+
+  mFrozen = false;
+
+  if (mStatus == eActive) {
+    MOZ_ASSERT(mWorkerManagerWrapper);
+    mWorkerManagerWrapper->Manager()->UpdateFrozen();
+  }
+
+  return IPC_OK();
+}
+
+void SharedWorkerParent::ManagerCreated(
+    already_AddRefed<SharedWorkerManagerWrapper> aWorkerManagerWrapper) {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(!mWorkerManagerWrapper);
+  MOZ_ASSERT(mStatus == ePending || mStatus == eClosed);
+
+  RefPtr<SharedWorkerManagerWrapper> wrapper = aWorkerManagerWrapper;
+
+  // Already gone.
+  if (mStatus == eClosed) {
+    wrapper->Manager()->RemoveActor(this);
+    return;
+  }
+
+  mStatus = eActive;
+  mWorkerManagerWrapper = wrapper;
+
+  mWorkerManagerWrapper->Manager()->UpdateFrozen();
+  mWorkerManagerWrapper->Manager()->UpdateSuspend();
+}
+
+void SharedWorkerParent::ErrorPropagation(nsresult aError) {
+  AssertIsOnBackgroundThread();
+  MOZ_ASSERT(NS_FAILED(aError));
+  MOZ_ASSERT(mStatus == ePending || mStatus == eClosed);
+
+  // Already gone.
+  if (mStatus == eClosed) {
+    return;
+  }
+
+  Unused << SendError(aError);
+}
+
+}  // namespace dom
+}  // namespace mozilla
diff --git a/dom/workers/sharedworkers/SharedWorkerParent.h b/dom/workers/sharedworkers/SharedWorkerParent.h
new file mode 100644
index 0000000000..c91e66cc2e
--- /dev/null
+++ b/dom/workers/sharedworkers/SharedWorkerParent.h
@@ -0,0 +1,81 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_dom_SharedWorkerParent_h
+#define mozilla_dom_dom_SharedWorkerParent_h
+
+#include "mozilla/dom/PSharedWorkerParent.h"
+#include "mozilla/dom/quota/CheckedUnsafePtr.h"
+#include "mozilla/ipc/BackgroundUtils.h"
+#include "nsISupportsImpl.h"
+
+namespace mozilla::dom {
+
+class MessagePortIdentifier;
+class RemoteWorkerData;
+class SharedWorkerManagerWrapper;
+
+/**
+ * PBackground actor that relays life-cycle events (freeze/thaw, suspend/resume,
+ * close) to the PBackground SharedWorkerManager and relays error/termination
+ * back to the child.
+ */
+class SharedWorkerParent final
+    : public mozilla::dom::PSharedWorkerParent,
+      public SupportsCheckedUnsafePtr<CheckIf<DiagnosticAssertEnabled>> {
+ public:
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(SharedWorkerParent)
+
+  SharedWorkerParent();
+
+  void Initialize(const RemoteWorkerData& aData, uint64_t aWindowID,
+                  const MessagePortIdentifier& aPortIdentifier);
+
+  void ManagerCreated(
+      already_AddRefed<SharedWorkerManagerWrapper> aWorkerManagerWrapper);
+
+  void ErrorPropagation(nsresult aError);
+
+  mozilla::ipc::IPCResult RecvClose();
+
+  mozilla::ipc::IPCResult RecvSuspend();
+
+  mozilla::ipc::IPCResult RecvResume();
+
+  mozilla::ipc::IPCResult RecvFreeze();
+
+  mozilla::ipc::IPCResult RecvThaw();
+
+  bool IsSuspended() const { return mSuspended; }
+
+  bool IsFrozen() const { return mFrozen; }
+
+  uint64_t WindowID() const { return mWindowID; }
+
+ private:
+  ~SharedWorkerParent();
+
+  void ActorDestroy(IProtocol::ActorDestroyReason aReason) override;
+
+  nsCOMPtr<nsIEventTarget> mBackgroundEventTarget;
+  RefPtr<SharedWorkerManagerWrapper> mWorkerManagerWrapper;
+
+  enum {
+    eInit,
+    ePending,
+    eActive,
+    eClosed,
+  } mStatus;
+
+  uint64_t mWindowID;
+
+  bool mSuspended;
+  bool mFrozen;
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_dom_SharedWorkerParent_h
diff --git a/dom/workers/sharedworkers/SharedWorkerService.cpp b/dom/workers/sharedworkers/SharedWorkerService.cpp
new file mode 100644
index 0000000000..c7e3ca1d4c
--- /dev/null
+++ b/dom/workers/sharedworkers/SharedWorkerService.cpp
@@ -0,0 +1,261 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "SharedWorkerService.h"
+#include "mozilla/dom/MessagePort.h"
+#include "mozilla/dom/RemoteWorkerTypes.h"
+#include "mozilla/dom/SharedWorkerManager.h"
+#include "mozilla/ipc/BackgroundParent.h"
+#include "mozilla/ipc/URIUtils.h"
+#include "mozilla/BasePrincipal.h"
+#include "mozilla/ClearOnShutdown.h"
+#include "mozilla/SchedulerGroup.h"
+#include "mozilla/StaticMutex.h"
+#include "nsIPrincipal.h"
+#include "nsProxyRelease.h"
+
+namespace mozilla {
+
+using namespace ipc;
+
+namespace dom {
+
+namespace {
+
+StaticMutex sSharedWorkerMutex;
+
+StaticRefPtr<SharedWorkerService> sSharedWorkerService;
+
+class GetOrCreateWorkerManagerRunnable final : public Runnable {
+ public:
+  GetOrCreateWorkerManagerRunnable(SharedWorkerService* aService,
+                                   SharedWorkerParent* aActor,
+                                   const RemoteWorkerData& aData,
+                                   uint64_t aWindowID,
+                                   const MessagePortIdentifier& aPortIdentifier)
+      : Runnable("GetOrCreateWorkerManagerRunnable"),
+        mBackgroundEventTarget(GetCurrentSerialEventTarget()),
+        mService(aService),
+        mActor(aActor),
+        mData(aData),
+        mWindowID(aWindowID),
+        mPortIdentifier(aPortIdentifier) {}
+
+  NS_IMETHOD
+  Run() {
+    mService->GetOrCreateWorkerManagerOnMainThread(
+        mBackgroundEventTarget, mActor, mData, mWindowID, mPortIdentifier);
+
+    return NS_OK;
+  }
+
+ private:
+  nsCOMPtr<nsIEventTarget> mBackgroundEventTarget;
+  RefPtr<SharedWorkerService> mService;
+  RefPtr<SharedWorkerParent> mActor;
+  RemoteWorkerData mData;
+  uint64_t mWindowID;
+  UniqueMessagePortId mPortIdentifier;
+};
+
+class WorkerManagerCreatedRunnable final : public Runnable {
+ public:
+  WorkerManagerCreatedRunnable(
+      already_AddRefed<SharedWorkerManagerWrapper> aManagerWrapper,
+      SharedWorkerParent* aActor, const RemoteWorkerData& aData,
+      uint64_t aWindowID, UniqueMessagePortId& aPortIdentifier)
+      : Runnable("WorkerManagerCreatedRunnable"),
+        mManagerWrapper(aManagerWrapper),
+        mActor(aActor),
+        mData(aData),
+        mWindowID(aWindowID),
+        mPortIdentifier(std::move(aPortIdentifier)) {}
+
+  NS_IMETHOD
+  Run() {
+    AssertIsOnBackgroundThread();
+
+    if (NS_WARN_IF(
+            !mActor->CanSend() ||
+            !mManagerWrapper->Manager()->MaybeCreateRemoteWorker(
+                mData, mWindowID, mPortIdentifier, mActor->OtherPid()))) {
+      // If we cannot send, the error won't arrive, but we may log something.
+      mActor->ErrorPropagation(NS_ERROR_FAILURE);
+      return NS_OK;
+    }
+
+    mManagerWrapper->Manager()->AddActor(mActor);
+    mActor->ManagerCreated(mManagerWrapper.forget());
+    return NS_OK;
+  }
+
+ private:
+  RefPtr<SharedWorkerManagerWrapper> mManagerWrapper;
+  RefPtr<SharedWorkerParent> mActor;
+  RemoteWorkerData mData;
+  uint64_t mWindowID;
+  UniqueMessagePortId mPortIdentifier;
+};
+
+class ErrorPropagationRunnable final : public Runnable {
+ public:
+  ErrorPropagationRunnable(SharedWorkerParent* aActor, nsresult aError)
+      : Runnable("ErrorPropagationRunnable"), mActor(aActor), mError(aError) {}
+
+  NS_IMETHOD
+  Run() {
+    AssertIsOnBackgroundThread();
+    mActor->ErrorPropagation(mError);
+    return NS_OK;
+  }
+
+ private:
+  RefPtr<SharedWorkerParent> mActor;
+  nsresult mError;
+};
+
+}  // namespace
+
+/* static */
+already_AddRefed<SharedWorkerService> SharedWorkerService::GetOrCreate() {
+  AssertIsOnBackgroundThread();
+
+  StaticMutexAutoLock lock(sSharedWorkerMutex);
+
+  if (!sSharedWorkerService) {
+    sSharedWorkerService = new SharedWorkerService();
+    // ClearOnShutdown can only be called on main thread
+    nsresult rv = SchedulerGroup::Dispatch(NS_NewRunnableFunction(
+        "RegisterSharedWorkerServiceClearOnShutdown", []() {
+          StaticMutexAutoLock lock(sSharedWorkerMutex);
+          MOZ_ASSERT(sSharedWorkerService);
+          ClearOnShutdown(&sSharedWorkerService);
+        }));
+    Unused << NS_WARN_IF(NS_FAILED(rv));
+  }
+
+  RefPtr<SharedWorkerService> instance = sSharedWorkerService;
+  return instance.forget();
+}
+
+/* static */
+SharedWorkerService* SharedWorkerService::Get() {
+  StaticMutexAutoLock lock(sSharedWorkerMutex);
+
+  MOZ_ASSERT(sSharedWorkerService);
+  return sSharedWorkerService;
+}
+
+void SharedWorkerService::GetOrCreateWorkerManager(
+    SharedWorkerParent* aActor, const RemoteWorkerData& aData,
+    uint64_t aWindowID, const MessagePortIdentifier& aPortIdentifier) {
+  AssertIsOnBackgroundThread();
+
+  // The real check happens on main-thread.
+  RefPtr<GetOrCreateWorkerManagerRunnable> r =
+      new GetOrCreateWorkerManagerRunnable(this, aActor, aData, aWindowID,
+                                           aPortIdentifier);
+
+  nsresult rv = SchedulerGroup::Dispatch(r.forget());
+  Unused << NS_WARN_IF(NS_FAILED(rv));
+}
+
+void SharedWorkerService::GetOrCreateWorkerManagerOnMainThread(
+    nsIEventTarget* aBackgroundEventTarget, SharedWorkerParent* aActor,
+    const RemoteWorkerData& aData, uint64_t aWindowID,
+    UniqueMessagePortId& aPortIdentifier) {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(aBackgroundEventTarget);
+  MOZ_ASSERT(aActor);
+
+  auto partitionedPrincipalOrErr =
+      PrincipalInfoToPrincipal(aData.partitionedPrincipalInfo());
+  if (NS_WARN_IF(partitionedPrincipalOrErr.isErr())) {
+    ErrorPropagationOnMainThread(aBackgroundEventTarget, aActor,
+                                 partitionedPrincipalOrErr.unwrapErr());
+    return;
+  }
+
+  auto loadingPrincipalOrErr =
+      PrincipalInfoToPrincipal(aData.loadingPrincipalInfo());
+  if (NS_WARN_IF(loadingPrincipalOrErr.isErr())) {
+    ErrorPropagationOnMainThread(aBackgroundEventTarget, aActor,
+                                 loadingPrincipalOrErr.unwrapErr());
+    return;
+  }
+
+  RefPtr<SharedWorkerManagerHolder> managerHolder;
+
+  nsCOMPtr<nsIPrincipal> loadingPrincipal = loadingPrincipalOrErr.unwrap();
+  nsCOMPtr<nsIPrincipal> partitionedPrincipal =
+      partitionedPrincipalOrErr.unwrap();
+
+  nsCOMPtr<nsIPrincipal> effectiveStoragePrincipal = partitionedPrincipal;
+  if (aData.useRegularPrincipal()) {
+    effectiveStoragePrincipal = loadingPrincipal;
+  }
+
+  // Let's see if there is already a SharedWorker to share.
+  nsCOMPtr<nsIURI> resolvedScriptURL =
+      DeserializeURI(aData.resolvedScriptURL());
+  for (SharedWorkerManager* workerManager : mWorkerManagers) {
+    managerHolder = workerManager->MatchOnMainThread(
+        this, aData.domain(), resolvedScriptURL, aData.name(), loadingPrincipal,
+        BasePrincipal::Cast(effectiveStoragePrincipal)->OriginAttributesRef());
+    if (managerHolder) {
+      break;
+    }
+  }
+
+  // Let's create a new one.
+  if (!managerHolder) {
+    managerHolder = SharedWorkerManager::Create(
+        this, aBackgroundEventTarget, aData, loadingPrincipal,
+        BasePrincipal::Cast(effectiveStoragePrincipal)->OriginAttributesRef());
+
+    mWorkerManagers.AppendElement(managerHolder->Manager());
+  } else {
+    // We are attaching the actor to an existing one.
+    if (managerHolder->Manager()->IsSecureContext() !=
+        aData.isSecureContext()) {
+      ErrorPropagationOnMainThread(aBackgroundEventTarget, aActor,
+                                   NS_ERROR_DOM_SECURITY_ERR);
+      return;
+    }
+  }
+
+  RefPtr<SharedWorkerManagerWrapper> wrapper =
+      new SharedWorkerManagerWrapper(managerHolder.forget());
+
+  RefPtr<WorkerManagerCreatedRunnable> r = new WorkerManagerCreatedRunnable(
+      wrapper.forget(), aActor, aData, aWindowID, aPortIdentifier);
+  aBackgroundEventTarget->Dispatch(r.forget(), NS_DISPATCH_NORMAL);
+}
+
+void SharedWorkerService::ErrorPropagationOnMainThread(
+    nsIEventTarget* aBackgroundEventTarget, SharedWorkerParent* aActor,
+    nsresult aError) {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(aBackgroundEventTarget);
+  MOZ_ASSERT(aActor);
+  MOZ_ASSERT(NS_FAILED(aError));
+
+  RefPtr<ErrorPropagationRunnable> r =
+      new ErrorPropagationRunnable(aActor, aError);
+  aBackgroundEventTarget->Dispatch(r.forget(), NS_DISPATCH_NORMAL);
+}
+
+void SharedWorkerService::RemoveWorkerManagerOnMainThread(
+    SharedWorkerManager* aManager) {
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(aManager);
+  MOZ_ASSERT(mWorkerManagers.Contains(aManager));
+
+  mWorkerManagers.RemoveElement(aManager);
+}
+
+}  // namespace dom
+}  // namespace mozilla
diff --git a/dom/workers/sharedworkers/SharedWorkerService.h b/dom/workers/sharedworkers/SharedWorkerService.h
new file mode 100644
index 0000000000..c4671163bd
--- /dev/null
+++ b/dom/workers/sharedworkers/SharedWorkerService.h
@@ -0,0 +1,74 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_SharedWorkerService_h
+#define mozilla_dom_SharedWorkerService_h
+
+#include "mozilla/dom/quota/CheckedUnsafePtr.h"
+#include "nsISupportsImpl.h"
+#include "nsTArray.h"
+
+class nsIEventTarget;
+
+namespace mozilla {
+
+namespace ipc {
+class PrincipalInfo;
+}
+
+namespace dom {
+
+class MessagePortIdentifier;
+class RemoteWorkerData;
+class SharedWorkerManager;
+class SharedWorkerParent;
+class UniqueMessagePortId;
+
+/**
+ * PBackground service that creates and tracks the per-worker
+ * SharedWorkerManager instances, allowing rendezvous between SharedWorkerParent
+ * instances and the SharedWorkerManagers they want to talk to (1:1).
+ */
+class SharedWorkerService final {
+ public:
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(SharedWorkerService);
+
+  // This can be called on PBackground thread only.
+  static already_AddRefed<SharedWorkerService> GetOrCreate();
+
+  // The service, if already created, is available on any thread using this
+  // method.
+  static SharedWorkerService* Get();
+
+  // PBackground method only.
+  void GetOrCreateWorkerManager(SharedWorkerParent* aActor,
+                                const RemoteWorkerData& aData,
+                                uint64_t aWindowID,
+                                const MessagePortIdentifier& aPortIdentifier);
+
+  void GetOrCreateWorkerManagerOnMainThread(
+      nsIEventTarget* aBackgroundEventTarget, SharedWorkerParent* aActor,
+      const RemoteWorkerData& aData, uint64_t aWindowID,
+      UniqueMessagePortId& aPortIdentifier);
+
+  void RemoveWorkerManagerOnMainThread(SharedWorkerManager* aManager);
+
+ private:
+  SharedWorkerService() = default;
+  ~SharedWorkerService() = default;
+
+  void ErrorPropagationOnMainThread(nsIEventTarget* aBackgroundEventTarget,
+                                    SharedWorkerParent* aActor,
+                                    nsresult aError);
+
+  // Touched on main-thread only.
+  nsTArray<RefPtr<SharedWorkerManager>> mWorkerManagers;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_SharedWorkerService_h
diff --git a/dom/workers/sharedworkers/moz.build b/dom/workers/sharedworkers/moz.build
new file mode 100644
index 0000000000..2b83bc9525
--- /dev/null
+++ b/dom/workers/sharedworkers/moz.build
@@ -0,0 +1,28 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+EXPORTS.mozilla.dom += [
+    "SharedWorker.h",
+    "SharedWorkerChild.h",
+    "SharedWorkerManager.h",
+    "SharedWorkerParent.h",
+]
+
+UNIFIED_SOURCES += [
+    "SharedWorker.cpp",
+    "SharedWorkerChild.cpp",
+    "SharedWorkerManager.cpp",
+    "SharedWorkerParent.cpp",
+    "SharedWorkerService.cpp",
+]
+
+IPDL_SOURCES += [
+    "PSharedWorker.ipdl",
+]
+
+include("/ipc/chromium/chromium-config.mozbuild")
+
+FINAL_LIBRARY = "xul"
diff --git a/dom/workers/test/404_server.sjs b/dom/workers/test/404_server.sjs
new file mode 100644
index 0000000000..f83281efa8
--- /dev/null
+++ b/dom/workers/test/404_server.sjs
@@ -0,0 +1,9 @@
+function handleRequest(request, response) {
+  response.setStatusLine(request.httpVersion, 404, "Not found");
+
+  // Any valid JS.
+  if (request.queryString == "js") {
+    response.setHeader("Content-Type", "text/javascript", false);
+    response.write("4 + 4");
+  }
+}
diff --git a/dom/workers/test/WorkerDebugger.console_childWorker.js b/dom/workers/test/WorkerDebugger.console_childWorker.js
new file mode 100644
index 0000000000..8cee6809e5
--- /dev/null
+++ b/dom/workers/test/WorkerDebugger.console_childWorker.js
@@ -0,0 +1,3 @@
+"use strict";
+
+self.onmessage = function () {};
diff --git a/dom/workers/test/WorkerDebugger.console_debugger.js b/dom/workers/test/WorkerDebugger.console_debugger.js
new file mode 100644
index 0000000000..a8b2493200
--- /dev/null
+++ b/dom/workers/test/WorkerDebugger.console_debugger.js
@@ -0,0 +1,49 @@
+"use strict";
+
+function ok(a, msg) {
+  postMessage(JSON.stringify({ type: "status", what: !!a, msg }));
+}
+
+function is(a, b, msg) {
+  ok(a === b, msg);
+}
+
+function finish() {
+  postMessage(JSON.stringify({ type: "finish" }));
+}
+
+function magic() {
+  console.log("Hello from the debugger script!");
+
+  var foo = retrieveConsoleEvents();
+  ok(Array.isArray(foo), "We received an array.");
+  ok(foo.length >= 2, "At least 2 messages.");
+
+  is(
+    foo[0].arguments[0],
+    "Can you see this console message?",
+    "First message ok."
+  );
+  is(
+    foo[1].arguments[0],
+    "Can you see this second console message?",
+    "Second message ok."
+  );
+
+  setConsoleEventHandler(function (consoleData) {
+    is(consoleData.arguments[0], "Random message.", "Random message ok!");
+
+    // The consoleEventHandler can be null.
+    setConsoleEventHandler(null);
+
+    finish();
+  });
+}
+
+this.onmessage = function (event) {
+  switch (event.data) {
+    case "do magic":
+      magic();
+      break;
+  }
+};
diff --git a/dom/workers/test/WorkerDebugger.console_worker.js b/dom/workers/test/WorkerDebugger.console_worker.js
new file mode 100644
index 0000000000..a4d6af2e0f
--- /dev/null
+++ b/dom/workers/test/WorkerDebugger.console_worker.js
@@ -0,0 +1,10 @@
+"use strict";
+
+console.log("Can you see this console message?");
+console.warn("Can you see this second console message?");
+
+var worker = new Worker("WorkerDebugger.console_childWorker.js");
+
+setInterval(function () {
+  console.log("Random message.");
+}, 200);
diff --git a/dom/workers/test/WorkerDebugger.initialize_childWorker.js b/dom/workers/test/WorkerDebugger.initialize_childWorker.js
new file mode 100644
index 0000000000..a3a6d2bf80
--- /dev/null
+++ b/dom/workers/test/WorkerDebugger.initialize_childWorker.js
@@ -0,0 +1,7 @@
+"use strict";
+
+self.onmessage = function () {};
+
+// eslint-disable-next-line no-debugger
+debugger;
+postMessage("worker");
diff --git a/dom/workers/test/WorkerDebugger.initialize_debugger.js b/dom/workers/test/WorkerDebugger.initialize_debugger.js
new file mode 100644
index 0000000000..f52e95b159
--- /dev/null
+++ b/dom/workers/test/WorkerDebugger.initialize_debugger.js
@@ -0,0 +1,6 @@
+"use strict";
+
+var dbg = new Debugger(global);
+dbg.onDebuggerStatement = function (frame) {
+  frame.eval("postMessage('debugger');");
+};
diff --git a/dom/workers/test/WorkerDebugger.initialize_debugger_es_worker.js b/dom/workers/test/WorkerDebugger.initialize_debugger_es_worker.js
new file mode 100644
index 0000000000..d357fca2d3
--- /dev/null
+++ b/dom/workers/test/WorkerDebugger.initialize_debugger_es_worker.js
@@ -0,0 +1,10 @@
+"use strict";
+
+// The following check is one possible way to identify
+// if this script is loaded as a ES Module or the classic way.
+const isLoadedAsEsModule = this != globalThis;
+
+// We expect the debugger script to always be loaded as classic
+if (!isLoadedAsEsModule) {
+  postMessage("debugger script ran");
+}
diff --git a/dom/workers/test/WorkerDebugger.initialize_es_worker.js b/dom/workers/test/WorkerDebugger.initialize_es_worker.js
new file mode 100644
index 0000000000..1b9ddda769
--- /dev/null
+++ b/dom/workers/test/WorkerDebugger.initialize_es_worker.js
@@ -0,0 +1,10 @@
+"use strict";
+
+// The following check is one possible way to identify
+// if this script is loaded as a ES Module or the classic way.
+const isLoadedAsEsModule = this != globalThis;
+
+// Here we expect the worker to be loaded a ES Module
+if (isLoadedAsEsModule) {
+  postMessage("worker");
+}
diff --git a/dom/workers/test/WorkerDebugger.initialize_worker.js b/dom/workers/test/WorkerDebugger.initialize_worker.js
new file mode 100644
index 0000000000..2317335edc
--- /dev/null
+++ b/dom/workers/test/WorkerDebugger.initialize_worker.js
@@ -0,0 +1,10 @@
+"use strict";
+
+var worker = new Worker("WorkerDebugger.initialize_childWorker.js");
+worker.onmessage = function (event) {
+  postMessage("child:" + event.data);
+};
+
+// eslint-disable-next-line no-debugger
+debugger;
+postMessage("worker");
diff --git a/dom/workers/test/WorkerDebugger.postMessage_childWorker.js b/dom/workers/test/WorkerDebugger.postMessage_childWorker.js
new file mode 100644
index 0000000000..8cee6809e5
--- /dev/null
+++ b/dom/workers/test/WorkerDebugger.postMessage_childWorker.js
@@ -0,0 +1,3 @@
+"use strict";
+
+self.onmessage = function () {};
diff --git a/dom/workers/test/WorkerDebugger.postMessage_debugger.js b/dom/workers/test/WorkerDebugger.postMessage_debugger.js
new file mode 100644
index 0000000000..14236a4430
--- /dev/null
+++ b/dom/workers/test/WorkerDebugger.postMessage_debugger.js
@@ -0,0 +1,9 @@
+"use strict";
+
+this.onmessage = function (event) {
+  switch (event.data) {
+    case "ping":
+      postMessage("pong");
+      break;
+  }
+};
diff --git a/dom/workers/test/WorkerDebugger.postMessage_worker.js b/dom/workers/test/WorkerDebugger.postMessage_worker.js
new file mode 100644
index 0000000000..8ddf6cf865
--- /dev/null
+++ b/dom/workers/test/WorkerDebugger.postMessage_worker.js
@@ -0,0 +1,3 @@
+"use strict";
+
+var worker = new Worker("WorkerDebugger.postMessage_childWorker.js");
diff --git a/dom/workers/test/WorkerDebuggerGlobalScope.createSandbox_debugger.js b/dom/workers/test/WorkerDebuggerGlobalScope.createSandbox_debugger.js
new file mode 100644
index 0000000000..908c9f3161
--- /dev/null
+++ b/dom/workers/test/WorkerDebuggerGlobalScope.createSandbox_debugger.js
@@ -0,0 +1,9 @@
+"use strict";
+
+const SANDBOX_URL = "WorkerDebuggerGlobalScope.createSandbox_sandbox.js";
+
+var prototype = {
+  self: this,
+};
+var sandbox = createSandbox(SANDBOX_URL, prototype);
+loadSubScript(SANDBOX_URL, sandbox);
diff --git a/dom/workers/test/WorkerDebuggerGlobalScope.createSandbox_sandbox.js b/dom/workers/test/WorkerDebuggerGlobalScope.createSandbox_sandbox.js
new file mode 100644
index 0000000000..d2de6de924
--- /dev/null
+++ b/dom/workers/test/WorkerDebuggerGlobalScope.createSandbox_sandbox.js
@@ -0,0 +1,9 @@
+"use strict";
+
+self.addEventListener("message", function (event) {
+  switch (event.data) {
+    case "ping":
+      self.postMessage("pong");
+      break;
+  }
+});
diff --git a/dom/workers/test/WorkerDebuggerGlobalScope.createSandbox_worker.js b/dom/workers/test/WorkerDebuggerGlobalScope.createSandbox_worker.js
new file mode 100644
index 0000000000..8cee6809e5
--- /dev/null
+++ b/dom/workers/test/WorkerDebuggerGlobalScope.createSandbox_worker.js
@@ -0,0 +1,3 @@
+"use strict";
+
+self.onmessage = function () {};
diff --git a/dom/workers/test/WorkerDebuggerGlobalScope.enterEventLoop_childWorker.js b/dom/workers/test/WorkerDebuggerGlobalScope.enterEventLoop_childWorker.js
new file mode 100644
index 0000000000..495212066c
--- /dev/null
+++ b/dom/workers/test/WorkerDebuggerGlobalScope.enterEventLoop_childWorker.js
@@ -0,0 +1,16 @@
+"use strict";
+
+function f() {
+  // eslint-disable-next-line no-debugger
+  debugger;
+}
+
+self.onmessage = function (event) {
+  switch (event.data) {
+    case "ping":
+      // eslint-disable-next-line no-debugger
+      debugger;
+      postMessage("pong");
+      break;
+  }
+};
diff --git a/dom/workers/test/WorkerDebuggerGlobalScope.enterEventLoop_debugger.js b/dom/workers/test/WorkerDebuggerGlobalScope.enterEventLoop_debugger.js
new file mode 100644
index 0000000000..d2a1a21e85
--- /dev/null
+++ b/dom/workers/test/WorkerDebuggerGlobalScope.enterEventLoop_debugger.js
@@ -0,0 +1,29 @@
+"use strict";
+
+var frames = [];
+
+var dbg = new Debugger(global);
+dbg.onDebuggerStatement = function (frame) {
+  frames.push(frame);
+  postMessage("paused");
+  enterEventLoop();
+  frames.pop();
+  postMessage("resumed");
+};
+
+this.onmessage = function (event) {
+  switch (event.data) {
+    case "eval":
+      frames[frames.length - 1].eval("f()");
+      postMessage("evalled");
+      break;
+
+    case "ping":
+      postMessage("pong");
+      break;
+
+    case "resume":
+      leaveEventLoop();
+      break;
+  }
+};
diff --git a/dom/workers/test/WorkerDebuggerGlobalScope.enterEventLoop_worker.js b/dom/workers/test/WorkerDebuggerGlobalScope.enterEventLoop_worker.js
new file mode 100644
index 0000000000..7b30109615
--- /dev/null
+++ b/dom/workers/test/WorkerDebuggerGlobalScope.enterEventLoop_worker.js
@@ -0,0 +1,29 @@
+"use strict";
+
+function f() {
+  // eslint-disable-next-line no-debugger
+  debugger;
+}
+
+var worker = new Worker(
+  "WorkerDebuggerGlobalScope.enterEventLoop_childWorker.js"
+);
+
+worker.onmessage = function (event) {
+  postMessage("child:" + event.data);
+};
+
+self.onmessage = function (event) {
+  var message = event.data;
+  if (message.includes(":")) {
+    worker.postMessage(message.split(":")[1]);
+    return;
+  }
+  switch (message) {
+    case "ping":
+      // eslint-disable-next-line no-debugger
+      debugger;
+      postMessage("pong");
+      break;
+  }
+};
diff --git a/dom/workers/test/WorkerDebuggerGlobalScope.reportError_childWorker.js b/dom/workers/test/WorkerDebuggerGlobalScope.reportError_childWorker.js
new file mode 100644
index 0000000000..0fb4113a24
--- /dev/null
+++ b/dom/workers/test/WorkerDebuggerGlobalScope.reportError_childWorker.js
@@ -0,0 +1,5 @@
+"use strict";
+
+self.onerror = function () {
+  postMessage("error");
+};
diff --git a/dom/workers/test/WorkerDebuggerGlobalScope.reportError_debugger.js b/dom/workers/test/WorkerDebuggerGlobalScope.reportError_debugger.js
new file mode 100644
index 0000000000..b3d8e5d440
--- /dev/null
+++ b/dom/workers/test/WorkerDebuggerGlobalScope.reportError_debugger.js
@@ -0,0 +1,11 @@
+"use strict";
+
+this.onmessage = function (event) {
+  switch (event.data) {
+    case "report":
+      reportError("reported");
+      break;
+    case "throw":
+      throw new Error("thrown");
+  }
+};
diff --git a/dom/workers/test/WorkerDebuggerGlobalScope.reportError_worker.js b/dom/workers/test/WorkerDebuggerGlobalScope.reportError_worker.js
new file mode 100644
index 0000000000..67ccfc2ca0
--- /dev/null
+++ b/dom/workers/test/WorkerDebuggerGlobalScope.reportError_worker.js
@@ -0,0 +1,11 @@
+"use strict";
+
+var worker = new Worker("WorkerDebuggerGlobalScope.reportError_childWorker.js");
+
+worker.onmessage = function (event) {
+  postMessage("child:" + event.data);
+};
+
+self.onerror = function () {
+  postMessage("error");
+};
diff --git a/dom/workers/test/WorkerDebuggerGlobalScope.setImmediate_debugger.js b/dom/workers/test/WorkerDebuggerGlobalScope.setImmediate_debugger.js
new file mode 100644
index 0000000000..b2a01d380c
--- /dev/null
+++ b/dom/workers/test/WorkerDebuggerGlobalScope.setImmediate_debugger.js
@@ -0,0 +1,12 @@
+"use strict";
+
+this.onmessage = function (event) {
+  switch (event.data) {
+    case "ping":
+      setImmediate(function () {
+        postMessage("pong1");
+      });
+      postMessage("pong2");
+      break;
+  }
+};
diff --git a/dom/workers/test/WorkerDebuggerGlobalScope.setImmediate_worker.js b/dom/workers/test/WorkerDebuggerGlobalScope.setImmediate_worker.js
new file mode 100644
index 0000000000..8cee6809e5
--- /dev/null
+++ b/dom/workers/test/WorkerDebuggerGlobalScope.setImmediate_worker.js
@@ -0,0 +1,3 @@
+"use strict";
+
+self.onmessage = function () {};
diff --git a/dom/workers/test/WorkerDebuggerManager_childWorker.js b/dom/workers/test/WorkerDebuggerManager_childWorker.js
new file mode 100644
index 0000000000..8cee6809e5
--- /dev/null
+++ b/dom/workers/test/WorkerDebuggerManager_childWorker.js
@@ -0,0 +1,3 @@
+"use strict";
+
+self.onmessage = function () {};
diff --git a/dom/workers/test/WorkerDebuggerManager_worker.js b/dom/workers/test/WorkerDebuggerManager_worker.js
new file mode 100644
index 0000000000..0737d17ebc
--- /dev/null
+++ b/dom/workers/test/WorkerDebuggerManager_worker.js
@@ -0,0 +1,3 @@
+"use strict";
+
+var worker = new Worker("WorkerDebuggerManager_childWorker.js");
diff --git a/dom/workers/test/WorkerDebugger_childWorker.js b/dom/workers/test/WorkerDebugger_childWorker.js
new file mode 100644
index 0000000000..8cee6809e5
--- /dev/null
+++ b/dom/workers/test/WorkerDebugger_childWorker.js
@@ -0,0 +1,3 @@
+"use strict";
+
+self.onmessage = function () {};
diff --git a/dom/workers/test/WorkerDebugger_frozen_window1.html b/dom/workers/test/WorkerDebugger_frozen_window1.html
new file mode 100644
index 0000000000..05d65bbb54
--- /dev/null
+++ b/dom/workers/test/WorkerDebugger_frozen_window1.html
@@ -0,0 +1,15 @@
+<!DOCTYPE html>
+<html lang="en">
+  <head>
+    <meta charset="utf-8">
+    <script>
+      var worker = new Worker("WorkerDebugger_frozen_worker1.js");
+      worker.onmessage = function () {
+        opener.postMessage("ready", "*");
+      };
+    </script>
+  </head>
+  <body>
+    This is page 1.
+  </body>
+<html>
diff --git a/dom/workers/test/WorkerDebugger_frozen_window2.html b/dom/workers/test/WorkerDebugger_frozen_window2.html
new file mode 100644
index 0000000000..3a2445ba54
--- /dev/null
+++ b/dom/workers/test/WorkerDebugger_frozen_window2.html
@@ -0,0 +1,15 @@
+<!DOCTYPE html>
+<html lang="en">
+  <head>
+    <meta charset="utf-8">
+    <script>
+      var worker = new Worker("WorkerDebugger_frozen_worker2.js");
+      worker.onmessage = function () {
+        opener.postMessage("ready", "*");
+      };
+    </script>
+  </head>
+  <body>
+    This is page 2.
+  </body>
+<html>
diff --git a/dom/workers/test/WorkerDebugger_frozen_worker1.js b/dom/workers/test/WorkerDebugger_frozen_worker1.js
new file mode 100644
index 0000000000..371d2c064b
--- /dev/null
+++ b/dom/workers/test/WorkerDebugger_frozen_worker1.js
@@ -0,0 +1,5 @@
+"use strict";
+
+onmessage = function () {};
+
+postMessage("ready");
diff --git a/dom/workers/test/WorkerDebugger_frozen_worker2.js b/dom/workers/test/WorkerDebugger_frozen_worker2.js
new file mode 100644
index 0000000000..371d2c064b
--- /dev/null
+++ b/dom/workers/test/WorkerDebugger_frozen_worker2.js
@@ -0,0 +1,5 @@
+"use strict";
+
+onmessage = function () {};
+
+postMessage("ready");
diff --git a/dom/workers/test/WorkerDebugger_promise_debugger.js b/dom/workers/test/WorkerDebugger_promise_debugger.js
new file mode 100644
index 0000000000..dd4d1bf2c9
--- /dev/null
+++ b/dom/workers/test/WorkerDebugger_promise_debugger.js
@@ -0,0 +1,34 @@
+"use strict";
+
+var self = this;
+
+self.onmessage = function (event) {
+  if (event.data !== "resolve") {
+    return;
+  }
+  // This then-handler should be executed inside the top-level event loop,
+  // within the context of the debugger's global.
+  Promise.resolve().then(function () {
+    var dbg = new Debugger(global);
+    dbg.onDebuggerStatement = function () {
+      self.onmessage = function (e) {
+        if (e.data !== "resume") {
+          return;
+        }
+        // This then-handler should be executed inside the nested event loop,
+        // within the context of the debugger's global.
+        Promise.resolve().then(function () {
+          postMessage("resumed");
+          leaveEventLoop();
+        });
+      };
+      // Test bug 1392540 where DOM Promises from debugger principal
+      // where frozen while hitting a worker breakpoint.
+      Promise.resolve().then(() => {
+        postMessage("paused");
+      });
+      enterEventLoop();
+    };
+    postMessage("resolved");
+  });
+};
diff --git a/dom/workers/test/WorkerDebugger_promise_worker.js b/dom/workers/test/WorkerDebugger_promise_worker.js
new file mode 100644
index 0000000000..04db24b512
--- /dev/null
+++ b/dom/workers/test/WorkerDebugger_promise_worker.js
@@ -0,0 +1,26 @@
+"use strict";
+
+self.onmessage = function (event) {
+  if (event.data !== "resolve") {
+    return;
+  }
+  // This then-handler should be executed inside the top-level event loop,
+  // within the context of the worker's global.
+  Promise.resolve().then(function () {
+    self.onmessage = function (e) {
+      if (e.data !== "pause") {
+        return;
+      }
+      // This then-handler should be executed inside the top-level event loop,
+      // within the context of the worker's global. Because the debugger
+      // statement here below enters a nested event loop, the then-handler
+      // should not be executed until the debugger statement returns.
+      Promise.resolve().then(function () {
+        postMessage("resumed");
+      });
+      // eslint-disable-next-line no-debugger
+      debugger;
+    };
+    postMessage("resolved");
+  });
+};
diff --git a/dom/workers/test/WorkerDebugger_sharedWorker.js b/dom/workers/test/WorkerDebugger_sharedWorker.js
new file mode 100644
index 0000000000..037abe6d6d
--- /dev/null
+++ b/dom/workers/test/WorkerDebugger_sharedWorker.js
@@ -0,0 +1,16 @@
+"use strict";
+
+self.onconnect = function (event) {
+  event.ports[0].onmessage = function (e) {
+    switch (e.data) {
+      case "close":
+        close();
+        break;
+
+      case "close_loop":
+        close();
+        // Let's loop forever.
+        while (1) {}
+    }
+  };
+};
diff --git a/dom/workers/test/WorkerDebugger_suspended_debugger.js b/dom/workers/test/WorkerDebugger_suspended_debugger.js
new file mode 100644
index 0000000000..2ed4e16c44
--- /dev/null
+++ b/dom/workers/test/WorkerDebugger_suspended_debugger.js
@@ -0,0 +1,6 @@
+"use strict";
+
+var dbg = new Debugger(global);
+dbg.onDebuggerStatement = function (frame) {
+  postMessage("debugger");
+};
diff --git a/dom/workers/test/WorkerDebugger_suspended_worker.js b/dom/workers/test/WorkerDebugger_suspended_worker.js
new file mode 100644
index 0000000000..0ea27d29e8
--- /dev/null
+++ b/dom/workers/test/WorkerDebugger_suspended_worker.js
@@ -0,0 +1,7 @@
+"use strict";
+
+self.onmessage = function () {
+  postMessage("worker");
+  // eslint-disable-next-line no-debugger
+  debugger;
+};
diff --git a/dom/workers/test/WorkerDebugger_worker.js b/dom/workers/test/WorkerDebugger_worker.js
new file mode 100644
index 0000000000..e33eeaa4d3
--- /dev/null
+++ b/dom/workers/test/WorkerDebugger_worker.js
@@ -0,0 +1,9 @@
+"use strict";
+
+var worker = new Worker("WorkerDebugger_childWorker.js");
+self.onmessage = function (event) {
+  postMessage("child:" + event.data);
+};
+// eslint-disable-next-line no-debugger
+debugger;
+postMessage("worker");
diff --git a/dom/workers/test/WorkerTest.jsm b/dom/workers/test/WorkerTest.jsm
new file mode 100644
index 0000000000..702dc9e46a
--- /dev/null
+++ b/dom/workers/test/WorkerTest.jsm
@@ -0,0 +1,15 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+var EXPORTED_SYMBOLS = ["WorkerTest"];
+
+var WorkerTest = {
+  go(message, messageCallback, errorCallback) {
+    let worker = new ChromeWorker("WorkerTest_worker.js");
+    worker.onmessage = messageCallback;
+    worker.onerror = errorCallback;
+    worker.postMessage(message);
+    return worker;
+  },
+};
diff --git a/dom/workers/test/WorkerTest_badworker.js b/dom/workers/test/WorkerTest_badworker.js
new file mode 100644
index 0000000000..5fbd8a5e63
--- /dev/null
+++ b/dom/workers/test/WorkerTest_badworker.js
@@ -0,0 +1 @@
+// doesn't matter what is in here if the URL is bad
diff --git a/dom/workers/test/WorkerTest_subworker.js b/dom/workers/test/WorkerTest_subworker.js
new file mode 100644
index 0000000000..0022fc5046
--- /dev/null
+++ b/dom/workers/test/WorkerTest_subworker.js
@@ -0,0 +1,37 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+onmessage = function (event) {
+  let chromeURL = event.data.replace(
+    "test_chromeWorkerJSM.xhtml",
+    "WorkerTest_badworker.js"
+  );
+
+  let mochitestURL = event.data
+    .replace("test_chromeWorkerJSM.xhtml", "WorkerTest_badworker.js")
+    .replace(
+      "chrome://mochitests/content/chrome",
+      "http://mochi.test:8888/tests"
+    );
+
+  // We should be able to XHR to anything we want, including a chrome URL.
+  let xhr = new XMLHttpRequest();
+  xhr.open("GET", mochitestURL, false);
+  xhr.send();
+
+  if (!xhr.responseText) {
+    throw "Can't load script file via XHR!";
+  }
+
+  // We shouldn't be able to make a ChromeWorker to a non-chrome URL.
+  try {
+    new ChromeWorker(mochitestURL);
+  } catch (e) {
+    if (e.name === "SecurityError") {
+      postMessage("Done");
+      return;
+    }
+  }
+  throw "creating a chrome worker with a bad URL should throw a SecurityError";
+};
diff --git a/dom/workers/test/WorkerTest_worker.js b/dom/workers/test/WorkerTest_worker.js
new file mode 100644
index 0000000000..53a380be50
--- /dev/null
+++ b/dom/workers/test/WorkerTest_worker.js
@@ -0,0 +1,11 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+onmessage = function (event) {
+  let worker = new ChromeWorker("WorkerTest_subworker.js");
+  worker.onmessage = function (e) {
+    postMessage(e.data);
+  };
+  worker.postMessage(event.data);
+};
diff --git a/dom/workers/test/atob_worker.js b/dom/workers/test/atob_worker.js
new file mode 100644
index 0000000000..f55ec77e81
--- /dev/null
+++ b/dom/workers/test/atob_worker.js
@@ -0,0 +1,55 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+var data = [
+  -1,
+  0,
+  1,
+  1.5,
+  /* null ,*/ undefined,
+  true,
+  false,
+  "foo",
+  "123456789012345",
+  "1234567890123456",
+  "12345678901234567",
+];
+
+var str = "";
+for (var i = 0; i < 30; i++) {
+  data.push(str);
+  str += i % 2 ? "b" : "a";
+}
+
+onmessage = function (event) {
+  data.forEach(function (string) {
+    var encoded = btoa(string);
+    postMessage({ type: "btoa", value: encoded });
+    postMessage({ type: "atob", value: atob(encoded) });
+  });
+
+  var threw;
+  try {
+    atob();
+  } catch (e) {
+    threw = true;
+  }
+
+  if (!threw) {
+    throw "atob didn't throw when called without an argument!";
+  }
+  threw = false;
+
+  try {
+    btoa();
+  } catch (e) {
+    threw = true;
+  }
+
+  if (!threw) {
+    throw "btoa didn't throw when called without an argument!";
+  }
+
+  postMessage({ type: "done" });
+};
diff --git a/dom/workers/test/blank.html b/dom/workers/test/blank.html
new file mode 100644
index 0000000000..fcbbdb17e9
--- /dev/null
+++ b/dom/workers/test/blank.html
@@ -0,0 +1,14 @@
+<!DOCTYPE html>
+<html lang="en">
+  <head>
+    <meta charset="utf-8">
+    <title>Blank</title>
+  </head>
+  <body onload="notifyOnload();">
+    <script type="application/javascript">
+    function notifyOnload() {
+      opener.postMessage({event: 'load'}, '*');
+    }
+    </script>
+  </body>
+</html>
diff --git a/dom/workers/test/browser.toml b/dom/workers/test/browser.toml
new file mode 100644
index 0000000000..fb8148a159
--- /dev/null
+++ b/dom/workers/test/browser.toml
@@ -0,0 +1,53 @@
+[DEFAULT]
+support-files = [
+  "bug1047663_tab.html",
+  "bug1047663_worker.sjs",
+  "head.js",
+  "!/dom/base/test/file_empty.html",
+]
+
+["browser_WorkerDebugger.initialize.js"]
+support-files = [
+  "WorkerDebugger.initialize_debugger_es_worker.js",
+  "WorkerDebugger.initialize_es_worker.js",
+]
+skip-if = ["!nightly_build"] # to be enabled once ES module in workers is enabled (bug 1812591)
+
+["browser_bug1047663.js"]
+
+["browser_bug1104623.js"]
+run-if = ["buildapp == 'browser'"]
+
+["browser_consoleSharedWorkers.js"]
+skip-if = ["release_or_beta"] # requires dom.postMessage.sharedArrayBuffer.bypassCOOP_COEP.insecure.enabled
+support-files = [
+  "sharedWorker_console.js",
+  "empty.html",
+]
+
+["browser_fileURL.js"]
+support-files = [
+  "empty.html",
+  "empty_worker.js",
+]
+
+["browser_privilegedmozilla_remoteworker.js"]
+support-files = [
+  "file_service_worker.js",
+  "file_service_worker_container.html",
+]
+
+["browser_serviceworker_fetch_new_process.js"]
+support-files = [
+  "file_service_worker_fetch_synthetic.js",
+  "server_fetch_synthetic.sjs",
+]
+
+["browser_worker_use_counters.js"]
+support-files = [
+  "file_use_counter_worker.html",
+  "file_use_counter_worker.js",
+  "file_use_counter_shared_worker.js",
+  "file_use_counter_shared_worker_microtask.js",
+  "file_use_counter_service_worker.js",
+]
diff --git a/dom/workers/test/browser_WorkerDebugger.initialize.js b/dom/workers/test/browser_WorkerDebugger.initialize.js
new file mode 100644
index 0000000000..edc20af4e0
--- /dev/null
+++ b/dom/workers/test/browser_WorkerDebugger.initialize.js
@@ -0,0 +1,54 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+const wdm = Cc["@mozilla.org/dom/workers/workerdebuggermanager;1"].getService(
+  Ci.nsIWorkerDebuggerManager
+);
+
+const BASE_URL = "chrome://mochitests/content/browser/dom/workers/test/";
+const WORKER_URL = BASE_URL + "WorkerDebugger.initialize_es_worker.js";
+const DEBUGGER_URL =
+  BASE_URL + "WorkerDebugger.initialize_debugger_es_worker.js";
+
+add_task(async function test() {
+  const onDbg = waitForRegister(WORKER_URL);
+  const worker = new Worker(WORKER_URL, { type: "module" });
+
+  info("Wait for worker message");
+  await new Promise(resolve => (worker.onmessage = resolve));
+
+  const dbg = await onDbg;
+
+  info("Calling WorkerDebugger::Initialize");
+  const onDebuggerScriptEvaluated = new Promise(resolve => {
+    const listener = {
+      onMessage(msg) {
+        is(msg, "debugger script ran");
+        dbg.removeListener(listener);
+        resolve();
+      },
+    };
+    dbg.addListener(listener);
+  });
+  dbg.initialize(DEBUGGER_URL);
+  ok(true, "dbg.initialize didn't throw");
+
+  info("Waiting for debugger script to be evaluated and dispatching a message");
+  await onDebuggerScriptEvaluated;
+});
+
+function waitForRegister(url, dbgUrl) {
+  return new Promise(function (resolve) {
+    wdm.addListener({
+      onRegister(dbg) {
+        if (dbg.url !== url) {
+          return;
+        }
+        ok(true, "Debugger with url " + url + " should be registered.");
+        wdm.removeListener(this);
+        resolve(dbg);
+      },
+    });
+  });
+}
diff --git a/dom/workers/test/browser_bug1047663.js b/dom/workers/test/browser_bug1047663.js
new file mode 100644
index 0000000000..f55f1152f6
--- /dev/null
+++ b/dom/workers/test/browser_bug1047663.js
@@ -0,0 +1,56 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+"use strict";
+
+const EXAMPLE_URL = "https://example.com/browser/dom/workers/test/";
+const TAB_URL = EXAMPLE_URL + "bug1047663_tab.html";
+const WORKER_URL = EXAMPLE_URL + "bug1047663_worker.sjs";
+
+function test() {
+  waitForExplicitFinish();
+
+  (async function () {
+    // Disable rcwn to make cache behavior deterministic.
+    await SpecialPowers.pushPrefEnv({
+      set: [["network.http.rcwn.enabled", false]],
+    });
+
+    let tab = await addTab(TAB_URL);
+
+    // Create a worker. Post a message to it, and check the reply. Since the
+    // server side JavaScript file returns the first source for the first
+    // request, the reply should be "one". If the reply is correct, terminate
+    // the worker.
+    await createWorkerInTab(tab, WORKER_URL);
+    let message = await postMessageToWorkerInTab(tab, WORKER_URL, "ping");
+    is(message, "one");
+    await terminateWorkerInTab(tab, WORKER_URL);
+
+    // Create a second worker with the same URL. Post a message to it, and check
+    // the reply. The server side JavaScript file returns the second source for
+    // all subsequent requests, but since the cache is still enabled, the reply
+    // should still be "one". If the reply is correct, terminate the worker.
+    await createWorkerInTab(tab, WORKER_URL);
+    message = await postMessageToWorkerInTab(tab, WORKER_URL, "ping");
+    is(message, "one");
+    await terminateWorkerInTab(tab, WORKER_URL);
+
+    // Disable the cache in this tab. This should also disable the cache for all
+    // workers in this tab.
+    await disableCacheInTab(tab);
+
+    // Create a third worker with the same URL. Post a message to it, and check
+    // the reply. Since the server side JavaScript file returns the second
+    // source for all subsequent requests, and the cache is now disabled, the
+    // reply should now be "two". If the reply is correct, terminate the worker.
+    await createWorkerInTab(tab, WORKER_URL);
+    message = await postMessageToWorkerInTab(tab, WORKER_URL, "ping");
+    is(message, "two");
+    await terminateWorkerInTab(tab, WORKER_URL);
+
+    removeTab(tab);
+
+    finish();
+  })();
+}
diff --git a/dom/workers/test/browser_bug1104623.js b/dom/workers/test/browser_bug1104623.js
new file mode 100644
index 0000000000..7dc421b873
--- /dev/null
+++ b/dom/workers/test/browser_bug1104623.js
@@ -0,0 +1,60 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+function whenBrowserLoaded(aBrowser, aCallback) {
+  aBrowser.addEventListener(
+    "load",
+    function onLoad(event) {
+      if (event.target == aBrowser.contentDocument) {
+        aBrowser.removeEventListener("load", onLoad, true);
+        executeSoon(aCallback);
+      }
+    },
+    true
+  );
+}
+
+function test() {
+  waitForExplicitFinish();
+
+  let testURL =
+    "chrome://mochitests/content/chrome/dom/base/test/file_empty.html";
+
+  let tab = BrowserTestUtils.addTab(gBrowser, testURL);
+  gBrowser.selectedTab = tab;
+
+  whenBrowserLoaded(tab.linkedBrowser, function () {
+    let doc = tab.linkedBrowser.contentDocument;
+    let contentWin = tab.linkedBrowser.contentWindow;
+
+    let blob = new contentWin.Blob([
+      "onmessage = function() { postMessage(true); }",
+    ]);
+    ok(blob, "Blob has been created");
+
+    let blobURL = contentWin.URL.createObjectURL(blob);
+    ok(blobURL, "Blob URL has been created");
+
+    let worker = new contentWin.Worker(blobURL);
+    ok(worker, "Worker has been created");
+
+    worker.onerror = function (error) {
+      ok(false, "Worker.onerror:" + error.message);
+      worker.terminate();
+      contentWin.URL.revokeObjectURL(blob);
+      gBrowser.removeTab(tab);
+      executeSoon(finish);
+    };
+
+    worker.onmessage = function () {
+      ok(true, "Worker.onmessage");
+      worker.terminate();
+      contentWin.URL.revokeObjectURL(blob);
+      gBrowser.removeTab(tab);
+      executeSoon(finish);
+    };
+
+    worker.postMessage(true);
+  });
+}
diff --git a/dom/workers/test/browser_consoleSharedWorkers.js b/dom/workers/test/browser_consoleSharedWorkers.js
new file mode 100644
index 0000000000..54c1d8a73f
--- /dev/null
+++ b/dom/workers/test/browser_consoleSharedWorkers.js
@@ -0,0 +1,95 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+add_task(async function test() {
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      [
+        "dom.postMessage.sharedArrayBuffer.bypassCOOP_COEP.insecure.enabled",
+        true,
+      ],
+    ],
+  });
+
+  const testURL = getRootDirectory(gTestPath) + "empty.html";
+  let tab = BrowserTestUtils.addTab(gBrowser, testURL);
+  gBrowser.selectedTab = tab;
+
+  await BrowserTestUtils.browserLoaded(gBrowser.getBrowserForTab(tab));
+
+  let promise = new Promise(resolve => {
+    const ConsoleAPIStorage = SpecialPowers.Cc[
+      "@mozilla.org/consoleAPI-storage;1"
+    ].getService(SpecialPowers.Ci.nsIConsoleAPIStorage);
+
+    function consoleListener() {
+      this.onConsoleLogEvent = this.onConsoleLogEvent.bind(this);
+      ConsoleAPIStorage.addLogEventListener(
+        this.onConsoleLogEvent,
+        SpecialPowers.wrap(document).nodePrincipal
+      );
+      Services.obs.addObserver(this, "console-api-profiler");
+    }
+
+    var order = 0;
+    consoleListener.prototype = {
+      onConsoleLogEvent(aSubject) {
+        var obj = aSubject.wrappedJSObject;
+        if (order == 1) {
+          is(
+            obj.arguments[0],
+            "Hello world from a SharedWorker!",
+            "A message from a SharedWorker \\o/"
+          );
+          is(obj.ID, "sharedWorker_console.js", "The ID is SharedWorker");
+          is(obj.innerID, "SharedWorker", "The ID is SharedWorker");
+          is(order++, 1, "Then a first log message.");
+        } else {
+          is(
+            obj.arguments[0],
+            "Here is a SAB",
+            "A message from a SharedWorker \\o/"
+          );
+          is(
+            obj.arguments[1].constructor.name,
+            "SharedArrayBuffer",
+            "We got a direct reference to the SharedArrayBuffer coming from the worker thread"
+          );
+          is(obj.ID, "sharedWorker_console.js", "The ID is SharedWorker");
+          is(obj.innerID, "SharedWorker", "The ID is SharedWorker");
+          is(order++, 2, "Then a second log message.");
+
+          ConsoleAPIStorage.removeLogEventListener(this.onConsoleLogEvent);
+          resolve();
+        }
+      },
+
+      observe: (aSubject, aTopic) => {
+        ok(true, "Something has been received");
+
+        if (aTopic == "console-api-profiler") {
+          var obj = aSubject.wrappedJSObject;
+          is(
+            obj.arguments[0],
+            "Hello profiling from a SharedWorker!",
+            "A message from a SharedWorker \\o/"
+          );
+          is(order++, 0, "First a profiler message.");
+
+          Services.obs.removeObserver(cl, "console-api-profiler");
+        }
+      },
+    };
+
+    var cl = new consoleListener();
+  });
+
+  await SpecialPowers.spawn(tab.linkedBrowser, [], async function () {
+    new content.SharedWorker("sharedWorker_console.js");
+  });
+
+  await promise;
+
+  await BrowserTestUtils.removeTab(tab);
+});
diff --git a/dom/workers/test/browser_fileURL.js b/dom/workers/test/browser_fileURL.js
new file mode 100644
index 0000000000..9891bdcba9
--- /dev/null
+++ b/dom/workers/test/browser_fileURL.js
@@ -0,0 +1,73 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+"use strict";
+
+const EMPTY_URL = "/browser/dom/workers/test/empty.html";
+const WORKER_URL = "/browser/dom/workers/test/empty_worker.js";
+
+add_task(async function () {
+  let tab = BrowserTestUtils.addTab(
+    gBrowser,
+    "http://mochi.test:8888" + EMPTY_URL
+  );
+  gBrowser.selectedTab = tab;
+
+  let browser = gBrowser.getBrowserForTab(tab);
+  await BrowserTestUtils.browserLoaded(browser);
+
+  await SpecialPowers.spawn(
+    browser,
+    ["http://example.org" + WORKER_URL],
+    function (spec) {
+      return new content.Promise((resolve, reject) => {
+        let w = new content.window.Worker(spec);
+        w.onerror = _ => {
+          resolve();
+        };
+        w.onmessage = _ => {
+          reject();
+        };
+      });
+    }
+  );
+  ok(
+    true,
+    "The worker is not loaded when the script is from different origin."
+  );
+
+  BrowserTestUtils.removeTab(tab);
+});
+
+add_task(async function () {
+  let tab = BrowserTestUtils.addTab(
+    gBrowser,
+    "https://example.org" + EMPTY_URL
+  );
+  gBrowser.selectedTab = tab;
+
+  let browser = gBrowser.getBrowserForTab(tab);
+  await BrowserTestUtils.browserLoaded(browser);
+
+  await SpecialPowers.spawn(
+    browser,
+    ["http://example.org" + WORKER_URL],
+    function (spec) {
+      return new content.Promise((resolve, reject) => {
+        let w = new content.window.Worker(spec);
+        w.onerror = _ => {
+          resolve();
+        };
+        w.onmessage = _ => {
+          reject();
+        };
+      });
+    }
+  );
+  ok(
+    true,
+    "The worker is not loaded when the script is from different origin."
+  );
+
+  BrowserTestUtils.removeTab(tab);
+});
diff --git a/dom/workers/test/browser_privilegedmozilla_remoteworker.js b/dom/workers/test/browser_privilegedmozilla_remoteworker.js
new file mode 100644
index 0000000000..573cae5e61
--- /dev/null
+++ b/dom/workers/test/browser_privilegedmozilla_remoteworker.js
@@ -0,0 +1,116 @@
+add_setup(async function () {
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["browser.tabs.remote.separatePrivilegedMozillaWebContentProcess", true],
+      ["browser.tabs.remote.separatedMozillaDomains", "example.org"],
+      ["dom.ipc.processCount.web", 1],
+      ["dom.ipc.processCount.privilegedmozilla", 1],
+      ["dom.serviceWorkers.enabled", true],
+      ["dom.serviceWorkers.testing.enabled", true],
+    ],
+  });
+});
+
+// This test attempts to verify proper placement of spawned remoteworkers
+// by spawning them and then verifying that they were spawned in the expected
+// process by way of nsIWorkerDebuggerManager enumeration.
+//
+// Unfortunately, there's no other way to introspect where a worker global was
+// spawned at this time. (devtools just ends up enumerating all workers in all
+// processes and we don't want to depend on devtools in this test).
+//
+// As a result, this test currently only tests situations where it's known that
+// a remote worker will be spawned in the same process that is initiating its
+// spawning.
+//
+// This should be enhanced in the future.
+add_task(async function test_serviceworker() {
+  const basePath = "browser/dom/workers/test";
+  const pagePath = `${basePath}/file_service_worker_container.html`;
+  const scriptPath = `${basePath}/file_service_worker.js`;
+
+  Services.ppmm.releaseCachedProcesses();
+
+  async function runWorkerInProcess() {
+    function getActiveWorkerURLs() {
+      const wdm = Cc[
+        "@mozilla.org/dom/workers/workerdebuggermanager;1"
+      ].getService(Ci.nsIWorkerDebuggerManager);
+
+      const workerDebuggerUrls = Array.from(
+        wdm.getWorkerDebuggerEnumerator()
+      ).map(wd => {
+        return wd.url;
+      });
+
+      return workerDebuggerUrls;
+    }
+
+    return new Promise(resolve => {
+      content.navigator.serviceWorker.ready.then(({ active }) => {
+        const { port1, port2 } = new content.MessageChannel();
+        active.postMessage("webpage->serviceworker", [port2]);
+        port1.onmessage = evt => {
+          resolve({
+            msg: evt.data,
+            workerUrls: getActiveWorkerURLs(),
+          });
+        };
+      });
+    }).then(async res => {
+      // Unregister the service worker used in this test.
+      const registration = await content.navigator.serviceWorker.ready;
+      await registration.unregister();
+      return res;
+    });
+  }
+
+  const testCaseList = [
+    // TODO: find a reasonable way to test the non-privileged scenario
+    // (because more than 1 process is usually available and the worker
+    // can be launched in a different one from the one where the tab
+    // is running).
+    /*{
+      remoteType: "web",
+      hostname: "example.com",
+    },*/
+    {
+      remoteType: "privilegedmozilla",
+      hostname: `example.org`,
+    },
+  ];
+
+  for (const testCase of testCaseList) {
+    const { remoteType, hostname } = testCase;
+
+    info(`Test remote serviceworkers launch selects a ${remoteType} process`);
+
+    const tab = await BrowserTestUtils.openNewForegroundTab({
+      gBrowser,
+      url: `https://${hostname}/${pagePath}`,
+    });
+
+    is(
+      tab.linkedBrowser.remoteType,
+      remoteType,
+      `Got the expected remoteType for ${hostname} tab`
+    );
+
+    const results = await SpecialPowers.spawn(
+      tab.linkedBrowser,
+      [],
+      runWorkerInProcess
+    );
+
+    Assert.deepEqual(
+      results,
+      {
+        msg: "serviceworker-reply",
+        workerUrls: [`https://${hostname}/${scriptPath}`],
+      },
+      `Got the expected results for ${hostname} tab`
+    );
+
+    BrowserTestUtils.removeTab(tab);
+  }
+});
diff --git a/dom/workers/test/browser_serviceworker_fetch_new_process.js b/dom/workers/test/browser_serviceworker_fetch_new_process.js
new file mode 100644
index 0000000000..ae7d71c222
--- /dev/null
+++ b/dom/workers/test/browser_serviceworker_fetch_new_process.js
@@ -0,0 +1,405 @@
+const DIRPATH = getRootDirectory(gTestPath).replace(
+  "chrome://mochitests/content/",
+  ""
+);
+
+/**
+ * We choose blob contents that will roundtrip cleanly through the `textContent`
+ * of our returned HTML page.
+ */
+const TEST_BLOB_CONTENTS = `I'm a disk-backed test blob! Hooray!`;
+
+add_setup(async function () {
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      // Set preferences so that opening a page with the origin "example.org"
+      // will result in a remoteType of "privilegedmozilla" for both the
+      // page and the ServiceWorker.
+      ["browser.tabs.remote.separatePrivilegedMozillaWebContentProcess", true],
+      ["browser.tabs.remote.separatedMozillaDomains", "example.org"],
+      ["dom.ipc.processCount.privilegedmozilla", 1],
+      ["dom.ipc.processPrelaunch.enabled", false],
+      ["dom.serviceWorkers.enabled", true],
+      ["dom.serviceWorkers.testing.enabled", true],
+      // ServiceWorker worker instances should stay alive until explicitly
+      // caused to terminate by dropping these timeouts to 0 in
+      // `waitForWorkerAndProcessShutdown`.
+      ["dom.serviceWorkers.idle_timeout", 299999],
+      ["dom.serviceWorkers.idle_extended_timeout", 299999],
+    ],
+  });
+});
+
+function countRemoteType(remoteType) {
+  return ChromeUtils.getAllDOMProcesses().filter(
+    p => p.remoteType == remoteType
+  ).length;
+}
+
+/**
+ * Helper function to get a list of all current processes and their remote
+ * types.  Note that when in used in a templated literal that it is
+ * synchronously invoked when the string is evaluated and captures system state
+ * at that instant.
+ */
+function debugRemotes() {
+  return ChromeUtils.getAllDOMProcesses()
+    .map(p => p.remoteType || "parent")
+    .join(",");
+}
+
+/**
+ * Wait for there to be zero processes of the given remoteType.  This check is
+ * considered successful if there are already no processes of the given type
+ * at this very moment.
+ */
+async function waitForNoProcessesOfType(remoteType) {
+  info(`waiting for there to be no ${remoteType} procs`);
+  await TestUtils.waitForCondition(
+    () => countRemoteType(remoteType) == 0,
+    "wait for the worker's process to shutdown"
+  );
+}
+
+/**
+ * Given a ServiceWorkerRegistrationInfo with an active ServiceWorker that
+ * has no active ExtendableEvents but would otherwise continue running thanks
+ * to the idle keepalive:
+ * - Assert that there is a ServiceWorker instance in the given registration's
+ *   active slot.  (General invariant check.)
+ * - Assert that a single process with the given remoteType currently exists.
+ *   (This doesn't mean the SW is alive in that process, though this test
+ *   verifies that via other checks when appropriate.)
+ * - Induce the worker to shutdown by temporarily dropping the idle timeout to 0
+ *   and causing the idle timer to be reset due to rapid debugger attach/detach.
+ * - Wait for the the single process with the given remoteType to go away.
+ * - Reset the idle timeouts back to their previous high values.
+ */
+async function waitForWorkerAndProcessShutdown(swRegInfo, remoteType) {
+  info(`terminating worker and waiting for ${remoteType} procs to shut down`);
+  ok(swRegInfo.activeWorker, "worker should be in the active slot");
+  is(
+    countRemoteType(remoteType),
+    1,
+    `should have a single ${remoteType} process but have: ${debugRemotes()}`
+  );
+
+  // Let's not wait too long for the process to shutdown.
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["dom.serviceWorkers.idle_timeout", 0],
+      ["dom.serviceWorkers.idle_extended_timeout", 0],
+    ],
+  });
+
+  // We need to cause the worker to re-evaluate its idle timeout. The easiest
+  // way to do this I could think of is to attach and then detach the debugger
+  // from the active worker.
+  swRegInfo.activeWorker.attachDebugger();
+  await new Promise(resolve => Cu.dispatch(resolve));
+  swRegInfo.activeWorker.detachDebugger();
+
+  // Eventually the length will reach 0, meaning we're done!
+  await waitForNoProcessesOfType(remoteType);
+
+  is(
+    countRemoteType(remoteType),
+    0,
+    `processes with remoteType=${remoteType} type should have shut down`
+  );
+
+  // Make sure we never kill workers on idle except when this is called.
+  await SpecialPowers.popPrefEnv();
+}
+
+async function do_test_sw(host, remoteType, swMode, fileBlob) {
+  info(
+    `### entering test: host=${host}, remoteType=${remoteType}, mode=${swMode}`
+  );
+
+  const prin = Services.scriptSecurityManager.createContentPrincipal(
+    Services.io.newURI(`https://${host}`),
+    {}
+  );
+  const sw = `https://${host}/${DIRPATH}file_service_worker_fetch_synthetic.js`;
+  const scope = `https://${host}/${DIRPATH}server_fetch_synthetic.sjs`;
+
+  const swm = Cc["@mozilla.org/serviceworkers/manager;1"].getService(
+    Ci.nsIServiceWorkerManager
+  );
+  const swRegInfo = await swm.registerForTest(prin, scope, sw);
+  swRegInfo.QueryInterface(Ci.nsIServiceWorkerRegistrationInfo);
+
+  info(
+    `service worker registered: ${JSON.stringify({
+      principal: swRegInfo.principal.spec,
+      scope: swRegInfo.scope,
+    })}`
+  );
+
+  // Wait for the worker to install & shut down.
+  await TestUtils.waitForCondition(
+    () => swRegInfo.activeWorker,
+    "wait for the worker to become active"
+  );
+  await waitForWorkerAndProcessShutdown(swRegInfo, remoteType);
+
+  info(
+    `test navigation interception with mode=${swMode} starting from about:blank`
+  );
+  await BrowserTestUtils.withNewTab(
+    {
+      gBrowser,
+      url: "about:blank",
+    },
+    async browser => {
+      // NOTE: We intentionally trigger the navigation from content in order to
+      // make sure frontend doesn't eagerly process-switch for us.
+      SpecialPowers.spawn(
+        browser,
+        [scope, swMode, fileBlob],
+        // eslint-disable-next-line no-shadow
+        async (scope, swMode, fileBlob) => {
+          const pageUrl = `${scope}?mode=${swMode}`;
+          if (!fileBlob) {
+            content.location.href = pageUrl;
+          } else {
+            const doc = content.document;
+            const formElem = doc.createElement("form");
+            doc.body.appendChild(formElem);
+
+            formElem.action = pageUrl;
+            formElem.method = "POST";
+            formElem.enctype = "multipart/form-data";
+
+            const fileElem = doc.createElement("input");
+            formElem.appendChild(fileElem);
+
+            fileElem.type = "file";
+            fileElem.name = "foo";
+
+            fileElem.mozSetFileArray([fileBlob]);
+
+            formElem.submit();
+          }
+        }
+      );
+
+      await BrowserTestUtils.browserLoaded(browser);
+
+      is(
+        countRemoteType(remoteType),
+        1,
+        `should have spawned a content process with remoteType=${remoteType}`
+      );
+
+      const { source, blobContents } = await SpecialPowers.spawn(
+        browser,
+        [],
+        () => {
+          return {
+            source: content.document.getElementById("source").textContent,
+            blobContents: content.document.getElementById("blob").textContent,
+          };
+        }
+      );
+
+      is(
+        source,
+        swMode === "synthetic" ? "ServiceWorker" : "ServerJS",
+        "The page contents should come from the right place."
+      );
+
+      is(
+        blobContents,
+        fileBlob ? TEST_BLOB_CONTENTS : "",
+        "The request blob contents should be the blob/empty as appropriate."
+      );
+
+      // Ensure the worker was loaded in this process.
+      const workerDebuggerURLs = await SpecialPowers.spawn(
+        browser,
+        [sw],
+        async url => {
+          if (!content.navigator.serviceWorker.controller) {
+            throw new Error("document not controlled!");
+          }
+          const wdm = Cc[
+            "@mozilla.org/dom/workers/workerdebuggermanager;1"
+          ].getService(Ci.nsIWorkerDebuggerManager);
+
+          return Array.from(wdm.getWorkerDebuggerEnumerator())
+            .map(wd => {
+              return wd.url;
+            })
+            .filter(swURL => swURL == url);
+        }
+      );
+      if (remoteType.startsWith("webServiceWorker=")) {
+        Assert.notDeepEqual(
+          workerDebuggerURLs,
+          [sw],
+          "Isolated workers should not be running in the content child process"
+        );
+      } else {
+        Assert.deepEqual(
+          workerDebuggerURLs,
+          [sw],
+          "The worker should be running in the correct child process"
+        );
+      }
+
+      // Unregister the ServiceWorker.  The registration will continue to control
+      // `browser` and therefore continue to exist and its worker to continue
+      // running until the tab is closed.
+      await SpecialPowers.spawn(browser, [], async () => {
+        let registration = await content.navigator.serviceWorker.ready;
+        await registration.unregister();
+      });
+    }
+  );
+
+  // Now that the controlled tab is closed and the registration has been
+  // removed, the ServiceWorker will be made redundant which will forcibly
+  // terminate it, which will result in the shutdown of the given content
+  // process.  Wait for that to happen both as a verification and so the next
+  // test has a sufficiently clean slate.
+  await waitForNoProcessesOfType(remoteType);
+}
+
+/**
+ * Create a File-backed blob.  This will happen synchronously from the main
+ * thread, which isn't optimal, but the test blocks on this progress anyways.
+ * Bug 1669578 has been filed on improving this idiom and avoiding the sync
+ * writes.
+ */
+async function makeFileBlob(blobContents) {
+  const tmpFile = Cc["@mozilla.org/file/directory_service;1"]
+    .getService(Ci.nsIDirectoryService)
+    .QueryInterface(Ci.nsIProperties)
+    .get("TmpD", Ci.nsIFile);
+  tmpFile.append("test-file-backed-blob.txt");
+  tmpFile.createUnique(Ci.nsIFile.NORMAL_FILE_TYPE, 0o600);
+
+  var outStream = Cc[
+    "@mozilla.org/network/file-output-stream;1"
+  ].createInstance(Ci.nsIFileOutputStream);
+  outStream.init(
+    tmpFile,
+    0x02 | 0x08 | 0x20, // write, create, truncate
+    0o666,
+    0
+  );
+  outStream.write(blobContents, blobContents.length);
+  outStream.close();
+
+  const fileBlob = await File.createFromNsIFile(tmpFile);
+  return fileBlob;
+}
+
+function getSWTelemetrySums() {
+  let telemetry = Cc["@mozilla.org/base/telemetry;1"].getService(
+    Ci.nsITelemetry
+  );
+  let keyedhistograms = telemetry.getSnapshotForKeyedHistograms(
+    "main",
+    false
+  ).parent;
+  let keyedscalars = telemetry.getSnapshotForKeyedScalars("main", false).parent;
+  // We're not looking at the distribution of the histograms, just that they changed
+  return {
+    SERVICE_WORKER_RUNNING_All: keyedhistograms.SERVICE_WORKER_RUNNING
+      ? keyedhistograms.SERVICE_WORKER_RUNNING.All.sum
+      : 0,
+    SERVICE_WORKER_RUNNING_Fetch: keyedhistograms.SERVICE_WORKER_RUNNING
+      ? keyedhistograms.SERVICE_WORKER_RUNNING.Fetch.sum
+      : 0,
+    SERVICEWORKER_RUNNING_MAX_All: keyedscalars["serviceworker.running_max"]
+      ? keyedscalars["serviceworker.running_max"].All
+      : 0,
+    SERVICEWORKER_RUNNING_MAX_Fetch: keyedscalars["serviceworker.running_max"]
+      ? keyedscalars["serviceworker.running_max"].Fetch
+      : 0,
+  };
+}
+
+add_task(async function test() {
+  // Can't test telemetry without this since we may not be on the nightly channel
+  let oldCanRecord = Services.telemetry.canRecordExtended;
+  Services.telemetry.canRecordExtended = true;
+  registerCleanupFunction(() => {
+    Services.telemetry.canRecordExtended = oldCanRecord;
+  });
+
+  let initialSums = getSWTelemetrySums();
+
+  // ## Isolated Privileged Process
+  // Trigger a straightforward intercepted navigation with no request body that
+  // returns a synthetic response.
+  await do_test_sw("example.org", "privilegedmozilla", "synthetic", null);
+
+  // Trigger an intercepted navigation with FormData containing an
+  // <input type="file"> which will result in the request body containing a
+  // RemoteLazyInputStream which will be consumed in the content process by the
+  // ServiceWorker while generating the synthetic response.
+  const fileBlob = await makeFileBlob(TEST_BLOB_CONTENTS);
+  await do_test_sw("example.org", "privilegedmozilla", "synthetic", fileBlob);
+
+  // Trigger an intercepted navigation with FormData containing an
+  // <input type="file"> which will result in the request body containing a
+  // RemoteLazyInputStream which will be relayed back to the parent process
+  // via direct invocation of fetch() on the event.request but without any
+  // cloning.
+  await do_test_sw("example.org", "privilegedmozilla", "fetch", fileBlob);
+
+  // Same as the above but cloning the request before fetching it.
+  await do_test_sw("example.org", "privilegedmozilla", "clone", fileBlob);
+
+  // ## Fission Isolation
+  if (Services.appinfo.fissionAutostart) {
+    // ## ServiceWorker isolation
+    const isolateUrl = "example.com";
+    const isolateRemoteType = `webServiceWorker=https://` + isolateUrl;
+    await do_test_sw(isolateUrl, isolateRemoteType, "synthetic", null);
+    await do_test_sw(isolateUrl, isolateRemoteType, "synthetic", fileBlob);
+  }
+  let telemetrySums = getSWTelemetrySums();
+  info(JSON.stringify(telemetrySums));
+  info(
+    "Initial Running All: " +
+      initialSums.SERVICE_WORKER_RUNNING_All +
+      ", Fetch: " +
+      initialSums.SERVICE_WORKER_RUNNING_Fetch
+  );
+  info(
+    "Initial Max Running All: " +
+      initialSums.SERVICEWORKER_RUNNING_MAX_All +
+      ", Fetch: " +
+      initialSums.SERVICEWORKER_RUNNING_MAX_Fetch
+  );
+  info(
+    "Running All: " +
+      telemetrySums.SERVICE_WORKER_RUNNING_All +
+      ", Fetch: " +
+      telemetrySums.SERVICE_WORKER_RUNNING_Fetch
+  );
+  info(
+    "Max Running All: " +
+      telemetrySums.SERVICEWORKER_RUNNING_MAX_All +
+      ", Fetch: " +
+      telemetrySums.SERVICEWORKER_RUNNING_MAX_Fetch
+  );
+  Assert.greater(
+    telemetrySums.SERVICE_WORKER_RUNNING_All,
+    initialSums.SERVICE_WORKER_RUNNING_All,
+    "ServiceWorker running count changed"
+  );
+  Assert.greater(
+    telemetrySums.SERVICE_WORKER_RUNNING_Fetch,
+    initialSums.SERVICE_WORKER_RUNNING_Fetch,
+    "ServiceWorker running count changed"
+  );
+  // We don't use ok()'s for MAX because MAX may have been set before we
+  // set canRecordExtended, and if so we won't record a new value unless
+  // the max increases again.
+});
diff --git a/dom/workers/test/browser_worker_use_counters.js b/dom/workers/test/browser_worker_use_counters.js
new file mode 100644
index 0000000000..d651da31d8
--- /dev/null
+++ b/dom/workers/test/browser_worker_use_counters.js
@@ -0,0 +1,180 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+"use strict";
+
+const gHttpTestRoot = "https://example.com/browser/dom/workers/test/";
+
+function unscream(s) {
+  // Takes SCREAMINGCASE `s` and returns "Screamingcase".
+  return s.charAt(0) + s.slice(1).toLowerCase();
+}
+
+function screamToCamel(s) {
+  // Takes SCREAMING_CASE `s` and returns "screamingCase".
+  const pascal = s.split("_").map(unscream).join("");
+  return pascal.charAt(0).toLowerCase() + pascal.slice(1);
+}
+
+var check_use_counter_worker = async function (
+  use_counter_name,
+  worker_type,
+  content_task
+) {
+  info(`checking ${use_counter_name} use counters for ${worker_type} worker`);
+
+  let newTab = BrowserTestUtils.addTab(gBrowser, "about:blank");
+  gBrowser.selectedTab = newTab;
+  newTab.linkedBrowser.stop();
+
+  // Hold on to the current values of the instrumentation we're
+  // interested in.
+  await Services.fog.testFlushAllChildren();
+  let glean_before =
+    Glean[`useCounterWorker${unscream(worker_type)}`][
+      screamToCamel(use_counter_name)
+    ].testGetValue();
+  let glean_destructions_before =
+    Glean.useCounter[
+      `${worker_type.toLowerCase()}WorkersDestroyed`
+    ].testGetValue();
+
+  BrowserTestUtils.startLoadingURIString(
+    gBrowser.selectedBrowser,
+    gHttpTestRoot + "file_use_counter_worker.html"
+  );
+  await BrowserTestUtils.browserLoaded(gBrowser.selectedBrowser);
+  await content_task(gBrowser.selectedBrowser);
+
+  // Tear down the page.
+  let tabClosed = BrowserTestUtils.waitForTabClosing(newTab);
+  gBrowser.removeTab(newTab);
+  await tabClosed;
+
+  // Grab data again and compare.
+  // We'd like for this to be synchronous, but use counters are reported on
+  // worker destruction which we don't directly observe.
+  // So we check in a quick loop.
+  await BrowserTestUtils.waitForCondition(async () => {
+    await Services.fog.testFlushAllChildren();
+    return (
+      glean_before !=
+      Glean[`useCounterWorker${unscream(worker_type)}`][
+        screamToCamel(use_counter_name)
+      ].testGetValue()
+    );
+  });
+  let glean_after =
+    Glean[`useCounterWorker${unscream(worker_type)}`][
+      screamToCamel(use_counter_name)
+    ].testGetValue();
+  let glean_destructions_after =
+    Glean.useCounter[
+      `${worker_type.toLowerCase()}WorkersDestroyed`
+    ].testGetValue();
+
+  is(
+    glean_after,
+    glean_before + 1,
+    `Glean counter ${use_counter_name} for ${worker_type} worker is correct.`
+  );
+  // There might be other workers created by prior tests get destroyed during
+  // this tests.
+  Assert.greater(
+    glean_destructions_after,
+    glean_destructions_before ?? 0,
+    `Glean ${worker_type} worker counts are correct`
+  );
+};
+
+add_task(async function test_dedicated_worker() {
+  await check_use_counter_worker("CONSOLE_LOG", "DEDICATED", async browser => {
+    await ContentTask.spawn(browser, {}, function () {
+      return new Promise(resolve => {
+        let worker = new content.Worker("file_use_counter_worker.js");
+        worker.onmessage = function (e) {
+          if (e.data === "DONE") {
+            worker.terminate();
+            resolve();
+          }
+        };
+      });
+    });
+  });
+});
+
+add_task(async function test_shared_worker() {
+  await check_use_counter_worker("CONSOLE_LOG", "SHARED", async browser => {
+    await ContentTask.spawn(browser, {}, function () {
+      return new Promise(resolve => {
+        let worker = new content.SharedWorker(
+          "file_use_counter_shared_worker.js"
+        );
+        worker.port.onmessage = function (e) {
+          if (e.data === "DONE") {
+            resolve();
+          }
+        };
+        worker.port.postMessage("RUN");
+      });
+    });
+  });
+});
+
+add_task(async function test_shared_worker_microtask() {
+  await check_use_counter_worker("CONSOLE_LOG", "SHARED", async browser => {
+    await ContentTask.spawn(browser, {}, function () {
+      return new Promise(resolve => {
+        let worker = new content.SharedWorker(
+          "file_use_counter_shared_worker_microtask.js"
+        );
+        worker.port.onmessage = function (e) {
+          if (e.data === "DONE") {
+            resolve();
+          }
+        };
+        worker.port.postMessage("RUN");
+      });
+    });
+  });
+});
+
+add_task(async function test_service_worker() {
+  await check_use_counter_worker("CONSOLE_LOG", "SERVICE", async browser => {
+    await ContentTask.spawn(browser, {}, function () {
+      let waitForActivated = async function (registration) {
+        return new Promise(resolve => {
+          let worker =
+            registration.installing ||
+            registration.waiting ||
+            registration.active;
+          if (worker.state === "activated") {
+            resolve(worker);
+            return;
+          }
+
+          worker.addEventListener("statechange", function onStateChange() {
+            if (worker.state === "activated") {
+              worker.removeEventListener("statechange", onStateChange);
+              resolve(worker);
+            }
+          });
+        });
+      };
+
+      return new Promise(resolve => {
+        content.navigator.serviceWorker
+          .register("file_use_counter_service_worker.js")
+          .then(async registration => {
+            content.navigator.serviceWorker.onmessage = function (e) {
+              if (e.data === "DONE") {
+                registration.unregister().then(resolve);
+              }
+            };
+            let worker = await waitForActivated(registration);
+            worker.postMessage("RUN");
+          });
+      });
+    });
+  });
+});
diff --git a/dom/workers/test/bug1014466_data1.txt b/dom/workers/test/bug1014466_data1.txt
new file mode 100644
index 0000000000..a32a4347a4
--- /dev/null
+++ b/dom/workers/test/bug1014466_data1.txt
@@ -0,0 +1 @@
+1234567890
diff --git a/dom/workers/test/bug1014466_data2.txt b/dom/workers/test/bug1014466_data2.txt
new file mode 100644
index 0000000000..4d40154cef
--- /dev/null
+++ b/dom/workers/test/bug1014466_data2.txt
@@ -0,0 +1 @@
+ABCDEFGH
diff --git a/dom/workers/test/bug1014466_worker.js b/dom/workers/test/bug1014466_worker.js
new file mode 100644
index 0000000000..2161954d2b
--- /dev/null
+++ b/dom/workers/test/bug1014466_worker.js
@@ -0,0 +1,63 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+function ok(a, msg) {
+  postMessage({ type: "status", status: !!a, msg });
+}
+
+onmessage = function (event) {
+  function getResponse(url) {
+    var xhr = new XMLHttpRequest();
+    xhr.open("GET", url, false);
+    xhr.send();
+    return xhr.responseText;
+  }
+
+  const testFile1 = "bug1014466_data1.txt";
+  const testFile2 = "bug1014466_data2.txt";
+  const testData1 = getResponse(testFile1);
+  const testData2 = getResponse(testFile2);
+
+  var response_count = 0;
+  var xhr = new XMLHttpRequest();
+  xhr.onreadystatechange = function () {
+    if (xhr.readyState == xhr.DONE && xhr.status == 200) {
+      response_count++;
+      switch (response_count) {
+        case 1:
+          ok(xhr.responseText == testData1, "Check data 1");
+          test_data2();
+          break;
+        case 2:
+          ok(xhr.responseText == testData2, "Check data 2");
+          postMessage({ type: "finish" });
+          break;
+        default:
+          ok(false, "Unexpected response received");
+          postMessage({ type: "finish" });
+          break;
+      }
+    }
+  };
+  xhr.onerror = function (e) {
+    ok(false, "Got an error event: " + e);
+    postMessage({ type: "finish" });
+  };
+
+  function test_data1() {
+    xhr.open("GET", testFile1, true);
+    xhr.responseType = "text";
+    xhr.send();
+  }
+
+  function test_data2() {
+    xhr.abort();
+    xhr.open("GET", testFile2, true);
+    xhr.responseType = "text";
+    xhr.send();
+  }
+
+  test_data1();
+};
diff --git a/dom/workers/test/bug1020226_frame.html b/dom/workers/test/bug1020226_frame.html
new file mode 100644
index 0000000000..039dc9480a
--- /dev/null
+++ b/dom/workers/test/bug1020226_frame.html
@@ -0,0 +1,19 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1020226
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1020226</title>
+</head>
+<body>
+
+<script type="application/javascript">
+  var worker = new Worker("bug1020226_worker.js");
+  worker.onmessage = function(e) {
+    window.parent.postMessage("loaded", "*");
+  }
+</script>
+</body>
+</html>
diff --git a/dom/workers/test/bug1020226_worker.js b/dom/workers/test/bug1020226_worker.js
new file mode 100644
index 0000000000..c09abdd7de
--- /dev/null
+++ b/dom/workers/test/bug1020226_worker.js
@@ -0,0 +1,12 @@
+var p = new Promise(function (resolve, reject) {
+  // This causes a runnable to be queued.
+  reject(new Error());
+  postMessage("loaded");
+
+  // This prevents that runnable from running until the window calls terminate(),
+  // at which point the worker goes into the Canceling state and then an
+  // HoldWorker() is attempted, which fails, which used to result in
+  // multiple calls to the error reporter, one after the worker's context had
+  // been GCed.
+  while (true) {}
+});
diff --git a/dom/workers/test/bug1047663_tab.html b/dom/workers/test/bug1047663_tab.html
new file mode 100644
index 0000000000..62ab9be7d2
--- /dev/null
+++ b/dom/workers/test/bug1047663_tab.html
@@ -0,0 +1,8 @@
+<!DOCTYPE html>
+<html lang="en">
+  <head>
+    <meta charset="utf-8"/>
+  </head>
+  <body>
+  </body>
+</html>
diff --git a/dom/workers/test/bug1047663_worker.sjs b/dom/workers/test/bug1047663_worker.sjs
new file mode 100644
index 0000000000..169ca05f89
--- /dev/null
+++ b/dom/workers/test/bug1047663_worker.sjs
@@ -0,0 +1,41 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+"use strict";
+
+const WORKER_1 = `
+  "use strict";
+
+  self.onmessage = function () {
+    postMessage("one");
+  };
+`;
+
+const WORKER_2 = `
+  "use strict";
+
+  self.onmessage = function () {
+    postMessage("two");
+  };
+`;
+
+function handleRequest(request, response) {
+  let count = getState("count");
+  if (count === "") {
+    count = "1";
+  }
+
+  // This header is necessary for the cache to trigger.
+  response.setHeader("Cache-control", "max-age=3600");
+  response.setHeader("Content-Type", "text/javascript", false);
+
+  // If this is the first request, return the first source.
+  if (count === "1") {
+    response.write(WORKER_1);
+    setState("count", "2");
+  }
+  // For all subsequent requests, return the second source.
+  else {
+    response.write(WORKER_2);
+  }
+}
diff --git a/dom/workers/test/bug1060621_worker.js b/dom/workers/test/bug1060621_worker.js
new file mode 100644
index 0000000000..4137e3b06f
--- /dev/null
+++ b/dom/workers/test/bug1060621_worker.js
@@ -0,0 +1,2 @@
+navigator.foobar = 42;
+postMessage("done");
diff --git a/dom/workers/test/bug1062920_worker.js b/dom/workers/test/bug1062920_worker.js
new file mode 100644
index 0000000000..238bf949ec
--- /dev/null
+++ b/dom/workers/test/bug1062920_worker.js
@@ -0,0 +1,8 @@
+postMessage({
+  appCodeName: navigator.appCodeName,
+  appName: navigator.appName,
+  appVersion: navigator.appVersion,
+  platform: navigator.platform,
+  userAgent: navigator.userAgent,
+  product: navigator.product,
+});
diff --git a/dom/workers/test/bug1063538.sjs b/dom/workers/test/bug1063538.sjs
new file mode 100644
index 0000000000..7e4ba33998
--- /dev/null
+++ b/dom/workers/test/bug1063538.sjs
@@ -0,0 +1,11 @@
+const { setTimeout } = ChromeUtils.importESModule(
+  "resource://gre/modules/Timer.sys.mjs"
+);
+
+function handleRequest(request, response) {
+  response.processAsync();
+  response.write("Hello");
+  setTimeout(function () {
+    response.finish();
+  }, 100000); // wait 100 seconds.
+}
diff --git a/dom/workers/test/bug1063538_worker.js b/dom/workers/test/bug1063538_worker.js
new file mode 100644
index 0000000000..33e60f0a16
--- /dev/null
+++ b/dom/workers/test/bug1063538_worker.js
@@ -0,0 +1,25 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+var gURL = "http://example.org/tests/dom/workers/test/bug1063538.sjs";
+var xhr = new XMLHttpRequest({ mozAnon: true, mozSystem: true });
+var progressFired = false;
+
+xhr.onloadend = function (e) {
+  postMessage({ type: "finish", progressFired });
+  self.close();
+};
+
+xhr.onprogress = function (e) {
+  if (e.loaded > 0) {
+    progressFired = true;
+    xhr.abort();
+  }
+};
+
+onmessage = function (e) {
+  xhr.open("GET", gURL, true);
+  xhr.send();
+};
diff --git a/dom/workers/test/bug1104064_worker.js b/dom/workers/test/bug1104064_worker.js
new file mode 100644
index 0000000000..02b802a826
--- /dev/null
+++ b/dom/workers/test/bug1104064_worker.js
@@ -0,0 +1,10 @@
+onmessage = function () {
+  var counter = 0;
+  var id = setInterval(function () {
+    ++counter;
+    if (counter == 2) {
+      clearInterval(id);
+      postMessage("done");
+    }
+  }, 0);
+};
diff --git a/dom/workers/test/bug1132395_sharedWorker.js b/dom/workers/test/bug1132395_sharedWorker.js
new file mode 100644
index 0000000000..851c7f7f6c
--- /dev/null
+++ b/dom/workers/test/bug1132395_sharedWorker.js
@@ -0,0 +1,12 @@
+dump("SW created\n");
+onconnect = function (evt) {
+  dump("SW onconnect\n");
+  evt.ports[0].onmessage = function (e) {
+    dump("SW onmessage\n");
+    var blob = new Blob(["123"], { type: "text/plain" });
+    dump("SW blob created\n");
+    var url = URL.createObjectURL(blob);
+    dump("SW url created: " + url + "\n");
+    evt.ports[0].postMessage("alive \\o/");
+  };
+};
diff --git a/dom/workers/test/bug1132924_worker.js b/dom/workers/test/bug1132924_worker.js
new file mode 100644
index 0000000000..db67ba323c
--- /dev/null
+++ b/dom/workers/test/bug1132924_worker.js
@@ -0,0 +1,10 @@
+onmessage = function () {
+  var a = new XMLHttpRequest();
+  a.open("GET", "empty.html", false);
+  a.onreadystatechange = function () {
+    if (a.readyState == 4) {
+      postMessage(a.response);
+    }
+  };
+  a.send(null);
+};
diff --git a/dom/workers/test/bug978260_worker.js b/dom/workers/test/bug978260_worker.js
new file mode 100644
index 0000000000..126b9c901a
--- /dev/null
+++ b/dom/workers/test/bug978260_worker.js
@@ -0,0 +1,7 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+// Tell the main thread we're here.
+postMessage("loaded");
diff --git a/dom/workers/test/bug998474_worker.js b/dom/workers/test/bug998474_worker.js
new file mode 100644
index 0000000000..6f6b6a9212
--- /dev/null
+++ b/dom/workers/test/bug998474_worker.js
@@ -0,0 +1,7 @@
+self.addEventListener("connect", function (e) {
+  var port = e.ports[0];
+  port.onmessage = function (msg) {
+    // eslint-disable-next-line no-eval
+    port.postMessage(eval(msg.data));
+  };
+});
diff --git a/dom/workers/test/chrome.toml b/dom/workers/test/chrome.toml
new file mode 100644
index 0000000000..0b2d68da39
--- /dev/null
+++ b/dom/workers/test/chrome.toml
@@ -0,0 +1,120 @@
+[DEFAULT]
+skip-if = ["os == 'android'"]
+support-files = [
+  "WorkerDebugger.console_childWorker.js",
+  "WorkerDebugger.console_debugger.js",
+  "WorkerDebugger.console_worker.js",
+  "WorkerDebugger.initialize_childWorker.js",
+  "WorkerDebugger.initialize_debugger.js",
+  "WorkerDebugger.initialize_worker.js",
+  "WorkerDebugger.postMessage_childWorker.js",
+  "WorkerDebugger.postMessage_debugger.js",
+  "WorkerDebugger.postMessage_worker.js",
+  "WorkerDebuggerGlobalScope.createSandbox_debugger.js",
+  "WorkerDebuggerGlobalScope.createSandbox_sandbox.js",
+  "WorkerDebuggerGlobalScope.createSandbox_worker.js",
+  "WorkerDebuggerGlobalScope.enterEventLoop_childWorker.js",
+  "WorkerDebuggerGlobalScope.enterEventLoop_debugger.js",
+  "WorkerDebuggerGlobalScope.enterEventLoop_worker.js",
+  "WorkerDebuggerGlobalScope.reportError_childWorker.js",
+  "WorkerDebuggerGlobalScope.reportError_debugger.js",
+  "WorkerDebuggerGlobalScope.reportError_worker.js",
+  "WorkerDebuggerGlobalScope.setImmediate_debugger.js",
+  "WorkerDebuggerGlobalScope.setImmediate_worker.js",
+  "WorkerDebuggerManager_childWorker.js",
+  "WorkerDebuggerManager_worker.js",
+  "WorkerDebugger_childWorker.js",
+  "WorkerDebugger_frozen_window1.html",
+  "WorkerDebugger_frozen_window2.html",
+  "WorkerDebugger_frozen_worker1.js",
+  "WorkerDebugger_frozen_worker2.js",
+  "WorkerDebugger_promise_debugger.js",
+  "WorkerDebugger_promise_worker.js",
+  "WorkerDebugger_sharedWorker.js",
+  "WorkerDebugger_suspended_debugger.js",
+  "WorkerDebugger_suspended_worker.js",
+  "WorkerDebugger_worker.js",
+  "WorkerTest.jsm",
+  "WorkerTest_subworker.js",
+  "WorkerTest_worker.js",
+  "bug1062920_worker.js",
+  "chromeWorker_subworker.js",
+  "chromeWorker_worker_submod.sys.mjs",
+  "chromeWorker_worker.js",
+  "chromeWorker_worker.sys.mjs",
+  "dom_worker_helper.js",
+  "empty.html",
+  "fileBlobSubWorker_worker.js",
+  "fileBlob_worker.js",
+  "filePosting_worker.js",
+  "fileReadSlice_worker.js",
+  "fileReaderSyncErrors_worker.js",
+  "fileReaderSync_worker.js",
+  "fileSlice_worker.js",
+  "fileSubWorker_worker.js",
+  "file_worker.js",
+  "sharedWorker_privateBrowsing.js",
+  "sourcemap_header.js",
+  "sourcemap_header_debugger.js",
+]
+
+["test_WorkerDebugger.initialize.xhtml"]
+
+["test_WorkerDebugger.postMessage.xhtml"]
+
+["test_WorkerDebugger.xhtml"]
+
+["test_WorkerDebuggerGlobalScope.createSandbox.xhtml"]
+
+["test_WorkerDebuggerGlobalScope.enterEventLoop.xhtml"]
+
+["test_WorkerDebuggerGlobalScope.reportError.xhtml"]
+
+["test_WorkerDebuggerGlobalScope.setImmediate.xhtml"]
+
+["test_WorkerDebuggerManager.xhtml"]
+
+["test_WorkerDebugger_console.xhtml"]
+
+["test_WorkerDebugger_frozen.xhtml"]
+
+["test_WorkerDebugger_promise.xhtml"]
+
+["test_WorkerDebugger_suspended.xhtml"]
+
+["test_bug1062920.xhtml"]
+
+["test_chromeWorker.xhtml"]
+
+["test_chromeWorkerJSM.xhtml"]
+
+["test_file.xhtml"]
+skip-if = [
+  "os == 'linux' && bits == 64 && debug", # Bug 1765445
+  "apple_catalina && !debug", # Bug 1765445
+]
+
+["test_fileBlobPosting.xhtml"]
+
+["test_fileBlobSubWorker.xhtml"]
+
+["test_filePosting.xhtml"]
+
+["test_fileReadSlice.xhtml"]
+
+["test_fileReaderSync.xhtml"]
+
+["test_fileReaderSyncErrors.xhtml"]
+
+["test_fileSlice.xhtml"]
+
+["test_fileSubWorker.xhtml"]
+
+["test_readableStream_when_closing.html"]
+
+["test_sharedWorker_privateBrowsing.html"]
+
+["test_shutdownCheck.xhtml"]
+support-files = ["worker_shutdownCheck.js"]
+
+["test_sourcemap_header.html"]
diff --git a/dom/workers/test/chromeWorker_subworker.js b/dom/workers/test/chromeWorker_subworker.js
new file mode 100644
index 0000000000..6e89453150
--- /dev/null
+++ b/dom/workers/test/chromeWorker_subworker.js
@@ -0,0 +1,7 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+onmessage = function (event) {
+  postMessage("Done!");
+};
diff --git a/dom/workers/test/chromeWorker_worker.js b/dom/workers/test/chromeWorker_worker.js
new file mode 100644
index 0000000000..2d354b087b
--- /dev/null
+++ b/dom/workers/test/chromeWorker_worker.js
@@ -0,0 +1,20 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+if (!("ctypes" in self)) {
+  throw "No ctypes!";
+}
+
+// Go ahead and verify that the ctypes lazy getter actually works.
+if (ctypes.toString() != "[object ctypes]") {
+  throw "Bad ctypes object: " + ctypes.toString();
+}
+
+onmessage = function (event) {
+  let worker = new ChromeWorker("chromeWorker_subworker.js");
+  worker.onmessage = function (msg) {
+    postMessage(msg.data);
+  };
+  worker.postMessage(event.data);
+};
diff --git a/dom/workers/test/chromeWorker_worker.sys.mjs b/dom/workers/test/chromeWorker_worker.sys.mjs
new file mode 100644
index 0000000000..ee96d7829b
--- /dev/null
+++ b/dom/workers/test/chromeWorker_worker.sys.mjs
@@ -0,0 +1,16 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+// our onmessage handler lives in the module.
+import _ from "./chromeWorker_worker_submod.sys.mjs";
+
+if (!("ctypes" in self)) {
+  throw "No ctypes!";
+}
+
+// Go ahead and verify that the ctypes lazy getter actually works.
+if (ctypes.toString() != "[object ctypes]") {
+  throw "Bad ctypes object: " + ctypes.toString();
+}
diff --git a/dom/workers/test/chromeWorker_worker_submod.sys.mjs b/dom/workers/test/chromeWorker_worker_submod.sys.mjs
new file mode 100644
index 0000000000..c2fc29175c
--- /dev/null
+++ b/dom/workers/test/chromeWorker_worker_submod.sys.mjs
@@ -0,0 +1,9 @@
+onmessage = function (event) {
+  let worker = new ChromeWorker("chromeWorker_subworker.js");
+  worker.onmessage = function (msg) {
+    postMessage(msg.data);
+  };
+  worker.postMessage(event.data);
+};
+
+export default "go away linter";
diff --git a/dom/workers/test/clearTimeoutsImplicit_worker.js b/dom/workers/test/clearTimeoutsImplicit_worker.js
new file mode 100644
index 0000000000..dfb8d0f6ce
--- /dev/null
+++ b/dom/workers/test/clearTimeoutsImplicit_worker.js
@@ -0,0 +1,11 @@
+var count = 0;
+function timerFunction() {
+  if (++count == 30) {
+    postMessage("ready");
+    while (true) {}
+  }
+}
+
+for (var i = 0; i < 10; i++) {
+  setInterval(timerFunction, 500);
+}
diff --git a/dom/workers/test/clearTimeouts_worker.js b/dom/workers/test/clearTimeouts_worker.js
new file mode 100644
index 0000000000..6e6198c6b5
--- /dev/null
+++ b/dom/workers/test/clearTimeouts_worker.js
@@ -0,0 +1,12 @@
+var count = 0;
+function timerFunction() {
+  if (++count == 30) {
+    close();
+    postMessage("ready");
+    while (true) {}
+  }
+}
+
+for (var i = 0; i < 10; i++) {
+  setInterval(timerFunction, 500);
+}
diff --git a/dom/workers/test/consoleReplaceable_worker.js b/dom/workers/test/consoleReplaceable_worker.js
new file mode 100644
index 0000000000..7e6be8cdd6
--- /dev/null
+++ b/dom/workers/test/consoleReplaceable_worker.js
@@ -0,0 +1,24 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+onmessage = function (event) {
+  postMessage({ event: "console exists", status: !!console, last: false });
+  var logCalled = false;
+  console.log = function () {
+    logCalled = true;
+  };
+  console.log("foo");
+  postMessage({
+    event: "console.log is replaceable",
+    status: logCalled,
+    last: false,
+  });
+  console = 42;
+  postMessage({
+    event: "console is replaceable",
+    status: console === 42,
+    last: true,
+  });
+};
diff --git a/dom/workers/test/console_worker.js b/dom/workers/test/console_worker.js
new file mode 100644
index 0000000000..811dc12bae
--- /dev/null
+++ b/dom/workers/test/console_worker.js
@@ -0,0 +1,113 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+onmessage = function (event) {
+  // TEST: does console exist?
+  postMessage({ event: "console exists", status: !!console, last: false });
+
+  postMessage({
+    event: "console is the same object",
+    // eslint-disable-next-line no-self-compare
+    status: console === console,
+    last: false,
+  });
+
+  postMessage({ event: "trace without function", status: true, last: false });
+
+  for (var i = 0; i < 10; ++i) {
+    console.log(i, i, i);
+  }
+
+  function trace1() {
+    function trace2() {
+      function trace3() {
+        console.trace("trace " + i);
+      }
+      trace3();
+    }
+    trace2();
+  }
+  trace1();
+
+  foobar585956c = function (a) {
+    console.trace();
+    return a + "c";
+  };
+
+  function foobar585956b(a) {
+    return foobar585956c(a + "b");
+  }
+
+  function foobar585956a(omg) {
+    return foobar585956b(omg + "a");
+  }
+
+  function foobar646025(omg) {
+    console.log(omg, "o", "d");
+  }
+
+  function startTimer(timer) {
+    console.time(timer);
+  }
+
+  function stopTimer(timer) {
+    console.timeEnd(timer);
+  }
+
+  function timeStamp(label) {
+    console.timeStamp(label);
+  }
+
+  function testGroups() {
+    console.groupCollapsed("a", "group");
+    console.group("b", "group");
+    console.groupEnd();
+  }
+
+  foobar585956a("omg");
+  foobar646025("omg");
+  timeStamp();
+  timeStamp("foo");
+  testGroups();
+  startTimer("foo");
+  setTimeout(function () {
+    stopTimer("foo");
+    nextSteps(event);
+  }, 10);
+};
+
+function nextSteps(event) {
+  function namelessTimer() {
+    console.time();
+    console.timeEnd();
+  }
+
+  namelessTimer();
+
+  var str = "Test Message.";
+  console.log(str);
+  console.info(str);
+  console.warn(str);
+  console.error(str);
+  console.exception(str);
+  console.assert(true, str);
+  console.assert(false, str);
+  console.profile(str);
+  console.profileEnd(str);
+  console.timeStamp();
+  console.clear();
+  postMessage({ event: "4 messages", status: true, last: false });
+
+  // Recursive:
+  if (event.data == true) {
+    var worker = new Worker("console_worker.js");
+    worker.onmessage = function (msg) {
+      postMessage(msg.data);
+    };
+    worker.postMessage(false);
+  } else {
+    postMessage({ event: "bye bye", status: true, last: true });
+  }
+}
diff --git a/dom/workers/test/content_worker.js b/dom/workers/test/content_worker.js
new file mode 100644
index 0000000000..d79732b281
--- /dev/null
+++ b/dom/workers/test/content_worker.js
@@ -0,0 +1,12 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+var props = {
+  ctypes: 1,
+  OS: 1,
+};
+for (var prop in props) {
+  postMessage({ prop, value: self[prop] });
+}
+postMessage({ testfinished: 1 });
diff --git a/dom/workers/test/crashtests/1153636.html b/dom/workers/test/crashtests/1153636.html
new file mode 100644
index 0000000000..6ad0d550fd
--- /dev/null
+++ b/dom/workers/test/crashtests/1153636.html
@@ -0,0 +1,5 @@
+<script>
+
+new Worker("data:text/javascript;charset=UTF-8,self.addEventListener('',function(){},false);");
+
+</script>
diff --git a/dom/workers/test/crashtests/1158031.html b/dom/workers/test/crashtests/1158031.html
new file mode 100644
index 0000000000..6d896bc466
--- /dev/null
+++ b/dom/workers/test/crashtests/1158031.html
@@ -0,0 +1,11 @@
+<!DOCTYPE html>
+<script>
+
+function boom()
+{
+    var w = new Worker("data:text/javascript;charset=UTF-8,");
+    w.postMessage(new Blob([], {}));
+}
+
+</script>
+<body onload="boom();"></body>
diff --git a/dom/workers/test/crashtests/1228456.html b/dom/workers/test/crashtests/1228456.html
new file mode 100644
index 0000000000..6d1f0f0a72
--- /dev/null
+++ b/dom/workers/test/crashtests/1228456.html
@@ -0,0 +1,14 @@
+<!DOCTYPE html>
+<script>
+
+function boom()
+{
+    var w;
+    for (var i = 0; i < 99; ++i) {
+        w = new SharedWorker("data:text/javascript;charset=UTF-8," + encodeURIComponent(i + ";"));
+    }
+    w.port.postMessage("");
+}
+
+</script>
+<body onload="boom();"></body>
diff --git a/dom/workers/test/crashtests/1348882.html b/dom/workers/test/crashtests/1348882.html
new file mode 100644
index 0000000000..e0288c4ccb
--- /dev/null
+++ b/dom/workers/test/crashtests/1348882.html
@@ -0,0 +1,18 @@
+<!DOCTYPE>
+<html>
+<head>
+<meta charset="UTF-8">
+<script>
+function boom() {
+  let r = new Request("#a#a");
+  setTimeout(function(){
+    r.formData();
+    setTimeout(function(){
+      r.blob();
+    }, 0);
+  }, 0);
+}
+addEventListener("DOMContentLoaded", boom);
+</script>
+</head>
+</html>
diff --git a/dom/workers/test/crashtests/1819146.html b/dom/workers/test/crashtests/1819146.html
new file mode 100644
index 0000000000..611acb3ed2
--- /dev/null
+++ b/dom/workers/test/crashtests/1819146.html
@@ -0,0 +1,23 @@
+<!DOCTYPE html>
+<html>
+<head>
+    <script id="worker1" type="javascript/worker">
+        self.onmessage = async function (e) {
+          const abort = new AbortController()
+          const signal = abort.signal
+          abort.abort()
+          close()
+          try { await fetch(undefined, { signal: signal }) } catch (e) {}
+          await navigator.locks.request("weblock_0", { signal: signal }, () => {})
+          await fetch(undefined, { headers: [] })
+        }
+    </script>
+    <script>
+      document.addEventListener('DOMContentLoaded', () => {
+        const blob = new Blob([document.querySelector('#worker1').textContent], { type: 'text/javascript' })
+        const worker = new Worker(window.URL.createObjectURL(blob))
+        worker.postMessage([], [])
+      })
+    </script>
+</head>
+</html>
diff --git a/dom/workers/test/crashtests/1821066.html b/dom/workers/test/crashtests/1821066.html
new file mode 100644
index 0000000000..d654b37768
--- /dev/null
+++ b/dom/workers/test/crashtests/1821066.html
@@ -0,0 +1,9 @@
+<!DOCTYPE>
+<html>
+<head>
+<meta charset="UTF-8">
+<script>
+new Worker("data:text/javascript;charset=UTF-8,import { o } from '404.js'", {type: 'module'});
+</script>
+</head>
+</html>
diff --git a/dom/workers/test/crashtests/779707.html b/dom/workers/test/crashtests/779707.html
new file mode 100644
index 0000000000..97a8113dab
--- /dev/null
+++ b/dom/workers/test/crashtests/779707.html
@@ -0,0 +1,19 @@
+<!DOCTYPE html>
+<html>
+<head>
+<script>
+
+function boom()
+{
+  var x = new XMLHttpRequest();
+  x.open('GET', "data:text/plain,2", false);
+  x.send();
+
+  new Worker("data:text/javascript,3");
+}
+
+</script>
+</head>
+
+<body onload="boom();"></body>
+</html>
diff --git a/dom/workers/test/crashtests/943516.html b/dom/workers/test/crashtests/943516.html
new file mode 100644
index 0000000000..5f4667850f
--- /dev/null
+++ b/dom/workers/test/crashtests/943516.html
@@ -0,0 +1,10 @@
+<!--
+Any copyright is dedicated to the Public Domain.
+http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE html>
+<script>
+// Using a DOM bindings object as a weak map key should not crash when attempting to
+// call the preserve wrapper callback.
+new Worker("data:text/javascript;charset=UTF-8,(new WeakMap()).set(self, 0);")
+</script>
diff --git a/dom/workers/test/crashtests/crashtests.list b/dom/workers/test/crashtests/crashtests.list
new file mode 100644
index 0000000000..528f4c8a10
--- /dev/null
+++ b/dom/workers/test/crashtests/crashtests.list
@@ -0,0 +1,8 @@
+load 779707.html
+load 943516.html
+load 1153636.html
+load 1158031.html
+load 1228456.html
+load 1348882.html
+load 1821066.html
+load 1819146.html
diff --git a/dom/workers/test/csp_worker.js b/dom/workers/test/csp_worker.js
new file mode 100644
index 0000000000..04afa4bda1
--- /dev/null
+++ b/dom/workers/test/csp_worker.js
@@ -0,0 +1,26 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+onmessage = function (event) {
+  if (event.data.do == "eval") {
+    var res;
+    try {
+      // eslint-disable-next-line no-eval
+      res = eval("40+2");
+    } catch (ex) {
+      res = ex + "";
+    }
+    postMessage(res);
+  } else if (event.data.do == "nest") {
+    var worker = new Worker(event.data.uri);
+    if (--event.data.level) {
+      worker.postMessage(event.data);
+    } else {
+      worker.postMessage({ do: "eval" });
+    }
+    worker.onmessage = e => {
+      postMessage(e.data);
+    };
+  }
+};
diff --git a/dom/workers/test/csp_worker.js^headers^ b/dom/workers/test/csp_worker.js^headers^
new file mode 100644
index 0000000000..7b835bf2a8
--- /dev/null
+++ b/dom/workers/test/csp_worker.js^headers^
@@ -0,0 +1 @@
+Content-Security-Policy: default-src 'self' blob: ; script-src 'unsafe-eval'
diff --git a/dom/workers/test/dom_worker_helper.js b/dom/workers/test/dom_worker_helper.js
new file mode 100644
index 0000000000..e61b4793f2
--- /dev/null
+++ b/dom/workers/test/dom_worker_helper.js
@@ -0,0 +1,157 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+const wdm = Cc["@mozilla.org/dom/workers/workerdebuggermanager;1"].getService(
+  Ci.nsIWorkerDebuggerManager
+);
+
+const BASE_URL = "chrome://mochitests/content/chrome/dom/workers/test/";
+
+var gRemainingTests = 0;
+
+function waitForWorkerFinish() {
+  if (gRemainingTests == 0) {
+    SimpleTest.waitForExplicitFinish();
+  }
+  ++gRemainingTests;
+}
+
+function finish() {
+  --gRemainingTests;
+  if (gRemainingTests == 0) {
+    SimpleTest.finish();
+  }
+}
+
+function assertThrows(fun, message) {
+  let throws = false;
+  try {
+    fun();
+  } catch (e) {
+    throws = true;
+  }
+  ok(throws, message);
+}
+
+function generateDebuggers() {
+  return wdm.getWorkerDebuggerEnumerator();
+}
+
+function findDebugger(url) {
+  for (let dbg of generateDebuggers()) {
+    if (dbg.url === url) {
+      return dbg;
+    }
+  }
+  return null;
+}
+
+function waitForRegister(url, dbgUrl) {
+  return new Promise(function (resolve) {
+    wdm.addListener({
+      onRegister(dbg) {
+        if (dbg.url !== url) {
+          return;
+        }
+        ok(true, "Debugger with url " + url + " should be registered.");
+        wdm.removeListener(this);
+        if (dbgUrl) {
+          info("Initializing worker debugger with url " + url + ".");
+          dbg.initialize(dbgUrl);
+        }
+        resolve(dbg);
+      },
+    });
+  });
+}
+
+function waitForUnregister(url) {
+  return new Promise(function (resolve) {
+    wdm.addListener({
+      onUnregister(dbg) {
+        if (dbg.url !== url) {
+          return;
+        }
+        ok(true, "Debugger with url " + url + " should be unregistered.");
+        wdm.removeListener(this);
+        resolve();
+      },
+    });
+  });
+}
+
+function waitForDebuggerClose(dbg) {
+  return new Promise(function (resolve) {
+    dbg.addListener({
+      onClose() {
+        ok(true, "Debugger should be closed.");
+        dbg.removeListener(this);
+        resolve();
+      },
+    });
+  });
+}
+
+function waitForDebuggerError(dbg) {
+  return new Promise(function (resolve) {
+    dbg.addListener({
+      onError(filename, lineno, message) {
+        dbg.removeListener(this);
+        resolve(new Error(message, filename, lineno));
+      },
+    });
+  });
+}
+
+function waitForDebuggerMessage(dbg, message) {
+  return new Promise(function (resolve) {
+    dbg.addListener({
+      onMessage(message1) {
+        if (message !== message1) {
+          return;
+        }
+        ok(true, "Should receive " + message + " message from debugger.");
+        dbg.removeListener(this);
+        resolve();
+      },
+    });
+  });
+}
+
+function waitForWindowMessage(window, message) {
+  return new Promise(function (resolve) {
+    let onmessage = function (event) {
+      // eslint-disable-next-line no-self-compare
+      if (event.data !== event.data) {
+        return;
+      }
+      window.removeEventListener("message", onmessage);
+      resolve();
+    };
+    window.addEventListener("message", onmessage);
+  });
+}
+
+function waitForWorkerMessage(worker, message) {
+  return new Promise(function (resolve) {
+    worker.addEventListener("message", function onmessage(event) {
+      if (event.data !== message) {
+        return;
+      }
+      ok(true, "Should receive " + message + " message from worker.");
+      worker.removeEventListener("message", onmessage);
+      resolve();
+    });
+  });
+}
+
+function waitForMultiple(promises) {
+  // There used to be old logic which expects promises to be resolved in
+  // succession, but where it seems like this was an incorrect assumption.
+  // Assuming this change sticks, bug 1861778 tracks removing this method
+  // entirely in favor of Promise.all at the call-sites or transform the callers
+  // into explicitly documented awaited sequences.
+  return Promise.all(promises);
+}
diff --git a/dom/workers/test/dynamicImport_nested.mjs b/dom/workers/test/dynamicImport_nested.mjs
new file mode 100644
index 0000000000..688078d803
--- /dev/null
+++ b/dom/workers/test/dynamicImport_nested.mjs
@@ -0,0 +1,8 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+await import("./dynamicImport_postMessage.mjs");
+
+export const message = "first";
diff --git a/dom/workers/test/dynamicImport_postMessage.mjs b/dom/workers/test/dynamicImport_postMessage.mjs
new file mode 100644
index 0000000000..ddb9ee0644
--- /dev/null
+++ b/dom/workers/test/dynamicImport_postMessage.mjs
@@ -0,0 +1,8 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+postMessage("second");
+
+export const message = "second";
diff --git a/dom/workers/test/dynamicImport_worker.js b/dom/workers/test/dynamicImport_worker.js
new file mode 100644
index 0000000000..90bd422efe
--- /dev/null
+++ b/dom/workers/test/dynamicImport_worker.js
@@ -0,0 +1,14 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+onmessage = function (event) {
+  switch (event.data) {
+    case "start":
+      import("./dynamicImport_nested.mjs").then(m => postMessage(m.message));
+      break;
+    default:
+      throw new Error("Bad message: " + event.data);
+  }
+};
diff --git a/dom/workers/test/empty.html b/dom/workers/test/empty.html
new file mode 100644
index 0000000000..e69de29bb2
--- /dev/null
+++ b/dom/workers/test/empty.html
diff --git a/dom/workers/test/empty_worker.js b/dom/workers/test/empty_worker.js
new file mode 100644
index 0000000000..9dda1c9fd1
--- /dev/null
+++ b/dom/workers/test/empty_worker.js
@@ -0,0 +1 @@
+postMessage(42);
diff --git a/dom/workers/test/errorPropagation_iframe.html b/dom/workers/test/errorPropagation_iframe.html
new file mode 100644
index 0000000000..cbaed1778f
--- /dev/null
+++ b/dom/workers/test/errorPropagation_iframe.html
@@ -0,0 +1,56 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+  <meta charset="utf-8">
+  <body>
+    <script type="text/javascript">
+      var worker;
+
+      function start(workerCount, messageCallback) {
+        var seenWindowError;
+        window.onerror = function(message, filename, lineno) {
+          if (!seenWindowError) {
+            seenWindowError = true;
+            messageCallback({
+              type: "window",
+              data: { message, filename, lineno }
+            });
+            return true;
+          }
+          return undefined;
+        };
+
+        worker = new Worker("errorPropagation_worker.js");
+
+        worker.onmessage = function(event) {
+          messageCallback(event.data);
+        };
+
+        var seenWorkerError;
+        worker.onerror = function(event) {
+          if (!seenWorkerError) {
+            seenWorkerError = true;
+            messageCallback({
+              type: "worker",
+              data: {
+                message: event.message,
+                filename: event.filename,
+                lineno: event.lineno
+              }
+            });
+            event.preventDefault();
+          }
+        };
+
+        worker.postMessage(workerCount);
+      }
+
+      function stop() {
+        worker.terminate();
+      }
+    </script>
+  </body>
+</html>
diff --git a/dom/workers/test/errorPropagation_worker.js b/dom/workers/test/errorPropagation_worker.js
new file mode 100644
index 0000000000..679181e83a
--- /dev/null
+++ b/dom/workers/test/errorPropagation_worker.js
@@ -0,0 +1,51 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+var seenScopeError;
+onerror = function (message, filename, lineno) {
+  if (!seenScopeError) {
+    seenScopeError = true;
+    postMessage({
+      type: "scope",
+      data: { message, filename, lineno },
+    });
+    return true;
+  }
+  return undefined;
+};
+
+onmessage = function (event) {
+  var workerId = parseInt(event.data);
+
+  if (workerId > 1) {
+    var worker = new Worker("errorPropagation_worker.js");
+
+    worker.onmessage = function (msg) {
+      postMessage(msg.data);
+    };
+
+    var seenWorkerError;
+    worker.onerror = function (error) {
+      if (!seenWorkerError) {
+        seenWorkerError = true;
+        postMessage({
+          type: "worker",
+          data: {
+            message: error.message,
+            filename: error.filename,
+            lineno: error.lineno,
+          },
+        });
+        error.preventDefault();
+      }
+    };
+
+    worker.postMessage(workerId - 1);
+    return;
+  }
+
+  var interval = setInterval(function () {
+    throw new Error("expectedError");
+  }, 100);
+};
diff --git a/dom/workers/test/errorwarning_worker.js b/dom/workers/test/errorwarning_worker.js
new file mode 100644
index 0000000000..39e71f8414
--- /dev/null
+++ b/dom/workers/test/errorwarning_worker.js
@@ -0,0 +1,46 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+function errorHandler() {
+  postMessage({ type: "error" });
+}
+
+onmessage = function (event) {
+  if (event.data.errors) {
+    try {
+      // This is an error:
+      postMessage({ type: "ignore", value: b.aaa });
+    } catch (e) {
+      errorHandler();
+    }
+  } else {
+    var a = {};
+    // This is a warning:
+    postMessage({ type: "ignore", value: a.foo });
+  }
+
+  if (event.data.loop != 0) {
+    var worker = new Worker("errorwarning_worker.js");
+    worker.onerror = errorHandler;
+    worker.postMessage({
+      loop: event.data.loop - 1,
+      errors: event.data.errors,
+    });
+
+    worker.onmessage = function (e) {
+      postMessage(e.data);
+    };
+  } else {
+    postMessage({ type: "finish" });
+  }
+};
+
+onerror = errorHandler;
+// eslint-disable-next-line no-self-assign
+onerror = onerror;
+// eslint-disable-next-line no-self-compare
+if (!onerror || onerror != onerror) {
+  throw "onerror wasn't set properly";
+}
diff --git a/dom/workers/test/eventDispatch_worker.js b/dom/workers/test/eventDispatch_worker.js
new file mode 100644
index 0000000000..57bbc99aa3
--- /dev/null
+++ b/dom/workers/test/eventDispatch_worker.js
@@ -0,0 +1,84 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+const fakeEventType = "foo";
+
+function testEventTarget(event) {
+  if (event.target !== self) {
+    throw new Error("Event has a bad target!");
+  }
+  if (event.currentTarget) {
+    throw new Error("Event has a bad currentTarget!");
+  }
+  postMessage(event.data);
+}
+
+addEventListener(
+  fakeEventType,
+  function (event) {
+    throw new Error("Trusted event listener received untrusted event!");
+  },
+  false,
+  false
+);
+
+addEventListener(
+  fakeEventType,
+  function (event) {
+    if (event.target !== self || event.currentTarget !== self) {
+      throw new Error("Fake event has bad target!");
+    }
+    if (event.isTrusted) {
+      throw new Error("Event should be untrusted!");
+    }
+    event.stopImmediatePropagation();
+    postMessage(event.data);
+  },
+  false,
+  true
+);
+
+addEventListener(
+  fakeEventType,
+  function (event) {
+    throw new Error(
+      "This shouldn't get called because of stopImmediatePropagation."
+    );
+  },
+  false,
+  true
+);
+
+var count = 0;
+onmessage = function (event) {
+  if (event.target !== self || event.currentTarget !== self) {
+    throw new Error("Event has bad target!");
+  }
+
+  if (!count++) {
+    var exception;
+    try {
+      self.dispatchEvent(event);
+    } catch (e) {
+      exception = e;
+    }
+
+    if (!exception) {
+      throw new Error("Recursive dispatch didn't fail!");
+    }
+
+    event = new MessageEvent(fakeEventType, {
+      bubbles: event.bubbles,
+      cancelable: event.cancelable,
+      data: event.data,
+      origin: "*",
+      source: null,
+    });
+    self.dispatchEvent(event);
+
+    return;
+  }
+
+  setTimeout(testEventTarget, 0, event);
+};
diff --git a/dom/workers/test/fibonacci_worker.js b/dom/workers/test/fibonacci_worker.js
new file mode 100644
index 0000000000..0efe5a18d9
--- /dev/null
+++ b/dom/workers/test/fibonacci_worker.js
@@ -0,0 +1,24 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+onmessage = function (event) {
+  var n = parseInt(event.data);
+
+  if (n < 2) {
+    postMessage(n);
+    return;
+  }
+
+  var results = [];
+  for (var i = 1; i <= 2; i++) {
+    var worker = new Worker("fibonacci_worker.js");
+    worker.onmessage = function (msg) {
+      results.push(parseInt(msg.data));
+      if (results.length == 2) {
+        postMessage(results[0] + results[1]);
+      }
+    };
+    worker.postMessage(n - i);
+  }
+};
diff --git a/dom/workers/test/fileBlobSubWorker_worker.js b/dom/workers/test/fileBlobSubWorker_worker.js
new file mode 100644
index 0000000000..170362b1a4
--- /dev/null
+++ b/dom/workers/test/fileBlobSubWorker_worker.js
@@ -0,0 +1,17 @@
+/**
+ * Expects a blob. Returns an object containing the size, type.
+ *  Used to test posting of blob from worker to worker.
+ */
+onmessage = function (event) {
+  var worker = new Worker("fileBlob_worker.js");
+
+  worker.postMessage(event.data);
+
+  worker.onmessage = function (msg) {
+    postMessage(msg.data);
+  };
+
+  worker.onerror = function (error) {
+    postMessage(undefined);
+  };
+};
diff --git a/dom/workers/test/fileBlob_worker.js b/dom/workers/test/fileBlob_worker.js
new file mode 100644
index 0000000000..fbb50c7c10
--- /dev/null
+++ b/dom/workers/test/fileBlob_worker.js
@@ -0,0 +1,13 @@
+/**
+ * Expects a blob. Returns an object containing the size, type.
+ */
+onmessage = function (event) {
+  var file = event.data;
+
+  var rtnObj = new Object();
+
+  rtnObj.size = file.size;
+  rtnObj.type = file.type;
+
+  postMessage(rtnObj);
+};
diff --git a/dom/workers/test/filePosting_worker.js b/dom/workers/test/filePosting_worker.js
new file mode 100644
index 0000000000..052d400374
--- /dev/null
+++ b/dom/workers/test/filePosting_worker.js
@@ -0,0 +1,3 @@
+onmessage = function (event) {
+  postMessage(event.data);
+};
diff --git a/dom/workers/test/fileReadSlice_worker.js b/dom/workers/test/fileReadSlice_worker.js
new file mode 100644
index 0000000000..edbad88802
--- /dev/null
+++ b/dom/workers/test/fileReadSlice_worker.js
@@ -0,0 +1,16 @@
+/**
+ * Expects an object containing a blob, a start index and an end index
+ * for slicing. Returns the contents of the blob read as text.
+ */
+onmessage = function (event) {
+  var blob = event.data.blob;
+  var start = event.data.start;
+  var end = event.data.end;
+
+  var slicedBlob = blob.slice(start, end);
+
+  var fileReader = new FileReaderSync();
+  var text = fileReader.readAsText(slicedBlob);
+
+  postMessage(text);
+};
diff --git a/dom/workers/test/fileReaderSyncErrors_worker.js b/dom/workers/test/fileReaderSyncErrors_worker.js
new file mode 100644
index 0000000000..0ba91469c8
--- /dev/null
+++ b/dom/workers/test/fileReaderSyncErrors_worker.js
@@ -0,0 +1,82 @@
+/**
+ * Delegates "is" evaluation back to main thread.
+ */
+function is(actual, expected, message) {
+  var rtnObj = new Object();
+  rtnObj.actual = actual;
+  rtnObj.expected = expected;
+  rtnObj.message = message;
+  postMessage(rtnObj);
+}
+
+/**
+ * Tries to write to property.
+ */
+function writeProperty(file, property) {
+  var oldValue = file[property];
+  file[property] = -1;
+  is(file[property], oldValue, "Property " + property + " should be readonly.");
+}
+
+/**
+ * Passes junk arguments to FileReaderSync methods and expects an exception to
+ * be thrown.
+ */
+function fileReaderJunkArgument(blob) {
+  var fileReader = new FileReaderSync();
+
+  try {
+    fileReader.readAsBinaryString(blob);
+    is(
+      false,
+      true,
+      "Should have thrown an exception calling readAsBinaryString."
+    );
+  } catch (ex) {
+    is(true, true, "Should have thrown an exception.");
+  }
+
+  try {
+    fileReader.readAsDataURL(blob);
+    is(false, true, "Should have thrown an exception calling readAsDataURL.");
+  } catch (ex) {
+    is(true, true, "Should have thrown an exception.");
+  }
+
+  try {
+    fileReader.readAsArrayBuffer(blob);
+    is(
+      false,
+      true,
+      "Should have thrown an exception calling readAsArrayBuffer."
+    );
+  } catch (ex) {
+    is(true, true, "Should have thrown an exception.");
+  }
+
+  try {
+    fileReader.readAsText(blob);
+    is(false, true, "Should have thrown an exception calling readAsText.");
+  } catch (ex) {
+    is(true, true, "Should have thrown an exception.");
+  }
+}
+
+onmessage = function (event) {
+  var file = event.data;
+
+  // Test read only properties.
+  writeProperty(file, "size");
+  writeProperty(file, "type");
+  writeProperty(file, "name");
+
+  // Bad types.
+  fileReaderJunkArgument(undefined);
+  fileReaderJunkArgument(-1);
+  fileReaderJunkArgument(1);
+  fileReaderJunkArgument(new Object());
+  fileReaderJunkArgument("hello");
+
+  // Post undefined to indicate that testing has finished.
+  postMessage(undefined);
+};
diff --git a/dom/workers/test/fileReaderSync_worker.js b/dom/workers/test/fileReaderSync_worker.js
new file mode 100644
index 0000000000..d5512ef024
--- /dev/null
+++ b/dom/workers/test/fileReaderSync_worker.js
@@ -0,0 +1,25 @@
+var reader = new FileReaderSync();
+
+/**
+ * Expects an object containing a file and an encoding then uses a
+ * FileReaderSync to read the file. Returns an object containing the
+ * file read a binary string, text, url and ArrayBuffer.
+ */
+onmessage = function (event) {
+  var file = event.data.file;
+  var encoding = event.data.encoding;
+
+  var rtnObj = new Object();
+
+  if (encoding != undefined) {
+    rtnObj.text = reader.readAsText(file, encoding);
+  } else {
+    rtnObj.text = reader.readAsText(file);
+  }
+
+  rtnObj.bin = reader.readAsBinaryString(file);
+  rtnObj.url = reader.readAsDataURL(file);
+  rtnObj.arrayBuffer = reader.readAsArrayBuffer(file);
+
+  postMessage(rtnObj);
+};
diff --git a/dom/workers/test/fileSlice_worker.js b/dom/workers/test/fileSlice_worker.js
new file mode 100644
index 0000000000..94a283033a
--- /dev/null
+++ b/dom/workers/test/fileSlice_worker.js
@@ -0,0 +1,27 @@
+/**
+ * Expects an object containing a blob, a start offset, an end offset
+ * and an optional content type to slice the blob. Returns an object
+ * containing the size and type of the sliced blob.
+ */
+onmessage = function (event) {
+  var blob = event.data.blob;
+  var start = event.data.start;
+  var end = event.data.end;
+  var contentType = event.data.contentType;
+
+  var slicedBlob;
+  if (contentType == undefined && end == undefined) {
+    slicedBlob = blob.slice(start);
+  } else if (contentType == undefined) {
+    slicedBlob = blob.slice(start, end);
+  } else {
+    slicedBlob = blob.slice(start, end, contentType);
+  }
+
+  var rtnObj = new Object();
+
+  rtnObj.size = slicedBlob.size;
+  rtnObj.type = slicedBlob.type;
+
+  postMessage(rtnObj);
+};
diff --git a/dom/workers/test/fileSubWorker_worker.js b/dom/workers/test/fileSubWorker_worker.js
new file mode 100644
index 0000000000..8a5c002865
--- /dev/null
+++ b/dom/workers/test/fileSubWorker_worker.js
@@ -0,0 +1,17 @@
+/**
+ * Expects a file. Returns an object containing the size, type, name and path
+ * using another worker. Used to test posting of file from worker to worker.
+ */
+onmessage = function (event) {
+  var worker = new Worker("file_worker.js");
+
+  worker.postMessage(event.data);
+
+  worker.onmessage = function (msg) {
+    postMessage(msg.data);
+  };
+
+  worker.onerror = function (error) {
+    postMessage(undefined);
+  };
+};
diff --git a/dom/workers/test/file_bug1010784_worker.js b/dom/workers/test/file_bug1010784_worker.js
new file mode 100644
index 0000000000..3e88f5cc97
--- /dev/null
+++ b/dom/workers/test/file_bug1010784_worker.js
@@ -0,0 +1,9 @@
+onmessage = function (event) {
+  var xhr = new XMLHttpRequest();
+
+  xhr.open("GET", event.data, false);
+  xhr.send();
+  xhr.open("GET", event.data, false);
+  xhr.send();
+  postMessage("done");
+};
diff --git a/dom/workers/test/file_service_worker.js b/dom/workers/test/file_service_worker.js
new file mode 100644
index 0000000000..dd264e340e
--- /dev/null
+++ b/dom/workers/test/file_service_worker.js
@@ -0,0 +1,3 @@
+self.onmessage = evt => {
+  evt.ports[0].postMessage("serviceworker-reply");
+};
diff --git a/dom/workers/test/file_service_worker_container.html b/dom/workers/test/file_service_worker_container.html
new file mode 100644
index 0000000000..625e911adc
--- /dev/null
+++ b/dom/workers/test/file_service_worker_container.html
@@ -0,0 +1,15 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <meta charset="utf-8">
+    <script>
+      (async function () {
+        await navigator.serviceWorker.register("file_service_worker.js");
+        await navigator.serviceWorker.ready;
+      })();
+    </script>
+  </head>
+  <body>
+    Service Worker Container
+  </body>
+</html>
diff --git a/dom/workers/test/file_service_worker_fetch_synthetic.js b/dom/workers/test/file_service_worker_fetch_synthetic.js
new file mode 100644
index 0000000000..c58aeb294a
--- /dev/null
+++ b/dom/workers/test/file_service_worker_fetch_synthetic.js
@@ -0,0 +1,59 @@
+addEventListener("install", function (evt) {
+  evt.waitUntil(self.skipWaiting());
+});
+
+/**
+ * Given a multipart/form-data encoded string that we know to have only a single
+ * part, return the contents of the part.  (MIME multipart encoding is too
+ * exciting to delve into.)
+ */
+function extractBlobFromMultipartFormData(text) {
+  const lines = text.split(/\r\n/g);
+  const firstBlank = lines.indexOf("");
+  const foo = lines.slice(firstBlank + 1, -2).join("\n");
+  return foo;
+}
+
+self.addEventListener("fetch", event => {
+  const url = new URL(event.request.url);
+  const mode = url.searchParams.get("mode");
+
+  if (mode === "synthetic") {
+    event.respondWith(
+      (async () => {
+        // This works even if there wasn't a body explicitly associated with the
+        // request.  We just get a zero-length string in that case.
+        const requestBodyContents = await event.request.text();
+        const blobContents =
+          extractBlobFromMultipartFormData(requestBodyContents);
+
+        return new Response(
+          `<!DOCTYPE HTML><head><meta charset="utf-8"/></head><body>
+          <h1 id="url">${event.request.url}</h1>
+          <div id="source">ServiceWorker</div>
+          <div id="blob">${blobContents}</div>
+        </body>`,
+          { headers: { "Content-Type": "text/html" } }
+        );
+      })()
+    );
+  } else if (mode === "fetch") {
+    event.respondWith(fetch(event.request));
+  } else if (mode === "clone") {
+    // In order for the act of cloning to be interesting, we want the original
+    // request to remain alive so that any pipes end up having to buffer.
+    self.originalRequest = event.request;
+    event.respondWith(fetch(event.request.clone()));
+  } else {
+    event.respondWith(
+      new Response(
+        `<!DOCTYPE HTML><head><meta charset="utf-8"/></head><body>
+          <h1 id="error">Bad mode: ${mode}</h1>
+          <div id="source">ServiceWorker::Error</div>
+          <div id="blob">No, this is an error.</div>
+        </body>`,
+        { headers: { "Content-Type": "text/html" }, status: 400 }
+      )
+    );
+  }
+});
diff --git a/dom/workers/test/file_use_counter_service_worker.js b/dom/workers/test/file_use_counter_service_worker.js
new file mode 100644
index 0000000000..8ee0d2e04a
--- /dev/null
+++ b/dom/workers/test/file_use_counter_service_worker.js
@@ -0,0 +1,9 @@
+onmessage = async function (e) {
+  if (e.data === "RUN") {
+    console.log("worker runs");
+    await clients.claim();
+    clients.matchAll().then(res => {
+      res.forEach(client => client.postMessage("DONE"));
+    });
+  }
+};
diff --git a/dom/workers/test/file_use_counter_shared_worker.js b/dom/workers/test/file_use_counter_shared_worker.js
new file mode 100644
index 0000000000..7e4f95af3b
--- /dev/null
+++ b/dom/workers/test/file_use_counter_shared_worker.js
@@ -0,0 +1,10 @@
+onconnect = function (e) {
+  let port = e.ports[0];
+  port.onmessage = function (m) {
+    if (m.data === "RUN") {
+      console.log("worker runs");
+      port.postMessage("DONE");
+      close();
+    }
+  };
+};
diff --git a/dom/workers/test/file_use_counter_shared_worker_microtask.js b/dom/workers/test/file_use_counter_shared_worker_microtask.js
new file mode 100644
index 0000000000..b219da2225
--- /dev/null
+++ b/dom/workers/test/file_use_counter_shared_worker_microtask.js
@@ -0,0 +1,12 @@
+onconnect = function (e) {
+  let port = e.ports[0];
+  port.onmessage = function (m) {
+    if (m.data === "RUN") {
+      queueMicrotask(() => {
+        console.log("worker runs");
+      });
+      port.postMessage("DONE");
+      close();
+    }
+  };
+};
diff --git a/dom/workers/test/file_use_counter_worker.html b/dom/workers/test/file_use_counter_worker.html
new file mode 100644
index 0000000000..d034ad6f5f
--- /dev/null
+++ b/dom/workers/test/file_use_counter_worker.html
@@ -0,0 +1,13 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1202706
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1202706</title>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1202706">Mozilla Bug 1202706</a>
+</body>
+</html>
diff --git a/dom/workers/test/file_use_counter_worker.js b/dom/workers/test/file_use_counter_worker.js
new file mode 100644
index 0000000000..12046940a8
--- /dev/null
+++ b/dom/workers/test/file_use_counter_worker.js
@@ -0,0 +1,2 @@
+console.log("worker runs");
+postMessage("DONE");
diff --git a/dom/workers/test/file_worker.js b/dom/workers/test/file_worker.js
new file mode 100644
index 0000000000..6ed8fe1816
--- /dev/null
+++ b/dom/workers/test/file_worker.js
@@ -0,0 +1,16 @@
+/**
+ * Expects a file. Returns an object containing the size, type, name and path.
+ */
+onmessage = function (event) {
+  var file = event.data;
+
+  var rtnObj = new Object();
+
+  rtnObj.size = file.size;
+  rtnObj.type = file.type;
+  rtnObj.name = file.name;
+  rtnObj.path = file.path;
+  rtnObj.lastModified = file.lastModified;
+
+  postMessage(rtnObj);
+};
diff --git a/dom/workers/test/foreign.js b/dom/workers/test/foreign.js
new file mode 100644
index 0000000000..33c982fa8f
--- /dev/null
+++ b/dom/workers/test/foreign.js
@@ -0,0 +1 @@
+response = "bad";
diff --git a/dom/workers/test/head.js b/dom/workers/test/head.js
new file mode 100644
index 0000000000..ce6cebbd06
--- /dev/null
+++ b/dom/workers/test/head.js
@@ -0,0 +1,75 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+"use strict";
+
+/**
+ * Add a tab with given `url`. Returns a promise
+ * that will be resolved when the tab finished loading.
+ */
+function addTab(url) {
+  return BrowserTestUtils.openNewForegroundTab(gBrowser, TAB_URL);
+}
+
+/**
+ * Remove the given `tab`.
+ */
+function removeTab(tab) {
+  gBrowser.removeTab(tab);
+}
+
+/**
+ * Create a worker with the given `url` in the given `tab`.
+ */
+function createWorkerInTab(tab, url) {
+  info("Creating worker with url '" + url + "'\n");
+  return SpecialPowers.spawn(tab.linkedBrowser, [url], urlChild => {
+    if (!content._workers) {
+      content._workers = {};
+    }
+    content._workers[urlChild] = new content.Worker(urlChild);
+  });
+}
+
+/**
+ * Terminate the worker with the given `url` in the given `tab`.
+ */
+function terminateWorkerInTab(tab, url) {
+  info("Terminating worker with url '" + url + "'\n");
+  return SpecialPowers.spawn(tab.linkedBrowser, [url], urlChild => {
+    content._workers[urlChild].terminate();
+    delete content._workers[urlChild];
+  });
+}
+
+/**
+ * Post the given `message` to the worker with the given `url` in the given
+ * `tab`.
+ */
+function postMessageToWorkerInTab(tab, url, message) {
+  info("Posting message to worker with url '" + url + "'\n");
+  return SpecialPowers.spawn(
+    tab.linkedBrowser,
+    [url, message],
+    (urlChild, messageChild) => {
+      let worker = content._workers[urlChild];
+      worker.postMessage(messageChild);
+      return new Promise(function (resolve) {
+        worker.onmessage = function (event) {
+          worker.onmessage = null;
+          resolve(event.data);
+        };
+      });
+    }
+  );
+}
+
+/**
+ * Disable the cache in the given `tab`.
+ */
+function disableCacheInTab(tab) {
+  return SpecialPowers.spawn(tab.linkedBrowser, [], () => {
+    content.docShell.defaultLoadFlags =
+      Ci.nsIRequest.LOAD_BYPASS_CACHE | Ci.nsIRequest.INHIBIT_CACHING;
+  });
+}
diff --git a/dom/workers/test/importForeignScripts_worker.js b/dom/workers/test/importForeignScripts_worker.js
new file mode 100644
index 0000000000..4e3d65483f
--- /dev/null
+++ b/dom/workers/test/importForeignScripts_worker.js
@@ -0,0 +1,55 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+var target = self;
+var response;
+
+function runTests() {
+  response = "good";
+  try {
+    importScripts("http://example.org/tests/dom/workers/test/foreign.js");
+  } catch (e) {
+    dump("Got error " + e + " when calling importScripts");
+  }
+  if (response === "good") {
+    try {
+      importScripts("redirect_to_foreign.sjs");
+    } catch (e) {
+      dump("Got error " + e + " when calling importScripts");
+    }
+  }
+  target.postMessage(response);
+
+  // Now, test a nested worker.
+  if (location.search !== "?nested") {
+    var worker = new Worker("importForeignScripts_worker.js?nested");
+
+    worker.onmessage = function (e) {
+      target.postMessage(e.data);
+      target.postMessage("finish");
+    };
+
+    worker.onerror = function () {
+      target.postMessage("nested worker error");
+    };
+
+    worker.postMessage("start");
+  }
+}
+
+onmessage = function (e) {
+  if (e.data === "start") {
+    runTests();
+  }
+};
+
+onconnect = function (e) {
+  target = e.ports[0];
+  e.ports[0].onmessage = function (msg) {
+    if (msg.data === "start") {
+      runTests();
+    }
+  };
+};
diff --git a/dom/workers/test/importScripts_3rdParty_worker.js b/dom/workers/test/importScripts_3rdParty_worker.js
new file mode 100644
index 0000000000..326d48f77a
--- /dev/null
+++ b/dom/workers/test/importScripts_3rdParty_worker.js
@@ -0,0 +1,88 @@
+const workerURL =
+  "http://mochi.test:8888/tests/dom/workers/test/importScripts_3rdParty_worker.js";
+
+onmessage = function (a) {
+  if (a.data.nested) {
+    var worker = new Worker(workerURL);
+    worker.onmessage = function (event) {
+      postMessage(event.data);
+    };
+
+    worker.onerror = function (event) {
+      event.preventDefault();
+      postMessage({
+        error: event instanceof ErrorEvent && event.filename == workerURL,
+      });
+    };
+
+    a.data.nested = false;
+    worker.postMessage(a.data);
+    return;
+  }
+
+  // This first URL will use the same origin of this script.
+  var sameOriginURL = new URL(a.data.url);
+  var fileName1 = 42;
+
+  // This is cross-origin URL.
+  var crossOriginURL = new URL(a.data.url);
+  crossOriginURL.host = "example.com";
+  crossOriginURL.port = 80;
+  var fileName2 = 42;
+
+  if (a.data.test == "none") {
+    importScripts(crossOriginURL.href);
+    return;
+  }
+
+  try {
+    importScripts(sameOriginURL.href);
+  } catch (e) {
+    if (!(e instanceof SyntaxError)) {
+      postMessage({ result: false });
+      return;
+    }
+
+    fileName1 = e.fileName;
+  }
+
+  if (fileName1 != sameOriginURL.href || !fileName1) {
+    postMessage({ result: false });
+    return;
+  }
+
+  if (a.data.test == "try") {
+    var exception;
+    try {
+      importScripts(crossOriginURL.href);
+    } catch (e) {
+      fileName2 = e.filename;
+      exception = e;
+    }
+
+    postMessage({
+      result:
+        fileName2 == workerURL &&
+        exception.name == "NetworkError" &&
+        exception.code == DOMException.NETWORK_ERR,
+    });
+    return;
+  }
+
+  if (a.data.test == "eventListener") {
+    addEventListener("error", function (event) {
+      event.preventDefault();
+      postMessage({
+        result: event instanceof ErrorEvent && event.filename == workerURL,
+      });
+    });
+  }
+
+  if (a.data.test == "onerror") {
+    onerror = function (...args) {
+      postMessage({ result: args[1] == workerURL });
+    };
+  }
+
+  importScripts(crossOriginURL.href);
+};
diff --git a/dom/workers/test/importScripts_mixedcontent.html b/dom/workers/test/importScripts_mixedcontent.html
new file mode 100644
index 0000000000..2955fdc46e
--- /dev/null
+++ b/dom/workers/test/importScripts_mixedcontent.html
@@ -0,0 +1,46 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE html>
+<script>
+  function ok(cond, msg) {
+    window.parent.postMessage({status: "ok", data: cond, msg}, "*");
+  }
+  function finish() {
+    window.parent.postMessage({status: "done"}, "*");
+  }
+
+  function testSharedWorker() {
+    var sw = new SharedWorker("importForeignScripts_worker.js");
+    sw.port.onmessage = function(e) {
+      if (e.data == "finish") {
+        finish();
+        return;
+      }
+      ok(e.data === "good", "mixed content for shared workers is correctly blocked");
+    };
+
+    sw.onerror = function() {
+      ok(false, "Error on shared worker ");
+    };
+
+    sw.port.postMessage("start");
+  }
+
+  var worker = new Worker("importForeignScripts_worker.js");
+
+  worker.onmessage = function(e) {
+    if (e.data == "finish") {
+      testSharedWorker();
+      return;
+    }
+    ok(e.data === "good", "mixed content is correctly blocked");
+  }
+
+  worker.onerror = function() {
+    ok(false, "Error on worker");
+  }
+
+  worker.postMessage("start");
+</script>
diff --git a/dom/workers/test/importScripts_worker.js b/dom/workers/test/importScripts_worker.js
new file mode 100644
index 0000000000..ca46c949b9
--- /dev/null
+++ b/dom/workers/test/importScripts_worker.js
@@ -0,0 +1,62 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+// Try no args. This shouldn't do anything.
+importScripts();
+
+// This caused security exceptions in the past, make sure it doesn't!
+var constructor = {}.constructor;
+
+importScripts("importScripts_worker_imported1.js");
+
+// Try to call a function defined in the imported script.
+importedScriptFunction();
+
+function tryBadScripts() {
+  var badScripts = [
+    // Has a syntax error
+    "importScripts_worker_imported3.js",
+    // Throws an exception
+    "importScripts_worker_imported4.js",
+    // Shouldn't exist!
+    "http://example.com/non-existing/importScripts_worker_foo.js",
+    // Not a valid url
+    "http://notadomain::notafile aword",
+  ];
+
+  for (var i = 0; i < badScripts.length; i++) {
+    var caughtException = false;
+    var url = badScripts[i];
+    try {
+      importScripts(url);
+    } catch (e) {
+      caughtException = true;
+    }
+    if (!caughtException) {
+      throw "Bad script didn't throw exception: " + url;
+    }
+  }
+}
+
+const url = "data:text/javascript,const startResponse = 'started';";
+importScripts(url);
+
+onmessage = function (event) {
+  switch (event.data) {
+    case "start":
+      importScripts("importScripts_worker_imported2.js");
+      importedScriptFunction2();
+      tryBadScripts();
+      postMessage(startResponse);
+      break;
+    case "stop":
+      tryBadScripts();
+      postMessage("stopped");
+      break;
+    default:
+      throw new Error("Bad message: " + event.data);
+  }
+};
+
+tryBadScripts();
diff --git a/dom/workers/test/importScripts_worker_imported1.js b/dom/workers/test/importScripts_worker_imported1.js
new file mode 100644
index 0000000000..2a1d28c44d
--- /dev/null
+++ b/dom/workers/test/importScripts_worker_imported1.js
@@ -0,0 +1,9 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+// This caused security exceptions in the past, make sure it doesn't!
+var myConstructor = {}.constructor;
+
+// Try to call a function defined in the imported script.
+function importedScriptFunction() {}
diff --git a/dom/workers/test/importScripts_worker_imported2.js b/dom/workers/test/importScripts_worker_imported2.js
new file mode 100644
index 0000000000..3f275e237b
--- /dev/null
+++ b/dom/workers/test/importScripts_worker_imported2.js
@@ -0,0 +1,9 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+// This caused security exceptions in the past, make sure it doesn't!
+var myConstructor2 = {}.constructor;
+
+// Try to call a function defined in the imported script.
+function importedScriptFunction2() {}
diff --git a/dom/workers/test/importScripts_worker_imported3.js b/dom/workers/test/importScripts_worker_imported3.js
new file mode 100644
index 0000000000..c54be3e5f7
--- /dev/null
+++ b/dom/workers/test/importScripts_worker_imported3.js
@@ -0,0 +1,6 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+// Deliberate syntax error, should generate a worker exception!
+for (var index = 0; index < 100) {}
diff --git a/dom/workers/test/importScripts_worker_imported4.js b/dom/workers/test/importScripts_worker_imported4.js
new file mode 100644
index 0000000000..82f8708c59
--- /dev/null
+++ b/dom/workers/test/importScripts_worker_imported4.js
@@ -0,0 +1,6 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+// Deliberate throw, should generate a worker exception!
+throw new Error("Bah!");
diff --git a/dom/workers/test/instanceof_worker.js b/dom/workers/test/instanceof_worker.js
new file mode 100644
index 0000000000..a7f3ab418d
--- /dev/null
+++ b/dom/workers/test/instanceof_worker.js
@@ -0,0 +1,16 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+onmessage = function (event) {
+  postMessage({
+    event: "XMLHttpRequest",
+    status: new XMLHttpRequest() instanceof XMLHttpRequest,
+    last: false,
+  });
+  postMessage({
+    event: "XMLHttpRequestUpload",
+    status: new XMLHttpRequest().upload instanceof XMLHttpRequestUpload,
+    last: true,
+  });
+};
diff --git a/dom/workers/test/invalid.js b/dom/workers/test/invalid.js
new file mode 100644
index 0000000000..8912b7ee06
--- /dev/null
+++ b/dom/workers/test/invalid.js
@@ -0,0 +1 @@
+invalid>
diff --git a/dom/workers/test/json_worker.js b/dom/workers/test/json_worker.js
new file mode 100644
index 0000000000..229ac954c9
--- /dev/null
+++ b/dom/workers/test/json_worker.js
@@ -0,0 +1,354 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+var cyclicalObject = {};
+cyclicalObject.foo = cyclicalObject;
+
+var cyclicalArray = [];
+cyclicalArray.push(cyclicalArray);
+
+function makeNested(obj, count) {
+  var innermostobj;
+  for (var i = 0; i < count; i++) {
+    obj.foo = { bar: 5 };
+    innermostobj = obj.foo;
+    obj = innermostobj;
+  }
+  return innermostobj;
+}
+
+var nestedObject = {};
+makeNested(nestedObject, 100);
+
+var cyclicalObject = {};
+var innermost = makeNested(cyclicalObject, 1000);
+innermost.baz = cyclicalObject;
+
+var objectWithSaneGetter = {};
+objectWithSaneGetter.__defineGetter__("foo", function () {
+  return 5;
+});
+
+// We don't walk prototype chains for cloning so this won't actually do much...
+function objectWithSaneGetter2() {}
+objectWithSaneGetter2.prototype = {
+  get foo() {
+    return 5;
+  },
+};
+
+const throwingGetterThrownString = "bad";
+
+var objectWithThrowingGetter = {};
+objectWithThrowingGetter.__defineGetter__("foo", function () {
+  throw throwingGetterThrownString;
+});
+
+var typedArrayWithValues = new Int8Array(5);
+for (let index in typedArrayWithValues) {
+  typedArrayWithValues[index] = index;
+}
+
+var typedArrayWithFunBuffer = new Int8Array(4);
+for (let index in typedArrayWithFunBuffer) {
+  typedArrayWithFunBuffer[index] = 255;
+}
+
+var typedArrayWithFunBuffer2 = new Int32Array(typedArrayWithFunBuffer.buffer);
+
+var xhr = new XMLHttpRequest();
+
+var messages = [
+  {
+    type: "object",
+    value: {},
+    jsonValue: "{}",
+  },
+  {
+    type: "object",
+    value: { foo: "bar" },
+    jsonValue: '{"foo":"bar"}',
+  },
+  {
+    type: "object",
+    value: { foo: "bar", foo2: { bee: "bop" } },
+    jsonValue: '{"foo":"bar","foo2":{"bee":"bop"}}',
+  },
+  {
+    type: "object",
+    value: { foo: "bar", foo2: { bee: "bop" }, foo3: "baz" },
+    jsonValue: '{"foo":"bar","foo2":{"bee":"bop"},"foo3":"baz"}',
+  },
+  {
+    type: "object",
+    value: { foo: "bar", foo2: [1, 2, 3] },
+    jsonValue: '{"foo":"bar","foo2":[1,2,3]}',
+  },
+  {
+    type: "object",
+    value: cyclicalObject,
+  },
+  {
+    type: "object",
+    value: [null, 2, false, cyclicalObject],
+  },
+  {
+    type: "object",
+    value: cyclicalArray,
+  },
+  {
+    type: "object",
+    value: { foo: 1, bar: cyclicalArray },
+  },
+  {
+    type: "object",
+    value: nestedObject,
+    jsonValue: JSON.stringify(nestedObject),
+  },
+  {
+    type: "object",
+    value: cyclicalObject,
+  },
+  {
+    type: "object",
+    value: objectWithSaneGetter,
+    jsonValue: '{"foo":5}',
+  },
+  {
+    type: "object",
+    value: new objectWithSaneGetter2(),
+    jsonValue: "{}",
+  },
+  {
+    type: "object",
+    value: objectWithThrowingGetter,
+    exception: true,
+  },
+  {
+    type: "object",
+    array: true,
+    value: [9, 8, 7],
+    jsonValue: "[9,8,7]",
+  },
+  {
+    type: "object",
+    array: true,
+    value: [9, false, 10.5, { foo: "bar" }],
+    jsonValue: '[9,false,10.5,{"foo":"bar"}]',
+  },
+  {
+    type: "object",
+    shouldEqual: true,
+    value: null,
+  },
+  {
+    type: "undefined",
+    shouldEqual: true,
+    value: undefined,
+  },
+  {
+    type: "string",
+    shouldEqual: true,
+    value: "Hello",
+  },
+  {
+    type: "string",
+    shouldEqual: true,
+    value: JSON.stringify({ foo: "bar" }),
+    compareValue: '{"foo":"bar"}',
+  },
+  {
+    type: "number",
+    shouldEqual: true,
+    value: 1,
+  },
+  {
+    type: "number",
+    shouldEqual: true,
+    value: 0,
+  },
+  {
+    type: "number",
+    shouldEqual: true,
+    value: -1,
+  },
+  {
+    type: "number",
+    shouldEqual: true,
+    value: 12345678901234567000,
+  },
+  {
+    type: "number",
+    shouldEqual: true,
+    value: -12345678901234567000,
+  },
+  {
+    type: "number",
+    shouldEqual: true,
+    value: 0.25,
+  },
+  {
+    type: "number",
+    shouldEqual: true,
+    value: -0.25,
+  },
+  {
+    type: "boolean",
+    shouldEqual: true,
+    value: true,
+  },
+  {
+    type: "boolean",
+    shouldEqual: true,
+    value: false,
+  },
+  {
+    type: "object",
+    value(foo) {
+      return "Bad!";
+    },
+    exception: true,
+  },
+  {
+    type: "number",
+    isNaN: true,
+    value: NaN,
+  },
+  {
+    type: "number",
+    isInfinity: true,
+    value: Infinity,
+  },
+  {
+    type: "number",
+    isNegativeInfinity: true,
+    value: -Infinity,
+  },
+  {
+    type: "object",
+    value: new Int32Array(10),
+    jsonValue: '{"0":0,"1":0,"2":0,"3":0,"4":0,"5":0,"6":0,"7":0,"8":0,"9":0}',
+  },
+  {
+    type: "object",
+    value: new Float32Array(5),
+    jsonValue: '{"0":0,"1":0,"2":0,"3":0,"4":0}',
+  },
+  {
+    type: "object",
+    value: typedArrayWithValues,
+    jsonValue: '{"0":0,"1":1,"2":2,"3":3,"4":4}',
+  },
+  {
+    type: "number",
+    value: typedArrayWithValues[2],
+    compareValue: 2,
+    shouldEqual: true,
+  },
+  {
+    type: "object",
+    value: typedArrayWithValues.buffer,
+    jsonValue: "{}",
+  },
+  {
+    type: "object",
+    value: typedArrayWithFunBuffer2,
+    jsonValue: '{"0":-1}',
+  },
+  {
+    type: "object",
+    value: { foo: typedArrayWithFunBuffer2 },
+    jsonValue: '{"foo":{"0":-1}}',
+  },
+  {
+    type: "object",
+    value: [typedArrayWithFunBuffer2],
+    jsonValue: '[{"0":-1}]',
+  },
+  {
+    type: "object",
+    value: {
+      foo(a) {
+        alert(b);
+      },
+    },
+    exception: true,
+  },
+  {
+    type: "object",
+    value: xhr,
+    exception: true,
+  },
+  {
+    type: "number",
+    value: xhr.readyState,
+    shouldEqual: true,
+  },
+  {
+    type: "object",
+    value: { xhr },
+    exception: true,
+  },
+  {
+    type: "object",
+    value: self,
+    exception: true,
+  },
+  {
+    type: "object",
+    value: { p: ArrayBuffer.prototype },
+    exception: true,
+  },
+  {
+    type: "string",
+    shouldEqual: true,
+    value: "testFinished",
+  },
+];
+
+for (let index = 0; index < messages.length; index++) {
+  var message = messages[index];
+  if (message.hasOwnProperty("compareValue")) {
+    continue;
+  }
+  if (
+    message.hasOwnProperty("shouldEqual") ||
+    message.hasOwnProperty("shouldCompare")
+  ) {
+    message.compareValue = message.value;
+  }
+}
+
+onmessage = function (event) {
+  for (let index = 0; index < messages.length; index++) {
+    var exception = undefined;
+
+    try {
+      postMessage(messages[index].value);
+    } catch (e) {
+      if (e instanceof DOMException) {
+        if (e.code != DOMException.DATA_CLONE_ERR) {
+          throw "DOMException with the wrong code: " + e.code;
+        }
+      } else if (e != throwingGetterThrownString) {
+        throw "Exception of the wrong type: " + e;
+      }
+      exception = e;
+    }
+
+    if (
+      (exception !== undefined && !messages[index].exception) ||
+      (exception === undefined && messages[index].exception)
+    ) {
+      throw (
+        "Exception inconsistency [index = " +
+        index +
+        ", " +
+        messages[index].toSource() +
+        "]: " +
+        exception
+      );
+    }
+  }
+};
diff --git a/dom/workers/test/loadEncoding_worker.js b/dom/workers/test/loadEncoding_worker.js
new file mode 100644
index 0000000000..5e40478445
--- /dev/null
+++ b/dom/workers/test/loadEncoding_worker.js
@@ -0,0 +1,7 @@
+/*
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+*/
+// Bug 484305 - Load workers as UTF-8.
+postMessage({ encoding: "KOI8-R", text: "ðÒÉ×ÅÔ" });
+postMessage({ encoding: "UTF-8", text: "Привет" });
diff --git a/dom/workers/test/location_worker.js b/dom/workers/test/location_worker.js
new file mode 100644
index 0000000000..2f16364e1f
--- /dev/null
+++ b/dom/workers/test/location_worker.js
@@ -0,0 +1,12 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+for (var string in self.location) {
+  var value =
+    typeof self.location[string] === "function"
+      ? self.location[string]()
+      : self.location[string];
+  postMessage({ string, value });
+}
+postMessage({ string: "testfinished" });
diff --git a/dom/workers/test/longThread_worker.js b/dom/workers/test/longThread_worker.js
new file mode 100644
index 0000000000..4096354aca
--- /dev/null
+++ b/dom/workers/test/longThread_worker.js
@@ -0,0 +1,14 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+onmessage = function (event) {
+  switch (event.data) {
+    case "start":
+      for (var i = 0; i < 10000000; i++) {}
+      postMessage("done");
+      break;
+    default:
+      throw "Bad message: " + event.data;
+  }
+};
diff --git a/dom/workers/test/marionette/manifest.toml b/dom/workers/test/marionette/manifest.toml
new file mode 100644
index 0000000000..b801ae5719
--- /dev/null
+++ b/dom/workers/test/marionette/manifest.toml
@@ -0,0 +1,5 @@
+[DEFAULT]
+
+["test_service_workers_at_startup.py"]
+
+["test_service_workers_disabled.py"]
diff --git a/dom/workers/test/marionette/service_worker_utils.py b/dom/workers/test/marionette/service_worker_utils.py
new file mode 100644
index 0000000000..b29789b6f0
--- /dev/null
+++ b/dom/workers/test/marionette/service_worker_utils.py
@@ -0,0 +1,63 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+import os
+
+from marionette_driver import Wait
+from marionette_harness import MarionetteTestCase
+
+
+class MarionetteServiceWorkerTestCase(MarionetteTestCase):
+    def install_service_worker(self, path):
+        install_url = self.marionette.absolute_url(path)
+        self.marionette.navigate(install_url)
+        Wait(self.marionette).until(
+            lambda _: self.is_service_worker_registered,
+            message="Service worker not successfully installed",
+        )
+
+        # Wait for the registered service worker to be stored in the Firefox
+        # profile before restarting the instance to prevent intermittent
+        # failures (Bug 1665184).
+        Wait(self.marionette, timeout=10).until(
+            lambda _: self.profile_serviceworker_txt_exists,
+            message="Service worker not stored in profile",
+        )
+
+        # self.marionette.restart(in_app=True) will restore service workers if
+        # we don't navigate away before restarting.
+        self.marionette.navigate("about:blank")
+
+    # Using @property helps avoid the case where missing parens at the call site
+    # yields an unvarying 'true' value.
+    @property
+    def profile_serviceworker_txt_exists(self):
+        return "serviceworker.txt" in os.listdir(self.marionette.profile_path)
+
+    @property
+    def is_service_worker_registered(self):
+        with self.marionette.using_context("chrome"):
+            return self.marionette.execute_script(
+                """
+                let swm = Cc["@mozilla.org/serviceworkers/manager;1"].getService(
+                    Ci.nsIServiceWorkerManager
+                );
+                let ssm = Services.scriptSecurityManager;
+
+                let principal = ssm.createContentPrincipalFromOrigin(arguments[0]);
+
+                let serviceWorkers = swm.getAllRegistrations();
+                for (let i = 0; i < serviceWorkers.length; i++) {
+                    let sw = serviceWorkers.queryElementAt(
+                        i,
+                        Ci.nsIServiceWorkerRegistrationInfo
+                    );
+                    if (sw.principal.origin == principal.origin) {
+                        return true;
+                    }
+                }
+                return false;
+            """,
+                script_args=(self.marionette.absolute_url(""),),
+            )
diff --git a/dom/workers/test/marionette/test_service_workers_at_startup.py b/dom/workers/test/marionette/test_service_workers_at_startup.py
new file mode 100644
index 0000000000..14ff32f87f
--- /dev/null
+++ b/dom/workers/test/marionette/test_service_workers_at_startup.py
@@ -0,0 +1,31 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+import os
+import sys
+
+# Add this directory to the import path.
+sys.path.append(os.path.dirname(__file__))
+
+from marionette_driver import Wait
+from service_worker_utils import MarionetteServiceWorkerTestCase
+
+
+class ServiceWorkerAtStartupTestCase(MarionetteServiceWorkerTestCase):
+    def setUp(self):
+        super(ServiceWorkerAtStartupTestCase, self).setUp()
+        self.install_service_worker("serviceworker/install_serviceworker.html")
+
+    def tearDown(self):
+        self.marionette.restart(in_app=False, clean=True)
+        super(ServiceWorkerAtStartupTestCase, self).tearDown()
+
+    def test_registered_service_worker_after_restart(self):
+        self.marionette.restart()
+
+        Wait(self.marionette).until(
+            lambda _: self.is_service_worker_registered,
+            message="Service worker not registered after restart",
+        )
+        self.assertTrue(self.is_service_worker_registered)
diff --git a/dom/workers/test/marionette/test_service_workers_disabled.py b/dom/workers/test/marionette/test_service_workers_disabled.py
new file mode 100644
index 0000000000..deed164242
--- /dev/null
+++ b/dom/workers/test/marionette/test_service_workers_disabled.py
@@ -0,0 +1,37 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+import os
+import sys
+
+# Add this directory to the import path.
+sys.path.append(os.path.dirname(__file__))
+
+from service_worker_utils import MarionetteServiceWorkerTestCase
+
+
+class ServiceWorkersDisabledTestCase(MarionetteServiceWorkerTestCase):
+    def setUp(self):
+        super(ServiceWorkersDisabledTestCase, self).setUp()
+        self.install_service_worker("serviceworker/install_serviceworker.html")
+
+    def tearDown(self):
+        self.marionette.restart(in_app=False, clean=True)
+        super(ServiceWorkersDisabledTestCase, self).tearDown()
+
+    def test_service_workers_disabled_at_startup(self):
+        # self.marionette.set_pref sets preferences after startup.  Using it
+        # here causes intermittent failures.
+        self.marionette.instance.profile.set_preferences(
+            {
+                "dom.serviceWorkers.enabled": False,
+            }
+        )
+
+        self.marionette.restart()
+
+        self.assertFalse(
+            self.is_service_worker_registered,
+            "Service worker registration should have been purged",
+        )
diff --git a/dom/workers/test/mochitest.toml b/dom/workers/test/mochitest.toml
new file mode 100644
index 0000000000..5ae8094b58
--- /dev/null
+++ b/dom/workers/test/mochitest.toml
@@ -0,0 +1,365 @@
+[DEFAULT]
+support-files = [
+  "WorkerTest_badworker.js",
+  "atob_worker.js",
+  "blank.html",
+  "bug978260_worker.js",
+  "bug1014466_data1.txt",
+  "bug1014466_data2.txt",
+  "bug1014466_worker.js",
+  "bug1020226_worker.js",
+  "bug1020226_frame.html",
+  "bug998474_worker.js",
+  "bug1063538_worker.js",
+  "bug1063538.sjs",
+  "clearTimeouts_worker.js",
+  "clearTimeoutsImplicit_worker.js",
+  "content_worker.js",
+  "console_worker.js",
+  "consoleReplaceable_worker.js",
+  "csp_worker.js",
+  "csp_worker.js^headers^",
+  "dynamicImport_nested.mjs",
+  "dynamicImport_postMessage.mjs",
+  "dynamicImport_worker.js",
+  "404_server.sjs",
+  "errorPropagation_iframe.html",
+  "errorPropagation_worker.js",
+  "errorwarning_worker.js",
+  "eventDispatch_worker.js",
+  "fibonacci_worker.js",
+  "file_bug1010784_worker.js",
+  "foreign.js",
+  "importForeignScripts_worker.js",
+  "importScripts_mixedcontent.html",
+  "importScripts_worker.js",
+  "importScripts_worker_imported1.js",
+  "importScripts_worker_imported2.js",
+  "importScripts_worker_imported3.js",
+  "importScripts_worker_imported4.js",
+  "instanceof_worker.js",
+  "json_worker.js",
+  "loadEncoding_worker.js",
+  "location_worker.js",
+  "longThread_worker.js",
+  "multi_sharedWorker_frame.html",
+  "multi_sharedWorker_sharedWorker.js",
+  "navigator_languages_worker.js",
+  "navigator_worker.js",
+  "newError_worker.js",
+  "notification_worker.js",
+  "notification_worker_child-child.js",
+  "notification_worker_child-parent.js",
+  "notification_permission_worker.js",
+  "onLine_worker.js",
+  "onLine_worker_child.js",
+  "onLine_worker_head.js",
+  "promise_worker.js",
+  "recursion_worker.js",
+  "recursiveOnerror_worker.js",
+  "redirect_to_foreign.sjs",
+  "rvals_worker.js",
+  "sharedWorker_sharedWorker.js",
+  "simpleThread_worker.js",
+  "suspend_window.html",
+  "suspend_worker.js",
+  "terminate_worker.js",
+  "test_csp.html^headers^",
+  "test_csp.js",
+  "referrer_worker.html",
+  "sourcemap_header_iframe.html",
+  "sourcemap_header_worker.js",
+  "sourcemap_header_worker.js^headers^",
+  "threadErrors_worker1.js",
+  "threadErrors_worker2.js",
+  "threadErrors_worker3.js",
+  "threadErrors_worker4.js",
+  "threadTimeouts_worker.js",
+  "throwingOnerror_worker.js",
+  "timeoutTracing_worker.js",
+  "transferable_worker.js",
+  "test_worker_interfaces.js",
+  "worker_driver.js",
+  "worker_wrapper.js",
+  "bug1060621_worker.js",
+  "bug1062920_worker.js",
+  "bug1104064_worker.js",
+  "worker_consoleAndBlobs.js",
+  "bug1132395_sharedWorker.js",
+  "bug1132924_worker.js",
+  "empty.html",
+  "referrer.sjs",
+  "referrer_test_server.sjs",
+  "sharedWorker_ports.js",
+  "sharedWorker_lifetime.js",
+  "worker_referrer.js",
+  "importScripts_3rdParty_worker.js",
+  "invalid.js",
+  "worker_bug1278777.js",
+  "worker_setTimeoutWith0.js",
+  "worker_bug1301094.js",
+  "script_createFile.js",
+  "worker_suspended.js",
+  "window_suspended.html",
+  "suspend_blank.html",
+  "multi_sharedWorker_manager.js",
+  "multi_sharedWorker_frame_nobfcache.html",
+  "multi_sharedWorker_frame_nobfcache.html^headers^",
+  "multi_sharedWorker_frame_bfcache.html",
+  "navigate.html",
+  "!/dom/notification/test/mochitest/MockServices.js",
+  "!/dom/notification/test/mochitest/NotificationTest.js",
+  "!/dom/xhr/tests/relativeLoad_import.js",
+  "!/dom/xhr/tests/relativeLoad_worker.js",
+  "!/dom/xhr/tests/relativeLoad_worker2.js",
+  "!/dom/xhr/tests/subdir/relativeLoad_sub_worker.js",
+  "!/dom/xhr/tests/subdir/relativeLoad_sub_worker2.js",
+  "!/dom/xhr/tests/subdir/relativeLoad_sub_import.js",
+  "!/dom/events/test/event_leak_utils.js",
+]
+
+["test_404.html"]
+
+["test_atob.html"]
+
+["test_blobConstructor.html"]
+
+["test_blobWorkers.html"]
+
+["test_bug949946.html"]
+
+["test_bug978260.html"]
+
+["test_bug998474.html"]
+
+["test_bug1002702.html"]
+
+["test_bug1010784.html"]
+
+["test_bug1014466.html"]
+
+["test_bug1020226.html"]
+
+["test_bug1036484.html"]
+
+["test_bug1060621.html"]
+
+["test_bug1062920.html"]
+
+["test_bug1063538.html"]
+skip-if = [
+  "http3",
+  "http2",
+]
+
+["test_bug1104064.html"]
+
+["test_bug1132395.html"]
+skip-if = ["true"] # bug 1176225
+
+["test_bug1132924.html"]
+
+["test_bug1278777.html"]
+
+["test_bug1301094.html"]
+
+["test_bug1317725.html"]
+support-files = ["test_bug1317725.js"]
+
+["test_bug1824498.html"]
+support-files = ["worker_bug1824498.mjs"]
+
+["test_chromeWorker.html"]
+
+["test_clearTimeouts.html"]
+
+["test_clearTimeoutsImplicit.html"]
+
+["test_console.html"]
+
+["test_consoleAndBlobs.html"]
+
+["test_consoleReplaceable.html"]
+
+["test_contentWorker.html"]
+
+["test_csp.html"]
+
+["test_dataURLWorker.html"]
+
+["test_dynamicImport.html"]
+
+["test_dynamicImport_and_terminate.html"]
+support-files = ["worker_dynamicImport.mjs"]
+
+["test_dynamicImport_early_termination.html"]
+
+["test_errorPropagation.html"]
+skip-if = [
+  "http3",
+  "http2",
+]
+
+["test_errorwarning.html"]
+
+["test_eventDispatch.html"]
+
+["test_fibonacci.html"]
+
+["test_fileReaderSync_when_closing.html"]
+
+["test_importScripts.html"]
+
+["test_importScripts_1.html"]
+
+["test_importScripts_2.html"]
+
+["test_importScripts_3rdparty.html"]
+skip-if = [
+  "http3",
+  "http2",
+]
+
+["test_importScripts_mixedcontent.html"]
+tags = "mcb"
+
+["test_instanceof.html"]
+
+["test_json.html"]
+
+["test_loadEncoding.html"]
+
+["test_loadError.html"]
+
+["test_location.html"]
+skip-if = [
+  "http3",
+  "http2",
+]
+
+["test_longThread.html"]
+
+["test_multi_sharedWorker.html"]
+skip-if = [
+  "http3",
+  "http2",
+]
+
+["test_multi_sharedWorker_lifetimes_bfcache.html"]
+
+["test_multi_sharedWorker_lifetimes_nobfcache.html"]
+
+["test_navigator.html"]
+support-files = [
+  "test_navigator.js",
+  "test_navigator_iframe.html",
+  "test_navigator_iframe.js",
+]
+skip-if = [
+  "http3",
+  "http2",
+]
+
+["test_navigator_languages.html"]
+
+["test_navigator_secureContext.html"]
+scheme = "https"
+support-files = [
+  "test_navigator.js",
+  "test_navigator_iframe.html",
+  "test_navigator_iframe.js",
+]
+
+["test_navigator_workers_hardwareConcurrency.html"]
+
+["test_newError.html"]
+
+["test_notification.html"]
+
+["test_notification_child.html"]
+
+["test_notification_permission.html"]
+
+["test_onLine.html"]
+
+["test_promise.html"]
+
+["test_promise_resolved_with_string.html"]
+
+["test_recursion.html"]
+
+["test_recursiveOnerror.html"]
+skip-if = [
+  "http3",
+  "http2",
+]
+
+["test_referrer.html"]
+
+["test_referrer_header_worker.html"]
+skip-if = [
+  "http3",
+  "http2",
+]
+
+["test_resolveWorker-assignment.html"]
+
+["test_resolveWorker.html"]
+
+["test_rvals.html"]
+
+["test_setTimeoutWith0.html"]
+
+["test_sharedWorker.html"]
+
+["test_sharedWorker_lifetime.html"]
+
+["test_sharedWorker_ports.html"]
+
+["test_sharedWorker_thirdparty.html"]
+support-files = [
+  "sharedWorker_thirdparty_frame.html",
+  "sharedWorker_thirdparty_window.html",
+]
+skip-if = [
+  "http3",
+  "http2",
+]
+
+["test_sharedworker_event_listener_leaks.html"]
+skip-if = [
+  "bits == 64 && os == 'linux' && asan", # Disabled on Linux64 opt asan, bug 1493563
+  "os == 'win' && debug && xorigin", # high frequency intermittent
+]
+
+["test_simpleThread.html"]
+skip-if = [
+  "http3",
+  "http2",
+]
+
+["test_subworkers_suspended.html"]
+scheme = "https"
+
+["test_suspend.html"]
+
+["test_terminate.html"]
+
+["test_threadErrors.html"]
+
+["test_threadTimeouts.html"]
+
+["test_throwingOnerror.html"]
+
+["test_timeoutTracing.html"]
+
+["test_transferable.html"]
+
+["test_worker_interfaces.html"]
+skip-if = [
+  "http3",
+  "http2",
+]
+
+["test_worker_interfaces_secureContext.html"]
+scheme = "https"
diff --git a/dom/workers/test/multi_sharedWorker_frame.html b/dom/workers/test/multi_sharedWorker_frame.html
new file mode 100644
index 0000000000..94866b918d
--- /dev/null
+++ b/dom/workers/test/multi_sharedWorker_frame.html
@@ -0,0 +1,58 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+  <head>
+    <title>Test for SharedWorker</title>
+  </head>
+  <body>
+    <script type="text/javascript">
+      "use strict";
+
+      function postMessageToParentOrOpener(message) {
+        if (parent != window) {
+          parent.postMessage(message, "*");
+        }
+      }
+
+      function debug(message) {
+        if (typeof(message) != "string") {
+          throw new Error("debug() only accepts strings!");
+        }
+        postMessageToParentOrOpener(message);
+      }
+
+      let worker;
+
+      window.addEventListener("message", function(event) {
+        if (!worker) {
+          worker = new SharedWorker("multi_sharedWorker_sharedWorker.js",
+                                    "FrameWorker");
+          worker.onerror = function(error) {
+            debug("Worker error: " + error.message);
+            error.preventDefault();
+
+            let data = {
+              type: "error",
+              message: error.message,
+              filename: error.filename,
+              lineno: error.lineno,
+              isErrorEvent: error instanceof ErrorEvent
+            };
+            postMessageToParentOrOpener(data);
+          };
+
+          worker.port.onmessage = function(msg) {
+            debug("Worker message: " + JSON.stringify(msg.data));
+            postMessageToParentOrOpener(msg.data);
+          };
+        }
+
+        debug("Posting message: " + JSON.stringify(event.data));
+        worker.port.postMessage(event.data);
+      });
+    </script>
+  </body>
+</html>
diff --git a/dom/workers/test/multi_sharedWorker_frame_bfcache.html b/dom/workers/test/multi_sharedWorker_frame_bfcache.html
new file mode 100644
index 0000000000..dea14a8f78
--- /dev/null
+++ b/dom/workers/test/multi_sharedWorker_frame_bfcache.html
@@ -0,0 +1,13 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+  <head>
+    <title>Test for SharedWorker</title>
+  </head>
+  <body>
+    <script type="text/javascript" src=multi_sharedWorker_manager.js></script>
+  </body>
+</html>
diff --git a/dom/workers/test/multi_sharedWorker_frame_nobfcache.html b/dom/workers/test/multi_sharedWorker_frame_nobfcache.html
new file mode 100644
index 0000000000..dea14a8f78
--- /dev/null
+++ b/dom/workers/test/multi_sharedWorker_frame_nobfcache.html
@@ -0,0 +1,13 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+  <head>
+    <title>Test for SharedWorker</title>
+  </head>
+  <body>
+    <script type="text/javascript" src=multi_sharedWorker_manager.js></script>
+  </body>
+</html>
diff --git a/dom/workers/test/multi_sharedWorker_frame_nobfcache.html^headers^ b/dom/workers/test/multi_sharedWorker_frame_nobfcache.html^headers^
new file mode 100644
index 0000000000..2567dc2fe5
--- /dev/null
+++ b/dom/workers/test/multi_sharedWorker_frame_nobfcache.html^headers^
@@ -0,0 +1 @@
+Cache-Control: no-store
\ No newline at end of file
diff --git a/dom/workers/test/multi_sharedWorker_manager.js b/dom/workers/test/multi_sharedWorker_manager.js
new file mode 100644
index 0000000000..c0a9455ef1
--- /dev/null
+++ b/dom/workers/test/multi_sharedWorker_manager.js
@@ -0,0 +1,58 @@
+var query = window.location.search;
+var bc = new BroadcastChannel("bugSharedWorkerLiftetime" + query);
+bc.onmessage = msgEvent => {
+  var msg = msgEvent.data;
+  var command = msg.command;
+  if (command == "postToWorker") {
+    postToWorker(msg.workerMessage);
+  } else if (command == "navigate") {
+    window.location = msg.location;
+  } else if (command == "finish") {
+    bc.postMessage({ command: "finished" });
+    bc.close();
+    window.close();
+  }
+};
+
+window.onload = () => {
+  bc.postMessage({ command: "loaded" });
+};
+
+function debug(message) {
+  if (typeof message != "string") {
+    throw new Error("debug() only accepts strings!");
+  }
+  bc.postMessage({ command: "debug", message });
+}
+
+let worker;
+
+function postToWorker(msg) {
+  if (!worker) {
+    worker = new SharedWorker(
+      "multi_sharedWorker_sharedWorker.js",
+      "FrameWorker"
+    );
+    worker.onerror = function (error) {
+      debug("Worker error: " + error.message);
+      error.preventDefault();
+
+      let data = {
+        type: "error",
+        message: error.message,
+        filename: error.filename,
+        lineno: error.lineno,
+        isErrorEvent: error instanceof ErrorEvent,
+      };
+      bc.postMessage({ command: "fromWorker", workerMessage: data });
+    };
+
+    worker.port.onmessage = function (message) {
+      debug("Worker message: " + JSON.stringify(message.data));
+      bc.postMessage({ command: "fromWorker", workerMessage: message.data });
+    };
+  }
+
+  debug("Posting message: " + JSON.stringify(msg));
+  worker.port.postMessage(msg);
+}
diff --git a/dom/workers/test/multi_sharedWorker_sharedWorker.js b/dom/workers/test/multi_sharedWorker_sharedWorker.js
new file mode 100644
index 0000000000..3c3e4c5780
--- /dev/null
+++ b/dom/workers/test/multi_sharedWorker_sharedWorker.js
@@ -0,0 +1,73 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+"use strict";
+
+if (self.name != "FrameWorker") {
+  throw new Error("Bad worker name: " + self.name);
+}
+
+var registeredPorts = [];
+var errorCount = 0;
+var storedData;
+
+self.onconnect = function (event) {
+  var port = event.ports[0];
+
+  if (registeredPorts.length) {
+    let data = {
+      type: "connect",
+    };
+
+    registeredPorts.forEach(function (registeredPort) {
+      registeredPort.postMessage(data);
+    });
+  }
+
+  port.onmessage = function (msg) {
+    switch (msg.data.command) {
+      case "start":
+        break;
+
+      case "error":
+        throw new Error("Expected");
+
+      case "store":
+        storedData = msg.data.data;
+        break;
+
+      case "retrieve":
+        var data = {
+          type: "result",
+          data: storedData,
+        };
+        port.postMessage(data);
+        break;
+
+      default:
+        throw new Error("Unknown command '" + error.data.command + "'");
+    }
+  };
+
+  registeredPorts.push(port);
+};
+
+self.onerror = function (message, filename, lineno) {
+  if (!errorCount++) {
+    var data = {
+      type: "worker-error",
+      message,
+      filename,
+      lineno,
+    };
+
+    registeredPorts.forEach(function (registeredPort) {
+      registeredPort.postMessage(data);
+    });
+
+    // Prevent the error from propagating the first time only.
+    return true;
+  }
+  return undefined;
+};
diff --git a/dom/workers/test/navigate.html b/dom/workers/test/navigate.html
new file mode 100644
index 0000000000..e38ab4540a
--- /dev/null
+++ b/dom/workers/test/navigate.html
@@ -0,0 +1,13 @@
+<!DOCTYPE HTML>
+<script>
+  var bc = new BroadcastChannel("navigate");
+  bc.onmessage = (event) => {
+    if (event.data.command == "navigate") {
+      window.location = event.data.location;
+      bc.close();
+    }
+  }
+  window.onload = () => {
+    bc.postMessage({command: "loaded"});
+  }
+</script>
diff --git a/dom/workers/test/navigator_languages_worker.js b/dom/workers/test/navigator_languages_worker.js
new file mode 100644
index 0000000000..22ece09ef2
--- /dev/null
+++ b/dom/workers/test/navigator_languages_worker.js
@@ -0,0 +1,11 @@
+var active = true;
+onmessage = function (e) {
+  if (e.data == "finish") {
+    active = false;
+    return;
+  }
+
+  if (active) {
+    postMessage(navigator.languages);
+  }
+};
diff --git a/dom/workers/test/navigator_worker.js b/dom/workers/test/navigator_worker.js
new file mode 100644
index 0000000000..a9cd4f29d5
--- /dev/null
+++ b/dom/workers/test/navigator_worker.js
@@ -0,0 +1,87 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+// IMPORTANT: Do not change the list below without review from a DOM peer!
+var supportedProps = [
+  "appCodeName",
+  "appName",
+  "appVersion",
+  "globalPrivacyControl",
+  "platform",
+  "product",
+  "userAgent",
+  "onLine",
+  "language",
+  "languages",
+  { name: "locks", isSecureContext: true },
+  "mediaCapabilities",
+  "hardwareConcurrency",
+  { name: "storage", isSecureContext: true },
+  "connection",
+];
+
+self.onmessage = function (event) {
+  if (!event || !event.data) {
+    return;
+  }
+
+  startTest(event.data);
+};
+
+function startTest(channelData) {
+  // Prepare the interface map showing if a propery should exist in this build.
+  // For example, if interfaceMap[foo] = true means navigator.foo should exist.
+  var interfaceMap = {};
+
+  for (var prop of supportedProps) {
+    if (typeof prop === "string") {
+      interfaceMap[prop] = true;
+      continue;
+    }
+
+    if (
+      prop.isNightly === !channelData.isNightly ||
+      prop.release === !channelData.isRelease ||
+      prop.isSecureContext === !isSecureContext ||
+      prop.isAndroid === !channelData.isAndroid
+    ) {
+      interfaceMap[prop.name] = false;
+      continue;
+    }
+
+    interfaceMap[prop.name] = true;
+  }
+
+  for (var prop in navigator) {
+    // Make sure the list is current!
+    if (!interfaceMap[prop]) {
+      throw "Navigator has the '" + prop + "' property that isn't in the list!";
+    }
+  }
+
+  var obj;
+
+  for (var prop in interfaceMap) {
+    // Skip the property that is not supposed to exist in this build.
+    if (!interfaceMap[prop]) {
+      continue;
+    }
+
+    if (typeof navigator[prop] == "undefined") {
+      throw "Navigator has no '" + prop + "' property!";
+    }
+
+    obj = { name: prop };
+    obj.value = navigator[prop];
+
+    postMessage(JSON.stringify(obj));
+  }
+
+  obj = {
+    name: "testFinished",
+  };
+
+  postMessage(JSON.stringify(obj));
+}
diff --git a/dom/workers/test/newError_worker.js b/dom/workers/test/newError_worker.js
new file mode 100644
index 0000000000..46e6226f73
--- /dev/null
+++ b/dom/workers/test/newError_worker.js
@@ -0,0 +1,5 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+throw new Error("foo!");
diff --git a/dom/workers/test/notification_permission_worker.js b/dom/workers/test/notification_permission_worker.js
new file mode 100644
index 0000000000..0e6b96d975
--- /dev/null
+++ b/dom/workers/test/notification_permission_worker.js
@@ -0,0 +1,59 @@
+function info(message) {
+  dump("INFO: " + message + "\n");
+}
+
+function ok(test, message) {
+  postMessage({ type: "ok", test, message });
+}
+
+function is(a, b, message) {
+  postMessage({ type: "is", test1: a, test2: b, message });
+}
+
+if (self.Notification) {
+  var steps = [
+    function (done) {
+      info("Test notification permission");
+      ok(typeof Notification === "function", "Notification constructor exists");
+      ok(
+        Notification.permission === "denied",
+        "Notification.permission is denied."
+      );
+
+      var n = new Notification("Hello");
+      n.onerror = function (e) {
+        ok(true, "error called due to permission denied.");
+        done();
+      };
+    },
+  ];
+
+  onmessage = function (e) {
+    var context = {};
+    (function executeRemainingTests(remainingTests) {
+      if (!remainingTests.length) {
+        postMessage({ type: "finish" });
+        return;
+      }
+
+      var nextTest = remainingTests.shift();
+      var finishTest = executeRemainingTests.bind(null, remainingTests);
+      var startTest = nextTest.call.bind(nextTest, context, finishTest);
+
+      try {
+        startTest();
+        // if no callback was defined for test function,
+        // we must manually invoke finish to continue
+        if (nextTest.length === 0) {
+          finishTest();
+        }
+      } catch (ex) {
+        ok(false, "Test threw exception! " + nextTest + " " + ex);
+        finishTest();
+      }
+    })(steps);
+  };
+} else {
+  ok(true, "Notifications are not enabled in workers on the platform.");
+  postMessage({ type: "finish" });
+}
diff --git a/dom/workers/test/notification_worker.js b/dom/workers/test/notification_worker.js
new file mode 100644
index 0000000000..87aa02ac05
--- /dev/null
+++ b/dom/workers/test/notification_worker.js
@@ -0,0 +1,104 @@
+function ok(test, message) {
+  postMessage({ type: "ok", test, message });
+}
+
+function is(a, b, message) {
+  postMessage({ type: "is", test1: a, test2: b, message });
+}
+
+if (self.Notification) {
+  var steps = [
+    function () {
+      ok(typeof Notification === "function", "Notification constructor exists");
+      ok(Notification.permission, "Notification.permission exists");
+      ok(
+        typeof Notification.requestPermission === "undefined",
+        "Notification.requestPermission should not exist"
+      );
+    },
+
+    function (done) {
+      var options = {
+        dir: "auto",
+        lang: "",
+        body: "This is a notification body",
+        tag: "sometag",
+        icon: "icon.png",
+        data: ["a complex object that should be", { structured: "cloned" }],
+        mozbehavior: { vibrationPattern: [30, 200, 30] },
+      };
+      var notification = new Notification("This is a title", options);
+
+      ok(notification !== undefined, "Notification exists");
+      is(notification.onclick, null, "onclick() should be null");
+      is(notification.onshow, null, "onshow() should be null");
+      is(notification.onerror, null, "onerror() should be null");
+      is(notification.onclose, null, "onclose() should be null");
+      is(typeof notification.close, "function", "close() should exist");
+
+      is(notification.dir, options.dir, "auto should get set");
+      is(notification.lang, options.lang, "lang should get set");
+      is(notification.body, options.body, "body should get set");
+      is(notification.tag, options.tag, "tag should get set");
+      is(notification.icon, options.icon, "icon should get set");
+      is(
+        notification.data[0],
+        "a complex object that should be",
+        "data item 0 should be a matching string"
+      );
+      is(
+        notification.data[1].structured,
+        "cloned",
+        "data item 1 should be a matching object literal"
+      );
+
+      // store notification in test context
+      this.notification = notification;
+
+      notification.onshow = function () {
+        ok(true, "onshow handler should be called");
+        done();
+      };
+    },
+
+    function (done) {
+      var notification = this.notification;
+
+      notification.onclose = function () {
+        ok(true, "onclose handler should be called");
+        done();
+      };
+
+      notification.close();
+    },
+  ];
+
+  onmessage = function (e) {
+    var context = {};
+    (function executeRemainingTests(remainingTests) {
+      if (!remainingTests.length) {
+        postMessage({ type: "finish" });
+        return;
+      }
+
+      var nextTest = remainingTests.shift();
+      var finishTest = executeRemainingTests.bind(null, remainingTests);
+      var startTest = nextTest.call.bind(nextTest, context, finishTest);
+
+      try {
+        startTest();
+        // if no callback was defined for test function,
+        // we must manually invoke finish to continue
+        if (nextTest.length === 0) {
+          finishTest();
+        }
+      } catch (ex) {
+        ok(false, "Test threw exception! " + nextTest + " " + ex);
+        finishTest();
+      }
+    })(steps);
+  };
+} else {
+  ok(true, "Notifications are not enabled in workers on the platform.");
+  postMessage({ type: "finish" });
+}
diff --git a/dom/workers/test/notification_worker_child-child.js b/dom/workers/test/notification_worker_child-child.js
new file mode 100644
index 0000000000..236e314e47
--- /dev/null
+++ b/dom/workers/test/notification_worker_child-child.js
@@ -0,0 +1,93 @@
+function ok(test, message) {
+  postMessage({ type: "ok", test, message });
+}
+
+function is(a, b, message) {
+  postMessage({ type: "is", test1: a, test2: b, message });
+}
+
+if (self.Notification) {
+  var steps = [
+    function () {
+      ok(typeof Notification === "function", "Notification constructor exists");
+      ok(Notification.permission, "Notification.permission exists");
+      ok(
+        typeof Notification.requestPermission === "undefined",
+        "Notification.requestPermission should not exist"
+      );
+      //ok(typeof Notification.get === "function", "Notification.get exists");
+    },
+
+    function (done) {
+      var options = {
+        dir: "auto",
+        lang: "",
+        body: "This is a notification body",
+        tag: "sometag",
+        icon: "icon.png",
+      };
+      var notification = new Notification("This is a title", options);
+
+      ok(notification !== undefined, "Notification exists");
+      is(notification.onclick, null, "onclick() should be null");
+      is(notification.onshow, null, "onshow() should be null");
+      is(notification.onerror, null, "onerror() should be null");
+      is(notification.onclose, null, "onclose() should be null");
+      is(typeof notification.close, "function", "close() should exist");
+
+      is(notification.dir, options.dir, "auto should get set");
+      is(notification.lang, options.lang, "lang should get set");
+      is(notification.body, options.body, "body should get set");
+      is(notification.tag, options.tag, "tag should get set");
+      is(notification.icon, options.icon, "icon should get set");
+
+      // store notification in test context
+      this.notification = notification;
+
+      notification.onshow = function () {
+        ok(true, "onshow handler should be called");
+        done();
+      };
+    },
+
+    function (done) {
+      var notification = this.notification;
+
+      notification.onclose = function () {
+        ok(true, "onclose handler should be called");
+        done();
+      };
+
+      notification.close();
+    },
+  ];
+
+  onmessage = function (e) {
+    var context = {};
+    (function executeRemainingTests(remainingTests) {
+      if (!remainingTests.length) {
+        postMessage({ type: "finish" });
+        return;
+      }
+
+      var nextTest = remainingTests.shift();
+      var finishTest = executeRemainingTests.bind(null, remainingTests);
+      var startTest = nextTest.call.bind(nextTest, context, finishTest);
+
+      try {
+        startTest();
+        // if no callback was defined for test function,
+        // we must manually invoke finish to continue
+        if (nextTest.length === 0) {
+          finishTest();
+        }
+      } catch (ex) {
+        ok(false, "Test threw exception! " + nextTest + " " + ex);
+        finishTest();
+      }
+    })(steps);
+  };
+} else {
+  ok(true, "Notifications are not enabled in workers on the platform.");
+  postMessage({ type: "finish" });
+}
diff --git a/dom/workers/test/notification_worker_child-parent.js b/dom/workers/test/notification_worker_child-parent.js
new file mode 100644
index 0000000000..45dd061993
--- /dev/null
+++ b/dom/workers/test/notification_worker_child-parent.js
@@ -0,0 +1,26 @@
+function ok(test, message) {
+  postMessage({ type: "ok", test, message });
+}
+
+function is(a, b, message) {
+  postMessage({ type: "is", test1: a, test2: b, message });
+}
+
+if (self.Notification) {
+  var child = new Worker("notification_worker_child-child.js");
+  child.onerror = function (e) {
+    ok(false, "Error loading child worker " + e);
+    postMessage({ type: "finish" });
+  };
+
+  child.onmessage = function (e) {
+    postMessage(e.data);
+  };
+
+  onmessage = function (e) {
+    child.postMessage("start");
+  };
+} else {
+  ok(true, "Notifications are not enabled in workers on the platform.");
+  postMessage({ type: "finish" });
+}
diff --git a/dom/workers/test/onLine_worker.js b/dom/workers/test/onLine_worker.js
new file mode 100644
index 0000000000..94c10c699c
--- /dev/null
+++ b/dom/workers/test/onLine_worker.js
@@ -0,0 +1,70 @@
+/*
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/licenses/publicdomain/
+ */
+
+importScripts("onLine_worker_head.js");
+
+var N_CHILDREN = 3;
+var children = [];
+var finishedChildrenCount = 0;
+var lastTest = false;
+
+for (var event of ["online", "offline"]) {
+  addEventListener(
+    event,
+    makeHandler(
+      "addEventListener('%1', ..., false)",
+      event,
+      1,
+      "Parent Worker"
+    ),
+    false
+  );
+}
+
+onmessage = function (e) {
+  if (e.data === "lastTest") {
+    children.forEach(function (w) {
+      w.postMessage({ type: "lastTest" });
+    });
+    lastTest = true;
+  }
+};
+
+function setupChildren(cb) {
+  var readyCount = 0;
+  for (var i = 0; i < N_CHILDREN; ++i) {
+    var w = new Worker("onLine_worker_child.js");
+    children.push(w);
+
+    w.onerror = function (e) {
+      info("Error creating child " + e.message);
+    };
+
+    w.onmessage = function (e) {
+      if (e.data.type === "ready") {
+        info("Got ready from child");
+        readyCount++;
+        if (readyCount === N_CHILDREN) {
+          cb();
+        }
+      } else if (e.data.type === "finished") {
+        finishedChildrenCount++;
+
+        if (lastTest && finishedChildrenCount === N_CHILDREN) {
+          postMessage({ type: "finished" });
+          children = [];
+          close();
+        }
+      } else if (e.data.type === "ok") {
+        // Pass on test to page.
+        postMessage(e.data);
+      }
+    };
+  }
+}
+
+setupChildren(function () {
+  postMessage({ type: "ready" });
+});
diff --git a/dom/workers/test/onLine_worker_child.js b/dom/workers/test/onLine_worker_child.js
new file mode 100644
index 0000000000..92542c018f
--- /dev/null
+++ b/dom/workers/test/onLine_worker_child.js
@@ -0,0 +1,91 @@
+/*
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/licenses/publicdomain/
+ */
+
+/*
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/licenses/publicdomain/
+ */
+
+function info(text) {
+  dump("Test for Bug 925437: worker: " + text + "\n");
+}
+
+function ok(test, message) {
+  postMessage({ type: "ok", test, message });
+}
+
+/**
+ * Returns a handler function for an online/offline event. The returned handler
+ * ensures the passed event object has expected properties and that the handler
+ * is called at the right moment (according to the gState variable).
+ * @param nameTemplate The string identifying the hanlder. '%1' in that
+ *                     string will be replaced with the event name.
+ * @param eventName 'online' or 'offline'
+ * @param expectedState value of gState at the moment the handler is called.
+ *                       The handler increases gState by one before checking
+ *                       if it matches expectedState.
+ */
+function makeHandler(nameTemplate, eventName, expectedState, prefix, custom) {
+  prefix += ": ";
+  return function (e) {
+    var name = nameTemplate.replace(/%1/, eventName);
+    ok(e.constructor == Event, prefix + "event should be an Event");
+    ok(e.type == eventName, prefix + "event type should be " + eventName);
+    ok(!e.bubbles, prefix + "event should not bubble");
+    ok(!e.cancelable, prefix + "event should not be cancelable");
+    ok(
+      e.target == self,
+      prefix + "the event target should be the worker scope"
+    );
+    ok(
+      eventName == "online" ? navigator.onLine : !navigator.onLine,
+      prefix +
+        "navigator.onLine " +
+        navigator.onLine +
+        " should reflect event " +
+        eventName
+    );
+
+    if (custom) {
+      custom();
+    }
+  };
+}
+
+var lastTest = false;
+
+function lastTestTest() {
+  if (lastTest) {
+    postMessage({ type: "finished" });
+    close();
+  }
+}
+
+for (var event of ["online", "offline"]) {
+  addEventListener(
+    event,
+    makeHandler(
+      "addEventListener('%1', ..., false)",
+      event,
+      1,
+      "Child Worker",
+      lastTestTest
+    ),
+    false
+  );
+}
+
+onmessage = function (e) {
+  if (e.data.type === "lastTest") {
+    lastTest = true;
+  } else if (e.data.type === "navigatorState") {
+    ok(
+      e.data.state === navigator.onLine,
+      "Child and parent navigator state should match"
+    );
+  }
+};
+
+postMessage({ type: "ready" });
diff --git a/dom/workers/test/onLine_worker_head.js b/dom/workers/test/onLine_worker_head.js
new file mode 100644
index 0000000000..632821b1f4
--- /dev/null
+++ b/dom/workers/test/onLine_worker_head.js
@@ -0,0 +1,50 @@
+/*
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/licenses/publicdomain/
+ */
+
+function info(text) {
+  dump("Test for Bug 925437: worker: " + text + "\n");
+}
+
+function ok(test, message) {
+  postMessage({ type: "ok", test, message });
+}
+
+/**
+ * Returns a handler function for an online/offline event. The returned handler
+ * ensures the passed event object has expected properties and that the handler
+ * is called at the right moment (according to the gState variable).
+ * @param nameTemplate The string identifying the hanlder. '%1' in that
+ *                     string will be replaced with the event name.
+ * @param eventName 'online' or 'offline'
+ * @param expectedState value of gState at the moment the handler is called.
+ *                       The handler increases gState by one before checking
+ *                       if it matches expectedState.
+ */
+function makeHandler(nameTemplate, eventName, expectedState, prefix, custom) {
+  prefix += ": ";
+  return function (e) {
+    var name = nameTemplate.replace(/%1/, eventName);
+    ok(e.constructor == Event, prefix + "event should be an Event");
+    ok(e.type == eventName, prefix + "event type should be " + eventName);
+    ok(!e.bubbles, prefix + "event should not bubble");
+    ok(!e.cancelable, prefix + "event should not be cancelable");
+    ok(
+      e.target == self,
+      prefix + "the event target should be the worker scope"
+    );
+    ok(
+      eventName == "online" ? navigator.onLine : !navigator.onLine,
+      prefix +
+        "navigator.onLine " +
+        navigator.onLine +
+        " should reflect event " +
+        eventName
+    );
+
+    if (custom) {
+      custom();
+    }
+  };
+}
diff --git a/dom/workers/test/promise_worker.js b/dom/workers/test/promise_worker.js
new file mode 100644
index 0000000000..fd4a9177d6
--- /dev/null
+++ b/dom/workers/test/promise_worker.js
@@ -0,0 +1,1007 @@
+"use strict";
+
+function ok(a, msg) {
+  dump("OK: " + !!a + "  =>  " + a + " " + msg + "\n");
+  postMessage({ type: "status", status: !!a, msg: a + ": " + msg });
+}
+
+function is(a, b, msg) {
+  dump("IS: " + (a === b) + "  =>  " + a + " | " + b + " " + msg + "\n");
+  postMessage({
+    type: "status",
+    status: a === b,
+    msg: a + " === " + b + ": " + msg,
+  });
+}
+
+function isnot(a, b, msg) {
+  dump("ISNOT: " + (a !== b) + "  =>  " + a + " | " + b + " " + msg + "\n");
+  postMessage({
+    type: "status",
+    status: a !== b,
+    msg: a + " !== " + b + ": " + msg,
+  });
+}
+
+function promiseResolve() {
+  ok(Promise, "Promise object should exist");
+
+  var promise = new Promise(function (resolve, reject) {
+    ok(resolve, "Promise.resolve exists");
+    ok(reject, "Promise.reject exists");
+
+    resolve(42);
+  }).then(
+    function (what) {
+      ok(true, "Then - resolveCb has been called");
+      is(what, 42, "ResolveCb received 42");
+      runTest();
+    },
+    function () {
+      ok(false, "Then - rejectCb has been called");
+      runTest();
+    }
+  );
+}
+
+function promiseResolveNoArg() {
+  var promise = new Promise(function (resolve, reject) {
+    ok(resolve, "Promise.resolve exists");
+    ok(reject, "Promise.reject exists");
+
+    resolve();
+  }).then(
+    function (what) {
+      ok(true, "Then - resolveCb has been called");
+      is(what, undefined, "ResolveCb received undefined");
+      runTest();
+    },
+    function () {
+      ok(false, "Then - rejectCb has been called");
+      runTest();
+    }
+  );
+}
+
+function promiseRejectNoHandler() {
+  // This test only checks that the code that reports unhandled errors in the
+  // Promises implementation does not crash or leak.
+  var promise = new Promise(function (res, rej) {
+    noSuchMethod();
+  });
+  runTest();
+}
+
+function promiseReject() {
+  var promise = new Promise(function (resolve, reject) {
+    reject(42);
+  }).then(
+    function (what) {
+      ok(false, "Then - resolveCb has been called");
+      runTest();
+    },
+    function (what) {
+      ok(true, "Then - rejectCb has been called");
+      is(what, 42, "RejectCb received 42");
+      runTest();
+    }
+  );
+}
+
+function promiseRejectNoArg() {
+  var promise = new Promise(function (resolve, reject) {
+    reject();
+  }).then(
+    function (what) {
+      ok(false, "Then - resolveCb has been called");
+      runTest();
+    },
+    function (what) {
+      ok(true, "Then - rejectCb has been called");
+      is(what, undefined, "RejectCb received undefined");
+      runTest();
+    }
+  );
+}
+
+function promiseException() {
+  var promise = new Promise(function (resolve, reject) {
+    throw 42;
+  }).then(
+    function (what) {
+      ok(false, "Then - resolveCb has been called");
+      runTest();
+    },
+    function (what) {
+      ok(true, "Then - rejectCb has been called");
+      is(what, 42, "RejectCb received 42");
+      runTest();
+    }
+  );
+}
+
+function promiseAsync_TimeoutResolveThen() {
+  var handlerExecuted = false;
+
+  setTimeout(function () {
+    ok(handlerExecuted, "Handler should have been called before the timeout.");
+
+    // Allow other assertions to run so the test could fail before the next one.
+    setTimeout(runTest, 0);
+  }, 0);
+
+  Promise.resolve().then(function () {
+    handlerExecuted = true;
+  });
+
+  ok(!handlerExecuted, "Handlers are not called before 'then' returns.");
+}
+
+function promiseAsync_ResolveTimeoutThen() {
+  var handlerExecuted = false;
+
+  var promise = Promise.resolve();
+
+  setTimeout(function () {
+    ok(handlerExecuted, "Handler should have been called before the timeout.");
+
+    // Allow other assertions to run so the test could fail before the next one.
+    setTimeout(runTest, 0);
+  }, 0);
+
+  promise.then(function () {
+    handlerExecuted = true;
+  });
+
+  ok(!handlerExecuted, "Handlers are not called before 'then' returns.");
+}
+
+function promiseAsync_ResolveThenTimeout() {
+  var handlerExecuted = false;
+
+  Promise.resolve().then(function () {
+    handlerExecuted = true;
+  });
+
+  setTimeout(function () {
+    ok(handlerExecuted, "Handler should have been called before the timeout.");
+
+    // Allow other assertions to run so the test could fail before the next one.
+    setTimeout(runTest, 0);
+  }, 0);
+
+  ok(!handlerExecuted, "Handlers are not called before 'then' returns.");
+}
+
+function promiseAsync_SyncXHRAndImportScripts() {
+  var handlerExecuted = false;
+
+  Promise.resolve().then(function () {
+    handlerExecuted = true;
+
+    // Allow other assertions to run so the test could fail before the next one.
+    setTimeout(runTest, 0);
+  });
+
+  ok(!handlerExecuted, "Handlers are not called until the next microtask.");
+
+  var xhr = new XMLHttpRequest();
+  xhr.open("GET", "testXHR.txt", false);
+  xhr.send(null);
+
+  ok(!handlerExecuted, "Sync XHR should not trigger microtask execution.");
+
+  importScripts("../../../dom/xhr/tests/relativeLoad_import.js");
+
+  ok(!handlerExecuted, "importScripts should not trigger microtask execution.");
+}
+
+function promiseDoubleThen() {
+  var steps = 0;
+  var promise = new Promise(function (r1, r2) {
+    r1(42);
+  });
+
+  promise.then(
+    function (what) {
+      ok(true, "Then.resolve has been called");
+      is(what, 42, "Value == 42");
+      steps++;
+    },
+    function (what) {
+      ok(false, "Then.reject has been called");
+    }
+  );
+
+  promise.then(
+    function (what) {
+      ok(true, "Then.resolve has been called");
+      is(steps, 1, "Then.resolve - step == 1");
+      is(what, 42, "Value == 42");
+      runTest();
+    },
+    function (what) {
+      ok(false, "Then.reject has been called");
+    }
+  );
+}
+
+function promiseThenException() {
+  var promise = new Promise(function (resolve, reject) {
+    resolve(42);
+  });
+
+  promise
+    .then(function (what) {
+      ok(true, "Then.resolve has been called");
+      throw "booh";
+    })
+    .catch(function (e) {
+      ok(true, "Catch has been called!");
+      runTest();
+    });
+}
+
+function promiseThenCatchThen() {
+  var promise = new Promise(function (resolve, reject) {
+    resolve(42);
+  });
+
+  var promise2 = promise.then(
+    function (what) {
+      ok(true, "Then.resolve has been called");
+      is(what, 42, "Value == 42");
+      return what + 1;
+    },
+    function (what) {
+      ok(false, "Then.reject has been called");
+    }
+  );
+
+  isnot(promise, promise2, "These 2 promise objs are different");
+
+  promise2
+    .then(
+      function (what) {
+        ok(true, "Then.resolve has been called");
+        is(what, 43, "Value == 43");
+        return what + 1;
+      },
+      function (what) {
+        ok(false, "Then.reject has been called");
+      }
+    )
+    .catch(function () {
+      ok(false, "Catch has been called");
+    })
+    .then(
+      function (what) {
+        ok(true, "Then.resolve has been called");
+        is(what, 44, "Value == 44");
+        runTest();
+      },
+      function (what) {
+        ok(false, "Then.reject has been called");
+      }
+    );
+}
+
+function promiseRejectThenCatchThen() {
+  var promise = new Promise(function (resolve, reject) {
+    reject(42);
+  });
+
+  var promise2 = promise.then(
+    function (what) {
+      ok(false, "Then.resolve has been called");
+    },
+    function (what) {
+      ok(true, "Then.reject has been called");
+      is(what, 42, "Value == 42");
+      return what + 1;
+    }
+  );
+
+  isnot(promise, promise2, "These 2 promise objs are different");
+
+  promise2
+    .then(function (what) {
+      ok(true, "Then.resolve has been called");
+      is(what, 43, "Value == 43");
+      return what + 1;
+    })
+    .catch(function (what) {
+      ok(false, "Catch has been called");
+    })
+    .then(function (what) {
+      ok(true, "Then.resolve has been called");
+      is(what, 44, "Value == 44");
+      runTest();
+    });
+}
+
+function promiseRejectThenCatchThen2() {
+  var promise = new Promise(function (resolve, reject) {
+    reject(42);
+  });
+
+  promise
+    .then(function (what) {
+      ok(true, "Then.resolve has been called");
+      is(what, 42, "Value == 42");
+      return what + 1;
+    })
+    .catch(function (what) {
+      is(what, 42, "Value == 42");
+      ok(true, "Catch has been called");
+      return what + 1;
+    })
+    .then(function (what) {
+      ok(true, "Then.resolve has been called");
+      is(what, 43, "Value == 43");
+      runTest();
+    });
+}
+
+function promiseRejectThenCatchExceptionThen() {
+  var promise = new Promise(function (resolve, reject) {
+    reject(42);
+  });
+
+  promise
+    .then(
+      function (what) {
+        ok(false, "Then.resolve has been called");
+      },
+      function (what) {
+        ok(true, "Then.reject has been called");
+        is(what, 42, "Value == 42");
+        throw what + 1;
+      }
+    )
+    .catch(function (what) {
+      ok(true, "Catch has been called");
+      is(what, 43, "Value == 43");
+      return what + 1;
+    })
+    .then(function (what) {
+      ok(true, "Then.resolve has been called");
+      is(what, 44, "Value == 44");
+      runTest();
+    });
+}
+
+function promiseThenCatchOrderingResolve() {
+  var global = 0;
+  var f = new Promise(function (r1, r2) {
+    r1(42);
+  });
+
+  f.then(function () {
+    f.then(function () {
+      global++;
+    });
+    f.catch(function () {
+      global++;
+    });
+    f.then(function () {
+      global++;
+    });
+    setTimeout(function () {
+      is(global, 2, "Many steps... should return 2");
+      runTest();
+    }, 0);
+  });
+}
+
+function promiseThenCatchOrderingReject() {
+  var global = 0;
+  var f = new Promise(function (r1, r2) {
+    r2(42);
+  });
+
+  f.then(
+    function () {},
+    function () {
+      f.then(function () {
+        global++;
+      });
+      f.catch(function () {
+        global++;
+      });
+      f.then(
+        function () {},
+        function () {
+          global++;
+        }
+      );
+      setTimeout(function () {
+        is(global, 2, "Many steps... should return 2");
+        runTest();
+      }, 0);
+    }
+  );
+}
+
+function promiseThenNoArg() {
+  var promise = new Promise(function (resolve, reject) {
+    resolve(42);
+  });
+
+  var clone = promise.then();
+  isnot(promise, clone, "These 2 promise objs are different");
+  promise.then(function (v) {
+    clone.then(function (cv) {
+      is(v, cv, "Both resolve to the same value");
+      runTest();
+    });
+  });
+}
+
+function promiseThenUndefinedResolveFunction() {
+  var promise = new Promise(function (resolve, reject) {
+    reject(42);
+  });
+
+  try {
+    promise.then(undefined, function (v) {
+      is(v, 42, "Promise rejected with 42");
+      runTest();
+    });
+  } catch (e) {
+    ok(false, "then should not throw on undefined resolve function");
+  }
+}
+
+function promiseThenNullResolveFunction() {
+  var promise = new Promise(function (resolve, reject) {
+    reject(42);
+  });
+
+  try {
+    promise.then(null, function (v) {
+      is(v, 42, "Promise rejected with 42");
+      runTest();
+    });
+  } catch (e) {
+    ok(false, "then should not throw on null resolve function");
+  }
+}
+
+function promiseCatchNoArg() {
+  var promise = new Promise(function (resolve, reject) {
+    reject(42);
+  });
+
+  var clone = promise.catch();
+  isnot(promise, clone, "These 2 promise objs are different");
+  promise.catch(function (v) {
+    clone.catch(function (cv) {
+      is(v, cv, "Both reject to the same value");
+      runTest();
+    });
+  });
+}
+
+function promiseNestedPromise() {
+  new Promise(function (resolve, reject) {
+    resolve(
+      new Promise(function (r) {
+        ok(true, "Nested promise is executed");
+        r(42);
+      })
+    );
+  }).then(function (value) {
+    is(value, 42, "Nested promise is executed and then == 42");
+    runTest();
+  });
+}
+
+function promiseNestedNestedPromise() {
+  new Promise(function (resolve, reject) {
+    resolve(
+      new Promise(function (r) {
+        ok(true, "Nested promise is executed");
+        r(42);
+      }).then(function (what) {
+        return what + 1;
+      })
+    );
+  }).then(function (value) {
+    is(value, 43, "Nested promise is executed and then == 43");
+    runTest();
+  });
+}
+
+function promiseWrongNestedPromise() {
+  new Promise(function (resolve, reject) {
+    resolve(
+      new Promise(function (r, r2) {
+        ok(true, "Nested promise is executed");
+        r(42);
+      })
+    );
+    reject(42);
+  }).then(
+    function (value) {
+      is(value, 42, "Nested promise is executed and then == 42");
+      runTest();
+    },
+    function (value) {
+      ok(false, "This is wrong");
+    }
+  );
+}
+
+function promiseLoop() {
+  new Promise(function (resolve, reject) {
+    resolve(
+      new Promise(function (r1, r2) {
+        ok(true, "Nested promise is executed");
+        r1(
+          new Promise(function (r3, r4) {
+            ok(true, "Nested nested promise is executed");
+            r3(42);
+          })
+        );
+      })
+    );
+  }).then(
+    function (value) {
+      is(value, 42, "Nested nested promise is executed and then == 42");
+      runTest();
+    },
+    function (value) {
+      ok(false, "This is wrong");
+    }
+  );
+}
+
+function promiseStaticReject() {
+  var promise = Promise.reject(42).then(
+    function (what) {
+      ok(false, "This should not be called");
+    },
+    function (what) {
+      is(what, 42, "Value == 42");
+      runTest();
+    }
+  );
+}
+
+function promiseStaticResolve() {
+  var promise = Promise.resolve(42).then(
+    function (what) {
+      is(what, 42, "Value == 42");
+      runTest();
+    },
+    function () {
+      ok(false, "This should not be called");
+    }
+  );
+}
+
+function promiseResolveNestedPromise() {
+  var promise = Promise.resolve(
+    new Promise(
+      function (r, r2) {
+        ok(true, "Nested promise is executed");
+        r(42);
+      },
+      function () {
+        ok(false, "This should not be called");
+      }
+    )
+  ).then(
+    function (what) {
+      is(what, 42, "Value == 42");
+      runTest();
+    },
+    function () {
+      ok(false, "This should not be called");
+    }
+  );
+}
+
+function promiseUtilitiesDefined() {
+  ok(Promise.all, "Promise.all must be defined when Promise is enabled.");
+  ok(Promise.race, "Promise.race must be defined when Promise is enabled.");
+  runTest();
+}
+
+function promiseAllArray() {
+  var p = Promise.all([1, new Date(), Promise.resolve("firefox")]);
+  ok(p instanceof Promise, "Return value of Promise.all should be a Promise.");
+  p.then(
+    function (values) {
+      ok(Array.isArray(values), "Resolved value should be an array.");
+      is(
+        values.length,
+        3,
+        "Resolved array length should match iterable's length."
+      );
+      is(values[0], 1, "Array values should match.");
+      ok(values[1] instanceof Date, "Array values should match.");
+      is(values[2], "firefox", "Array values should match.");
+      runTest();
+    },
+    function () {
+      ok(
+        false,
+        "Promise.all shouldn't fail when iterable has no rejected Promises."
+      );
+      runTest();
+    }
+  );
+}
+
+function promiseAllWaitsForAllPromises() {
+  var arr = [
+    new Promise(function (resolve) {
+      setTimeout(resolve.bind(undefined, 1), 50);
+    }),
+    new Promise(function (resolve) {
+      setTimeout(resolve.bind(undefined, 2), 10);
+    }),
+    new Promise(function (resolve) {
+      setTimeout(
+        resolve.bind(
+          undefined,
+          new Promise(function (resolve2) {
+            resolve2(3);
+          })
+        ),
+        10
+      );
+    }),
+    new Promise(function (resolve) {
+      setTimeout(resolve.bind(undefined, 4), 20);
+    }),
+  ];
+
+  var p = Promise.all(arr);
+  p.then(
+    function (values) {
+      ok(Array.isArray(values), "Resolved value should be an array.");
+      is(
+        values.length,
+        4,
+        "Resolved array length should match iterable's length."
+      );
+      is(values[0], 1, "Array values should match.");
+      is(values[1], 2, "Array values should match.");
+      is(values[2], 3, "Array values should match.");
+      is(values[3], 4, "Array values should match.");
+      runTest();
+    },
+    function () {
+      ok(
+        false,
+        "Promise.all shouldn't fail when iterable has no rejected Promises."
+      );
+      runTest();
+    }
+  );
+}
+
+function promiseAllRejectFails() {
+  var arr = [
+    new Promise(function (resolve) {
+      setTimeout(resolve.bind(undefined, 1), 50);
+    }),
+    new Promise(function (resolve, reject) {
+      setTimeout(reject.bind(undefined, 2), 10);
+    }),
+    new Promise(function (resolve) {
+      setTimeout(resolve.bind(undefined, 3), 10);
+    }),
+    new Promise(function (resolve) {
+      setTimeout(resolve.bind(undefined, 4), 20);
+    }),
+  ];
+
+  var p = Promise.all(arr);
+  p.then(
+    function (values) {
+      ok(
+        false,
+        "Promise.all shouldn't resolve when iterable has rejected Promises."
+      );
+      runTest();
+    },
+    function (e) {
+      ok(
+        true,
+        "Promise.all should reject when iterable has rejected Promises."
+      );
+      is(e, 2, "Rejection value should match.");
+      runTest();
+    }
+  );
+}
+
+function promiseRaceEmpty() {
+  var p = Promise.race([]);
+  ok(p instanceof Promise, "Should return a Promise.");
+  // An empty race never resolves!
+  runTest();
+}
+
+function promiseRaceValuesArray() {
+  var p = Promise.race([true, new Date(), 3]);
+  ok(p instanceof Promise, "Should return a Promise.");
+  p.then(
+    function (winner) {
+      is(winner, true, "First value should win.");
+      runTest();
+    },
+    function (err) {
+      ok(false, "Should not fail " + err + ".");
+      runTest();
+    }
+  );
+}
+
+function promiseRacePromiseArray() {
+  var arr = [
+    new Promise(function (resolve) {
+      resolve("first");
+    }),
+    Promise.resolve("second"),
+    new Promise(function () {}),
+    new Promise(function (resolve) {
+      setTimeout(function () {
+        setTimeout(function () {
+          resolve("fourth");
+        }, 0);
+      }, 0);
+    }),
+  ];
+
+  var p = Promise.race(arr);
+  p.then(function (winner) {
+    is(winner, "first", "First queued resolution should win the race.");
+    runTest();
+  });
+}
+
+function promiseRaceReject() {
+  var p = Promise.race([
+    Promise.reject(new Error("Fail bad!")),
+    new Promise(function (resolve) {
+      setTimeout(resolve, 0);
+    }),
+  ]);
+
+  p.then(
+    function () {
+      ok(false, "Should not resolve when winning Promise rejected.");
+      runTest();
+    },
+    function (e) {
+      ok(true, "Should be rejected");
+      ok(e instanceof Error, "Should reject with Error.");
+      ok(e.message == "Fail bad!", "Message should match.");
+      runTest();
+    }
+  );
+}
+
+function promiseRaceThrow() {
+  var p = Promise.race([
+    new Promise(function (resolve) {
+      nonExistent();
+    }),
+    new Promise(function (resolve) {
+      setTimeout(resolve, 0);
+    }),
+  ]);
+
+  p.then(
+    function () {
+      ok(false, "Should not resolve when winning Promise had an error.");
+      runTest();
+    },
+    function (e) {
+      ok(true, "Should be rejected");
+      ok(
+        e instanceof ReferenceError,
+        "Should reject with ReferenceError for function nonExistent()."
+      );
+      runTest();
+    }
+  );
+}
+
+function promiseResolveArray() {
+  var p = Promise.resolve([1, 2, 3]);
+  ok(p instanceof Promise, "Should return a Promise.");
+  p.then(function (v) {
+    ok(Array.isArray(v), "Resolved value should be an Array");
+    is(v.length, 3, "Length should match");
+    is(v[0], 1, "Resolved value should match original");
+    is(v[1], 2, "Resolved value should match original");
+    is(v[2], 3, "Resolved value should match original");
+    runTest();
+  });
+}
+
+function promiseResolveThenable() {
+  var p = Promise.resolve({
+    then(onFulfill, onReject) {
+      onFulfill(2);
+    },
+  });
+  ok(p instanceof Promise, "Should cast to a Promise.");
+  p.then(
+    function (v) {
+      is(v, 2, "Should resolve to 2.");
+      runTest();
+    },
+    function (e) {
+      ok(false, "promiseResolveThenable should've resolved");
+      runTest();
+    }
+  );
+}
+
+function promiseResolvePromise() {
+  var original = Promise.resolve(true);
+  var cast = Promise.resolve(original);
+
+  ok(cast instanceof Promise, "Should cast to a Promise.");
+  is(cast, original, "Should return original Promise.");
+  cast.then(function (v) {
+    is(v, true, "Should resolve to true.");
+    runTest();
+  });
+}
+
+// Bug 1009569.
+// Ensure that thenables are run on a clean stack asynchronously.
+// Test case adopted from
+// https://gist.github.com/getify/d64bb01751b50ed6b281#file-bug1-js.
+function promiseResolveThenableCleanStack() {
+  function immed(s) {
+    x++;
+    s();
+  }
+  function incX() {
+    x++;
+  }
+
+  var x = 0;
+  var thenable = { then: immed };
+  var results = [];
+
+  var p = Promise.resolve(thenable).then(incX);
+  results.push(x);
+
+  // check what happens after all "next cycle" steps
+  // have had a chance to complete
+  setTimeout(function () {
+    // Result should be [0, 2] since `thenable` will be called async.
+    is(results[0], 0, "Expected thenable to be called asynchronously");
+    // See Bug 1023547 comment 13 for why this check has to be gated on p.
+    p.then(function () {
+      results.push(x);
+      is(results[1], 2, "Expected thenable to be called asynchronously");
+      runTest();
+    });
+  }, 1000);
+}
+
+// Bug 1062323
+function promiseWrapperAsyncResolution() {
+  var p = new Promise(function (resolve, reject) {
+    resolve();
+  });
+
+  var results = [];
+  var q = p
+    .then(function () {
+      results.push("1-1");
+    })
+    .then(function () {
+      results.push("1-2");
+    })
+    .then(function () {
+      results.push("1-3");
+    });
+
+  var r = p
+    .then(function () {
+      results.push("2-1");
+    })
+    .then(function () {
+      results.push("2-2");
+    })
+    .then(function () {
+      results.push("2-3");
+    });
+
+  Promise.all([q, r]).then(
+    function () {
+      var match =
+        results[0] == "1-1" &&
+        results[1] == "2-1" &&
+        results[2] == "1-2" &&
+        results[3] == "2-2" &&
+        results[4] == "1-3" &&
+        results[5] == "2-3";
+      ok(match, "Chained promises should resolve asynchronously.");
+      runTest();
+    },
+    function () {
+      ok(false, "promiseWrapperAsyncResolution: One of the promises failed.");
+      runTest();
+    }
+  );
+}
+
+var tests = [
+  promiseResolve,
+  promiseReject,
+  promiseException,
+  promiseAsync_TimeoutResolveThen,
+  promiseAsync_ResolveTimeoutThen,
+  promiseAsync_ResolveThenTimeout,
+  promiseAsync_SyncXHRAndImportScripts,
+  promiseDoubleThen,
+  promiseThenException,
+  promiseThenCatchThen,
+  promiseRejectThenCatchThen,
+  promiseRejectThenCatchThen2,
+  promiseRejectThenCatchExceptionThen,
+  promiseThenCatchOrderingResolve,
+  promiseThenCatchOrderingReject,
+  promiseNestedPromise,
+  promiseNestedNestedPromise,
+  promiseWrongNestedPromise,
+  promiseLoop,
+  promiseStaticReject,
+  promiseStaticResolve,
+  promiseResolveNestedPromise,
+  promiseResolveNoArg,
+  promiseRejectNoArg,
+
+  promiseThenNoArg,
+  promiseThenUndefinedResolveFunction,
+  promiseThenNullResolveFunction,
+  promiseCatchNoArg,
+  promiseRejectNoHandler,
+
+  promiseUtilitiesDefined,
+
+  promiseAllArray,
+  promiseAllWaitsForAllPromises,
+  promiseAllRejectFails,
+
+  promiseRaceEmpty,
+  promiseRaceValuesArray,
+  promiseRacePromiseArray,
+  promiseRaceReject,
+  promiseRaceThrow,
+
+  promiseResolveArray,
+  promiseResolveThenable,
+  promiseResolvePromise,
+
+  promiseResolveThenableCleanStack,
+
+  promiseWrapperAsyncResolution,
+];
+
+function runTest() {
+  if (!tests.length) {
+    postMessage({ type: "finish" });
+    return;
+  }
+
+  var test = tests.shift();
+  test();
+}
+
+onmessage = function () {
+  runTest();
+};
diff --git a/dom/workers/test/recursion_worker.js b/dom/workers/test/recursion_worker.js
new file mode 100644
index 0000000000..84eb6d9740
--- /dev/null
+++ b/dom/workers/test/recursion_worker.js
@@ -0,0 +1,47 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+// This function should never run on a too much recursion error.
+onerror = function (event) {
+  postMessage(event.message);
+};
+
+// Pure JS recursion
+function recurse() {
+  recurse();
+}
+
+// JS -> C++ -> JS -> C++ recursion
+function recurse2() {
+  var xhr = new XMLHttpRequest();
+  xhr.onreadystatechange = function () {
+    xhr.open("GET", "nonexistent.file");
+  };
+  xhr.open("GET", "nonexistent.file");
+}
+
+var messageCount = 0;
+onmessage = function (event) {
+  switch (++messageCount) {
+    case 2:
+      recurse2();
+
+      // An exception thrown from an event handler like xhr.onreadystatechange
+      // should not leave an exception pending in the code that generated the
+      // event.
+      postMessage("Done");
+      return;
+
+    case 1:
+      recurse();
+      throw "Exception should have prevented us from getting here!";
+
+    default:
+      throw "Weird number of messages: " + messageCount;
+  }
+
+  // eslint-disable-next-line no-unreachable
+  throw "Impossible to get here!";
+};
diff --git a/dom/workers/test/recursiveOnerror_worker.js b/dom/workers/test/recursiveOnerror_worker.js
new file mode 100644
index 0000000000..35d2e2b80d
--- /dev/null
+++ b/dom/workers/test/recursiveOnerror_worker.js
@@ -0,0 +1,11 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+onerror = function (message, filename, lineno) {
+  throw new Error("2");
+};
+
+onmessage = function (event) {
+  throw new Error("1");
+};
diff --git a/dom/workers/test/redirect_to_foreign.sjs b/dom/workers/test/redirect_to_foreign.sjs
new file mode 100644
index 0000000000..06fd12052b
--- /dev/null
+++ b/dom/workers/test/redirect_to_foreign.sjs
@@ -0,0 +1,7 @@
+function handleRequest(request, response) {
+  response.setStatusLine("1.1", 302, "Found");
+  response.setHeader(
+    "Location",
+    "http://example.org/tests/dom/workers/test/foreign.js"
+  );
+}
diff --git a/dom/workers/test/referrer.sjs b/dom/workers/test/referrer.sjs
new file mode 100644
index 0000000000..f91c434c16
--- /dev/null
+++ b/dom/workers/test/referrer.sjs
@@ -0,0 +1,14 @@
+function handleRequest(request, response) {
+  if (request.queryString == "result") {
+    response.write(getState("referer"));
+    setState("referer", "INVALID");
+  } else if (request.queryString == "worker") {
+    response.setHeader("Content-Type", "text/javascript", false);
+    response.write("onmessage = function() { postMessage(42); }");
+    setState("referer", request.getHeader("referer"));
+  } else if (request.queryString == "import") {
+    setState("referer", request.getHeader("referer"));
+    response.setHeader("Content-Type", "text/javascript", false);
+    response.write("'hello world'");
+  }
+}
diff --git a/dom/workers/test/referrer_test_server.sjs b/dom/workers/test/referrer_test_server.sjs
new file mode 100644
index 0000000000..80bd2bee54
--- /dev/null
+++ b/dom/workers/test/referrer_test_server.sjs
@@ -0,0 +1,97 @@
+const SJS = "referrer_test_server.sjs?";
+const SHARED_KEY = SJS;
+
+var SAME_ORIGIN = "https://example.com/tests/dom/workers/test/" + SJS;
+var CROSS_ORIGIN = "https://test2.example.com/tests/dom/workers/test/" + SJS;
+var DOWNGRADE = "http://example.com/tests/dom/workers/test/" + SJS;
+
+function createUrl(aRequestType, aPolicy) {
+  var searchParams = new URLSearchParams();
+  searchParams.append("ACTION", "request-worker");
+  searchParams.append("Referrer-Policy", aPolicy);
+  searchParams.append("TYPE", aRequestType);
+
+  var url = SAME_ORIGIN;
+
+  if (aRequestType === "cross-origin") {
+    url = CROSS_ORIGIN;
+  } else if (aRequestType === "downgrade") {
+    url = DOWNGRADE;
+  }
+
+  return url + searchParams.toString();
+}
+function createWorker(aRequestType, aPolicy) {
+  return `
+    onmessage = function() {
+      fetch("${createUrl(aRequestType, aPolicy)}").then(function () {
+        postMessage(42);
+        close();
+      });
+    }
+  `;
+}
+
+function handleRequest(request, response) {
+  var params = new URLSearchParams(request.queryString);
+  var policy = params.get("Referrer-Policy");
+  var type = params.get("TYPE");
+  var action = params.get("ACTION");
+  response.setHeader("Content-Security-Policy", "default-src *", false);
+  response.setHeader("Access-Control-Allow-Origin", "*", false);
+
+  if (policy) {
+    response.setHeader("Referrer-Policy", policy, false);
+  }
+
+  if (action === "test") {
+    response.setHeader("Content-Type", "text/javascript", false);
+    response.write(createWorker(type, policy));
+    return;
+  }
+
+  if (action === "resetState") {
+    setSharedState(SHARED_KEY, "{}");
+    response.write("");
+    return;
+  }
+
+  if (action === "get-test-results") {
+    response.setHeader("Cache-Control", "no-cache", false);
+    response.setHeader("Content-Type", "text/plain", false);
+    response.write(getSharedState(SHARED_KEY));
+    return;
+  }
+
+  if (action === "request-worker") {
+    var result = getSharedState(SHARED_KEY);
+    result = result ? JSON.parse(result) : {};
+    var referrerLevel = "none";
+    var test = {};
+
+    if (request.hasHeader("Referer")) {
+      var referrer = request.getHeader("Referer");
+      if (referrer.indexOf("referrer_test_server") > 0) {
+        referrerLevel = "full";
+      } else if (referrer.indexOf("https://example.com") == 0) {
+        referrerLevel = "origin";
+      } else {
+        // this is never supposed to happen
+        referrerLevel = "other-origin";
+      }
+      test.referrer = referrer;
+    } else {
+      test.referrer = "";
+    }
+
+    test.policy = referrerLevel;
+    test.expected = policy;
+
+    // test id equals type + "-" + policy
+    // Ex: same-origin-default
+    result[type + "-" + policy] = test;
+    setSharedState(SHARED_KEY, JSON.stringify(result));
+
+    response.write("'hello world'");
+  }
+}
diff --git a/dom/workers/test/referrer_worker.html b/dom/workers/test/referrer_worker.html
new file mode 100644
index 0000000000..f4c6719912
--- /dev/null
+++ b/dom/workers/test/referrer_worker.html
@@ -0,0 +1,144 @@
+<!DOCTYPE html>
+<html>
+<head>
+</head>
+<body onload="tests.next();">
+<script type="text/javascript">
+const SJS = "referrer_test_server.sjs?";
+const BASE_URL = "https://example.com/tests/dom/workers/test/" + SJS;
+const GET_RESULT = BASE_URL + 'ACTION=get-test-results';
+const RESET_STATE = BASE_URL + 'ACTION=resetState';
+
+function ok(val, message) {
+  val = val ? "true" : "false";
+  window.parent.postMessage("SimpleTest.ok(" + val + ", '" + message + "');", "*");
+}
+
+function info(val) {
+  window.parent.postMessage("SimpleTest.info(" + val + ");", "*");
+}
+
+function is(a, b, message) {
+  ok(a == b, message);
+}
+
+function finish() {
+  // Let window.onerror have a chance to fire
+  setTimeout(function() {
+    setTimeout(function() {
+      tests.return();
+      window.parent.postMessage("SimpleTest.finish();", "*");
+    }, 0);
+  }, 0);
+}
+
+var testCases = {
+  'same-origin':  { 'Referrer-Policy' : { 'default' : 'full',
+                                          'origin' : 'origin',
+                                          'origin-when-cross-origin' : 'full',
+                                          'unsafe-url' : 'full',
+                                          'same-origin' : 'full',
+                                          'strict-origin' : 'origin',
+                                          'strict-origin-when-cross-origin' : 'full',
+                                          'no-referrer' : 'none',
+                                          'unsafe-url, no-referrer' : 'none',
+                                          'invalid' : 'full' }},
+
+  'cross-origin':  { 'Referrer-Policy' : { 'default' : 'origin',
+                                           'origin' : 'origin',
+                                           'origin-when-cross-origin' : 'origin',
+                                           'unsafe-url' : 'full',
+                                           'same-origin' : 'none',
+                                           'strict-origin' : 'origin',
+                                           'strict-origin-when-cross-origin' : 'origin',
+                                           'no-referrer' : 'none',
+                                           'unsafe-url, no-referrer' : 'none',
+                                           'invalid' : 'origin' }},
+
+  // Downgrading in worker is blocked entirely without unblock option
+  // https://bugzilla.mozilla.org/show_bug.cgi?id=1198078#c17
+  // Skip the downgrading test
+  /* 'downgrade':  { 'Referrer-Policy' : { 'default' : 'full',
+                                          'origin'  : 'full',
+                                          'origin-when-cross-origin"'  : 'full',
+                                          'unsafe-url'  : 'full',
+                                          'same-origin' : 'none',
+                                          'strict-origin' : 'none',
+                                          'strict-origin-when-cross-origin' : 'none',
+                                          'no-referrer'  : 'full',
+                                          'unsafe-url, no-referrer' : 'none',
+                                          'invalid'  : 'full' }}, */
+
+
+};
+
+var advance = function() { tests.next(); };
+
+/**
+ * helper to perform an XHR
+ * to do checkIndividualResults and resetState
+ */
+function doXHR(aUrl, onSuccess, onFail) {
+  var xhr = new XMLHttpRequest({mozSystem: true});
+  xhr.responseType = "json";
+  xhr.onload = function () {
+    onSuccess(xhr);
+  };
+  xhr.onerror = function () {
+    onFail(xhr);
+  };
+  xhr.open('GET', aUrl, true);
+  xhr.send(null);
+}
+
+
+function resetState() {
+  doXHR(RESET_STATE,
+    advance,
+    function(xhr) {
+      ok(false, "error in reset state");
+      finish();
+    });
+}
+
+function checkIndividualResults(aType, aPolicy, aExpected) {
+  var onload = xhr => {
+    var results = xhr.response;
+    dump(JSON.stringify(xhr.response));
+    // test id equals type + "-" + policy
+    // Ex: same-origin-default
+    var id = aType + "-" + aPolicy;
+    ok(id in results, id + " tests have to be performed.");
+    is(results[id].policy, aExpected, id + ' --- ' + results[id].policy + ' (' + results[id].referrer + ')');
+    advance();
+  };
+  var onerror = xhr => {
+    ok(false, "Can't get results from the counter server.");
+    finish();
+  };
+  doXHR(GET_RESULT, onload, onerror);
+}
+
+var tests = (function*() {
+
+  for (var type in testCases) {
+    for (var policy in testCases[type]['Referrer-Policy']) {
+      yield resetState();
+      var searchParams = new URLSearchParams();
+      searchParams.append("TYPE", type);
+      searchParams.append("ACTION", "test");
+      searchParams.append("Referrer-Policy", policy);
+      var worker = new Worker(BASE_URL + searchParams.toString());
+      worker.onmessage = function () {
+        advance();
+      };
+      yield worker.postMessage(42);
+      yield checkIndividualResults(type, policy, escape(testCases[type]['Referrer-Policy'][policy]));
+    }
+  }
+
+  finish();
+})();
+</script>
+</body>
+</html>
diff --git a/dom/workers/test/rvals_worker.js b/dom/workers/test/rvals_worker.js
new file mode 100644
index 0000000000..221d701443
--- /dev/null
+++ b/dom/workers/test/rvals_worker.js
@@ -0,0 +1,13 @@
+onmessage = function (evt) {
+  postMessage(postMessage("ignore") == undefined);
+
+  var id = setInterval(function () {}, 200);
+  postMessage(clearInterval(id) == undefined);
+
+  id = setTimeout(function () {}, 200);
+  postMessage(clearTimeout(id) == undefined);
+
+  postMessage(dump(42 + "\n") == undefined);
+
+  postMessage("finished");
+};
diff --git a/dom/workers/test/script_createFile.js b/dom/workers/test/script_createFile.js
new file mode 100644
index 0000000000..09f7be509e
--- /dev/null
+++ b/dom/workers/test/script_createFile.js
@@ -0,0 +1,43 @@
+/* eslint-env mozilla/chrome-script */
+
+// eslint-disable-next-line mozilla/reject-importGlobalProperties
+Cu.importGlobalProperties(["File"]);
+
+addMessageListener("file.open", function (e) {
+  var tmpFile = Cc["@mozilla.org/file/directory_service;1"]
+    .getService(Ci.nsIDirectoryService)
+    .QueryInterface(Ci.nsIProperties)
+    .get("TmpD", Ci.nsIFile);
+  tmpFile.append("file.txt");
+  tmpFile.createUnique(Ci.nsIFile.NORMAL_FILE_TYPE, 0o600);
+
+  File.createFromNsIFile(tmpFile).then(function (file) {
+    sendAsyncMessage("file.opened", { data: file });
+  });
+});
+
+addMessageListener("nonEmptyFile.open", function (e) {
+  var tmpFile = Cc["@mozilla.org/file/directory_service;1"]
+    .getService(Ci.nsIDirectoryService)
+    .QueryInterface(Ci.nsIProperties)
+    .get("TmpD", Ci.nsIFile);
+  tmpFile.append("file.txt");
+  tmpFile.createUnique(Ci.nsIFile.NORMAL_FILE_TYPE, 0o600);
+
+  var outStream = Cc[
+    "@mozilla.org/network/file-output-stream;1"
+  ].createInstance(Ci.nsIFileOutputStream);
+  outStream.init(
+    tmpFile,
+    0x02 | 0x08 | 0x20, // write, create, truncate
+    0o666,
+    0
+  );
+  var fileData = "Hello world!";
+  outStream.write(fileData, fileData.length);
+  outStream.close();
+
+  File.createFromNsIFile(tmpFile).then(function (file) {
+    sendAsyncMessage("nonEmptyFile.opened", { data: file });
+  });
+});
diff --git a/dom/workers/test/server_fetch_synthetic.sjs b/dom/workers/test/server_fetch_synthetic.sjs
new file mode 100644
index 0000000000..703b26d0d2
--- /dev/null
+++ b/dom/workers/test/server_fetch_synthetic.sjs
@@ -0,0 +1,50 @@
+const CC = Components.Constructor;
+const BinaryInputStream = CC(
+  "@mozilla.org/binaryinputstream;1",
+  "nsIBinaryInputStream",
+  "setInputStream"
+);
+
+function log(str) {
+  //dump(`SJS LOG: ${str}\n`);
+}
+
+/**
+ * Given a multipart/form-data encoded string that we know to have only a single
+ * part, return the contents of the part.  (MIME multipart encoding is too
+ * exciting to delve into.)
+ */
+function extractBlobFromMultipartFormData(text) {
+  const lines = text.split(/\r\n/g);
+  const firstBlank = lines.indexOf("");
+  const foo = lines.slice(firstBlank + 1, -2).join("\n");
+  return foo;
+}
+
+async function handleRequest(request, response) {
+  let blobContents = "";
+  if (request.method !== "POST") {
+  } else {
+    var body = new BinaryInputStream(request.bodyInputStream);
+
+    var avail;
+    var bytes = [];
+
+    while ((avail = body.available()) > 0) {
+      Array.prototype.push.apply(bytes, body.readByteArray(avail));
+    }
+    let requestBodyContents = String.fromCharCode.apply(null, bytes);
+    log(requestBodyContents);
+    blobContents = extractBlobFromMultipartFormData(requestBodyContents);
+  }
+
+  log("Setting Headers");
+  response.setHeader("Content-Type", "text/html", false);
+  response.setStatusLine(request.httpVersion, "200", "OK");
+  response.write(`<!DOCTYPE HTML><head><meta charset="utf-8"/></head><body>
+          <h1 id="url">${request.scheme}${request.host}${request.port}${request.path}</h1>
+          <div id="source">ServerJS</div>
+          <div id="blob">${blobContents}</div>
+        </body>`);
+  log("Done");
+}
diff --git a/dom/workers/test/sharedWorker_console.js b/dom/workers/test/sharedWorker_console.js
new file mode 100644
index 0000000000..d78fca94c6
--- /dev/null
+++ b/dom/workers/test/sharedWorker_console.js
@@ -0,0 +1,12 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+"use strict";
+
+onconnect = function (evt) {
+  console.profile("Hello profiling from a SharedWorker!");
+  console.log("Hello world from a SharedWorker!");
+  console.log("Here is a SAB", new SharedArrayBuffer(1024));
+  evt.ports[0].postMessage("ok!");
+};
diff --git a/dom/workers/test/sharedWorker_lifetime.js b/dom/workers/test/sharedWorker_lifetime.js
new file mode 100644
index 0000000000..594bd5833d
--- /dev/null
+++ b/dom/workers/test/sharedWorker_lifetime.js
@@ -0,0 +1,5 @@
+onconnect = function (e) {
+  setTimeout(function () {
+    e.ports[0].postMessage("Still alive!");
+  }, 500);
+};
diff --git a/dom/workers/test/sharedWorker_ports.js b/dom/workers/test/sharedWorker_ports.js
new file mode 100644
index 0000000000..6bdb5695db
--- /dev/null
+++ b/dom/workers/test/sharedWorker_ports.js
@@ -0,0 +1,30 @@
+var port;
+onconnect = function (evt) {
+  evt.source.postMessage({ type: "connected" });
+
+  if (!port) {
+    port = evt.source;
+    evt.source.onmessage = function (evtFromPort) {
+      port.postMessage({
+        type: "status",
+        test: "Port from the main-thread!" == evtFromPort.data,
+        msg: "The message is coming from the main-thread",
+      });
+      port.postMessage({
+        type: "status",
+        test: evtFromPort.ports.length == 1,
+        msg: "1 port transferred",
+      });
+
+      evtFromPort.ports[0].onmessage = function (evtFromPort2) {
+        port.postMessage({
+          type: "status",
+          test: evtFromPort2.data.type == "connected",
+          msg: "The original message received",
+        });
+        port.postMessage({ type: "finish" });
+        close();
+      };
+    };
+  }
+};
diff --git a/dom/workers/test/sharedWorker_privateBrowsing.js b/dom/workers/test/sharedWorker_privateBrowsing.js
new file mode 100644
index 0000000000..c16bd209f0
--- /dev/null
+++ b/dom/workers/test/sharedWorker_privateBrowsing.js
@@ -0,0 +1,4 @@
+var counter = 0;
+onconnect = function (evt) {
+  evt.ports[0].postMessage(++counter);
+};
diff --git a/dom/workers/test/sharedWorker_sharedWorker.js b/dom/workers/test/sharedWorker_sharedWorker.js
new file mode 100644
index 0000000000..a7f859919f
--- /dev/null
+++ b/dom/workers/test/sharedWorker_sharedWorker.js
@@ -0,0 +1,100 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+"use strict";
+
+if (!("self" in this)) {
+  throw new Error("No 'self' exists on SharedWorkerGlobalScope!");
+}
+if (this !== self) {
+  throw new Error("'self' not equal to global object!");
+}
+if (!(self instanceof SharedWorkerGlobalScope)) {
+  throw new Error("self not a SharedWorkerGlobalScope instance!");
+}
+
+var propsToCheck = [
+  "location",
+  "navigator",
+  "close",
+  "importScripts",
+  "setTimeout",
+  "clearTimeout",
+  "setInterval",
+  "clearInterval",
+  "dump",
+  "atob",
+  "btoa",
+];
+
+for (var index = 0; index < propsToCheck.length; index++) {
+  var prop = propsToCheck[index];
+  if (!(prop in self)) {
+    throw new Error("SharedWorkerGlobalScope has no '" + prop + "' property!");
+  }
+}
+
+onconnect = function (event) {
+  if (!("SharedWorkerGlobalScope" in self)) {
+    throw new Error("SharedWorkerGlobalScope should be visible!");
+  }
+  if (!(self instanceof SharedWorkerGlobalScope)) {
+    throw new Error("The global should be a SharedWorkerGlobalScope!");
+  }
+  if (!(self instanceof WorkerGlobalScope)) {
+    throw new Error("The global should be a WorkerGlobalScope!");
+  }
+  if ("DedicatedWorkerGlobalScope" in self) {
+    throw new Error("DedicatedWorkerGlobalScope should not be visible!");
+  }
+  if (!(event instanceof MessageEvent)) {
+    throw new Error("'connect' event is not a MessageEvent!");
+  }
+  if (!("ports" in event)) {
+    throw new Error("'connect' event doesn't have a 'ports' property!");
+  }
+  if (event.ports.length != 1) {
+    throw new Error(
+      "'connect' event has a 'ports' property with length '" +
+        event.ports.length +
+        "'!"
+    );
+  }
+  if (!event.ports[0]) {
+    throw new Error("'connect' event has a null 'ports[0]' property!");
+  }
+  if (!(event.ports[0] instanceof MessagePort)) {
+    throw new Error(
+      "'connect' event has a 'ports[0]' property that isn't a " + "MessagePort!"
+    );
+  }
+  if (!(event.ports[0] == event.source)) {
+    throw new Error("'connect' event source property is incorrect!");
+  }
+  if (event.data) {
+    throw new Error("'connect' event has data: " + event.data);
+  }
+
+  // Statement after return should trigger a warning, but NOT fire error events
+  // at us.
+  (function () {
+    return;
+    // eslint-disable-next-line no-unreachable
+    1;
+  });
+
+  event.ports[0].onmessage = function (msg) {
+    if (!(msg instanceof MessageEvent)) {
+      throw new Error("'message' event is not a MessageEvent!");
+    }
+    if (!("ports" in msg)) {
+      throw new Error("'message' event doesn't have a 'ports' property!");
+    }
+    if (msg.ports === null) {
+      throw new Error("'message' event has a null 'ports' property!");
+    }
+    msg.target.postMessage(msg.data);
+    throw new Error(msg.data);
+  };
+};
diff --git a/dom/workers/test/sharedWorker_thirdparty_frame.html b/dom/workers/test/sharedWorker_thirdparty_frame.html
new file mode 100644
index 0000000000..ebd78412a6
--- /dev/null
+++ b/dom/workers/test/sharedWorker_thirdparty_frame.html
@@ -0,0 +1,16 @@
+<!DOCTYPE HTML>
+<script>
+  let params = new URLSearchParams(document.location.search.substring(1));
+  let name = params.get('name');
+  try {
+    let worker = new SharedWorker('sharedWorker_sharedWorker.js',
+                                  { name });
+    worker.port.addEventListener('message', evt => {
+      parent.postMessage( { name, result: 'allowed' }, '*');
+    }, { once: true });
+    worker.port.start();
+    worker.port.postMessage('ping');
+  } catch(e) {
+    parent.postMessage({ name, result: 'blocked' }, '*');
+  }
+</script>
diff --git a/dom/workers/test/sharedWorker_thirdparty_window.html b/dom/workers/test/sharedWorker_thirdparty_window.html
new file mode 100644
index 0000000000..f5f01066c2
--- /dev/null
+++ b/dom/workers/test/sharedWorker_thirdparty_window.html
@@ -0,0 +1,26 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test for SharedWorker in 3rd Party Iframes</title>
+</head>
+<body>
+  <script>
+
+  let url = new URL(window.location);
+
+  let frame = document.createElement('iframe');
+  frame.src =
+    'http://example.org/tests/dom/workers/test/sharedWorker_thirdparty_frame.html?name=' + url.searchParams.get('name');
+  document.body.appendChild(frame);
+  window.addEventListener('message', evt => {
+    frame.remove();
+    opener.postMessage(evt.data, "*");
+  }, {once: true});
+
+  </script>
+</body>
+</html>
diff --git a/dom/workers/test/simpleThread_worker.js b/dom/workers/test/simpleThread_worker.js
new file mode 100644
index 0000000000..9d6fb30f2f
--- /dev/null
+++ b/dom/workers/test/simpleThread_worker.js
@@ -0,0 +1,52 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+"use strict";
+
+function messageListener(event) {
+  var exception;
+  try {
+    event.bubbles = true;
+  } catch (e) {
+    exception = e;
+  }
+
+  if (!(exception instanceof TypeError)) {
+    throw exception;
+  }
+
+  switch (event.data) {
+    case "no-op":
+      break;
+    case "components":
+      postMessage(Components.toString());
+      break;
+    case "start":
+      for (var i = 0; i < 1000; i++) {}
+      postMessage("started");
+      break;
+    case "stop":
+      self.postMessage("no-op");
+      postMessage("stopped");
+      self.removeEventListener("message", messageListener);
+      break;
+    default:
+      throw "Bad message: " + event.data;
+  }
+}
+
+if (!("DedicatedWorkerGlobalScope" in self)) {
+  throw new Error("DedicatedWorkerGlobalScope should be visible!");
+}
+if (!(self instanceof DedicatedWorkerGlobalScope)) {
+  throw new Error("The global should be a SharedWorkerGlobalScope!");
+}
+if (!(self instanceof WorkerGlobalScope)) {
+  throw new Error("The global should be a WorkerGlobalScope!");
+}
+if ("SharedWorkerGlobalScope" in self) {
+  throw new Error("SharedWorkerGlobalScope should not be visible!");
+}
+
+addEventListener("message", { handleEvent: messageListener });
diff --git a/dom/workers/test/sourcemap_header.js b/dom/workers/test/sourcemap_header.js
new file mode 100644
index 0000000000..9f10b35ed9
--- /dev/null
+++ b/dom/workers/test/sourcemap_header.js
@@ -0,0 +1,65 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+"use strict";
+
+(async () => {
+  SimpleTest.waitForExplicitFinish();
+
+  const HTTP_BASE_URL = "http://mochi.test:8888/tests/dom/workers/test/";
+  const IFRAME_URL = HTTP_BASE_URL + "sourcemap_header_iframe.html";
+  const WORKER_URL = HTTP_BASE_URL + "sourcemap_header_worker.js";
+  const DEBUGGER_URL = BASE_URL + "sourcemap_header_debugger.js";
+
+  const workerFrame = document.getElementById("worker-frame");
+  ok(workerFrame, "has frame");
+
+  await new Promise(r => {
+    workerFrame.onload = r;
+    workerFrame.src = IFRAME_URL;
+  });
+
+  info("Start worker and watch for registration");
+  const workerLoadedChannel = new MessageChannel();
+
+  const loadDebuggerAndWorker = Promise.all([
+    waitForRegister(WORKER_URL, DEBUGGER_URL),
+    // We need to wait for the worker to load so a Debugger.Source will be
+    // guaranteed to exist.
+    new Promise(r => {
+      workerLoadedChannel.port1.onmessage = r;
+    }),
+  ]);
+  workerFrame.contentWindow.postMessage(WORKER_URL, "*", [
+    workerLoadedChannel.port2,
+  ]);
+  const [dbg] = await loadDebuggerAndWorker;
+
+  // Wait for the debugger server to reply with the sourceMapURL of the
+  // loaded worker scripts.
+  info("Querying for the sourceMapURL of the worker script");
+  const urls = await new Promise(res => {
+    dbg.addListener({
+      onMessage(msg) {
+        const data = JSON.parse(msg);
+        if (data.type !== "response-sourceMapURL") {
+          return;
+        }
+        dbg.removeListener(this);
+        res(data.value);
+      },
+    });
+    dbg.postMessage(
+      JSON.stringify({
+        type: "request-sourceMapURL",
+        url: WORKER_URL,
+      })
+    );
+  });
+
+  ok(Array.isArray(urls) && urls.length === 1, "has a single source actor");
+  is(urls[0], "worker-header.js.map", "has the right map URL");
+
+  SimpleTest.finish();
+})();
diff --git a/dom/workers/test/sourcemap_header_debugger.js b/dom/workers/test/sourcemap_header_debugger.js
new file mode 100644
index 0000000000..bb8ed0c1f7
--- /dev/null
+++ b/dom/workers/test/sourcemap_header_debugger.js
@@ -0,0 +1,29 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+"use strict";
+
+addEventListener("message", function (event) {
+  let data;
+  try {
+    data = JSON.parse(event.data);
+  } catch {}
+
+  switch (data.type) {
+    case "request-sourceMapURL":
+      const dbg = new Debugger(global);
+      const sourceMapURLs = dbg
+        .findSources()
+        .filter(source => source.url === data.url)
+        .map(source => source.sourceMapURL);
+
+      postMessage(
+        JSON.stringify({
+          type: "response-sourceMapURL",
+          value: sourceMapURLs,
+        })
+      );
+      break;
+  }
+});
diff --git a/dom/workers/test/sourcemap_header_iframe.html b/dom/workers/test/sourcemap_header_iframe.html
new file mode 100644
index 0000000000..82278f41a1
--- /dev/null
+++ b/dom/workers/test/sourcemap_header_iframe.html
@@ -0,0 +1,19 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<head>
+  <script>
+    self.onmessage = (msg) => {
+      const workerLoadedPort = msg.ports[0];
+      const worker = new Worker(msg.data);
+      worker.onmessage = () => {
+        workerLoadedPort.postMessage("worker loaded");
+      };
+    };
+  </script>
+</head>
+<body></body>
+</html>
diff --git a/dom/workers/test/sourcemap_header_worker.js b/dom/workers/test/sourcemap_header_worker.js
new file mode 100644
index 0000000000..ca094686d3
--- /dev/null
+++ b/dom/workers/test/sourcemap_header_worker.js
@@ -0,0 +1,8 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+// Send a message pack so the test knows that the source has loaded before
+// it tries to search for the Debugger.Source.
+postMessage("loaded");
diff --git a/dom/workers/test/sourcemap_header_worker.js^headers^ b/dom/workers/test/sourcemap_header_worker.js^headers^
new file mode 100644
index 0000000000..833288ef02
--- /dev/null
+++ b/dom/workers/test/sourcemap_header_worker.js^headers^
@@ -0,0 +1 @@
+X-SourceMap: worker-header.js.map
diff --git a/dom/workers/test/suspend_blank.html b/dom/workers/test/suspend_blank.html
new file mode 100644
index 0000000000..b6dd0075e6
--- /dev/null
+++ b/dom/workers/test/suspend_blank.html
@@ -0,0 +1,23 @@
+<!DOCTYPE HTML>
+<script>
+  var interval;
+  var finish = false;
+  var bc = new BroadcastChannel("suspendBlank");
+  bc.onmessage = (msgEvent) => {
+    var msg = msgEvent.data;
+    var command = msg.command;
+    if (command == "navigateBack") {
+      finish = true;
+      history.back();
+    }
+  }
+  window.onpagehide = () => {
+    bc.postMessage({command: "pagehide"});
+    if (finish) {
+      bc.close();
+    }
+  }
+  window.onload = () => {
+    bc.postMessage({command: "loaded"});
+  }
+</script>
diff --git a/dom/workers/test/suspend_window.html b/dom/workers/test/suspend_window.html
new file mode 100644
index 0000000000..9bede3aaa6
--- /dev/null
+++ b/dom/workers/test/suspend_window.html
@@ -0,0 +1,82 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<head>
+  <meta charset="utf-8">
+  <title>Test for DOM Worker Threads Suspending</title>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<pre id="test">
+<div id="output"></div>
+<script class="testbody" type="text/javascript">
+
+  var worker;
+  var finish = false;
+  var bc = new BroadcastChannel("suspendWindow");
+  bc.onmessage = (msgEvent) => {
+    var msg = msgEvent.data;
+    var command = msg.command;
+    if (command == "startWorker") {
+      startWorker();
+    } else if (command == "navigate") {
+      window.location = "suspend_blank.html";
+    } else if (command == "finish") {
+      finish = true;
+      terminateWorker();
+      bc.postMessage({command: "finished"});
+      bc.close();
+      window.close();
+    }
+  }
+
+  function messageCallback(data) {
+    if (finish) {
+      return;
+    }
+    bc.postMessage({command: "messageCallback", data});
+  }
+
+  function errorCallback(msg) {
+    if (finish) {
+      return;
+    }
+    bc.postMessage({command: "errorCallback", data: msg});
+  }
+
+  var output = document.getElementById("output");
+
+  function terminateWorker() {
+    if (worker) {
+      worker.postMessage("stop");
+      worker = null;
+    }
+  }
+
+  function startWorker() {
+    var lastData;
+    worker = new Worker("suspend_worker.js");
+
+    worker.onmessage = function(event) {
+      output.textContent = (lastData ? lastData + " -> " : "") + event.data;
+      lastData = event.data;
+      messageCallback(event.data);
+    };
+
+    worker.onerror = function(event) {
+      this.terminate();
+      errorCallback(event.message);
+    };
+  }
+
+  window.onload = () => {
+    bc.postMessage({command: "loaded"});
+  }
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/suspend_worker.js b/dom/workers/test/suspend_worker.js
new file mode 100644
index 0000000000..e024972737
--- /dev/null
+++ b/dom/workers/test/suspend_worker.js
@@ -0,0 +1,13 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+var counter = 0;
+
+var interval = setInterval(function () {
+  postMessage(++counter);
+}, 100);
+
+onmessage = function (event) {
+  clearInterval(interval);
+};
diff --git a/dom/workers/test/terminate_worker.js b/dom/workers/test/terminate_worker.js
new file mode 100644
index 0000000000..7b9984e869
--- /dev/null
+++ b/dom/workers/test/terminate_worker.js
@@ -0,0 +1,11 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+onmessage = function (event) {
+  throw "No messages should reach me!";
+};
+
+setInterval(function () {
+  postMessage("Still alive!");
+}, 100);
diff --git a/dom/workers/test/test_404.html b/dom/workers/test/test_404.html
new file mode 100644
index 0000000000..59ab691e02
--- /dev/null
+++ b/dom/workers/test/test_404.html
@@ -0,0 +1,39 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<!--
+Tests of DOM Worker Threads
+-->
+<head>
+  <title>Test for DOM Worker Threads</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<pre id="test">
+<script class="testbody" type="text/javascript">
+
+  var worker = new Worker("nonexistent_worker.js");
+
+  worker.onmessage = function(event) {
+    ok(false, "Shouldn't ever get a message!");
+    SimpleTest.finish();
+  }
+
+  worker.onerror = function(event) {
+    is(event.target, worker);
+    event.preventDefault();
+    SimpleTest.finish();
+  };
+
+  worker.postMessage("dummy");
+
+  SimpleTest.waitForExplicitFinish();
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_WorkerDebugger.initialize.xhtml b/dom/workers/test/test_WorkerDebugger.initialize.xhtml
new file mode 100644
index 0000000000..9e7ec2e9a6
--- /dev/null
+++ b/dom/workers/test/test_WorkerDebugger.initialize.xhtml
@@ -0,0 +1,56 @@
+<?xml version="1.0"?>
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<window title="Test for WorkerDebugger.initialize"
+        xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
+        onload="test();">
+
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"/>
+  <script src="chrome://mochikit/content/tests/SimpleTest/EventUtils.js"/>
+  <script type="application/javascript" src="dom_worker_helper.js"/>
+
+  <script type="application/javascript">
+  <![CDATA[
+
+    const WORKER_URL = "WorkerDebugger.initialize_worker.js";
+    const CHILD_WORKER_URL = "WorkerDebugger.initialize_childWorker.js";
+    const DEBUGGER_URL = BASE_URL + "WorkerDebugger.initialize_debugger.js";
+
+    function test() {
+      (async function() {
+        SimpleTest.waitForExplicitFinish();
+
+        info("Create a worker that creates a child worker, wait for their " +
+             "debuggers to be registered, and initialize them.");
+        let promise = waitForMultiple([
+          waitForRegister(WORKER_URL, DEBUGGER_URL),
+          waitForRegister(CHILD_WORKER_URL, DEBUGGER_URL)
+        ]);
+        let worker = new Worker(WORKER_URL);
+        await promise;
+
+        info("Check that the debuggers are initialized before the workers " +
+             "start running.");
+        await waitForMultiple([
+          waitForWorkerMessage(worker, "debugger"),
+          waitForWorkerMessage(worker, "worker"),
+          waitForWorkerMessage(worker, "child:debugger"),
+          waitForWorkerMessage(worker, "child:worker")
+        ]);
+
+        SimpleTest.finish();
+      })();
+    }
+
+  ]]>
+  </script>
+
+  <body xmlns="http://www.w3.org/1999/xhtml">
+    <p id="display"></p>
+    <div id="content" style="display:none;"></div>
+    <pre id="test"></pre>
+  </body>
+  <label id="test-result"/>
+</window>
diff --git a/dom/workers/test/test_WorkerDebugger.postMessage.xhtml b/dom/workers/test/test_WorkerDebugger.postMessage.xhtml
new file mode 100644
index 0000000000..58e15b3a05
--- /dev/null
+++ b/dom/workers/test/test_WorkerDebugger.postMessage.xhtml
@@ -0,0 +1,59 @@
+<?xml version="1.0"?>
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<window title="Test for WorkerDebugger.postMessage"
+        xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
+        onload="test();">
+
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"/>
+  <script src="chrome://mochikit/content/tests/SimpleTest/EventUtils.js"/>
+  <script type="application/javascript" src="dom_worker_helper.js"/>
+
+  <script type="application/javascript">
+  <![CDATA[
+
+    const WORKER_URL = "WorkerDebugger.postMessage_worker.js";
+    const CHILD_WORKER_URL = "WorkerDebugger.postMessage_childWorker.js";
+    const DEBUGGER_URL = BASE_URL + "WorkerDebugger.postMessage_debugger.js";
+
+    function test() {
+      (async function() {
+        SimpleTest.waitForExplicitFinish();
+
+        info("Create a worker that creates a child worker, wait for their " +
+             "debuggers to be registered, and initialize them.");
+        let promise = waitForMultiple([
+          waitForRegister(WORKER_URL, DEBUGGER_URL),
+          waitForRegister(CHILD_WORKER_URL, DEBUGGER_URL)
+        ]);
+        let worker = new Worker(WORKER_URL);
+        let [dbg, childDbg] = await promise;
+
+        info("Send a request to the worker debugger. This should cause the " +
+             "the worker debugger to send a response.");
+        promise = waitForDebuggerMessage(dbg, "pong");
+        dbg.postMessage("ping");
+        await promise;
+
+        info("Send a request to the child worker debugger. This should cause " +
+             "the child worker debugger to send a response.");
+        promise = waitForDebuggerMessage(childDbg, "pong");
+        childDbg.postMessage("ping");
+        await promise;
+
+        SimpleTest.finish();
+      })();
+    }
+
+  ]]>
+  </script>
+
+  <body xmlns="http://www.w3.org/1999/xhtml">
+    <p id="display"></p>
+    <div id="content" style="display:none;"></div>
+    <pre id="test"></pre>
+  </body>
+  <label id="test-result"/>
+</window>
diff --git a/dom/workers/test/test_WorkerDebugger.xhtml b/dom/workers/test/test_WorkerDebugger.xhtml
new file mode 100644
index 0000000000..d0810b851a
--- /dev/null
+++ b/dom/workers/test/test_WorkerDebugger.xhtml
@@ -0,0 +1,145 @@
+<?xml version="1.0"?>
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<window title="Test for WorkerDebugger"
+        xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
+
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"/>
+  <script src="chrome://mochikit/content/tests/SimpleTest/EventUtils.js"/>
+  <script type="application/javascript" src="dom_worker_helper.js"/>
+
+  <script type="application/javascript">
+  <![CDATA[
+
+    const WORKER_URL = "WorkerDebugger_worker.js";
+    const CHILD_WORKER_URL = "WorkerDebugger_childWorker.js";
+    const SHARED_WORKER_URL = "WorkerDebugger_sharedWorker.js";
+
+    add_task(
+      async function runTest() {
+        info("Create a top-level chrome worker that creates a non-top-level " +
+             "content worker and wait for their debuggers to be registered.");
+        let promise = waitForMultiple([
+          waitForRegister(WORKER_URL),
+          waitForRegister(CHILD_WORKER_URL)
+        ]);
+        worker = new ChromeWorker(WORKER_URL);
+        let [dbg, childDbg] = await promise;
+
+        info("Check that the top-level chrome worker debugger has the " +
+             "correct properties.");
+        is(dbg.isChrome, true,
+           "Chrome worker debugger should be chrome.");
+        is(dbg.parent, null,
+           "Top-level debugger should not have parent.");
+        is(dbg.type, Ci.nsIWorkerDebugger.TYPE_DEDICATED,
+           "Chrome worker debugger should be dedicated.");
+        is(dbg.window, window,
+           "Top-level dedicated worker debugger should have window.");
+
+        info("Check that the non-top-level content worker debugger has the " +
+             "correct properties.");
+        is(childDbg.isChrome, false,
+           "Content worker debugger should be content.");
+        is(childDbg.parent, dbg,
+           "Non-top-level worker debugger should have parent.");
+        is(childDbg.type, Ci.nsIWorkerDebugger.TYPE_DEDICATED,
+           "Content worker debugger should be dedicated.");
+        is(childDbg.window, window,
+           "Non-top-level worker debugger should have window.");
+
+        info("Terminate the top-level chrome worker and the non-top-level " +
+             "content worker, and wait for their debuggers to be " +
+             "unregistered and closed.");
+        promise = waitForMultiple([
+          waitForUnregister(CHILD_WORKER_URL),
+          waitForDebuggerClose(childDbg),
+          waitForUnregister(WORKER_URL),
+          waitForDebuggerClose(dbg),
+        ]);
+        worker.terminate();
+        await promise;
+
+        info("Create a shared worker and wait for its debugger to be " +
+             "registered");
+        promise = waitForRegister(SHARED_WORKER_URL);
+        worker = new SharedWorker(SHARED_WORKER_URL);
+        let sharedDbg = await promise;
+
+        info("Check that the shared worker debugger has the correct " +
+             "properties.");
+        is(sharedDbg.isChrome, false,
+           "Shared worker debugger should be content.");
+        is(sharedDbg.parent, null,
+           "Shared worker debugger should not have parent.");
+        is(sharedDbg.type, Ci.nsIWorkerDebugger.TYPE_SHARED,
+           "Shared worker debugger should be shared.");
+        is(sharedDbg.window, null,
+           "Shared worker debugger should not have window.");
+
+        info("Create a shared worker with the same URL and check that its " +
+             "debugger is not registered again.");
+        let listener = {
+          onRegistered () {
+            ok(false,
+               "Shared worker debugger should not be registered again.");
+          },
+        };
+        wdm.addListener(listener);
+
+        let secondWorker = new SharedWorker(SHARED_WORKER_URL);
+
+        info("Send a message to the shared worker to tell it to close " +
+             "itself, and wait for its debugger to be closed.");
+        promise = waitForMultiple([
+          waitForUnregister(SHARED_WORKER_URL),
+          waitForDebuggerClose(sharedDbg)
+        ]);
+        secondWorker.port.start();
+        secondWorker.port.postMessage("close");
+        await promise;
+        worker = null;
+        secondWorker = null;
+
+        info("Create a SharedWorker again for the infinite loop test.")
+        promise = waitForRegister(SHARED_WORKER_URL);
+        // Give it an explicit name so we don't reuse the above SharedWorker.
+        worker = new SharedWorker(SHARED_WORKER_URL, "loopy");
+        sharedDbg = await promise;
+
+        info("Send a message to the shared worker to tell it to close " +
+             "itself, then loop forever, and wait for its debugger to be closed.");
+        promise = waitForMultiple([
+          waitForUnregister(SHARED_WORKER_URL),
+          waitForDebuggerClose(sharedDbg)
+        ]);
+
+        // When the closing process begins, we schedule a timer to terminate
+        // the worker in case it's in an infinite loop, which is exactly what
+        // we do in this test.  The default delay is 30 seconds.  This test
+        // previously waited 15 seconds for reasons that were poorly justified.
+        // We now set it to 100ms because we just want to make sure that the
+        // timeout mechanism to force cancellation from the parent properly
+        // works (as long as the parent thread isn't blocked).
+        await SpecialPowers.pushPrefEnv({"set": [[ "dom.worker.canceling.timeoutMilliseconds", 100 ]]});
+
+        worker.port.start();
+        worker.port.postMessage("close_loop");
+        await promise;
+
+        wdm.removeListener(listener);
+      }
+    );
+
+  ]]>
+  </script>
+
+  <body xmlns="http://www.w3.org/1999/xhtml">
+    <p id="display"></p>
+    <div id="content" style="display:none;"></div>
+    <pre id="test"></pre>
+  </body>
+  <label id="test-result"/>
+</window>
diff --git a/dom/workers/test/test_WorkerDebuggerGlobalScope.createSandbox.xhtml b/dom/workers/test/test_WorkerDebuggerGlobalScope.createSandbox.xhtml
new file mode 100644
index 0000000000..89114f5e49
--- /dev/null
+++ b/dom/workers/test/test_WorkerDebuggerGlobalScope.createSandbox.xhtml
@@ -0,0 +1,49 @@
+<?xml version="1.0"?>
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<window title="Test for WorkerDebuggerGlobalScope.createSandbox"
+        xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
+        onload="test();">
+
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"/>
+  <script src="chrome://mochikit/content/tests/SimpleTest/EventUtils.js"/>
+  <script type="application/javascript" src="dom_worker_helper.js"/>
+
+  <script type="application/javascript">
+  <![CDATA[
+
+    const WORKER_URL = "WorkerDebuggerGlobalScope.createSandbox_worker.js";
+    const DEBUGGER_URL = BASE_URL + "WorkerDebuggerGlobalScope.createSandbox_debugger.js";
+
+    function test() {
+      (async function() {
+        SimpleTest.waitForExplicitFinish();
+
+        info("Create a worker, wait for its debugger to be registered, and " +
+             "initialize it.");
+        let promise = waitForRegister(WORKER_URL, DEBUGGER_URL);
+        let worker = new Worker(WORKER_URL);
+        let dbg = await promise;
+
+        info("Send a request to the worker debugger. This should cause the " +
+             "worker debugger to send a response from within a sandbox.");
+        promise = waitForDebuggerMessage(dbg, "pong");
+        dbg.postMessage("ping");
+        await promise;
+
+        SimpleTest.finish();
+      })();
+    }
+
+  ]]>
+  </script>
+
+  <body xmlns="http://www.w3.org/1999/xhtml">
+    <p id="display"></p>
+    <div id="content" style="display:none;"></div>
+    <pre id="test"></pre>
+  </body>
+  <label id="test-result"/>
+</window>
diff --git a/dom/workers/test/test_WorkerDebuggerGlobalScope.enterEventLoop.xhtml b/dom/workers/test/test_WorkerDebuggerGlobalScope.enterEventLoop.xhtml
new file mode 100644
index 0000000000..d5cff95d39
--- /dev/null
+++ b/dom/workers/test/test_WorkerDebuggerGlobalScope.enterEventLoop.xhtml
@@ -0,0 +1,124 @@
+<?xml version="1.0"?>
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<window title="Test for WorkerDebuggerGlobalScope.enterEventLoop"
+        xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
+        onload="test();">
+
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"/>
+  <script src="chrome://mochikit/content/tests/SimpleTest/EventUtils.js"/>
+  <script type="application/javascript" src="dom_worker_helper.js"/>
+
+  <script type="application/javascript">
+  <![CDATA[
+
+    const WORKER_URL = "WorkerDebuggerGlobalScope.enterEventLoop_worker.js";
+    const CHILD_WORKER_URL = "WorkerDebuggerGlobalScope.enterEventLoop_childWorker.js";
+    const DEBUGGER_URL = BASE_URL + "WorkerDebuggerGlobalScope.enterEventLoop_debugger.js";
+
+    function test() {
+      (async function() {
+        SimpleTest.waitForExplicitFinish();
+
+        info("Create a worker that creates a child worker, wait for their " +
+             "debuggers to be registered, and initialize them.");
+        let promise = waitForMultiple([
+          waitForRegister(WORKER_URL, DEBUGGER_URL),
+          waitForRegister(CHILD_WORKER_URL, DEBUGGER_URL)
+        ]);
+        let worker = new Worker(WORKER_URL);
+        let [dbg, childDbg] = await promise;
+
+        info("Send a request to the child worker. This should cause the " +
+             "child worker debugger to enter a nested event loop.");
+        promise = waitForDebuggerMessage(childDbg, "paused");
+        worker.postMessage("child:ping");
+        await promise;
+
+        info("Send a request to the child worker debugger. This should cause " +
+             "the child worker debugger to enter a second nested event loop.");
+        promise = waitForDebuggerMessage(childDbg, "paused");
+        childDbg.postMessage("eval");
+        await promise;
+
+        info("Send a request to the child worker debugger. This should cause " +
+             "the child worker debugger to leave its second nested event " +
+             "loop. The child worker debugger should not send a response " +
+             "for its previous request until after it has left the nested " +
+             "event loop.");
+        promise = waitForMultiple([
+          waitForDebuggerMessage(childDbg, "resumed"),
+          waitForDebuggerMessage(childDbg, "evalled")
+        ]);
+        childDbg.postMessage("resume");
+        await promise;
+
+        info("Send a request to the child worker debugger. This should cause " +
+             "the child worker debugger to leave its first nested event loop." +
+             "The child worker should not send a response for its earlier " +
+             "request until after the child worker debugger has left the " +
+             "nested event loop.");
+        promise = waitForMultiple([
+          waitForDebuggerMessage(childDbg, "resumed"),
+          waitForWorkerMessage(worker, "child:pong")
+        ]);
+        childDbg.postMessage("resume");
+        await promise;
+
+        info("Send a request to the worker. This should cause the worker " +
+             "debugger to enter a nested event loop.");
+        promise = waitForDebuggerMessage(dbg, "paused");
+        worker.postMessage("ping");
+        await promise;
+
+        info("Terminate the worker. This should not cause the worker " +
+             "debugger to terminate as well.");
+        worker.terminate();
+
+        worker.onmessage = function () {
+          ok(false, "Worker should have been terminated.");
+        };
+
+        info("Send a request to the worker debugger. This should cause the " +
+             "worker debugger to enter a second nested event loop.");
+        promise = waitForDebuggerMessage(dbg, "paused");
+        dbg.postMessage("eval");
+        await promise;
+
+        info("Send a request to the worker debugger. This should cause the " +
+             "worker debugger to leave its second nested event loop. The " +
+             "worker debugger should not send a response for the previous " +
+             "request until after leaving the nested event loop.");
+        promise = waitForMultiple([
+          waitForDebuggerMessage(dbg, "resumed"),
+          waitForDebuggerMessage(dbg, "evalled")
+        ]);
+        dbg.postMessage("resume");
+        await promise;
+
+        info("Send a request to the worker debugger. This should cause the " +
+             "worker debugger to leave its first nested event loop. The " +
+             "worker should not send a response for its earlier request, " +
+             "since it has been terminated.");
+        promise = waitForMultiple([
+          waitForDebuggerMessage(dbg, "resumed"),
+        ]);
+        dbg.postMessage("resume");
+        await promise;
+
+        SimpleTest.finish();
+      })();
+    }
+
+  ]]>
+  </script>
+
+  <body xmlns="http://www.w3.org/1999/xhtml">
+    <p id="display"></p>
+    <div id="content" style="display:none;"></div>
+    <pre id="test"></pre>
+  </body>
+  <label id="test-result"/>
+</window>
diff --git a/dom/workers/test/test_WorkerDebuggerGlobalScope.reportError.xhtml b/dom/workers/test/test_WorkerDebuggerGlobalScope.reportError.xhtml
new file mode 100644
index 0000000000..20e731c1cf
--- /dev/null
+++ b/dom/workers/test/test_WorkerDebuggerGlobalScope.reportError.xhtml
@@ -0,0 +1,95 @@
+<?xml version="1.0"?>
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<window title="Test for WorkerDebuggerGlobalScope.reportError"
+        xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
+        onload="test();">
+
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"/>
+  <script src="chrome://mochikit/content/tests/SimpleTest/EventUtils.js"/>
+  <script type="application/javascript" src="dom_worker_helper.js"/>
+
+  <script type="application/javascript">
+  <![CDATA[
+
+    const WORKER_URL = "WorkerDebuggerGlobalScope.reportError_worker.js";
+    const CHILD_WORKER_URL = "WorkerDebuggerGlobalScope.reportError_childWorker.js";
+    const DEBUGGER_URL = BASE_URL + "WorkerDebuggerGlobalScope.reportError_debugger.js";
+
+    function test() {
+      (async function() {
+        SimpleTest.waitForExplicitFinish();
+
+        info("Create a worker that creates a child worker, wait for their " +
+             "debuggers to be registered, and initialize them.");
+        let promise = waitForMultiple([
+          waitForRegister(WORKER_URL, DEBUGGER_URL),
+          waitForRegister(CHILD_WORKER_URL, DEBUGGER_URL)
+        ]);
+        let worker = new Worker(WORKER_URL);
+        let [dbg, childDbg] = await promise;
+
+        worker.onmessage = function () {
+          ok(false, "Debugger error events should not be fired at workers.");
+        };
+
+        info("Send a request to the worker debugger. This should cause the " +
+             "worker debugger to report an error.");
+        promise = waitForDebuggerError(dbg);
+        dbg.postMessage("report");
+        let error = await promise;
+        is(error.fileName, DEBUGGER_URL,
+           "fileName should be name of file from which error is reported.");
+        is(error.lineNumber, 6,
+           "lineNumber should be line number from which error is reported.");
+        is(error.message, "reported", "message should be reported.");
+
+        info("Send a request to the worker debugger. This should cause the " +
+             "worker debugger to throw an error.");
+        promise = waitForDebuggerError(dbg);
+        dbg.postMessage("throw");
+        error = await promise;
+        is(error.fileName, DEBUGGER_URL,
+           "fileName should be name of file from which error is thrown");
+        is(error.lineNumber, 9,
+           "lineNumber should be line number from which error is thrown");
+        is(error.message, "Error: thrown", "message should be Error: thrown");
+
+        info("Send a reqeust to the child worker debugger. This should cause " +
+             "the child worker debugger to report an error.");
+        promise = waitForDebuggerError(childDbg);
+        childDbg.postMessage("report");
+        error = await promise;
+        is(error.fileName, DEBUGGER_URL,
+           "fileName should be name of file from which error is reported.");
+        is(error.lineNumber, 6,
+           "lineNumber should be line number from which error is reported.");
+        is(error.message, "reported", "message should be reported.");
+
+        info("Send a message to the child worker debugger. This should cause " +
+             "the child worker debugger to throw an error.");
+        promise = waitForDebuggerError(childDbg);
+        childDbg.postMessage("throw");
+        error = await promise;
+        is(error.fileName, DEBUGGER_URL,
+           "fileName should be name of file from which error is thrown");
+        is(error.lineNumber, 9,
+           "lineNumber should be line number from which error is thrown");
+        is(error.message, "Error: thrown", "message should be Error: thrown");
+
+        SimpleTest.finish();
+      })();
+    }
+
+  ]]>
+  </script>
+
+  <body xmlns="http://www.w3.org/1999/xhtml">
+    <p id="display"></p>
+    <div id="content" style="display:none;"></div>
+    <pre id="test"></pre>
+  </body>
+  <label id="test-result"/>
+</window>
diff --git a/dom/workers/test/test_WorkerDebuggerGlobalScope.setImmediate.xhtml b/dom/workers/test/test_WorkerDebuggerGlobalScope.setImmediate.xhtml
new file mode 100644
index 0000000000..4b09f01708
--- /dev/null
+++ b/dom/workers/test/test_WorkerDebuggerGlobalScope.setImmediate.xhtml
@@ -0,0 +1,52 @@
+<?xml version="1.0"?>
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<window title="Test for WorkerDebuggerGlobalScope.setImmediate"
+        xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
+        onload="test();">
+
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"/>
+  <script src="chrome://mochikit/content/tests/SimpleTest/EventUtils.js"/>
+  <script type="application/javascript" src="dom_worker_helper.js"/>
+
+  <script type="application/javascript">
+  <![CDATA[
+
+    const WORKER_URL = "WorkerDebuggerGlobalScope.setImmediate_worker.js";
+    const DEBUGGER_URL = BASE_URL + "WorkerDebuggerGlobalScope.setImmediate_debugger.js";
+
+    function test() {
+      (async function() {
+        SimpleTest.waitForExplicitFinish();
+
+        let promise = waitForRegister(WORKER_URL, DEBUGGER_URL);
+        let worker = new Worker(WORKER_URL);
+        let dbg = await promise;
+
+        info("Send a request to the worker debugger. This should cause a " +
+             "the worker debugger to send two responses. The worker debugger " +
+             "should send the second response before the first one, since " +
+             "the latter is delayed until the next tick of the event loop.");
+        promise = waitForMultiple([
+          waitForDebuggerMessage(dbg, "pong2"),
+          waitForDebuggerMessage(dbg, "pong1")
+        ]);
+        dbg.postMessage("ping");
+        await promise;
+
+        SimpleTest.finish();
+      })();
+    }
+
+  ]]>
+  </script>
+
+  <body xmlns="http://www.w3.org/1999/xhtml">
+    <p id="display"></p>
+    <div id="content" style="display:none;"></div>
+    <pre id="test"></pre>
+  </body>
+  <label id="test-result"/>
+</window>
diff --git a/dom/workers/test/test_WorkerDebuggerManager.xhtml b/dom/workers/test/test_WorkerDebuggerManager.xhtml
new file mode 100644
index 0000000000..1ed09563de
--- /dev/null
+++ b/dom/workers/test/test_WorkerDebuggerManager.xhtml
@@ -0,0 +1,99 @@
+<?xml version="1.0"?>
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<window title="Test for WorkerDebuggerManager"
+        xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
+
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"/>
+  <script src="chrome://mochikit/content/tests/SimpleTest/EventUtils.js"/>
+  <script type="application/javascript" src="dom_worker_helper.js"/>
+
+  <script type="application/javascript">
+  <![CDATA[
+
+    const WORKER_URL = "WorkerDebuggerManager_worker.js";
+    const CHILD_WORKER_URL = "WorkerDebuggerManager_childWorker.js";
+
+    add_task(
+      async function runTest() {
+        info("Check that worker debuggers are not enumerated before they are " +
+             "registered.");
+        ok(!findDebugger(WORKER_URL),
+           "Worker debugger should not be enumerated before it is registered.");
+        ok(!findDebugger(CHILD_WORKER_URL),
+           "Child worker debugger should not be enumerated before it is " +
+           "registered.");
+
+        info("Create a worker that creates a child worker, and wait for " +
+             "their debuggers to be registered.");
+        let promise = waitForMultiple([
+          waitForRegister(WORKER_URL),
+          waitForRegister(CHILD_WORKER_URL)
+        ]);
+        let worker = new Worker(WORKER_URL);
+        let [dbg, childDbg] = await promise;
+
+        info("Check that worker debuggers are enumerated after they are " +
+             "registered.");
+        ok(findDebugger(WORKER_URL),
+           "Worker debugger should be enumerated after it is registered.");
+        ok(findDebugger(CHILD_WORKER_URL),
+           "Child worker debugger should be enumerated after it is " +
+           "registered.");
+
+        info("Check that worker debuggers are not closed before they are " +
+             "unregistered.");
+        is(dbg.isClosed, false,
+           "Worker debugger should not be closed before it is unregistered.");
+        is(childDbg.isClosed, false,
+           "Child worker debugger should not be closed before it is " +
+           "unregistered");
+
+        info("Terminate the worker and the child worker, and wait for their " +
+             "debuggers to be unregistered.");
+        promise = waitForMultiple([
+          waitForUnregister(CHILD_WORKER_URL),
+          waitForUnregister(WORKER_URL),
+        ]);
+        worker.terminate();
+        await promise;
+
+        info("Check that worker debuggers are not enumerated after they are " +
+             "unregistered.");
+        ok(!findDebugger(WORKER_URL),
+           "Worker debugger should not be enumerated after it is " +
+           "unregistered.");
+        ok(!findDebugger(CHILD_WORKER_URL),
+           "Child worker debugger should not be enumerated after it is " +
+           "unregistered.");
+
+        info("Check that worker debuggers are closed after they are " +
+             "unregistered.");
+        is(dbg.isClosed, true,
+           "Worker debugger should be closed after it is unregistered.");
+        is(childDbg.isClosed, true,
+           "Child worker debugger should be closed after it is unregistered.");
+
+        info("Check that property accesses on worker debuggers throws " +
+             "after they are closed.");
+        assertThrows(() => dbg.url,
+                     "Property accesses on worker debugger should throw " +
+                     "after it is closed.");
+        assertThrows(() => childDbg.url,
+                     "Property accesses on child worker debugger should " +
+                     "throw after it is closed.");
+      }
+    );
+
+  ]]>
+  </script>
+
+  <body xmlns="http://www.w3.org/1999/xhtml">
+    <p id="display"></p>
+    <div id="content" style="display:none;"></div>
+    <pre id="test"></pre>
+  </body>
+  <label id="test-result"/>
+</window>
diff --git a/dom/workers/test/test_WorkerDebugger_console.xhtml b/dom/workers/test/test_WorkerDebugger_console.xhtml
new file mode 100644
index 0000000000..b38ccdac45
--- /dev/null
+++ b/dom/workers/test/test_WorkerDebugger_console.xhtml
@@ -0,0 +1,98 @@
+<?xml version="1.0"?>
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<window title="Test for WorkerDebuggerGlobalScope.console methods"
+        xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
+        onload="test();">
+
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"/>
+  <script src="chrome://mochikit/content/tests/SimpleTest/EventUtils.js"/>
+  <script type="application/javascript" src="dom_worker_helper.js"/>
+
+  <script type="application/javascript">
+  <![CDATA[
+
+    const WORKER_URL = "WorkerDebugger.console_worker.js";
+    const CHILD_WORKER_URL = "WorkerDebugger.console_childWorker.js";
+    const DEBUGGER_URL = BASE_URL + "WorkerDebugger.console_debugger.js";
+
+    consoleMessagesReceived = 0;
+    function test() {
+      const ConsoleAPIStorage = SpecialPowers.Cc[
+        "@mozilla.org/consoleAPI-storage;1"
+      ].getService(SpecialPowers.Ci.nsIConsoleAPIStorage);
+
+      function consoleListener() {
+        this.observe = this.observe.bind(this);
+        ConsoleAPIStorage.addLogEventListener(this.observe, SpecialPowers.wrap(document).nodePrincipal);
+      }
+
+      consoleListener.prototype  = {
+        observe(aSubject) {
+          var obj = aSubject.wrappedJSObject;
+          if (obj.arguments[0] == "Hello from the debugger script!" &&
+              !consoleMessagesReceived) {
+            consoleMessagesReceived++;
+            ok(true, "Something has been received");
+            ConsoleAPIStorage.removeLogEventListener(this.observe);
+          }
+        }
+      }
+
+      var cl = new consoleListener();
+
+      (async function() {
+        SimpleTest.waitForExplicitFinish();
+
+        info("Create a worker that creates a child worker, wait for their " +
+             "debuggers to be registered, and initialize them.");
+        let promise = waitForMultiple([
+          waitForRegister(WORKER_URL, DEBUGGER_URL),
+          waitForRegister(CHILD_WORKER_URL, DEBUGGER_URL)
+        ]);
+        let worker = new Worker(WORKER_URL);
+        let [dbg, childDbg] = await promise;
+
+        info("Send a request to the worker debugger. This should cause the " +
+             "the worker debugger to send a response.");
+        dbg.addListener({
+          onMessage(msg) {
+            try {
+              msg = JSON.parse(msg);
+            } catch(e) {
+              ok(false, "Something went wrong");
+              return;
+            }
+
+            if (msg.type == 'finish') {
+              ok(consoleMessagesReceived, "We received something via debugger console!");
+              dbg.removeListener(this);
+              SimpleTest.finish();
+              return;
+            }
+
+            if (msg.type == 'status') {
+              ok(msg.what, msg.msg);
+              return;
+            }
+
+            ok(false, "Something went wrong");
+          }
+        });
+
+        dbg.postMessage("do magic");
+      })();
+    }
+
+  ]]>
+  </script>
+
+  <body xmlns="http://www.w3.org/1999/xhtml">
+    <p id="display"></p>
+    <div id="content" style="display:none;"></div>
+    <pre id="test"></pre>
+  </body>
+  <label id="test-result"/>
+</window>
diff --git a/dom/workers/test/test_WorkerDebugger_frozen.xhtml b/dom/workers/test/test_WorkerDebugger_frozen.xhtml
new file mode 100644
index 0000000000..f29def78ce
--- /dev/null
+++ b/dom/workers/test/test_WorkerDebugger_frozen.xhtml
@@ -0,0 +1,72 @@
+<?xml version="1.0"?>
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<window title="Test for WorkerDebugger with frozen workers"
+        xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
+
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"/>
+  <script src="chrome://mochikit/content/tests/SimpleTest/EventUtils.js"/>
+  <script type="application/javascript" src="dom_worker_helper.js"/>
+
+  <script type="application/javascript">
+  <![CDATA[
+
+    const WINDOW1_URL = "WorkerDebugger_frozen_window1.html";
+    const WINDOW2_URL = "WorkerDebugger_frozen_window2.html";
+
+    const WORKER1_URL = "WorkerDebugger_frozen_worker1.js";
+    const WORKER2_URL = "WorkerDebugger_frozen_worker2.js";
+
+    add_task(
+      async function runTest() {
+        await SpecialPowers.pushPrefEnv({set:
+          [["browser.sessionhistory.max_total_viewers", 10]]});
+
+        let promise = waitForMultiple([
+          waitForRegister(WORKER1_URL),
+          waitForWindowMessage(window, "ready"),
+        ]);
+        let testWin = window.open(WINDOW1_URL, "testWin");;
+        let [dbg1] = await promise;
+        is(dbg1.isClosed, false,
+           "debugger for worker on page 1 should not be closed");
+
+        promise = waitForMultiple([
+          waitForUnregister(WORKER1_URL),
+          waitForDebuggerClose(dbg1),
+          waitForRegister(WORKER2_URL),
+          waitForWindowMessage(window, "ready"),
+        ]);
+        testWin.location = WINDOW2_URL;
+        let [,, dbg2] = await promise;
+        is(dbg1.isClosed, true,
+           "debugger for worker on page 1 should be closed");
+        is(dbg2.isClosed, false,
+           "debugger for worker on page 2 should not be closed");
+
+        promise = Promise.all([
+          waitForUnregister(WORKER2_URL),
+          waitForDebuggerClose(dbg2),
+          waitForRegister(WORKER1_URL)
+        ]);
+        testWin.history.back();
+        [,, dbg1] = await promise;
+        is(dbg1.isClosed, false,
+           "debugger for worker on page 1 should not be closed");
+        is(dbg2.isClosed, true,
+           "debugger for worker on page 2 should be closed");
+      }
+    );
+
+  ]]>
+  </script>
+
+  <body xmlns="http://www.w3.org/1999/xhtml">
+    <p id="display"></p>
+    <div id="content" style="display:none;"></div>
+    <pre id="test"></pre>
+  </body>
+  <label id="test-result"/>
+</window>
diff --git a/dom/workers/test/test_WorkerDebugger_promise.xhtml b/dom/workers/test/test_WorkerDebugger_promise.xhtml
new file mode 100644
index 0000000000..14d50969b5
--- /dev/null
+++ b/dom/workers/test/test_WorkerDebugger_promise.xhtml
@@ -0,0 +1,68 @@
+<?xml version="1.0"?>
+<!--
+  Any copyright is dedicated to the Public Domain.
++  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<window title="Test for WorkerDebugger with DOM Promises"
+        xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
+        onload="test();">
+
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"/>
+  <script src="chrome://mochikit/content/tests/SimpleTest/EventUtils.js"/>
+  <script type="application/javascript" src="dom_worker_helper.js"/>
+
+  <script type="application/javascript">
+  <![CDATA[
+
+    const WORKER_URL = "WorkerDebugger_promise_worker.js";
+    const DEBUGGER_URL = BASE_URL + "WorkerDebugger_promise_debugger.js";
+
+    function test() {
+      (async function() {
+        SimpleTest.waitForExplicitFinish();
+
+        let promise = waitForRegister(WORKER_URL, DEBUGGER_URL);
+        let worker = new Worker(WORKER_URL);
+        let dbg = await promise;
+
+        info("Send a request to the worker. This should cause the worker " +
+             "to send a response.");
+        promise = waitForWorkerMessage(worker, "resolved");
+        worker.postMessage("resolve");
+        await promise;
+
+        info("Send a request to the debugger. This should cause the debugger " +
+             "to send a response.");
+        promise = waitForDebuggerMessage(dbg, "resolved");
+        dbg.postMessage("resolve");
+        await promise;
+
+        info("Send a request to the worker. This should cause the debugger " +
+             "to enter a nested event loop.");
+        promise = waitForDebuggerMessage(dbg, "paused");
+        worker.postMessage("pause");
+        await promise;
+
+        info("Send a request to the debugger. This should cause the debugger " +
+             "to leave the nested event loop.");
+        promise = waitForMultiple([
+          waitForDebuggerMessage(dbg, "resumed"),
+          waitForWorkerMessage(worker, "resumed")
+        ]);
+        dbg.postMessage("resume");
+        await promise;
+
+        SimpleTest.finish();
+      })();
+    }
+
+  ]]>
+  </script>
+
+  <body xmlns="http://www.w3.org/1999/xhtml">
+    <p id="display"></p>
+    <div id="content" style="display:none;"></div>
+    <pre id="test"></pre>
+  </body>
+  <label id="test-result"/>
+</window>
diff --git a/dom/workers/test/test_WorkerDebugger_suspended.xhtml b/dom/workers/test/test_WorkerDebugger_suspended.xhtml
new file mode 100644
index 0000000000..d0c9bff552
--- /dev/null
+++ b/dom/workers/test/test_WorkerDebugger_suspended.xhtml
@@ -0,0 +1,72 @@
+<?xml version="1.0"?>
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<window title="Test for WorkerDebugger with suspended workers"
+        xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
+        onload="test();">
+
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"/>
+  <script src="chrome://mochikit/content/tests/SimpleTest/EventUtils.js"/>
+  <script type="application/javascript" src="dom_worker_helper.js"/>
+
+  <script type="application/javascript">
+  <![CDATA[
+
+    const WORKER_URL = "WorkerDebugger_suspended_worker.js";
+    const DEBUGGER_URL = BASE_URL + "WorkerDebugger_suspended_debugger.js";
+
+    function test() {
+      (async function() {
+        SimpleTest.waitForExplicitFinish();
+
+        info("Create a worker, wait for its debugger to be registered, and " +
+             "initialize it.");
+        let promise = waitForRegister(WORKER_URL, DEBUGGER_URL);
+        let worker = new Worker(WORKER_URL);
+        let dbg = await promise;
+
+        info("Send a request to the worker. This should cause both the " +
+             "worker and the worker debugger to send a response.");
+        promise = waitForMultiple([
+          waitForWorkerMessage(worker, "worker"),
+          waitForDebuggerMessage(dbg, "debugger")
+        ]);
+        worker.postMessage("ping");
+        await promise;
+
+        info("Suspend the workers for this window, and send another request " +
+             "to the worker. This should cause only the worker debugger to " +
+             "send a response.");
+        let windowUtils = window.windowUtils;
+        windowUtils.suspendTimeouts();
+        function onmessage() {
+          ok(false, "The worker should not send a response.");
+        };
+        worker.addEventListener("message", onmessage);
+        promise = waitForDebuggerMessage(dbg, "debugger");
+        worker.postMessage("ping");
+        await promise;
+        worker.removeEventListener("message", onmessage);
+
+        info("Resume the workers for this window. This should cause the " +
+             "worker to send a response to the previous request.");
+        promise = waitForWorkerMessage(worker, "worker");
+        windowUtils.resumeTimeouts();
+        await promise;
+
+        SimpleTest.finish();
+      })();
+    }
+
+  ]]>
+  </script>
+
+  <body xmlns="http://www.w3.org/1999/xhtml">
+    <p id="display"></p>
+    <div id="content" style="display:none;"></div>
+    <pre id="test"></pre>
+  </body>
+  <label id="test-result"/>
+</window>
diff --git a/dom/workers/test/test_atob.html b/dom/workers/test/test_atob.html
new file mode 100644
index 0000000000..0e82029b46
--- /dev/null
+++ b/dom/workers/test/test_atob.html
@@ -0,0 +1,57 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test for DOM Worker Threads</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<p id="display"></p>
+<div id="content" style="display: none"></div>
+<pre id="test">
+<script src="atob_worker.js" language="javascript"></script>
+<script class="testbody" type="text/javascript">
+
+  var dataIndex = 0;
+
+  var worker = new Worker("atob_worker.js");
+  worker.onmessage = function(event) {
+    switch (event.data.type) {
+      case "done":
+        is(dataIndex, data.length, "Saw all values");
+        SimpleTest.finish();
+        return;
+      case "btoa":
+        is(btoa(data[dataIndex]), event.data.value,
+           "Good btoa value " + dataIndex);
+        break;
+      case "atob":
+        is(atob(btoa(data[dataIndex])) + "", event.data.value,
+           "Good round trip value " + dataIndex);
+        dataIndex++;
+        break;
+      default:
+        ok(false, "Worker posted a bad message: " + event.message);
+        worker.terminate();
+        SimpleTest.finish();
+    }
+  }
+
+  worker.onerror = function(event) {
+    ok(false, "Worker threw an error: " + event.message);
+    worker.terminate();
+    SimpleTest.finish();
+  }
+
+  worker.postMessage("go");
+
+  SimpleTest.waitForExplicitFinish();
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_blobConstructor.html b/dom/workers/test/test_blobConstructor.html
new file mode 100644
index 0000000000..4aff5b545b
--- /dev/null
+++ b/dom/workers/test/test_blobConstructor.html
@@ -0,0 +1,60 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE html>
+<html>
+<!--
+Tests of DOM Worker Blob constructor
+-->
+<head>
+  <title>Test for DOM Worker Blob constructor</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script class="testbody" type="text/javascript">
+(function() {
+  onerror = function(e) {
+    ok(false, "Main Thread had an error: " + event.data);
+    SimpleTest.finish();
+  };
+  function f() {
+    onmessage = function(e) {
+      var b = new Blob([e.data, "World"],{type: "text/plain"});
+      var fr = new FileReaderSync();
+      postMessage({text: fr.readAsText(b), type: b.type});
+    };
+  }
+  var b = new Blob([f,"f();"]);
+  var u = URL.createObjectURL(b);
+  var w = new Worker(u);
+  w.onmessage = function(e) {
+    URL.revokeObjectURL(u);
+    is(e.data.text, fr.result);
+    is(e.data.type, "text/plain");
+    SimpleTest.finish();
+  };
+  w.onerror = function(e) {
+    is(e.target, w);
+    ok(false, "Worker had an error: " + e.message);
+    SimpleTest.finish();
+  };
+
+  b = new Blob(["Hello, "]);
+  var fr = new FileReader();
+  fr.readAsText(new Blob([b, "World"],{}));
+  fr.onload = function() {
+    w.postMessage(b);
+  };
+  SimpleTest.waitForExplicitFinish();
+})();
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_blobWorkers.html b/dom/workers/test/test_blobWorkers.html
new file mode 100644
index 0000000000..6ecd6c6f4b
--- /dev/null
+++ b/dom/workers/test/test_blobWorkers.html
@@ -0,0 +1,31 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+  <head>
+    <script src="/tests/SimpleTest/SimpleTest.js">
+    </script>
+    <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  </head>
+  <body>
+    <script type="text/javascript">
+      const message = "hi";
+
+      const workerScript =
+        "onmessage = function(event) {" +
+        "  postMessage(event.data);" +
+        "};";
+
+      var worker = new Worker(URL.createObjectURL(new Blob([workerScript])));
+      worker.onmessage = function(event) {
+        is(event.data, message, "Got correct message");
+        SimpleTest.finish();
+      };
+      worker.postMessage(message);
+
+      SimpleTest.waitForExplicitFinish();
+    </script>
+  </body>
+</html>
diff --git a/dom/workers/test/test_bug1002702.html b/dom/workers/test/test_bug1002702.html
new file mode 100644
index 0000000000..c020dcfd05
--- /dev/null
+++ b/dom/workers/test/test_bug1002702.html
@@ -0,0 +1,26 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test for bug 1002702</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<p id="display"></p>
+<div id="content" style="display: none"></div>
+<pre id="test"></pre>
+<script class="testbody" type="text/javascript">
+
+var port = new SharedWorker('data:application/javascript,1').port;
+port.close();
+SpecialPowers.forceGC();
+ok(true, "No crash \\o/");
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_bug1010784.html b/dom/workers/test/test_bug1010784.html
new file mode 100644
index 0000000000..3e2f62971d
--- /dev/null
+++ b/dom/workers/test/test_bug1010784.html
@@ -0,0 +1,35 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1010784
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1010784</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1010784">Mozilla Bug 1010784</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script type="application/javascript">
+
+  var worker = new Worker("file_bug1010784_worker.js");
+
+  worker.onmessage = function(event) {
+    is(event.data, "done", "Got correct result");
+    SimpleTest.finish();
+  }
+
+  worker.postMessage("testXHR.txt");
+
+  SimpleTest.waitForExplicitFinish();
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_bug1014466.html b/dom/workers/test/test_bug1014466.html
new file mode 100644
index 0000000000..26ef2fb316
--- /dev/null
+++ b/dom/workers/test/test_bug1014466.html
@@ -0,0 +1,42 @@
+<!--
+2   Any copyright is dedicated to the Public Domain.
+3   http://creativecommons.org/publicdomain/zero/1.0/
+4 -->
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1014466
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1014466</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1014466">Mozilla Bug 1014466</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script type="application/javascript">
+
+  var worker = new Worker("bug1014466_worker.js");
+
+  worker.onmessage = function(event) {
+    if (event.data.type == 'finish') {
+      SimpleTest.finish();
+    } else if (event.data.type == 'status') {
+      ok(event.data.status, event.data.msg);
+    }
+  };
+
+  worker.postMessage(true);
+
+  SimpleTest.waitForExplicitFinish();
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_bug1020226.html b/dom/workers/test/test_bug1020226.html
new file mode 100644
index 0000000000..1ed69db41e
--- /dev/null
+++ b/dom/workers/test/test_bug1020226.html
@@ -0,0 +1,38 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1020226
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1020226</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1020226">Mozilla Bug 1020226</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+<iframe id="iframe" src="bug1020226_frame.html" onload="finishTest();">
+</iframe>
+</div>
+<pre id="test">
+<script type="application/javascript">
+function finishTest() {
+  document.getElementById("iframe").onload = null;
+  window.onmessage = function(e) {
+    info("Got message");
+    document.getElementById("iframe").src = "about:blank";
+    // We aren't really interested in the test, it shouldn't crash when the
+    // worker is GCed later.
+    ok(true, "Should not crash");
+    SimpleTest.finish();
+  };
+}
+
+SimpleTest.waitForExplicitFinish();
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_bug1036484.html b/dom/workers/test/test_bug1036484.html
new file mode 100644
index 0000000000..feada50f5a
--- /dev/null
+++ b/dom/workers/test/test_bug1036484.html
@@ -0,0 +1,52 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<!--
+Tests of DOM Worker Threads: bug 1036484
+-->
+<head>
+  <title>Test for DOM Worker Threads: bug 1036484</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<pre id="test">
+<script class="testbody" type="text/javascript">
+
+function test(script) {
+  var worker = new Worker(script);
+
+  worker.onmessage = function(event) {
+    ok(false, "Shouldn't ever get a message!");
+  }
+
+  worker.onerror = function(event) {
+    is(event.target, worker);
+    event.preventDefault();
+    runTests();
+  };
+
+  worker.postMessage("dummy");
+}
+
+var tests = [ '404_server.sjs', '404_server.sjs?js' ];
+function runTests() {
+  if (!tests.length) {
+    SimpleTest.finish();
+    return;
+  }
+
+  var script = tests.shift();
+  test(script);
+}
+
+SimpleTest.waitForExplicitFinish();
+runTests();
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_bug1060621.html b/dom/workers/test/test_bug1060621.html
new file mode 100644
index 0000000000..d2af81c93e
--- /dev/null
+++ b/dom/workers/test/test_bug1060621.html
@@ -0,0 +1,30 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test for URLSearchParams object in workers</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<p id="display"></p>
+<div id="content" style="display: none"></div>
+<pre id="test"></pre>
+<script class="testbody" type="text/javascript">
+
+  var worker = new Worker("bug1060621_worker.js");
+
+  worker.onmessage = function(event) {
+    ok(true, "The operation is done. We should not leak.");
+    SimpleTest.finish();
+  };
+
+  SimpleTest.waitForExplicitFinish();
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_bug1062920.html b/dom/workers/test/test_bug1062920.html
new file mode 100644
index 0000000000..bea2b7f461
--- /dev/null
+++ b/dom/workers/test/test_bug1062920.html
@@ -0,0 +1,69 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test for navigator property override</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<p id="display"></p>
+<div id="content" style="display: none"></div>
+<pre id="test"></pre>
+<script class="testbody" type="text/javascript">
+
+  function checkValues() {
+    var worker = new Worker("bug1062920_worker.js");
+
+    worker.onmessage = function(event) {
+      var ifr = document.createElement('IFRAME');
+      ifr.src = "about:blank";
+
+      ifr.addEventListener('load', function() {
+        var nav = ifr.contentWindow.navigator;
+        is(event.data.appCodeName, nav.appCodeName, "appCodeName should match");
+        is(event.data.appName, nav.appName, "appName should match");
+        is(event.data.appVersion, nav.appVersion, "appVersion should match");
+        is(event.data.platform, nav.platform, "platform should match");
+        is(event.data.userAgent, nav.userAgent, "userAgent should match");
+        is(event.data.product, nav.product, "product should match");
+        runTests();
+      });
+
+      document.getElementById('content').appendChild(ifr);
+    };
+  }
+
+  function replaceAndCheckValues() {
+    SpecialPowers.pushPrefEnv({"set": [
+      ["general.appversion.override", "appVersion overridden"],
+      ["general.platform.override", "platform overridden"],
+      ["general.useragent.override", "userAgent overridden"]
+    ]}, checkValues);
+  }
+
+  var tests = [
+    checkValues,
+    replaceAndCheckValues
+  ];
+
+  function runTests() {
+    if (!tests.length) {
+      SimpleTest.finish();
+      return;
+    }
+
+    var test = tests.shift();
+    test();
+  }
+
+  SimpleTest.waitForExplicitFinish();
+  runTests();
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_bug1062920.xhtml b/dom/workers/test/test_bug1062920.xhtml
new file mode 100644
index 0000000000..0dfeccfb77
--- /dev/null
+++ b/dom/workers/test/test_bug1062920.xhtml
@@ -0,0 +1,64 @@
+<?xml version="1.0"?>
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<window title="DOM Worker Threads Test"
+        xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
+
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"/>
+  <script src="chrome://mochikit/content/tests/SimpleTest/EventUtils.js"/>
+  <script type="application/javascript" src="dom_worker_helper.js"/>
+
+  <script type="application/javascript">
+
+  function checkValues() {
+    var worker = new Worker("bug1062920_worker.js");
+
+    worker.onmessage = function(event) {
+      is(event.data.appCodeName, navigator.appCodeName, "appCodeName should match");
+      is(event.data.appVersion, navigator.appVersion, "appVersion should match");
+      isnot(event.data.appVersion, "appVersion overridden", "appVersion is not overridden");
+      is(event.data.platform, navigator.platform, "platform should match");
+      isnot(event.data.platform, "platform overridden", "platform is not overridden");
+      is(event.data.userAgent, navigator.userAgent, "userAgent should match");
+      is(event.data.product, navigator.product, "product should match");
+      runTests();
+    };
+  }
+
+  function replaceAndCheckValues() {
+    SpecialPowers.pushPrefEnv({"set": [
+      ["general.appversion.override", "appVersion overridden"],
+      ["general.platform.override", "platform overridden"],
+      ["general.useragent.override", "userAgent overridden"]
+    ]}, checkValues);
+  }
+
+  var tests = [
+    replaceAndCheckValues,
+    checkValues
+  ];
+
+  function runTests() {
+    if (!tests.length) {
+      SimpleTest.finish();
+      return;
+    }
+
+    var test = tests.shift();
+    test();
+  }
+
+  SimpleTest.waitForExplicitFinish();
+  runTests();
+
+  </script>
+
+  <body xmlns="http://www.w3.org/1999/xhtml">
+    <p id="display"></p>
+    <div id="content" style="display:none;"></div>
+    <pre id="test"></pre>
+  </body>
+  <label id="test-result"/>
+</window>
diff --git a/dom/workers/test/test_bug1063538.html b/dom/workers/test/test_bug1063538.html
new file mode 100644
index 0000000000..a1dc6624b9
--- /dev/null
+++ b/dom/workers/test/test_bug1063538.html
@@ -0,0 +1,47 @@
+<!--
+2   Any copyright is dedicated to the Public Domain.
+3   http://creativecommons.org/publicdomain/zero/1.0/
+4 -->
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1063538
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1063538</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1063538">Mozilla Bug 1063538</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script type="application/javascript">
+
+function runTest() {
+  var worker = new Worker("bug1063538_worker.js");
+
+  worker.onmessage = function(e) {
+    if (e.data.type == 'finish') {
+      ok(e.data.progressFired, "Progress was fired.");
+      SimpleTest.finish();
+    }
+  };
+
+  worker.postMessage(true);
+}
+
+SimpleTest.waitForExplicitFinish();
+
+addLoadEvent(function() {
+  SpecialPowers.pushPermissions([{'type': 'systemXHR', 'allow': true, 'context': document}], runTest);
+});
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_bug1104064.html b/dom/workers/test/test_bug1104064.html
new file mode 100644
index 0000000000..1c8b3ac92c
--- /dev/null
+++ b/dom/workers/test/test_bug1104064.html
@@ -0,0 +1,27 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test for bug 1104064</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<script class="testbody" type="text/javascript">
+
+var worker = new Worker("bug1104064_worker.js");
+worker.onmessage = function() {
+  ok(true, "setInterval has been called twice.");
+  SimpleTest.finish();
+}
+worker.postMessage("go");
+
+SimpleTest.waitForExplicitFinish();
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_bug1132395.html b/dom/workers/test/test_bug1132395.html
new file mode 100644
index 0000000000..8d424e5ad4
--- /dev/null
+++ b/dom/workers/test/test_bug1132395.html
@@ -0,0 +1,40 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test for 1132395</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+
+<script class="testbody" type="text/javascript">
+
+// This test is full of dummy debug messages. This is because I need to follow
+// an hard-to-reproduce timeout failure.
+
+info("test started");
+var sw = new SharedWorker('bug1132395_sharedWorker.js');
+sw.port.onmessage = function(event) {
+  info("sw.onmessage received");
+  ok(true, "We didn't crash.");
+  SimpleTest.finish();
+}
+
+sw.onerror = function(event) {
+  ok(false, "Failed to create a ServiceWorker");
+  SimpleTest.finish();
+}
+
+info("sw.postmessage called");
+sw.port.postMessage('go');
+
+SimpleTest.waitForExplicitFinish();
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_bug1132924.html b/dom/workers/test/test_bug1132924.html
new file mode 100644
index 0000000000..b5b952e908
--- /dev/null
+++ b/dom/workers/test/test_bug1132924.html
@@ -0,0 +1,28 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test for 1132924</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+
+<script class="testbody" type="text/javascript">
+
+SimpleTest.waitForExplicitFinish();
+var w = new Worker('bug1132924_worker.js');
+w.onmessage = function(event) {
+  ok(true, "We are still alive.");
+  SimpleTest.finish();
+}
+
+w.postMessage('go');
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_bug1278777.html b/dom/workers/test/test_bug1278777.html
new file mode 100644
index 0000000000..c995212bd0
--- /dev/null
+++ b/dom/workers/test/test_bug1278777.html
@@ -0,0 +1,31 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1278777
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1278777</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+  <a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1278777">Mozilla Bug 1278777</a>
+  <script type="application/javascript">
+
+SimpleTest.waitForExplicitFinish();
+
+var worker = new Worker('worker_bug1278777.js');
+worker.onerror = function() {
+  ok(false, "We should not see any error.");
+  SimpleTest.finish();
+}
+
+worker.onmessage = function(e) {
+  ok(e.data, "Everything seems ok.");
+  SimpleTest.finish();
+}
+
+  </script>
+</body>
+</html>
diff --git a/dom/workers/test/test_bug1301094.html b/dom/workers/test/test_bug1301094.html
new file mode 100644
index 0000000000..efe25fa3a9
--- /dev/null
+++ b/dom/workers/test/test_bug1301094.html
@@ -0,0 +1,69 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1301094
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1301094</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+  <a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1301094">Mozilla Bug 1301094</a>
+  <input id="file" type="file"></input>
+  <script type="application/javascript">
+
+SimpleTest.waitForExplicitFinish();
+
+var url = SimpleTest.getTestFileURL("script_createFile.js");
+script = SpecialPowers.loadChromeScript(url);
+
+var mainThreadOk, workerOk;
+
+function maybeFinish() {
+  if (mainThreadOk & workerOk) {
+    SimpleTest.finish();
+  }
+}
+
+function onOpened(message) {
+  var input = document.getElementById('file');
+  SpecialPowers.wrap(input).mozSetDndFilesAndDirectories([message.data]);
+
+  var worker = new Worker('worker_bug1301094.js');
+  worker.onerror = function() {
+    ok(false, "We should not see any error.");
+    SimpleTest.finish();
+  }
+
+  worker.onmessage = function(e) {
+    ok(e.data, "Everything seems OK on the worker-side.");
+
+    workerOk = true;
+    maybeFinish();
+  }
+
+  is(input.files.length, 1, "We have something");
+  ok(input.files[0] instanceof Blob, "We have one Blob");
+  worker.postMessage(input.files[0]);
+
+  var xhr = new XMLHttpRequest();
+  xhr.open("POST", 'worker_bug1301094.js', false);
+  xhr.onload = function() {
+    ok(xhr.responseText, "Everything seems OK on the main-thread-side.");
+    mainThreadOk = true;
+    maybeFinish();
+  };
+
+  var fd = new FormData();
+  fd.append('file', input.files[0]);
+  xhr.send(fd);
+}
+
+script.addMessageListener("file.opened", onOpened);
+script.sendAsyncMessage("file.open");
+
+  </script>
+</body>
+</html>
diff --git a/dom/workers/test/test_bug1317725.html b/dom/workers/test/test_bug1317725.html
new file mode 100644
index 0000000000..7da3fc2644
--- /dev/null
+++ b/dom/workers/test/test_bug1317725.html
@@ -0,0 +1,49 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test for bug 1317725</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+
+<input type="file" id="file" />
+
+<script class="testbody" type="text/javascript">
+
+SimpleTest.waitForExplicitFinish();
+
+var url = SimpleTest.getTestFileURL("script_createFile.js");
+script = SpecialPowers.loadChromeScript(url);
+
+function onOpened(message) {
+  var input = document.getElementById('file');
+  SpecialPowers.wrap(input).mozSetFileArray([message.data]);
+
+  var worker = new Worker("test_bug1317725.js");
+  worker.onerror = function(e) {
+    ok(false, "We should not see any error.");
+    SimpleTest.finish();
+  }
+
+  worker.onmessage = function(e) {
+    ok(e.data, "Everything seems OK on the worker-side.");
+    SimpleTest.finish();
+  }
+
+  is(input.files.length, 1, "We have something");
+  ok(input.files[0] instanceof Blob, "We have one Blob");
+  worker.postMessage(input.files[0]);
+}
+
+script.addMessageListener("file.opened", onOpened);
+script.sendAsyncMessage("file.open");
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_bug1317725.js b/dom/workers/test/test_bug1317725.js
new file mode 100644
index 0000000000..858488fac3
--- /dev/null
+++ b/dom/workers/test/test_bug1317725.js
@@ -0,0 +1,8 @@
+onmessage = function (e) {
+  var data = new FormData();
+  data.append("Filedata", e.data.slice(0, 127), encodeURI(e.data.name));
+  var xhr = new XMLHttpRequest();
+  xhr.open("POST", location.href, false);
+  xhr.send(data);
+  postMessage("No crash \\o/");
+};
diff --git a/dom/workers/test/test_bug1824498.html b/dom/workers/test/test_bug1824498.html
new file mode 100644
index 0000000000..ea01cabe1b
--- /dev/null
+++ b/dom/workers/test/test_bug1824498.html
@@ -0,0 +1,38 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test for Worker Import failure (Bug 1824498)</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1824498">
+Worker Import failure test: Bug 1824498
+</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script class="testbody" type="text/javascript">
+
+SimpleTest.waitForExplicitFinish();
+
+document.addEventListener("DOMContentLoaded", async () => {
+  await SpecialPowers.pushPrefEnv(
+    { set: [["dom.workers.modules.enabled", true ]] });
+
+  const worker = new Worker("worker_bug1824498.mjs", {"type": "module"})
+  worker.onerror = function(event) {
+    ok(true, "not assert");
+    SimpleTest.finish();
+  };
+});
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_bug949946.html b/dom/workers/test/test_bug949946.html
new file mode 100644
index 0000000000..41b021a098
--- /dev/null
+++ b/dom/workers/test/test_bug949946.html
@@ -0,0 +1,26 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test for bug 949946</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<p id="display"></p>
+<div id="content" style="display: none"></div>
+<pre id="test"></pre>
+<script class="testbody" type="text/javascript">
+
+new SharedWorker('sharedWorker_sharedWorker.js');
+new SharedWorker('sharedWorker_sharedWorker.js', ':');
+new SharedWorker('sharedWorker_sharedWorker.js', '|||');
+ok(true, "3 SharedWorkers created!");
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_bug978260.html b/dom/workers/test/test_bug978260.html
new file mode 100644
index 0000000000..056b8b6c72
--- /dev/null
+++ b/dom/workers/test/test_bug978260.html
@@ -0,0 +1,35 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test for DOM Worker Threads</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<p id="display"></p>
+<div id="content" style="display: none"></div>
+<pre id="test">
+<script class="testbody" type="text/javascript">
+
+  SimpleTest.waitForExplicitFinish();
+
+  var xhr = new XMLHttpRequest();
+  xhr.onload = function () {
+    var worker = new Worker("bug978260_worker.js");
+    worker.onmessage = function(event) {
+      is(event.data, "loaded");
+      SimpleTest.finish();
+    }
+  }
+
+  xhr.open('GET', '/', false);
+  xhr.send();
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_bug998474.html b/dom/workers/test/test_bug998474.html
new file mode 100644
index 0000000000..93632a5de4
--- /dev/null
+++ b/dom/workers/test/test_bug998474.html
@@ -0,0 +1,40 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test for bug 998474</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body onload="boom();">
+<p id="display"></p>
+<div id="content" style="display: none"></div>
+<pre id="test"></pre>
+<script class="testbody" type="text/javascript">
+
+function boom()
+{
+  var worker = new SharedWorker("bug998474_worker.js");
+
+  setTimeout(function() {
+    port = worker.port;
+    port.postMessage("");
+
+    setTimeout(function() {
+      port.start();
+      ok(true, "Still alive!");
+      SimpleTest.finish();
+    }, 150);
+  }, 150);
+}
+
+SimpleTest.waitForExplicitFinish();
+SimpleTest.requestFlakyTimeout("untriaged");
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_chromeWorker.html b/dom/workers/test/test_chromeWorker.html
new file mode 100644
index 0000000000..35d5c08928
--- /dev/null
+++ b/dom/workers/test/test_chromeWorker.html
@@ -0,0 +1,26 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<html>
+<head>
+  <title>Test for DOM Worker Threads</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<pre id="test">
+<script class="testbody" type="text/javascript">
+
+  try {
+    var worker = new ChromeWorker("simpleThread_worker.js");
+    ok(false, "ChromeWorker constructor should be blocked!");
+  }
+  catch (e) {
+    ok(true, "ChromeWorker constructor wasn't blocked!");
+  }
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_chromeWorker.xhtml b/dom/workers/test/test_chromeWorker.xhtml
new file mode 100644
index 0000000000..65d14f8851
--- /dev/null
+++ b/dom/workers/test/test_chromeWorker.xhtml
@@ -0,0 +1,58 @@
+<?xml version="1.0"?>
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<window title="DOM Worker Threads Test"
+        xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
+
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"/>
+  <script src="chrome://mochikit/content/tests/SimpleTest/EventUtils.js"/>
+  <script type="application/javascript" src="dom_worker_helper.js"/>
+
+  <script type="application/javascript">
+  <![CDATA[
+
+    add_task(async function classic_worker_test() {
+      let worker = window.classicWorker = new ChromeWorker("chromeWorker_worker.js");
+      await new Promise((resolve, reject) => {
+        worker.onmessage = function(event) {
+          is(event.data, "Done!", "Got the done message!");
+          resolve();
+        };
+        worker.onerror = function(event) {
+          ok(false, "Classic Worker had an error: " + event.message);
+          worker.terminate();
+          reject();
+        };
+        worker.postMessage("go");
+      });
+    });
+
+    add_task(async function module_worker_test() {
+      waitForWorkerFinish();
+
+      let worker = window.moduleWorker = new ChromeWorker("chromeWorker_worker.sys.mjs", { type: "module" });
+      await new Promise((resolve, reject) => {
+        worker.onmessage = function(event) {
+          is(event.data, "Done!", "Got the done message!");
+          resolve();
+        };
+        worker.onerror = function(event) {
+          ok(false, "Module Worker had an error: " + event.message);
+          worker.terminate();
+          reject();
+        };
+        worker.postMessage("go");
+      });
+    });
+  ]]>
+  </script>
+
+  <body xmlns="http://www.w3.org/1999/xhtml">
+    <p id="display"></p>
+    <div id="content" style="display:none;"></div>
+    <pre id="test"></pre>
+  </body>
+  <label id="test-result"/>
+</window>
diff --git a/dom/workers/test/test_chromeWorkerJSM.xhtml b/dom/workers/test/test_chromeWorkerJSM.xhtml
new file mode 100644
index 0000000000..6341737815
--- /dev/null
+++ b/dom/workers/test/test_chromeWorkerJSM.xhtml
@@ -0,0 +1,54 @@
+<?xml version="1.0"?>
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<window title="DOM Worker Threads Test"
+        xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
+        onload="test();">
+
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"/>
+  <script src="chrome://mochikit/content/tests/SimpleTest/EventUtils.js"/>
+  <script type="application/javascript" src="dom_worker_helper.js"/>
+
+  <script type="application/javascript">
+  <![CDATA[
+
+    function test()
+    {
+      waitForWorkerFinish();
+
+      var worker;
+
+      function done()
+      {
+        worker = null;
+        finish();
+      }
+
+      function messageCallback(event) {
+        is(event.data, "Done", "Correct message");
+        done();
+      }
+
+      function errorCallback(event) {
+        ok(false, "Worker had an error: " + event.message);
+        done();
+      }
+
+      const {WorkerTest} = ChromeUtils.import("chrome://mochitests/content/chrome/dom/workers/test/WorkerTest.jsm");
+
+      worker = WorkerTest.go(window.location.href, messageCallback,
+                             errorCallback);
+    }
+
+  ]]>
+  </script>
+
+  <body xmlns="http://www.w3.org/1999/xhtml">
+    <p id="display"></p>
+    <div id="content" style="display:none;"></div>
+    <pre id="test"></pre>
+  </body>
+  <label id="test-result"/>
+</window>
diff --git a/dom/workers/test/test_clearTimeouts.html b/dom/workers/test/test_clearTimeouts.html
new file mode 100644
index 0000000000..caa87fbf56
--- /dev/null
+++ b/dom/workers/test/test_clearTimeouts.html
@@ -0,0 +1,31 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test for DOM Worker Threads</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<p id="display"></p>
+<div id="content" style="display: none"></div>
+<pre id="test">
+<script class="testbody" type="text/javascript">
+
+  new Worker("clearTimeouts_worker.js").onmessage = function(event) {
+    event.target.terminate();
+
+    is(event.data, "ready", "Correct message");
+    setTimeout(function() { SimpleTest.finish(); }, 1000);
+  }
+
+  SimpleTest.waitForExplicitFinish();
+  SimpleTest.requestFlakyTimeout("untriaged");
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_clearTimeoutsImplicit.html b/dom/workers/test/test_clearTimeoutsImplicit.html
new file mode 100644
index 0000000000..59a37974ca
--- /dev/null
+++ b/dom/workers/test/test_clearTimeoutsImplicit.html
@@ -0,0 +1,31 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test for DOM Worker Threads</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<p id="display"></p>
+<div id="content" style="display: none"></div>
+<pre id="test">
+<script class="testbody" type="text/javascript">
+
+  new Worker("clearTimeoutsImplicit_worker.js").onmessage = function(event) {
+    event.target.terminate();
+
+    is(event.data, "ready", "Correct message");
+    setTimeout(function() { SimpleTest.finish(); }, 1000);
+  }
+
+  SimpleTest.waitForExplicitFinish();
+  SimpleTest.requestFlakyTimeout("untriaged");
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_console.html b/dom/workers/test/test_console.html
new file mode 100644
index 0000000000..b8c0f189ab
--- /dev/null
+++ b/dom/workers/test/test_console.html
@@ -0,0 +1,44 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<!--
+Tests of DOM Worker Console
+-->
+<head>
+  <title>Test for DOM Worker Console</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script class="testbody" language="javascript">
+  var worker = new Worker("console_worker.js");
+
+  worker.onmessage = function(event) {
+    is(event.target, worker, "Worker and target match!");
+    ok(event.data.status, event.data.event);
+
+    if (!event.data.status || event.data.last)
+      SimpleTest.finish();
+  };
+
+  worker.onerror = function(event) {
+    ok(false, "Worker had an error: " + event.message);
+    SimpleTest.finish();
+  }
+
+  worker.postMessage(true);
+
+  SimpleTest.waitForExplicitFinish();
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_consoleAndBlobs.html b/dom/workers/test/test_consoleAndBlobs.html
new file mode 100644
index 0000000000..e07cfe5dca
--- /dev/null
+++ b/dom/workers/test/test_consoleAndBlobs.html
@@ -0,0 +1,46 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+  <head>
+    <title>Test for console API and blobs</title>
+    <script src="/tests/SimpleTest/SimpleTest.js">
+    </script>
+    <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css">
+  </head>
+  <body>
+    <script type="text/javascript">
+  const ConsoleAPIStorage = SpecialPowers.Cc[
+    "@mozilla.org/consoleAPI-storage;1"
+  ].getService(SpecialPowers.Ci.nsIConsoleAPIStorage);
+
+  function consoleListener() {
+    this.observe = this.observe.bind(this);
+    ConsoleAPIStorage.addLogEventListener(this.observe, SpecialPowers.wrap(document).nodePrincipal);
+  }
+
+  var order = 0;
+  consoleListener.prototype  = {
+    observe(aSubject) {
+    ok(true, "Something has been received");
+
+    var obj = aSubject.wrappedJSObject;
+    if (obj.arguments[0] && obj.arguments[0].msg === 'consoleAndBlobs') {
+      ConsoleAPIStorage.removeLogEventListener(this.observe);
+      is(obj.arguments[0].blob.size, 3, "The size is correct");
+      is(obj.arguments[0].blob.type, 'foo/bar', "The type is correct");
+      SimpleTest.finish();
+    }
+  }
+  }
+
+  var cl = new consoleListener();
+
+  new Worker('worker_consoleAndBlobs.js');
+  SimpleTest.waitForExplicitFinish();
+
+    </script>
+  </body>
+</html>
diff --git a/dom/workers/test/test_consoleReplaceable.html b/dom/workers/test/test_consoleReplaceable.html
new file mode 100644
index 0000000000..b8a60411e4
--- /dev/null
+++ b/dom/workers/test/test_consoleReplaceable.html
@@ -0,0 +1,44 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<!--
+Tests of DOM Worker Console
+-->
+<head>
+  <title>Test for DOM Worker Console</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script class="testbody" language="javascript">
+  var worker = new Worker("consoleReplaceable_worker.js");
+
+  worker.onmessage = function(event) {
+    is(event.target, worker, "Worker and target match!");
+    ok(event.data.status, event.data.event);
+
+    if (event.data.last)
+      SimpleTest.finish();
+  };
+
+  worker.onerror = function(event) {
+    ok(false, "Worker had an error: " + event.message);
+    SimpleTest.finish();
+  }
+
+  worker.postMessage(true);
+
+  SimpleTest.waitForExplicitFinish();
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_contentWorker.html b/dom/workers/test/test_contentWorker.html
new file mode 100644
index 0000000000..38891a88c5
--- /dev/null
+++ b/dom/workers/test/test_contentWorker.html
@@ -0,0 +1,48 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test for DOM Worker privileged properties</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script class="testbody" language="javascript">
+
+  var workerFilename = "content_worker.js";
+  var worker = new Worker(workerFilename);
+
+  var props = {
+    'ctypes': 1,
+    'OS': 1
+  };
+
+  worker.onmessage = function(event) {
+    if (event.data.testfinished) {
+      SimpleTest.finish();
+      return;
+    }
+    var prop = event.data.prop;
+    ok(prop in props, "checking " + prop);
+    is(event.data.value, undefined, prop + " should be undefined");
+  };
+
+  worker.onerror = function(event) {
+    ok(false, "Worker had an error: " + event.message);
+    SimpleTest.finish();
+  }
+
+  SimpleTest.waitForExplicitFinish();
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_csp.html b/dom/workers/test/test_csp.html
new file mode 100644
index 0000000000..f3ef747372
--- /dev/null
+++ b/dom/workers/test/test_csp.html
@@ -0,0 +1,18 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test for DOM Worker + CSP</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<p id="display"></p>
+<div id="content" style="display: none"></div>
+<pre id="test"></pre>
+</body>
+<script type="text/javascript" src="test_csp.js"></script>
+</html>
diff --git a/dom/workers/test/test_csp.html^headers^ b/dom/workers/test/test_csp.html^headers^
new file mode 100644
index 0000000000..1c93210799
--- /dev/null
+++ b/dom/workers/test/test_csp.html^headers^
@@ -0,0 +1,2 @@
+Cache-Control: no-cache
+Content-Security-Policy: default-src 'self' blob:
diff --git a/dom/workers/test/test_csp.js b/dom/workers/test/test_csp.js
new file mode 100644
index 0000000000..8c2b53586a
--- /dev/null
+++ b/dom/workers/test/test_csp.js
@@ -0,0 +1,54 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+var tests = 3;
+
+SimpleTest.waitForExplicitFinish();
+
+testDone = function (event) {
+  if (!--tests) {
+    SimpleTest.finish();
+  }
+};
+
+// Workers don't inherit CSP
+worker = new Worker("csp_worker.js");
+worker.postMessage({ do: "eval" });
+worker.onmessage = function (event) {
+  is(event.data, 42, "Eval succeeded!");
+  testDone();
+};
+
+// blob: workers *do* inherit CSP
+xhr = new XMLHttpRequest();
+xhr.open("GET", "csp_worker.js");
+xhr.responseType = "blob";
+xhr.send();
+xhr.onload = e => {
+  uri = URL.createObjectURL(e.target.response);
+  worker = new Worker(uri);
+  worker.postMessage({ do: "eval" });
+  worker.onmessage = function (event) {
+    is(event.data, "EvalError: call to eval() blocked by CSP", "Eval threw");
+    testDone();
+  };
+};
+
+xhr = new XMLHttpRequest();
+xhr.open("GET", "csp_worker.js");
+xhr.responseType = "blob";
+xhr.send();
+xhr.onload = e => {
+  uri = URL.createObjectURL(e.target.response);
+  worker = new Worker(uri);
+  worker.postMessage({ do: "nest", uri, level: 3 });
+  worker.onmessage = function (event) {
+    is(
+      event.data,
+      "EvalError: call to eval() blocked by CSP",
+      "Eval threw in nested worker"
+    );
+    testDone();
+  };
+};
diff --git a/dom/workers/test/test_dataURLWorker.html b/dom/workers/test/test_dataURLWorker.html
new file mode 100644
index 0000000000..145b0e43f1
--- /dev/null
+++ b/dom/workers/test/test_dataURLWorker.html
@@ -0,0 +1,30 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+  <head>
+    <script src="/tests/SimpleTest/SimpleTest.js">
+    </script>
+    <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  </head>
+  <body>
+    <script type="text/javascript">
+      const message = "hi";
+      const url = "DATA:text/plain," +
+        "onmessage = function(event) {" +
+        "  postMessage(event.data);" +
+        "};";
+
+      var worker = new Worker(url);
+      worker.onmessage = function(event) {
+        is(event.data, message, "Got correct message");
+        SimpleTest.finish();
+      };
+      worker.postMessage(message);
+
+      SimpleTest.waitForExplicitFinish();
+    </script>
+  </body>
+</html>
diff --git a/dom/workers/test/test_dynamicImport.html b/dom/workers/test/test_dynamicImport.html
new file mode 100644
index 0000000000..bffef87d2d
--- /dev/null
+++ b/dom/workers/test/test_dynamicImport.html
@@ -0,0 +1,76 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<!--
+Tests of Worker Dynamic Import (Bug 1540913)
+Ensure that the script loader doesn't accidentally reorder events due to async work
+done by dynamic import
+-->
+<head>
+  <title>Test for Worker Dynamic Import (Bug 1540913)</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body onload="onLoad()">
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1540913">Worker Dynamic Import
+ Bug 1540913</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script class="testbody" type="text/javascript">
+SimpleTest.waitForExplicitFinish();
+
+async function onLoad() {
+  await SpecialPowers.pushPrefEnv(
+      { set: [["dom.workers.modules.enabled", true ]] });
+
+  const workers = [
+    new Worker("dynamicImport_worker.js", {type: "classic"}),
+    new Worker("dynamicImport_worker.js", {type: "module"})
+  ];
+
+  let successCount = 0;
+
+  for (const worker of workers) {
+    const events = [];
+    worker.onmessage = function(event) {
+      switch (event.data) {
+        case "first":
+          ok(events.length === 1 && events[0] === "second",
+             "first dynamic import returned");
+          events.push(event.data);
+          successCount++;
+          // Cheap way to make sure we only finish successfully after
+          // both the module and classic test is finished.
+          if (successCount == 2) {
+            SimpleTest.finish();
+          }
+          break;
+        case "second":
+          ok(events.length === 0,
+             "second dynamic import returned");
+          events.push(event.data);
+          break;
+        default:
+          ok(false, "Unexpected message:" + event.data);
+          SimpleTest.finish();
+      }
+    };
+
+    worker.onerror = function(event) {
+      ok(false, "Worker had an error:" + event.message);
+      SimpleTest.finish();
+    }
+
+    worker.postMessage("start");
+  }
+}
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_dynamicImport_and_terminate.html b/dom/workers/test/test_dynamicImport_and_terminate.html
new file mode 100644
index 0000000000..cf355572e6
--- /dev/null
+++ b/dom/workers/test/test_dynamicImport_and_terminate.html
@@ -0,0 +1,34 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test for Worker create script loader failure</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script class="testbody" type="text/javascript">
+
+SimpleTest.waitForExplicitFinish();
+
+document.addEventListener("DOMContentLoaded", () => {
+  const worker = new Worker("worker_dynamicImport.mjs", {"type": "module"});
+  setTimeout(() => {
+    worker.terminate();
+    ok(true, "done");
+    SimpleTest.finish();
+  }, 0);
+});
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_dynamicImport_early_termination.html b/dom/workers/test/test_dynamicImport_early_termination.html
new file mode 100644
index 0000000000..fb9096df14
--- /dev/null
+++ b/dom/workers/test/test_dynamicImport_early_termination.html
@@ -0,0 +1,79 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<!--
+Tests of Worker Dynamic Import (Bug 1540913)
+Ensure that the script loader doesn't fail if requests are terminated early.
+-->
+<head>
+  <title>Test for Worker Dynamic Import (Bug 1540913)</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body onload="onLoad()">
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1540913">Worker Dynamic Import
+ Bug 1540913</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script class="testbody" type="text/javascript">
+SimpleTest.waitForExplicitFinish();
+
+async function onLoad() {
+  await SpecialPowers.pushPrefEnv(
+      { set: [["dom.workers.modules.enabled", true ]] });
+
+  const workers = [
+    new Worker("dynamicImport_worker.js", {type: "classic"}),
+    new Worker("dynamicImport_worker.js", {type: "module"})
+  ]
+
+  let successCount = 0;
+
+  // In the implementation of dynamic import, every dynamic import has
+  // it's own ScriptLoader. To ensure that this is working correctly,
+  // this tests that if we re-order the dynamic import order,
+  // worker termination works as expected.
+  for (const worker of workers) {
+    const events = [];
+    worker.onmessage = function(event) {
+      switch (event.data) {
+        case "first":
+          ok(false, "first dynamic import returned");
+          SimpleTest.finish();
+          break;
+        case "second":
+          ok(events.length === 0,
+             "second dynamic import returned");
+          events.push(event.data);
+          worker.terminate()
+          successCount++;
+          // Cheap way to make sure we only finish successfully after
+          // both the module and classic test is finished.
+          if (successCount == 2) {
+            SimpleTest.finish();
+          }
+          break;
+        default:
+          ok(false, "Unexpected message:" + event.data);
+          SimpleTest.finish();
+      }
+    };
+
+    worker.onerror = function(event) {
+      ok(false, "Worker had an error:" + event.message);
+      SimpleTest.finish();
+    }
+
+    worker.postMessage("start");
+  }
+}
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_errorPropagation.html b/dom/workers/test/test_errorPropagation.html
new file mode 100644
index 0000000000..8eb899fe7e
--- /dev/null
+++ b/dom/workers/test/test_errorPropagation.html
@@ -0,0 +1,65 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+  <head>
+    <meta charset="utf-8">
+    <script src="/tests/SimpleTest/SimpleTest.js">
+    </script>
+    <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  </head>
+  <body>
+    <iframe id="workerFrame" src="errorPropagation_iframe.html"
+            onload="workerFrameLoaded();"></iframe>
+    <script type="text/javascript">
+      const workerCount = 3;
+
+      const errorMessage = "Error: expectedError";
+      const errorFilename = "http://mochi.test:8888/tests/dom/workers/test/" +
+                            "errorPropagation_worker.js";
+      const errorLineno = 49;
+
+      var workerFrame;
+
+      scopeErrorCount = 0;
+      workerErrorCount = 0;
+      windowErrorCount = 0;
+
+      function messageListener(event) {
+        if (event.type == "scope") {
+          scopeErrorCount++;
+        }
+        else if (event.type == "worker") {
+          workerErrorCount++;
+        }
+        else if (event.type == "window") {
+          windowErrorCount++;
+        }
+        else {
+          ok(false, "Bad event type: " + event.type);
+        }
+
+        is(event.data.message, errorMessage, "Correct message event.message");
+        is(event.data.filename, errorFilename,
+           "Correct message event.filename");
+        is(event.data.lineno, errorLineno, "Correct message event.lineno");
+
+        if (windowErrorCount == 1) {
+          is(scopeErrorCount, workerCount, "Good number of scope errors");
+          is(workerErrorCount, workerCount, "Good number of worker errors");
+          workerFrame.stop();
+          SimpleTest.finish();
+        }
+      }
+
+      function workerFrameLoaded() {
+        workerFrame = document.getElementById("workerFrame").contentWindow;
+        workerFrame.start(workerCount, messageListener);
+      }
+
+      SimpleTest.waitForExplicitFinish();
+    </script>
+  </body>
+</html>
diff --git a/dom/workers/test/test_errorwarning.html b/dom/workers/test/test_errorwarning.html
new file mode 100644
index 0000000000..282b46ec20
--- /dev/null
+++ b/dom/workers/test/test_errorwarning.html
@@ -0,0 +1,93 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<!--
+Test javascript.options.strict in Workers
+-->
+<head>
+  <title>Test javascript.options.strict in Workers</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script class="testbody" language="javascript">
+
+  var errors = 0;
+  function errorHandler(e) {
+    ok(true, "An error has been received!");
+    errors++;
+  }
+
+  function test_noErrors() {
+    errors = 0;
+
+    var worker = new Worker('errorwarning_worker.js');
+    worker.onerror = errorHandler;
+    worker.onmessage = function(e) {
+      if (e.data.type == 'ignore')
+        return;
+
+      if (e.data.type == 'error') {
+        errorHandler();
+        return;
+      }
+
+      if (e.data.type == 'finish') {
+        ok(errors == 0, "Here we are with 0 errors!");
+        runTests();
+      }
+    }
+
+    onerror = errorHandler;
+    worker.postMessage({ loop: 5, errors: false });
+  }
+
+  function test_errors() {
+    errors = 0;
+
+    var worker = new Worker('errorwarning_worker.js');
+    worker.onerror = errorHandler;
+    worker.onmessage = function(e) {
+      if (e.data.type == 'ignore')
+        return;
+
+      if (e.data.type == 'error') {
+        errorHandler();
+        return;
+      }
+
+      if (e.data.type == 'finish') {
+        ok(errors != 0, "Here we are with errors!");
+        runTests();
+      }
+    }
+
+    onerror = errorHandler;
+    worker.postMessage({ loop: 5, errors: true });
+  }
+
+  var tests = [ test_noErrors, test_errors ];
+  function runTests() {
+    var test = tests.shift();
+    if (test) {
+      test();
+    } else {
+      SimpleTest.finish();
+    }
+  }
+
+  runTests();
+  SimpleTest.waitForExplicitFinish();
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_eventDispatch.html b/dom/workers/test/test_eventDispatch.html
new file mode 100644
index 0000000000..e6bbd7e2d1
--- /dev/null
+++ b/dom/workers/test/test_eventDispatch.html
@@ -0,0 +1,32 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+  <head>
+    <script src="/tests/SimpleTest/SimpleTest.js">
+    </script>
+    <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  </head>
+  <body>
+    <script type="text/javascript">
+      const message = "Hi";
+
+      var messageCount = 0;
+
+      var worker = new Worker("eventDispatch_worker.js");
+      worker.onmessage = function(event) {
+        is(event.data, message, "Got correct data.");
+        if (!messageCount++) {
+          event.target.postMessage(event.data);
+          return;
+        }
+        SimpleTest.finish();
+      }
+      worker.postMessage(message);
+
+      SimpleTest.waitForExplicitFinish();
+    </script>
+  </body>
+</html>
diff --git a/dom/workers/test/test_fibonacci.html b/dom/workers/test/test_fibonacci.html
new file mode 100644
index 0000000000..c3e3e98574
--- /dev/null
+++ b/dom/workers/test/test_fibonacci.html
@@ -0,0 +1,51 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<!--
+Tests of DOM Worker Threads with Fibonacci
+-->
+<head>
+  <title>Test for DOM Worker Threads with Fibonacci</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=450452">DOM Worker Threads Fibonacci</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script class="testbody" type="text/javascript">
+
+  const seqNum = 5;
+
+  function recursivefib(n) {
+    return n < 2 ? n : recursivefib(n - 1) + recursivefib(n - 2);
+  }
+
+  var worker = new Worker("fibonacci_worker.js");
+
+  worker.onmessage = function(event) {
+    is(event.target, worker);
+    is(event.data, recursivefib(seqNum));
+    SimpleTest.finish();
+  };
+
+  worker.onerror = function(event) {
+    is(event.target, worker);
+    ok(false, "Worker had an error: " + event.message);
+    SimpleTest.finish();
+  };
+
+  worker.postMessage(seqNum);
+
+  SimpleTest.waitForExplicitFinish();
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_file.xhtml b/dom/workers/test/test_file.xhtml
new file mode 100644
index 0000000000..2b628e7f4d
--- /dev/null
+++ b/dom/workers/test/test_file.xhtml
@@ -0,0 +1,96 @@
+<?xml version="1.0"?>
+<?xml-stylesheet type="text/css" href="chrome://global/skin"?>
+<?xml-stylesheet type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css"?>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=123456
+-->
+<window title="Mozilla Bug 123456"
+        xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"/>
+  <script type="application/javascript" src="dom_worker_helper.js"/>
+
+  <!-- test results are displayed in the html:body -->
+  <body xmlns="http://www.w3.org/1999/xhtml">
+  <a href="https://bugzilla.mozilla.org/show_bug.cgi?id=123456"
+     target="_blank">Mozilla Bug 123456</a>
+
+  <div id="content" style="display: none">
+    <input id="fileList" type="file"></input>
+  </div>
+
+  </body>
+
+  <!-- test code goes here -->
+  <script type="application/javascript">
+  <![CDATA[
+
+  /** Test for Bug 123456 **/
+
+  var fileNum = 0;
+
+  /**
+   * Create a file which contains the given data and optionally adds the specified file extension.
+   */
+  function createFileWithData(fileData, /** optional */ extension) {
+    var testFile = Cc["@mozilla.org/file/directory_service;1"]
+                       .getService(Ci.nsIProperties)
+                       .get("ProfD", Ci.nsIFile);
+    var fileExtension = (extension == undefined) ? "" : "." + extension;
+    testFile.append("workerFile" + fileNum++ + fileExtension);
+
+    var outStream = Cc["@mozilla.org/network/file-output-stream;1"]
+                        .createInstance(Ci.nsIFileOutputStream);
+    outStream.init(testFile, 0x02 | 0x08 | 0x20, // write, create, truncate
+                   0o666, 0);
+    outStream.write(fileData, fileData.length);
+    outStream.close();
+
+    var fileList = document.getElementById('fileList');
+    fileList.value = testFile.path;
+
+    return fileList.files[0];
+  }
+
+  /**
+   * Create a worker to access file properties.
+   */
+  function accessFileProperties(file, expectedSize, expectedType) {
+    waitForWorkerFinish();
+
+    var worker = new Worker("file_worker.js");
+
+    worker.onerror = function(event) {
+      ok(false, "Worker had an error: " + event.message);
+      finish();
+    };
+
+    worker.onmessage = function(event) {
+      is(event.data.size, expectedSize, "size proproperty accessed from worker is not the same as on main thread.");
+      is(event.data.type, expectedType, "type proproperty accessed from worker is incorrect.");
+      is(event.data.name, file.name, "name proproperty accessed from worker is incorrect.");
+      is(event.data.lastModified, file.lastModified, "lastModified proproperty accessed from worker is incorrect.");
+      finish();
+    };
+
+    worker.postMessage(file);
+  }
+
+  // Empty file.
+  accessFileProperties(createFileWithData(""), 0, "");
+
+  // Typical use case.
+  accessFileProperties(createFileWithData("Hello"), 5, "");
+
+  // Longish file.
+  var text = "";
+  for (var i = 0; i < 10000; ++i) {
+    text += "long";
+  }
+  accessFileProperties(createFileWithData(text), 40000, "");
+
+  // Type detection based on extension.
+  accessFileProperties(createFileWithData("text", "txt"), 4, "text/plain");
+
+  ]]>
+  </script>
+</window>
diff --git a/dom/workers/test/test_fileBlobPosting.xhtml b/dom/workers/test/test_fileBlobPosting.xhtml
new file mode 100644
index 0000000000..61f4a8e909
--- /dev/null
+++ b/dom/workers/test/test_fileBlobPosting.xhtml
@@ -0,0 +1,85 @@
+<?xml version="1.0"?>
+<?xml-stylesheet type="text/css" href="chrome://global/skin"?>
+<?xml-stylesheet type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css"?>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=664783
+-->
+<window title="Mozilla Bug 664783"
+        xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"/>
+  <script type="application/javascript" src="dom_worker_helper.js"/>
+
+  <!-- test results are displayed in the html:body -->
+  <body xmlns="http://www.w3.org/1999/xhtml">
+  <a href="https://bugzilla.mozilla.org/show_bug.cgi?id=664783"
+     target="_blank">Mozilla Bug 664783</a>
+
+  <div id="content" style="display: none">
+    <input id="fileList" type="file"></input>
+  </div>
+
+  </body>
+
+  <!-- test code goes here -->
+  <script type="application/javascript">
+  <![CDATA[
+
+  /** Test for Bug 664783 **/
+
+  var fileNum = 0;
+
+  /**
+   * Create a file which contains the given data.
+   */
+  function createFileWithData(fileData) {
+    var testFile = Cc["@mozilla.org/file/directory_service;1"]
+                       .getService(Ci.nsIProperties)
+                       .get("ProfD", Ci.nsIFile);
+    testFile.append("workerBlobPosting" + fileNum++);
+
+    var outStream = Cc["@mozilla.org/network/file-output-stream;1"]
+                        .createInstance(Ci.nsIFileOutputStream);
+    outStream.init(testFile, 0x02 | 0x08 | 0x20, // write, create, truncate
+                   0o666, 0);
+    outStream.write(fileData, fileData.length);
+    outStream.close();
+
+    var fileList = document.getElementById('fileList');
+    fileList.value = testFile.path;
+
+    return fileList.files[0];
+  }
+
+  /**
+   * Create a worker which posts the same blob given. Used to test cloning of blobs.
+   * Checks the size, type, name and path of the file posted from the worker to ensure it
+   * is the same as the original.
+   */
+  function postBlob(file) {
+    var worker = new Worker("filePosting_worker.js");
+
+    worker.onerror = function(event) {
+      ok(false, "Worker had an error: " + event.message);
+      finish();
+    };
+
+    worker.onmessage = function(event) {
+      console.log(event.data);
+      is(event.data.size, file.size, "size of file posted from worker does not match file posted to worker.");
+      finish();
+    };
+
+    var blob = file.slice();
+    worker.postMessage(blob);
+    waitForWorkerFinish();
+  }
+
+  // Empty file.
+  postBlob(createFileWithData(""));
+
+  // Typical use case.
+  postBlob(createFileWithData("Hello"));
+
+  ]]>
+  </script>
+</window>
diff --git a/dom/workers/test/test_fileBlobSubWorker.xhtml b/dom/workers/test/test_fileBlobSubWorker.xhtml
new file mode 100644
index 0000000000..8b67552788
--- /dev/null
+++ b/dom/workers/test/test_fileBlobSubWorker.xhtml
@@ -0,0 +1,97 @@
+<?xml version="1.0"?>
+<?xml-stylesheet type="text/css" href="chrome://global/skin"?>
+<?xml-stylesheet type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css"?>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=664783
+-->
+<window title="Mozilla Bug 664783"
+        xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"/>
+  <script type="application/javascript" src="dom_worker_helper.js"/>
+
+  <!-- test results are displayed in the html:body -->
+  <body xmlns="http://www.w3.org/1999/xhtml">
+  <a href="https://bugzilla.mozilla.org/show_bug.cgi?id=664783"
+     target="_blank">Mozilla Bug 664783</a>
+
+  <div id="content" style="display: none">
+    <input id="fileList" type="file"></input>
+  </div>
+
+  </body>
+
+  <!-- test code goes here -->
+  <script type="application/javascript">
+  <![CDATA[
+
+  /** Test for Bug 664783 **/
+
+  var fileNum = 0;
+
+  /**
+   * Create a file which contains the given data and optionally adds the specified file extension.
+   */
+  function createFileWithData(fileData, /** optional */ extension) {
+    var testFile = Cc["@mozilla.org/file/directory_service;1"]
+                       .getService(Ci.nsIProperties)
+                       .get("ProfD", Ci.nsIFile);
+    var fileExtension = (extension == undefined) ? "" : "." + extension;
+    testFile.append("workerBlobSubWorker" + fileNum++ + fileExtension);
+
+    var outStream = Cc["@mozilla.org/network/file-output-stream;1"]
+                        .createInstance(Ci.nsIFileOutputStream);
+    outStream.init(testFile, 0x02 | 0x08 | 0x20, // write, create, truncate
+                   0o666, 0);
+    outStream.write(fileData, fileData.length);
+    outStream.close();
+
+    var fileList = document.getElementById('fileList');
+    fileList.value = testFile.path;
+
+    return fileList.files[0];
+  }
+
+  /**
+   * Create a worker to access blob properties.
+   */
+  function accessFileProperties(file, expectedSize) {
+    var worker = new Worker("fileBlobSubWorker_worker.js");
+
+    worker.onerror = function(event) {
+      ok(false, "Worker had an error: " + event.message);
+      finish();
+    };
+
+    worker.onmessage = function(event) {
+      if (event.data == undefined) {
+        ok(false, "Worker had an error.");
+      } else {
+        is(event.data.size, expectedSize, "size proproperty accessed from worker is not the same as on main thread.");
+      }
+      finish();
+    };
+
+    var blob = file.slice();
+    worker.postMessage(blob);
+    waitForWorkerFinish();
+  }
+
+  // Empty file.
+  accessFileProperties(createFileWithData(""), 0);
+
+  // Typical use case.
+  accessFileProperties(createFileWithData("Hello"), 5);
+
+  // Longish file.
+  var text = "";
+  for (var i = 0; i < 10000; ++i) {
+    text += "long";
+  }
+  accessFileProperties(createFileWithData(text), 40000);
+
+  // Type detection based on extension.
+  accessFileProperties(createFileWithData("text", "txt"), 4);
+
+  ]]>
+  </script>
+</window>
diff --git a/dom/workers/test/test_filePosting.xhtml b/dom/workers/test/test_filePosting.xhtml
new file mode 100644
index 0000000000..3ffa219516
--- /dev/null
+++ b/dom/workers/test/test_filePosting.xhtml
@@ -0,0 +1,85 @@
+<?xml version="1.0"?>
+<?xml-stylesheet type="text/css" href="chrome://global/skin"?>
+<?xml-stylesheet type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css"?>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=664783
+-->
+<window title="Mozilla Bug 664783"
+        xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"/>
+  <script type="application/javascript" src="dom_worker_helper.js"/>
+
+  <!-- test results are displayed in the html:body -->
+  <body xmlns="http://www.w3.org/1999/xhtml">
+  <a href="https://bugzilla.mozilla.org/show_bug.cgi?id=664783"
+     target="_blank">Mozilla Bug 664783</a>
+
+  <div id="content" style="display: none">
+    <input id="fileList" type="file"></input>
+  </div>
+
+  </body>
+
+  <!-- test code goes here -->
+  <script type="application/javascript">
+  <![CDATA[
+
+  /** Test for Bug 664783 **/
+
+  var fileNum = 0;
+
+  /**
+   * Create a file which contains the given data.
+   */
+  function createFileWithData(fileData) {
+    var testFile = Cc["@mozilla.org/file/directory_service;1"]
+                       .getService(Ci.nsIProperties)
+                       .get("ProfD", Ci.nsIFile);
+    testFile.append("workerFilePosting" + fileNum++);
+
+    var outStream = Cc["@mozilla.org/network/file-output-stream;1"]
+                        .createInstance(Ci.nsIFileOutputStream);
+    outStream.init(testFile, 0x02 | 0x08 | 0x20, // write, create, truncate
+                   0o666, 0);
+    outStream.write(fileData, fileData.length);
+    outStream.close();
+
+    var fileList = document.getElementById('fileList');
+    fileList.value = testFile.path;
+
+    return fileList.files[0];
+  }
+
+  /**
+   * Create a worker which posts the same file given. Used to test cloning of files.
+   * Checks the size, type, name and path of the file posted from the worker to ensure it
+   * is the same as the original.
+   */
+  function postFile(file) {
+    var worker = new Worker("file_worker.js");
+
+    worker.onerror = function(event) {
+      ok(false, "Worker had an error: " + event.message);
+      finish();
+    };
+
+    worker.onmessage = function(event) {
+      is(event.data.size, file.size, "size of file posted from worker does not match file posted to worker.");
+      is(event.data.type, file.type, "type of file posted from worker does not match file posted to worker.");
+      is(event.data.name, file.name, "name of file posted from worker does not match file posted to worker.");
+      finish();
+    };
+
+    worker.postMessage(file);
+    waitForWorkerFinish();
+  }
+
+  // Empty file.
+  postFile(createFileWithData(""));
+
+  // Typical use case.
+  postFile(createFileWithData("Hello"));
+
+  ]]>
+  </script>
+</window>
diff --git a/dom/workers/test/test_fileReadSlice.xhtml b/dom/workers/test/test_fileReadSlice.xhtml
new file mode 100644
index 0000000000..fa396e88e8
--- /dev/null
+++ b/dom/workers/test/test_fileReadSlice.xhtml
@@ -0,0 +1,93 @@
+<?xml version="1.0"?>
+<?xml-stylesheet type="text/css" href="chrome://global/skin"?>
+<?xml-stylesheet type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css"?>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=664783
+-->
+<window title="Mozilla Bug 664783"
+        xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"/>
+  <script type="application/javascript" src="dom_worker_helper.js"/>
+
+  <!-- test results are displayed in the html:body -->
+  <body xmlns="http://www.w3.org/1999/xhtml">
+  <a href="https://bugzilla.mozilla.org/show_bug.cgi?id=664783"
+     target="_blank">Mozilla Bug 664783</a>
+
+  <div id="content" style="display: none">
+    <input id="fileList" type="file"></input>
+  </div>
+
+  </body>
+
+  <!-- test code goes here -->
+  <script type="application/javascript">
+  <![CDATA[
+
+  if (navigator.platform.startsWith("Win")) {
+    SimpleTest.expectAssertions(0, 1);
+  }
+
+  /** Test for Bug 664783 **/
+
+  var fileNum = 0;
+
+  /**
+   * Create a file which contains the given data.
+   */
+  function createFileWithData(fileData) {
+    var testFile = Cc["@mozilla.org/file/directory_service;1"]
+                       .getService(Ci.nsIProperties)
+                       .get("ProfD", Ci.nsIFile);
+    testFile.append("workerReadSlice" + fileNum++);
+
+    var outStream = Cc["@mozilla.org/network/file-output-stream;1"]
+                        .createInstance(Ci.nsIFileOutputStream);
+    outStream.init(testFile, 0x02 | 0x08 | 0x20, // write, create, truncate
+                   0o666, 0);
+    outStream.write(fileData, fileData.length);
+    outStream.close();
+
+    var fileList = document.getElementById('fileList');
+    fileList.value = testFile.path;
+
+    return fileList.files[0];
+  }
+
+  /**
+   * Creates a worker which slices a blob to the given start and end offset and
+   * reads the content as text.
+   */
+  function readSlice(blob, start, end, expectedText) {
+    var worker = new Worker("fileReadSlice_worker.js");
+
+    worker.onerror = function(event) {
+      ok(false, "Worker had an error: " + event.message);
+      finish();
+    };
+
+    worker.onmessage = function(event) {
+      is(event.data, expectedText, "Text from sliced blob in worker is incorrect.");
+      finish();
+    };
+
+    var params = {blob, start, end};
+    worker.postMessage(params);
+    waitForWorkerFinish();
+  }
+
+  // Empty file.
+  readSlice(createFileWithData(""), 0, 0, "");
+
+  // Typical use case.
+  readSlice(createFileWithData("HelloBye"), 5, 8, "Bye");
+
+  // End offset too large.
+  readSlice(createFileWithData("HelloBye"), 5, 9, "Bye");
+
+  // Start of file.
+  readSlice(createFileWithData("HelloBye"), 0, 5, "Hello");
+
+  ]]>
+  </script>
+</window>
diff --git a/dom/workers/test/test_fileReaderSync.xhtml b/dom/workers/test/test_fileReaderSync.xhtml
new file mode 100644
index 0000000000..bba2890b5e
--- /dev/null
+++ b/dom/workers/test/test_fileReaderSync.xhtml
@@ -0,0 +1,198 @@
+<?xml version="1.0"?>
+<?xml-stylesheet type="text/css" href="chrome://global/skin"?>
+<?xml-stylesheet type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css"?>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=664783
+-->
+<window title="Mozilla Bug 664783"
+        xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"/>
+  <script type="application/javascript" src="dom_worker_helper.js"/>
+
+  <!-- test results are displayed in the html:body -->
+  <body xmlns="http://www.w3.org/1999/xhtml">
+  <a href="https://bugzilla.mozilla.org/show_bug.cgi?id=664783"
+     target="_blank">Mozilla Bug 664783</a>
+
+  <div id="content" style="display: none">
+    <input id="fileList" type="file"></input>
+  </div>
+
+  </body>
+
+  <!-- test code goes here -->
+  <script type="application/javascript">
+  <![CDATA[
+
+  /** Test for Bug 664783 **/
+
+  var fileNum = 0;
+
+  /**
+   * Create a file which contains the given data and optionally adds the specified file extension.
+   */
+  function createFileWithData(fileData, /** optional */ extension) {
+    var testFile = Cc["@mozilla.org/file/directory_service;1"]
+                       .getService(Ci.nsIProperties)
+                       .get("ProfD", Ci.nsIFile);
+    var fileExtension = (extension == undefined) ? "" : "." + extension;
+    testFile.append("workerFileReaderSync" + fileNum++ + fileExtension);
+
+    var outStream = Cc["@mozilla.org/network/file-output-stream;1"]
+                        .createInstance(Ci.nsIFileOutputStream);
+    outStream.init(testFile, 0x02 | 0x08 | 0x20, // write, create, truncate
+                   0o666, 0);
+    outStream.write(fileData, fileData.length);
+    outStream.close();
+
+    var fileList = document.getElementById('fileList');
+    fileList.value = testFile.path;
+
+    return fileList.files[0];
+  }
+
+  function convertToUTF16(s) {
+    res = "";
+    for (var i = 0; i < s.length; ++i) {
+      c = s.charCodeAt(i);
+      res += String.fromCharCode(c & 255, c >>> 8);
+    }
+    return res;
+  }
+
+  /**
+   * Converts the given string to a data URL of the specified mime type.
+   */
+  function convertToDataURL(mime, s) {
+    return "data:" + mime + ";base64," + btoa(s);
+  }
+
+  /**
+   * Create a worker to read a file containing fileData using FileReaderSync and
+   * checks the return type against the expected type. Optionally set an encoding
+   * for reading the file as text.
+   */
+  function readFileData(fileData, expectedText, /** optional */ encoding) {
+    var worker = new Worker("fileReaderSync_worker.js");
+
+    worker.onmessage = function(event) {
+      is(event.data.text, expectedText, "readAsText in worker returned incorrect result.");
+      is(event.data.bin, fileData, "readAsBinaryString in worker returned incorrect result.");
+      is(event.data.url, convertToDataURL("application/octet-stream", fileData), "readAsDataURL in worker returned incorrect result.");
+      is(event.data.arrayBuffer.byteLength, fileData.length, "readAsArrayBuffer returned buffer of incorrect length.");
+      finish();
+    };
+
+    worker.onerror = function(event) {
+      ok(false, "Worker had an error: " + event.message);
+      finish();
+    };
+
+    var params = {file: createFileWithData(fileData), encoding};
+
+    worker.postMessage(params);
+
+    waitForWorkerFinish();
+  }
+
+  /**
+   * Create a worker which reuses a FileReaderSync to read multiple files as DataURLs.
+   */
+  function reuseReaderForURL(files, expected) {
+    var worker = new Worker("fileReaderSync_worker.js");
+
+    worker.onerror = function(event) {
+      ok(false, "Worker had an error: " + event.message);
+      finish();
+    };
+
+    var k = 0;
+    worker.onmessage = function(event) {
+      is(event.data.url, expected[k], "readAsDataURL in worker returned incorrect result when reusing FileReaderSync.");
+      k++;
+      finish();
+    };
+
+    for (var i = 0; i < files.length; ++i) {
+      var params = {file: files[i], encoding: undefined};
+      worker.postMessage(params);
+      waitForWorkerFinish();
+    }
+  }
+
+  /**
+   * Create a worker which reuses a FileReaderSync to read multiple files as text.
+   */
+  function reuseReaderForText(fileData, expected) {
+    var worker = new Worker("fileReaderSync_worker.js");
+
+    worker.onerror = function(event) {
+      ok(false, "Worker had an error: " + event.message);
+      finish();
+    };
+
+    var k = 0;
+    worker.onmessage = function(event) {
+      is(event.data.text, expected[k++], "readAsText in worker returned incorrect result when reusing FileReaderSync.");
+      finish();
+    };
+
+    for (var i = 0; i < fileData.length; ++i) {
+      var params = {file: createFileWithData(fileData[i]), encoding: undefined};
+      worker.postMessage(params);
+      waitForWorkerFinish();
+    }
+  }
+
+
+  /**
+   * Creates a a worker which reads a file containing fileData as an ArrayBuffer.
+   * Verifies that the ArrayBuffer when interpreted as a string matches the original data.
+   */
+  function readArrayBuffer(fileData) {
+    var worker = new Worker("fileReaderSync_worker.js");
+
+    worker.onmessage = function(event) {
+      var view = new Uint8Array(event.data.arrayBuffer);
+      is(event.data.arrayBuffer.byteLength, fileData.length, "readAsArrayBuffer returned buffer of incorrect length.");
+      is(String.fromCharCode.apply(String, view), fileData, "readAsArrayBuffer returned buffer containing incorrect data.");
+      finish();
+    };
+
+    worker.onerror = function(event) {
+      ok(false, "Worker had an error: " + event.message);
+      finish();
+    };
+
+    var params = {file: createFileWithData(fileData), encoding: undefined};
+
+    worker.postMessage(params);
+
+    waitForWorkerFinish();
+  }
+
+  // Empty file.
+  readFileData("", "");
+
+  // Typical use case.
+  readFileData("text", "text");
+
+  // Test reading UTF-16 characters.
+  readFileData(convertToUTF16("text"), "text", "UTF-16");
+
+  // First read a file of type "text/plain", then read a file of type "application/octet-stream".
+  reuseReaderForURL([createFileWithData("text", "txt"), createFileWithData("text")],
+                    [convertToDataURL("text/plain", "text"),
+                     convertToDataURL("application/octet-stream", "text")]);
+
+  // First read UTF-16 characters marked using BOM, then read UTF-8 characters.
+  reuseReaderForText([convertToUTF16("\ufefftext"), "text"],
+                     ["text", "text"]);
+
+  // Reading data as ArrayBuffer.
+  readArrayBuffer("");
+  readArrayBuffer("text");
+
+  ]]>
+  </script>
+</window>
diff --git a/dom/workers/test/test_fileReaderSyncErrors.xhtml b/dom/workers/test/test_fileReaderSyncErrors.xhtml
new file mode 100644
index 0000000000..626b67e1ba
--- /dev/null
+++ b/dom/workers/test/test_fileReaderSyncErrors.xhtml
@@ -0,0 +1,83 @@
+<?xml version="1.0"?>
+<?xml-stylesheet type="text/css" href="chrome://global/skin"?>
+<?xml-stylesheet type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css"?>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=664783
+-->
+<window title="Mozilla Bug 664783"
+        xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"/>
+  <script type="application/javascript" src="dom_worker_helper.js"/>
+
+  <!-- test results are displayed in the html:body -->
+  <body xmlns="http://www.w3.org/1999/xhtml">
+  <a href="https://bugzilla.mozilla.org/show_bug.cgi?id=664783"
+     target="_blank">Mozilla Bug 664783</a>
+
+  <div id="content" style="display: none">
+    <input id="fileList" type="file"></input>
+  </div>
+
+  </body>
+
+  <!-- test code goes here -->
+  <script type="application/javascript">
+  <![CDATA[
+
+  /** Test for Bug 664783 **/
+
+  var fileNum = 0;
+
+  /**
+   * Create a file which contains the given data.
+   */
+  function createFileWithData(fileData) {
+    var testFile = Cc["@mozilla.org/file/directory_service;1"]
+                       .getService(Ci.nsIProperties)
+                       .get("ProfD", Ci.nsIFile);
+    testFile.append("workerFileReaderSyncErrors" + fileNum++);
+
+    var outStream = Cc["@mozilla.org/network/file-output-stream;1"]
+                        .createInstance(Ci.nsIFileOutputStream);
+    outStream.init(testFile, 0x02 | 0x08 | 0x20, // write, create, truncate
+                   0o666, 0);
+    outStream.write(fileData, fileData.length);
+    outStream.close();
+
+    var fileList = document.getElementById('fileList');
+    fileList.value = testFile.path;
+
+    return fileList.files[0];
+  }
+
+  /**
+   * Creates a worker which runs errors cases.
+   */
+  function runWorkerErrors(file) {
+    var worker = new Worker("fileReaderSyncErrors_worker.js");
+
+    worker.onerror = function(event) {
+      ok(false, "Worker had an error: " + event.message);
+      finish();
+    };
+
+    worker.onmessage = function(event) {
+      if(event.data == undefined) {
+        // Worker returns undefined when tests have finished running.
+        finish();
+      } else {
+        // Otherwise worker will return results of tests to be evaluated.
+        is(event.data.actual, event.data.expected, event.data.message);
+      }
+    };
+
+    worker.postMessage(file);
+    waitForWorkerFinish();
+  }
+
+  // Run worker which creates exceptions.
+  runWorkerErrors(createFileWithData("text"));
+
+  ]]>
+  </script>
+</window>
diff --git a/dom/workers/test/test_fileReaderSync_when_closing.html b/dom/workers/test/test_fileReaderSync_when_closing.html
new file mode 100644
index 0000000000..d5fadbaa65
--- /dev/null
+++ b/dom/workers/test/test_fileReaderSync_when_closing.html
@@ -0,0 +1,54 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <meta charset="utf-8">
+  <title>Test for FileReaderSync when the worker is closing</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+  <script type="application/javascript">
+
+// In order to exercise FileReaderSync::SyncRead's syncLoop-using AsyncWait()
+// path, we need to provide a stream that will both 1) not have all the data
+// immediately available (eliminating memory-backed Blobs) and 2) return
+// NS_BASE_STREAM_WOULD_BLOCK.  Under e10s, any Blob/File sourced from the
+// parent process (as loadChromeScript performs) will be backed by an
+// RemoteLazyInputStream and will behave this way on first use (when it is in
+// the eInit state).  For ease of testing, we reuse script_createFile.js which
+// involves a file on disk, but a memory-backed Blob from the parent process
+// would be equally fine.  Under non-e10s, this File will not do the right
+// thing because a synchronous nsFileInputStream will be made directly
+// available and the AsyncWait path won't be taken, but the test will still
+// pass.
+
+var url = SimpleTest.getTestFileURL("script_createFile.js");
+var script = SpecialPowers.loadChromeScript(url);
+
+function onOpened(message) {
+  function workerCode() {
+    onmessage = function(e) {
+      self.close();
+      var fr = new FileReaderSync();
+      self.postMessage(fr.readAsText(e.data));
+    }
+  }
+
+  var b = new Blob([workerCode+'workerCode();']);
+  var w = new Worker(URL.createObjectURL(b));
+  w.onmessage = function(e) {
+    is(e.data, "Hello world!", "The blob content is OK!");
+    SimpleTest.finish();
+  }
+
+  w.postMessage(message.data);
+}
+
+script.addMessageListener("nonEmptyFile.opened", onOpened);
+script.sendAsyncMessage("nonEmptyFile.open");
+
+SimpleTest.waitForExplicitFinish();
+
+  </script>
+</body>
+</html>
diff --git a/dom/workers/test/test_fileSlice.xhtml b/dom/workers/test/test_fileSlice.xhtml
new file mode 100644
index 0000000000..c352404cc1
--- /dev/null
+++ b/dom/workers/test/test_fileSlice.xhtml
@@ -0,0 +1,105 @@
+<?xml version="1.0"?>
+<?xml-stylesheet type="text/css" href="chrome://global/skin"?>
+<?xml-stylesheet type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css"?>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=664783
+-->
+<window title="Mozilla Bug 664783"
+        xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"/>
+  <script type="application/javascript" src="dom_worker_helper.js"/>
+
+  <!-- test results are displayed in the html:body -->
+  <body xmlns="http://www.w3.org/1999/xhtml">
+  <a href="https://bugzilla.mozilla.org/show_bug.cgi?id=664783"
+     target="_blank">Mozilla Bug 664783</a>
+
+  <div id="content" style="display: none">
+    <input id="fileList" type="file"></input>
+  </div>
+
+  </body>
+
+  <!-- test code goes here -->
+  <script type="application/javascript">
+  <![CDATA[
+
+  /** Test for Bug 664783 **/
+
+  var fileNum = 0;
+
+  /**
+   * Create a file which contains the given data and optionally adds the specified file extension.
+   */
+  function createFileWithData(fileData, /** optional */ extension) {
+    var testFile = Cc["@mozilla.org/file/directory_service;1"]
+                       .getService(Ci.nsIProperties)
+                       .get("ProfD", Ci.nsIFile);
+    var fileExtension = (extension == undefined) ? "" : "." + extension;
+    testFile.append("workerSlice" + fileNum++ + fileExtension);
+
+    var outStream = Cc["@mozilla.org/network/file-output-stream;1"]
+                        .createInstance(Ci.nsIFileOutputStream);
+    outStream.init(testFile, 0x02 | 0x08 | 0x20, // write, create, truncate
+                   0o666, 0);
+    outStream.write(fileData, fileData.length);
+    outStream.close();
+
+    var fileList = document.getElementById('fileList');
+    fileList.value = testFile.path;
+
+    return fileList.files[0];
+  }
+
+  /**
+   * Starts a worker which slices the blob to the given start offset and optional end offset and
+   * content type. It then verifies that the size and type of the sliced blob is correct.
+   */
+  function createSlice(blob, start, expectedLength, /** optional */ end, /** optional */ contentType) {
+    var worker = new Worker("fileSlice_worker.js");
+
+    worker.onerror = function(event) {
+      ok(false, "Worker had an error: " + event.message);
+      finish();
+    };
+
+    worker.onmessage = function(event) {
+      is(event.data.size, expectedLength, "size property of slice is incorrect.");
+      is(event.data.type, contentType ? contentType : blob.type, "type property of slice is incorrect.");
+      finish();
+    };
+
+    var params = {blob, start, end, contentType};
+    worker.postMessage(params);
+    waitForWorkerFinish();
+  }
+
+  // Empty file.
+  createSlice(createFileWithData(""), 0, 0, 0);
+
+  // Typical use case.
+  createSlice(createFileWithData("Hello"), 1, 1, 2);
+
+  // Longish file.
+  var text = "";
+  for (var i = 0; i < 10000; ++i) {
+    text += "long";
+  }
+  createSlice(createFileWithData(text), 2000, 2000, 4000);
+
+  // Slice to different type.
+  createSlice(createFileWithData("text", "txt"), 0, 2, 2, "image/png");
+
+  // Length longer than blob.
+  createSlice(createFileWithData("text"), 0, 4, 20);
+
+  // Start longer than blob.
+  createSlice(createFileWithData("text"), 20, 0, 4);
+
+  // No optional arguments
+  createSlice(createFileWithData("text"), 0, 4);
+  createSlice(createFileWithData("text"), 2, 2);
+
+  ]]>
+  </script>
+</window>
diff --git a/dom/workers/test/test_fileSubWorker.xhtml b/dom/workers/test/test_fileSubWorker.xhtml
new file mode 100644
index 0000000000..92aa3b1a17
--- /dev/null
+++ b/dom/workers/test/test_fileSubWorker.xhtml
@@ -0,0 +1,98 @@
+<?xml version="1.0"?>
+<?xml-stylesheet type="text/css" href="chrome://global/skin"?>
+<?xml-stylesheet type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css"?>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=664783
+-->
+<window title="Mozilla Bug 664783"
+        xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"/>
+  <script type="application/javascript" src="dom_worker_helper.js"/>
+
+  <!-- test results are displayed in the html:body -->
+  <body xmlns="http://www.w3.org/1999/xhtml">
+  <a href="https://bugzilla.mozilla.org/show_bug.cgi?id=664783"
+     target="_blank">Mozilla Bug 664783</a>
+
+  <div id="content" style="display: none">
+    <input id="fileList" type="file"></input>
+  </div>
+
+  </body>
+
+  <!-- test code goes here -->
+  <script type="application/javascript">
+  <![CDATA[
+
+  /** Test for Bug 664783 **/
+
+  var fileNum = 0;
+
+  /**
+   * Create a file which contains the given data and optionally adds the specified file extension.
+   */
+  function createFileWithData(fileData, /** optional */ extension) {
+    var testFile = Cc["@mozilla.org/file/directory_service;1"]
+                       .getService(Ci.nsIProperties)
+                       .get("ProfD", Ci.nsIFile);
+    var fileExtension = (extension == undefined) ? "" : "." + extension;
+    testFile.append("workerSubWorker" + fileNum++ + fileExtension);
+
+    var outStream = Cc["@mozilla.org/network/file-output-stream;1"]
+                        .createInstance(Ci.nsIFileOutputStream);
+    outStream.init(testFile, 0x02 | 0x08 | 0x20, // write, create, truncate
+                   0o666, 0);
+    outStream.write(fileData, fileData.length);
+    outStream.close();
+
+    var fileList = document.getElementById('fileList');
+    fileList.value = testFile.path;
+
+    return fileList.files[0];
+  }
+
+  /**
+   * Create a worker to access file properties.
+   */
+  function accessFileProperties(file, expectedSize, expectedType) {
+    var worker = new Worker("fileSubWorker_worker.js");
+
+    worker.onerror = function(event) {
+      ok(false, "Worker had an error: " + event.message);
+      finish();
+    };
+
+    worker.onmessage = function(event) {
+      if (event.data == undefined) {
+        ok(false, "Worker had an error.");
+      } else {
+        is(event.data.size, expectedSize, "size proproperty accessed from worker is not the same as on main thread.");
+        is(event.data.type, expectedType, "type proproperty accessed from worker is incorrect.");
+        is(event.data.name, file.name, "name proproperty accessed from worker is incorrect.");
+      }
+      finish();
+    };
+
+    worker.postMessage(file);
+    waitForWorkerFinish();
+  }
+
+  // Empty file.
+  accessFileProperties(createFileWithData(""), 0, "");
+
+  // Typical use case.
+  accessFileProperties(createFileWithData("Hello"), 5, "");
+
+  // Longish file.
+  var text = "";
+  for (var i = 0; i < 10000; ++i) {
+    text += "long";
+  }
+  accessFileProperties(createFileWithData(text), 40000, "");
+
+  // Type detection based on extension.
+  accessFileProperties(createFileWithData("text", "txt"), 4, "text/plain");
+
+  ]]>
+  </script>
+</window>
diff --git a/dom/workers/test/test_importScripts.html b/dom/workers/test/test_importScripts.html
new file mode 100644
index 0000000000..0e6a3dde5e
--- /dev/null
+++ b/dom/workers/test/test_importScripts.html
@@ -0,0 +1,53 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<!--
+Tests of DOM Worker Threads (Bug 437152)
+-->
+<head>
+  <title>Test for DOM Worker Threads (Bug 437152)</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=437152">DOM Worker Threads Bug 437152</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script class="testbody" type="text/javascript">
+
+  var worker = new Worker("importScripts_worker.js");
+
+  worker.onmessage = function(event) {
+    switch (event.data) {
+      case "started":
+        worker.postMessage("stop");
+        break;
+      case "stopped":
+        ok(true, "worker correctly stopped");
+        SimpleTest.finish();
+        break;
+      default:
+        ok(false, "Unexpected message:" + event.data);
+        SimpleTest.finish();
+    }
+  };
+
+  worker.onerror = function(event) {
+    ok(false, "Worker had an error:" + event.message);
+    SimpleTest.finish();
+  }
+
+  worker.postMessage("start");
+
+  SimpleTest.waitForExplicitFinish();
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_importScripts_1.html b/dom/workers/test/test_importScripts_1.html
new file mode 100644
index 0000000000..2c75a3ed91
--- /dev/null
+++ b/dom/workers/test/test_importScripts_1.html
@@ -0,0 +1,35 @@
+<head>
+  <title>Test for ServiceWorker importScripts</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<script id="worker" type="javascript/worker">
+onconnect = async function(e) {
+    e.ports[0].onmessage = async function(msg) {
+      try {
+        self.importScripts("N:", "");
+      } catch (ex) {
+        e.source.postMessage("done");
+      }
+    };
+};
+</script>
+<script>
+SimpleTest.waitForExplicitFinish();
+document.addEventListener("DOMContentLoaded", async () => {
+    const blob = new Blob([document.querySelector('#worker').textContent],
+                          {type: "text/javascript"});
+    const sw = new SharedWorker(window.URL.createObjectURL(blob));
+    sw.port.postMessage([], []);
+    sw.port.onmessage = function(e) {
+      if (e.data == "done") {
+        ok(true);
+        SimpleTest.finish();
+      }
+    };
+});
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_importScripts_2.html b/dom/workers/test/test_importScripts_2.html
new file mode 100644
index 0000000000..f40b9a64ed
--- /dev/null
+++ b/dom/workers/test/test_importScripts_2.html
@@ -0,0 +1,34 @@
+<head>
+  <title>Test for Worker importScripts</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<script id="worker" type="javascript/worker">
+onmessage = async function(msg) {
+  try {
+    self.importScripts("N:", "");
+  } catch (ex) {
+    postMessage("done");
+  }
+};
+
+</script>
+<script>
+SimpleTest.waitForExplicitFinish();
+document.addEventListener("DOMContentLoaded", async () => {
+    const blob = new Blob([document.querySelector('#worker').textContent],
+                          {type: "text/javascript"});
+    const worker = new Worker(window.URL.createObjectURL(blob));
+    worker.postMessage([], []);
+    worker.onmessage = function(e) {
+      if (e.data == "done") {
+        ok(true);
+        SimpleTest.finish();
+      }
+    };
+});
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_importScripts_3rdparty.html b/dom/workers/test/test_importScripts_3rdparty.html
new file mode 100644
index 0000000000..7f10f23faf
--- /dev/null
+++ b/dom/workers/test/test_importScripts_3rdparty.html
@@ -0,0 +1,136 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test for 3rd party imported script and muted errors</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<script type="text/javascript">
+
+const workerURL = 'http://mochi.test:8888/tests/dom/workers/test/importScripts_3rdParty_worker.js';
+
+const sameOriginURL = 'http://mochi.test:8888/tests/dom/workers/test/invalid.js'
+
+var tests = [
+  function() {
+    var worker = new Worker("importScripts_3rdParty_worker.js");
+    worker.onmessage = function(event) {
+      ok("result" in event.data && event.data.result, "It seems we don't share data!");
+      next();
+    };
+
+    worker.postMessage({ url: sameOriginURL, test: 'try', nested: false });
+  },
+
+  function() {
+    var worker = new Worker("importScripts_3rdParty_worker.js");
+    worker.onmessage = function(event) {
+      ok("result" in event.data && event.data.result, "It seems we don't share data in nested workers!");
+      next();
+    };
+
+    worker.postMessage({ url: sameOriginURL, test: 'try', nested: true });
+  },
+
+  function() {
+    var worker = new Worker("importScripts_3rdParty_worker.js");
+    worker.onmessage = function(event) {
+      ok("result" in event.data && event.data.result, "It seems we don't share data via eventListener!");
+      next();
+    };
+
+    worker.postMessage({ url: sameOriginURL, test: 'eventListener', nested: false });
+  },
+
+  function() {
+    var worker = new Worker("importScripts_3rdParty_worker.js");
+    worker.onmessage = function(event) {
+      ok("result" in event.data && event.data.result, "It seems we don't share data in nested workers via eventListener!");
+      next();
+    };
+
+    worker.postMessage({ url: sameOriginURL, test: 'eventListener', nested: true });
+  },
+
+  function() {
+    var worker = new Worker("importScripts_3rdParty_worker.js");
+    worker.onmessage = function(event) {
+      ok("result" in event.data && event.data.result, "It seems we don't share data via onerror!");
+      next();
+    };
+    worker.onerror = function(event) {
+      event.preventDefault();
+    }
+
+    worker.postMessage({ url: sameOriginURL, test: 'onerror', nested: false });
+  },
+
+  function() {
+    var worker = new Worker("importScripts_3rdParty_worker.js");
+    worker.onerror = function(event) {
+      event.preventDefault();
+      ok(event instanceof ErrorEvent, "ErrorEvent received.");
+      is(event.filename, workerURL, "ErrorEvent.filename is correct");
+      next();
+    };
+
+    worker.postMessage({ url: sameOriginURL, test: 'none', nested: false });
+  },
+
+  function() {
+    var worker = new Worker("importScripts_3rdParty_worker.js");
+    worker.addEventListener("error", function(event) {
+      event.preventDefault();
+      ok(event instanceof ErrorEvent, "ErrorEvent received.");
+      is(event.filename, workerURL, "ErrorEvent.filename is correct");
+      next();
+    });
+
+    worker.postMessage({ url: sameOriginURL, test: 'none', nested: false });
+  },
+
+  function() {
+    var worker = new Worker("importScripts_3rdParty_worker.js");
+    worker.onerror = function(event) {
+      ok(false, "No error should be received!");
+    };
+
+    worker.onmessage = function(event) {
+      ok("error" in event.data && event.data.error, "The error has been fully received from a nested worker");
+      next();
+    };
+    worker.postMessage({ url: sameOriginURL, test: 'none', nested: true });
+  },
+
+  function() {
+    var url = URL.createObjectURL(new Blob(["%&%^&%^"]));
+    var worker = new Worker(url);
+    worker.onerror = function(event) {
+      event.preventDefault();
+      ok(event instanceof Event, "Event received.");
+      next();
+    };
+  }
+];
+
+function next() {
+  if (!tests.length) {
+    SimpleTest.finish();
+    return;
+  }
+
+  var test = tests.shift();
+  test();
+}
+
+SimpleTest.waitForExplicitFinish();
+next();
+
+</script>
+</body>
+</html>
diff --git a/dom/workers/test/test_importScripts_mixedcontent.html b/dom/workers/test/test_importScripts_mixedcontent.html
new file mode 100644
index 0000000000..04281deaea
--- /dev/null
+++ b/dom/workers/test/test_importScripts_mixedcontent.html
@@ -0,0 +1,50 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Bug 1198078 - test that we respect mixed content blocking in importScript() inside workers</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1198078">DOM Worker Threads Bug 1198078</a>
+<iframe></iframe>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script class="testbody" type="text/javascript">
+
+  onmessage = function(event) {
+    switch (event.data.status) {
+      case "done":
+        SimpleTest.finish();
+        break;
+      case "ok":
+        ok(event.data.data, event.data.msg);
+        break;
+      default:
+        ok(false, "Unexpected message:" + event.data);
+        SimpleTest.finish();
+    }
+  };
+
+  SimpleTest.waitForExplicitFinish();
+  onload = function() {
+    SpecialPowers.pushPrefEnv({"set": [
+      ["dom.workers.sharedWorkers.enabled", true],
+      ["security.mixed_content.block_active_content", false],
+    ]}, function() {
+      var iframe = document.querySelector("iframe");
+      iframe.src = "https://example.com/tests/dom/workers/test/importScripts_mixedcontent.html";
+    });
+  };
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_instanceof.html b/dom/workers/test/test_instanceof.html
new file mode 100644
index 0000000000..3a66674877
--- /dev/null
+++ b/dom/workers/test/test_instanceof.html
@@ -0,0 +1,40 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<!--
+Tests of DOM Worker JSON messages
+-->
+<head>
+  <title>Test for DOM Worker Navigator</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script src="json_worker.js" language="javascript"></script>
+<script class="testbody" language="javascript">
+
+  var worker = new Worker("instanceof_worker.js");
+
+  worker.onmessage = function(event) {
+    ok(event.data.status, event.data.event);
+
+    if (event.data.last)
+      SimpleTest.finish();
+  };
+
+  worker.postMessage(42);
+
+  SimpleTest.waitForExplicitFinish();
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_json.html b/dom/workers/test/test_json.html
new file mode 100644
index 0000000000..26e951aa63
--- /dev/null
+++ b/dom/workers/test/test_json.html
@@ -0,0 +1,89 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<!--
+Tests of DOM Worker JSON messages
+-->
+<head>
+  <title>Test for DOM Worker Navigator</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script src="json_worker.js" language="javascript"></script>
+<script class="testbody" language="javascript">
+
+  ok(messages.length, "No messages to test!");
+
+  var worker = new Worker("json_worker.js");
+
+  var index = 0;
+  worker.onmessage = function(event) {
+    var key = messages[index++];
+
+    // Loop for the ones we shouldn't receive.
+    while (key.exception) {
+      key = messages[index++];
+    }
+
+    is(typeof event.data, key.type, "Bad type! " + messages.indexOf(key));
+
+    if (key.array) {
+      is(event.data instanceof Array, key.array,
+         "Array mismatch! " + messages.indexOf(key));
+    }
+
+    if (key.isNaN) {
+      ok(isNaN(event.data), "Should be NaN!" + messages.indexOf(key));
+    }
+
+    if (key.isInfinity) {
+      is(event.data, Infinity, "Should be Infinity!" + messages.indexOf(key));
+    }
+
+    if (key.isNegativeInfinity) {
+      is(event.data, -Infinity, "Should be -Infinity!" + messages.indexOf(key));
+    }
+
+    if (key.shouldCompare || key.shouldEqual) {
+      ok(event.data == key.compareValue,
+         "Values don't compare! "  + messages.indexOf(key));
+    }
+
+    if (key.shouldEqual) {
+      ok(event.data === key.compareValue,
+         "Values don't equal! " + messages.indexOf(key));
+    }
+
+    if (key.jsonValue) {
+      is(JSON.stringify(event.data), key.jsonValue,
+         "Object stringification inconsistent!" + messages.indexOf(key));
+    }
+
+    if (event.data == "testFinished") {
+      is(index, messages.length, "Didn't see the right number of messages!");
+      SimpleTest.finish();
+    }
+  };
+
+  worker.onerror = function(event) {
+    ok(false, "Worker had an error: " + event.message);
+    SimpleTest.finish();
+  }
+
+  worker.postMessage("start");
+
+  SimpleTest.waitForExplicitFinish();
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_loadEncoding.html b/dom/workers/test/test_loadEncoding.html
new file mode 100644
index 0000000000..e7afb2fc82
--- /dev/null
+++ b/dom/workers/test/test_loadEncoding.html
@@ -0,0 +1,50 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Bug 484305 - Load workers as UTF-8</title>
+  <meta http-equiv="content-type" content="text/html; charset=KOI8-R">
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=484305">Bug 484305 - Load workers as UTF-8</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script class="testbody" type="text/javascript">
+
+SimpleTest.waitForExplicitFinish();
+
+var canonical = String.fromCharCode(0x41F, 0x440, 0x438, 0x432, 0x435, 0x442);
+ok(document.inputEncoding === "KOI8-R", "Document encoding is KOI8-R");
+
+// Worker sends two strings, one with `canonical` encoded in KOI8-R and one as UTF-8.
+// Since Worker scripts should always be decoded using UTF-8, even if the owning document's charset is different, the UTF-8 decode should match, while KOI8-R should fail.
+var counter = 0;
+var worker = new Worker("loadEncoding_worker.js");
+worker.onmessage = function(e) {
+  if (e.data.encoding === "KOI8-R") {
+    ok(e.data.text !== canonical, "KOI8-R decoded text should not match");
+  } else if (e.data.encoding === "UTF-8") {
+    ok(e.data.text === canonical, "UTF-8 decoded text should match");
+  }
+  counter++;
+  if (counter === 2)
+    SimpleTest.finish();
+}
+
+worker.onerror = function(e) {
+  ok(false, "Worker error");
+  SimpleTest.finish();
+}
+</script>
+
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_loadError.html b/dom/workers/test/test_loadError.html
new file mode 100644
index 0000000000..dec29d00c4
--- /dev/null
+++ b/dom/workers/test/test_loadError.html
@@ -0,0 +1,67 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<html>
+<head>
+  <title>Test for DOM Worker Threads</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<pre id="test">
+<script class="testbody" type="text/javascript">
+"use strict";
+
+function nextTest() {
+  (function(){
+    function workerfunc() {
+      var subworker = new Worker("about:blank");
+      subworker.onerror = function(e) {
+        e.preventDefault();
+        postMessage("ERROR");
+      }
+    }
+    var b = new Blob([workerfunc+'workerfunc();']);
+    var u = URL.createObjectURL(b);
+    function callworker(i) {
+      var w = new Worker(u);
+      URL.revokeObjectURL(u);
+      w.onmessage = function(e) {
+        is(i, 0, 'Message received');
+        is(e.data, "ERROR",
+           "Should catch the error when loading inner script");
+        if (++i < 2) callworker(i);
+        else SimpleTest.finish();
+      };
+      w.onerror = function(e) {
+        is(i, 1, 'OnError received');
+        SimpleTest.finish();
+      }
+    }
+    callworker(0);
+  })();
+}
+
+try {
+  var worker = new Worker("about:blank");
+  worker.onerror = function(e) {
+    e.preventDefault();
+    nextTest();
+  }
+
+  worker.onmessage = function(event) {
+    ok(false, "Shouldn't get a message!");
+    SimpleTest.finish();
+  }
+} catch (e) {
+  ok(false, "This should not happen.");
+}
+
+
+SimpleTest.waitForExplicitFinish();
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_location.html b/dom/workers/test/test_location.html
new file mode 100644
index 0000000000..55c94ae1cf
--- /dev/null
+++ b/dom/workers/test/test_location.html
@@ -0,0 +1,72 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<!--
+Tests of DOM Worker Location
+-->
+<head>
+  <title>Test for DOM Worker Location</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script class="testbody" language="javascript">
+
+  var thisFilename = "test_location.html";
+  var workerFilename = "location_worker.js";
+
+  var href = window.location.href
+  var queryPos = href.lastIndexOf(window.location.search);
+  var baseHref = href.substr(0, href.substr(0, queryPos).lastIndexOf("/") + 1);
+
+  var path = window.location.pathname;
+  var basePath = path.substr(0, path.lastIndexOf("/") + 1);
+
+  var strings = {
+    "toString": baseHref + workerFilename,
+    "href": baseHref + workerFilename,
+    "protocol": window.location.protocol,
+    "host": window.location.host,
+    "hostname": window.location.hostname,
+    "port": window.location.port,
+    "pathname": basePath + workerFilename,
+    "search": "",
+    "hash": "",
+    "origin": "http://mochi.test:8888"
+  };
+
+  var lastSlash = href.substr(0, queryPos).lastIndexOf("/") + 1;
+  is(thisFilename,
+     href.substr(lastSlash, queryPos - lastSlash),
+     "Correct filename ");
+
+  var worker = new Worker(workerFilename);
+
+  worker.onmessage = function(event) {
+    if (event.data.string == "testfinished") {
+      SimpleTest.finish();
+      return;
+    }
+    ok(event.data.string in strings, event.data.string);
+    is(event.data.value, strings[event.data.string], event.data.string);
+  };
+
+  worker.onerror = function(event) {
+    ok(false, "Worker had an error: " + event.message);
+    SimpleTest.finish();
+  }
+
+  SimpleTest.waitForExplicitFinish();
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_longThread.html b/dom/workers/test/test_longThread.html
new file mode 100644
index 0000000000..80602419ca
--- /dev/null
+++ b/dom/workers/test/test_longThread.html
@@ -0,0 +1,58 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<!--
+Tests of DOM Worker Threads (Bug 437152)
+-->
+<head>
+  <title>Test for DOM Worker Threads (Bug 437152)</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=437152">DOM Worker Threads Bug 437152</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script class="testbody" type="text/javascript">
+
+  const numThreads = 5;
+  var doneThreads = 0;
+
+  function onmessage(event) {
+    switch (event.data) {
+      case "done":
+        if (++doneThreads == numThreads) {
+          ok(true, "All messages received from workers");
+          SimpleTest.finish();
+        }
+        break;
+      default:
+        ok(false, "Unexpected message");
+        SimpleTest.finish();
+    }
+  }
+
+  function onerror(event) {
+    ok(false, "Worker had an error");
+    SimpleTest.finish();
+  }
+
+  for (var i = 0; i < numThreads; i++) {
+    var worker = new Worker("longThread_worker.js");
+    worker.onmessage = onmessage;
+    worker.onerror = onerror;
+    worker.postMessage("start");
+  }
+
+  SimpleTest.waitForExplicitFinish();
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_multi_sharedWorker.html b/dom/workers/test/test_multi_sharedWorker.html
new file mode 100644
index 0000000000..7bfbeaa9e9
--- /dev/null
+++ b/dom/workers/test/test_multi_sharedWorker.html
@@ -0,0 +1,241 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+  <head>
+    <title>Test for SharedWorker</title>
+    <script src="/tests/SimpleTest/SimpleTest.js"></script>
+    <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css">
+      <script class="testbody" type="text/javascript">
+        "use strict";
+
+        const basePath =
+          location.pathname.substring(0,
+                                      location.pathname.lastIndexOf("/") + 1);
+        const baseURL = location.origin + basePath;
+
+        const frameRelativeURL = "multi_sharedWorker_frame.html";
+        const frameAbsoluteURL = baseURL + frameRelativeURL;
+        const workerAbsoluteURL =
+          baseURL + "multi_sharedWorker_sharedWorker.js";
+
+        const storedData = "0123456789abcdefghijklmnopqrstuvwxyz";
+        const errorMessage = "Error: Expected";
+        const errorLineno = 34;
+
+        let testGenerator = (function*() {
+          SimpleTest.waitForExplicitFinish();
+
+          window.addEventListener("message", function(event) {
+            if (typeof(event.data) == "string") {
+              info(event.data);
+            } else {
+              sendToGenerator(event);
+            }
+          });
+
+          let frame1 = document.getElementById("frame1");
+          frame1.src = frameRelativeURL;
+          frame1.onload = sendToGenerator;
+
+          yield undefined;
+
+          frame1 = frame1.contentWindow;
+
+          let frame2 = document.getElementById("frame2");
+          frame2.src = frameAbsoluteURL;
+          frame2.onload = sendToGenerator;
+
+          yield undefined;
+
+          frame2 = frame2.contentWindow;
+
+          let data = {
+            command: "start"
+          };
+
+          frame1.postMessage(data, "*");
+          frame2.postMessage(data, "*");
+
+          let event = yield undefined;
+          ok(event instanceof MessageEvent, "Got a MessageEvent");
+          is(event.source, frame1, "First window got the event");
+          is(event.data.type, "connect", "Got a connect message");
+
+          data = {
+            command: "retrieve"
+          };
+          frame1.postMessage(data, "*");
+
+          event = yield undefined;
+          ok(event instanceof MessageEvent, "Got a MessageEvent");
+          is(event.source, frame1, "First window got the event");
+          is(event.data.type, "result", "Got a result message");
+          is(event.data.data, undefined, "No data stored yet");
+
+          frame2.postMessage(data, "*");
+
+          event = yield undefined;
+          ok(event instanceof MessageEvent, "Got a MessageEvent");
+          is(event.source, frame2, "Second window got the event");
+          is(event.data.type, "result", "Got a result message");
+          is(event.data.data, undefined, "No data stored yet");
+
+          data = {
+            command: "store",
+            data: storedData
+          };
+          frame2.postMessage(data, "*");
+
+          data = {
+            command: "retrieve"
+          };
+          frame1.postMessage(data, "*");
+
+          event = yield undefined;
+          ok(event instanceof MessageEvent, "Got a MessageEvent");
+          is(event.source, frame1, "First window got the event");
+          is(event.data.type, "result", "Got a result message");
+          is(event.data.data, storedData, "Got stored data");
+
+          // This will generate two MessageEvents, one for each window.
+          let sawFrame1Error = false;
+          let sawFrame2Error = false;
+
+          data = {
+            command: "error"
+          };
+          frame1.postMessage(data, "*");
+
+          // First event.
+          event = yield undefined;
+
+          ok(event instanceof MessageEvent, "Got a MessageEvent");
+          is(event.data.type, "worker-error", "Got an error message");
+          is(event.data.message, errorMessage, "Got correct error message");
+          is(event.data.filename, workerAbsoluteURL, "Got correct filename");
+          is(event.data.lineno, errorLineno, "Got correct lineno");
+          if (event.source == frame1) {
+            is(sawFrame1Error, false, "Haven't seen error for frame1 yet");
+            sawFrame1Error = true;
+          } else if (event.source == frame2) {
+            is(sawFrame2Error, false, "Haven't seen error for frame1 yet");
+            sawFrame2Error = true;
+          } else {
+            ok(false, "Saw error from unknown window");
+          }
+
+          // Second event
+          event = yield undefined;
+
+          ok(event instanceof MessageEvent, "Got a MessageEvent");
+          is(event.data.type, "worker-error", "Got an error message");
+          is(event.data.message, errorMessage, "Got correct error message");
+          is(event.data.filename, workerAbsoluteURL, "Got correct filename");
+          is(event.data.lineno, errorLineno, "Got correct lineno");
+          if (event.source == frame1) {
+            is(sawFrame1Error, false, "Haven't seen error for frame1 yet");
+            sawFrame1Error = true;
+          } else if (event.source == frame2) {
+            is(sawFrame2Error, false, "Haven't seen error for frame1 yet");
+            sawFrame2Error = true;
+          } else {
+            ok(false, "Saw error from unknown window");
+          }
+
+          is(sawFrame1Error, true, "Saw error for frame1");
+          is(sawFrame2Error, true, "Saw error for frame2");
+
+          // This will generate two MessageEvents, one for each window.
+          sawFrame1Error = false;
+          sawFrame2Error = false;
+
+          data = {
+            command: "error"
+          };
+          frame1.postMessage(data, "*");
+
+          // First event.
+          event = yield undefined;
+
+          ok(event instanceof MessageEvent, "Got a MessageEvent");
+          is(event.data.type, "error", "Got an error message");
+          is(event.data.message, errorMessage, "Got correct error message");
+          is(event.data.filename, workerAbsoluteURL, "Got correct filename");
+          is(event.data.lineno, errorLineno, "Got correct lineno");
+          is(event.data.isErrorEvent, true, "Frame got an ErrorEvent");
+          if (event.source == frame1) {
+            is(sawFrame1Error, false, "Haven't seen error for frame1 yet");
+            sawFrame1Error = true;
+          } else if (event.source == frame2) {
+            is(sawFrame2Error, false, "Haven't seen error for frame1 yet");
+            sawFrame2Error = true;
+          } else {
+            ok(false, "Saw error from unknown window");
+          }
+
+          // Second event
+          event = yield undefined;
+
+          ok(event instanceof MessageEvent, "Got a MessageEvent");
+          is(event.data.type, "error", "Got an error message");
+          is(event.data.message, errorMessage, "Got correct error message");
+          is(event.data.filename, workerAbsoluteURL, "Got correct filename");
+          is(event.data.lineno, errorLineno, "Got correct lineno");
+          is(event.data.isErrorEvent, true, "Frame got an ErrorEvent");
+          if (event.source == frame1) {
+            is(sawFrame1Error, false, "Haven't seen error for frame1 yet");
+            sawFrame1Error = true;
+          } else if (event.source == frame2) {
+            is(sawFrame2Error, false, "Haven't seen error for frame1 yet");
+            sawFrame2Error = true;
+          } else {
+            ok(false, "Saw error from unknown window");
+          }
+
+          is(sawFrame1Error, true, "Saw error for frame1");
+          is(sawFrame2Error, true, "Saw error for frame2");
+
+          // Try a shared worker in a different origin.
+          frame1 = document.getElementById("frame1");
+          frame1.src = "http://example.org" + basePath + frameRelativeURL;
+          frame1.onload = sendToGenerator;
+          yield undefined;
+
+          frame1 = frame1.contentWindow;
+
+          data = {
+            command: "retrieve"
+          };
+          frame1.postMessage(data, "*");
+
+          event = yield undefined;
+          ok(event instanceof MessageEvent, "Got a MessageEvent");
+          is(event.source, frame1, "First window got the event");
+          is(event.data.type, "result", "Got a result message");
+          is(event.data.data, undefined, "No data stored yet");
+
+          frame2.postMessage(data, "*");
+
+          event = yield undefined;
+          ok(event instanceof MessageEvent, "Got a MessageEvent");
+          is(event.source, frame2, "First window got the event");
+          is(event.data.type, "result", "Got a result message");
+          is(event.data.data, storedData, "Got stored data");
+
+          window.removeEventListener("message", sendToGenerator);
+
+          SimpleTest.finish();
+        })();
+
+        let sendToGenerator = testGenerator.next.bind(testGenerator);
+
+      </script>
+  </head>
+  <body onload="testGenerator.next();">
+    <iframe id="frame1"></iframe>
+    <iframe id="frame2"></iframe>
+  </body>
+</html>
diff --git a/dom/workers/test/test_multi_sharedWorker_lifetimes_bfcache.html b/dom/workers/test/test_multi_sharedWorker_lifetimes_bfcache.html
new file mode 100644
index 0000000000..346950020f
--- /dev/null
+++ b/dom/workers/test/test_multi_sharedWorker_lifetimes_bfcache.html
@@ -0,0 +1,151 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+  <head>
+    <title>Test for SharedWorker</title>
+    <script src="/tests/SimpleTest/SimpleTest.js"></script>
+    <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css">
+      <script class="testbody" type="text/javascript">
+        "use strict";
+        const windowRelativeURL = "multi_sharedWorker_frame_bfcache.html";
+        // This suffix will be used as a search query parameter when we are
+        // navigating from navigate.html to the multi_sharedWorker_frame_bfcache
+        // page again. Since we are not using history.back() we are not loading
+        // that page from bfcache, but instead loading it anew, while the page
+        // we loaded initially stays in bfcache. In order to not kick out the
+        // page that is currently in the bfcache, we need to use a different
+        // BroadcastChannel. So we use search query param as part of
+        // BroadcastChannel's  name.
+        const suffix = "?3";
+        const storedData = "0123456789abcdefghijklmnopqrstuvwxyz";
+        var bc, bc2, bc3;
+        SimpleTest.waitForExplicitFinish();
+
+
+        function postToWorker(aBc, workerMessage) {
+          aBc.postMessage({command: "postToWorker", workerMessage});
+        }
+
+        let testGenerator = (function*() {
+
+          bc = new BroadcastChannel("bugSharedWorkerLiftetime");
+          bc3 = new BroadcastChannel("bugSharedWorkerLiftetime" + suffix);
+          bc.onmessage = (event) => {
+            var msg = event.data;
+            var command = msg.command;
+            if (command == "debug") {
+              info(msg.message);
+            } else if (command == "fromWorker" || command == "loaded") {
+              sendToGenerator(msg.workerMessage);
+            }
+          }
+          bc3.onmessage = (event) => {
+            var msg = event.data;
+            var command = msg.command;
+            if (command == "finished") {
+              bc.close();
+              bc3.close();
+              bc2.close();
+              SimpleTest.finish();
+            } else if (command == "debug") {
+              info(msg.message);
+            } else if (command == "fromWorker" || command == "loaded") {
+              sendToGenerator(msg.workerMessage);
+            }
+          }
+          bc2 = new BroadcastChannel("navigate");
+          bc2.onmessage = (event) => {
+            if (event.data.command == "loaded") {
+              sendToGenerator();
+            }
+          }
+
+          // Open the window
+          window.open(windowRelativeURL, "testWin", "noopener");
+          yield undefined;
+
+          postToWorker(bc, { command: "retrieve" });
+
+          var msg = yield undefined;
+          is(msg.type, "result", "Got a result message");
+          is(msg.data, undefined, "No data stored");
+
+          postToWorker(bc, { command: "store", data: storedData });
+          postToWorker(bc, { command: "retrieve" });
+
+          msg = yield undefined;
+          is(msg.type, "result", "Got a result message");
+          is(msg.data, storedData, "Got stored data");
+
+
+          // Navigate when the bfcache is enabled.
+          info("Navigating to a different page");
+          bc.postMessage({command: "navigate", location: "navigate.html"});
+          yield undefined;
+
+          for (let i = 0; i < 3; i++) {
+            info("Running GC");
+            SpecialPowers.exactGC(sendToGenerator);
+            yield undefined;
+
+            // It seems using SpecialPowers.executeSoon() would make the
+            // entryGlobal being the BrowserChildGlobal (and that would make the
+            // baseURI in the location assignment below being incorrect);
+            // setTimeout on the otherhand ensures the entryGlobal is this
+            // window.
+            info("Waiting the event queue to clear");
+            setTimeout(sendToGenerator, 0);
+            yield undefined;
+          }
+
+          info("Navigating to " + windowRelativeURL);
+          bc2.postMessage({command: "navigate", location: windowRelativeURL + suffix});
+          yield undefined;
+
+          postToWorker(bc3, { command: "retrieve" });
+
+          msg = yield undefined;
+          is(msg.type, "result", "Got a result message");
+          is(msg.data, storedData, "Still have data stored");
+
+          bc3.postMessage({command: "finish"});
+        })();
+
+        let sendToGenerator = testGenerator.next.bind(testGenerator);
+
+        function runTest() {
+          if (isXOrigin) {
+            // Bug 1746646: Make mochitests work with TCP enabled (cookieBehavior = 5)
+            // Acquire storage access permission here so that the BroadcastChannel used to
+            // communicate with the opened windows works in xorigin tests. Otherwise,
+            // the iframe containing this page is isolated from first-party storage access,
+            // which isolates BroadcastChannel communication.
+            SpecialPowers.wrap(document).notifyUserGestureActivation();
+            SpecialPowers.pushPermissions([{'type': 'storageAccessAPI', 'allow': 1, 'context': document}], () =>{
+              SpecialPowers.wrap(document).requestStorageAccess().then(() => {
+                // If Fission is disabled, the pref is no-op.
+                SpecialPowers.pushPrefEnv({set: [
+                  ["fission.bfcacheInParent", true],
+                  ["privacy.partition.always_partition_third_party_non_cookie_storage", false],
+                ]}, () => {
+                  testGenerator.next();
+                });
+              }).then(() => {
+                SpecialPowers.removePermission("3rdPartyStorage^http://mochi.test:8888", "http://mochi.xorigin-test:8888");
+              });
+            });
+          } else {
+            // If Fission is disabled, the pref is no-op.
+            SpecialPowers.pushPrefEnv({set: [["fission.bfcacheInParent", true]]}, () => {
+              testGenerator.next();
+            });
+          }
+        }
+      </script>
+  </head>
+  <body onload="runTest()">
+  </body>
+</html>
diff --git a/dom/workers/test/test_multi_sharedWorker_lifetimes_nobfcache.html b/dom/workers/test/test_multi_sharedWorker_lifetimes_nobfcache.html
new file mode 100644
index 0000000000..5049ead1a9
--- /dev/null
+++ b/dom/workers/test/test_multi_sharedWorker_lifetimes_nobfcache.html
@@ -0,0 +1,126 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+  <head>
+    <title>Test for SharedWorker</title>
+    <script src="/tests/SimpleTest/SimpleTest.js"></script>
+    <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css">
+      <script class="testbody" type="text/javascript">
+        "use strict";
+
+        function runTest() {
+          const windowRelativeURL = "multi_sharedWorker_frame_nobfcache.html";
+          const storedData = "0123456789abcdefghijklmnopqrstuvwxyz";
+          var bc, bc2;
+          bc = new BroadcastChannel("bugSharedWorkerLiftetime");
+          bc.onmessage = (event) => {
+            var msg = event.data;
+            var command = msg.command;
+            if (command == "finished") {
+              bc.close();
+              bc2.close();
+              SimpleTest.finish();
+            } else if (command == "debug") {
+              info(msg.message);
+            } else if (command == "fromWorker" || command == "loaded") {
+              sendToGenerator(msg.workerMessage);
+            }
+          }
+          bc2 = new BroadcastChannel("navigate");
+          bc2.onmessage = (event) => {
+            if (event.data.command == "loaded") {
+              sendToGenerator();
+            }
+          }
+
+          function postToWorker(workerMessage) {
+            bc.postMessage({command: "postToWorker", workerMessage});
+          }
+
+          let testGenerator = (function*() {
+            SimpleTest.waitForExplicitFinish();
+
+            // Open the window
+            window.open(windowRelativeURL, "testWin", "noopener");
+            yield undefined;
+
+            // Retrieve data from worker
+            postToWorker({ command: "retrieve" });
+
+            let msg = yield undefined;
+
+            // Verify there is no data stored
+            is(msg.type, "result", "Got a result message");
+            is(msg.data, undefined, "No data stored yet");
+
+            // Store data, and retrieve it
+            postToWorker({ command: "store", data: storedData });
+            postToWorker({ command: "retrieve" });
+
+            msg = yield undefined;
+            // Verify there is data stored
+            is(msg.type, "result", "Got a result message");
+            is(msg.data, storedData, "Got stored data");
+
+
+            info("Navigating to a different page");
+            // Current subpage should not go into bfcache because of the Cache-Control
+            // headers we have set.
+            bc.postMessage({command: "navigate", location: "navigate.html"});
+            yield undefined;
+
+            info("Navigating to " + windowRelativeURL);
+            bc2.postMessage({command: "navigate", location: windowRelativeURL });
+            yield undefined;
+
+            postToWorker({ command: "retrieve" });
+
+            msg = yield undefined;
+            is(msg.type, "result", "Got a result message");
+            is(msg.data, undefined, "No data stored");
+
+            postToWorker({ command: "store", data: storedData });
+            postToWorker({ command: "retrieve" });
+
+            msg = yield undefined;
+            is(msg.type, "result", "Got a result message");
+            is(msg.data, storedData, "Got stored data");
+
+            bc.postMessage({command: "finish"});
+          })();
+
+          let sendToGenerator = testGenerator.next.bind(testGenerator);
+          testGenerator.next();
+        }
+
+        SimpleTest.waitForExplicitFinish();
+        if (isXOrigin) {
+          // Bug 1746646: Make mochitests work with TCP enabled (cookieBehavior = 5)
+          // Acquire storage access permission here so that the BroadcastChannel used to
+          // communicate with the opened windows works in xorigin tests. Otherwise,
+          // the iframe containing this page is isolated from first-party storage access,
+          // which isolates BroadcastChannel communication.
+          SpecialPowers.wrap(document).notifyUserGestureActivation();
+          SpecialPowers.pushPrefEnv({
+            set: [["privacy.partition.always_partition_third_party_non_cookie_storage", false]],
+          }).then(() => {
+            SpecialPowers.pushPermissions([{'type': 'storageAccessAPI', 'allow': 1, 'context': document}], () =>{
+              SpecialPowers.wrap(document).requestStorageAccess().then(() => {
+                runTest();
+              }).then(() => {
+                SpecialPowers.removePermission("3rdPartyStorage^http://mochi.test:8888", "http://mochi.xorigin-test:8888");
+              });
+            });
+          });
+        } else {
+          runTest();
+        }
+
+      </script>
+  </head>
+  <body>
+  </body>
+</html>
diff --git a/dom/workers/test/test_navigator.html b/dom/workers/test/test_navigator.html
new file mode 100644
index 0000000000..a9ca9cad66
--- /dev/null
+++ b/dom/workers/test/test_navigator.html
@@ -0,0 +1,27 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<!--
+Tests of DOM Worker Navigator
+-->
+<head>
+  <title>Test for DOM Worker Navigator</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script>
+  ok(!self.isSecureContext, "This test should not be running in a secure context");
+</script>
+<script type="text/javascript" src="test_navigator.js"></script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_navigator.js b/dom/workers/test/test_navigator.js
new file mode 100644
index 0000000000..c1eab3aa89
--- /dev/null
+++ b/dom/workers/test/test_navigator.js
@@ -0,0 +1,10 @@
+SimpleTest.waitForExplicitFinish();
+
+// This test loads in an iframe, to ensure that the navigator instance is
+// loaded with the correct value of the preference.
+SpecialPowers.pushPrefEnv({ set: [["dom.netinfo.enabled", true]] }, () => {
+  let iframe = document.createElement("iframe");
+  iframe.id = "f1";
+  iframe.src = "test_navigator_iframe.html";
+  document.body.appendChild(iframe);
+});
diff --git a/dom/workers/test/test_navigator_iframe.html b/dom/workers/test/test_navigator_iframe.html
new file mode 100644
index 0000000000..907739e90a
--- /dev/null
+++ b/dom/workers/test/test_navigator_iframe.html
@@ -0,0 +1,24 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<!--
+Sub-tests of DOM Worker Navigator tests.
+-->
+<head>
+  <title>Test for DOM Worker Navigator</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script type="text/javascript" src="test_navigator_iframe.js"></script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_navigator_iframe.js b/dom/workers/test/test_navigator_iframe.js
new file mode 100644
index 0000000000..248d7ed2cd
--- /dev/null
+++ b/dom/workers/test/test_navigator_iframe.js
@@ -0,0 +1,65 @@
+var worker = new Worker("navigator_worker.js");
+
+var is = window.parent.is;
+var ok = window.parent.ok;
+var SimpleTest = window.parent.SimpleTest;
+
+worker.onmessage = function (event) {
+  var args = JSON.parse(event.data);
+
+  if (args.name == "testFinished") {
+    SimpleTest.finish();
+    return;
+  }
+
+  if (typeof navigator[args.name] == "undefined") {
+    ok(false, "Navigator has no '" + args.name + "' property!");
+    return;
+  }
+
+  if (args.name === "languages") {
+    is(
+      navigator.languages.toString(),
+      args.value.toString(),
+      "languages matches"
+    );
+    return;
+  }
+
+  const objectProperties = [
+    "connection",
+    "gpu",
+    "locks",
+    "mediaCapabilities",
+    "storage",
+  ];
+
+  if (objectProperties.includes(args.name)) {
+    is(
+      typeof navigator[args.name],
+      typeof args.value,
+      `${args.name} type matches`
+    );
+    return;
+  }
+
+  is(
+    navigator[args.name],
+    args.value,
+    "Mismatched navigator string for " + args.name + "!"
+  );
+};
+
+worker.onerror = function (event) {
+  ok(false, "Worker had an error: " + event.message);
+  SimpleTest.finish();
+};
+
+var { AppConstants } = SpecialPowers.ChromeUtils.importESModule(
+  "resource://gre/modules/AppConstants.sys.mjs"
+);
+var isNightly = AppConstants.NIGHTLY_BUILD;
+var isRelease = AppConstants.RELEASE_OR_BETA;
+var isAndroid = AppConstants.platform == "android";
+
+worker.postMessage({ isNightly, isRelease, isAndroid });
diff --git a/dom/workers/test/test_navigator_languages.html b/dom/workers/test/test_navigator_languages.html
new file mode 100644
index 0000000000..e4b6fec9a6
--- /dev/null
+++ b/dom/workers/test/test_navigator_languages.html
@@ -0,0 +1,58 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<!--
+Tests of DOM Worker Navigator
+-->
+<head>
+  <title>Test for DOM Worker Navigator.languages</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script class="testbody" language="javascript">
+
+  var tests = [
+    { expectedLanguages: 'en,it', inputLanguages: 'en,it' },
+    { expectedLanguages: 'it,en,fr', inputLanguages: 'it,en,fr' },
+    { expectedLanguages: SpecialPowers.Services.locale.webExposedLocales[0], inputLanguages: '' },
+    { expectedLanguages: 'en,it', inputLanguages: 'en,it' },
+  ];
+  var test;
+  function runTests() {
+    if (!tests.length) {
+      worker.postMessage('finish');
+      SimpleTest.finish();
+      return;
+    }
+
+    test = tests.shift();
+    SpecialPowers.pushPrefEnv({"set": [["intl.accept_languages", test.inputLanguages]]}, function() {
+      worker.postMessage(true);
+    });
+  }
+
+  SimpleTest.waitForExplicitFinish();
+
+  var worker = new Worker("navigator_languages_worker.js");
+
+  worker.onmessage = function(event) {
+    is(event.data.toString(), navigator.languages.toString(), "The languages match.");
+    is(event.data.toString(), test.expectedLanguages, "This is the correct result.");
+    runTests();
+  }
+
+  runTests();
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_navigator_secureContext.html b/dom/workers/test/test_navigator_secureContext.html
new file mode 100644
index 0000000000..ac5ceb6628
--- /dev/null
+++ b/dom/workers/test/test_navigator_secureContext.html
@@ -0,0 +1,27 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<!--
+Tests of DOM Worker Navigator
+-->
+<head>
+  <title>Test for DOM Worker Navigator</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script>
+  ok(self.isSecureContext, "This test should be running in a secure context");
+</script>
+<script type="text/javascript" src="test_navigator.js"></script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_navigator_workers_hardwareConcurrency.html b/dom/workers/test/test_navigator_workers_hardwareConcurrency.html
new file mode 100644
index 0000000000..e80c211ce7
--- /dev/null
+++ b/dom/workers/test/test_navigator_workers_hardwareConcurrency.html
@@ -0,0 +1,56 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <meta charset="utf-8">
+  <title>Test for Navigator.hardwareConcurrency</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  <script type="application/javascript">
+  "use strict";
+
+  SimpleTest.waitForExplicitFinish();
+
+  function getWorkerHardwareConcurrency(onmessage) {
+    var script = "postMessage(navigator.hardwareConcurrency)";
+    var url = URL.createObjectURL(new Blob([script]));
+    var w = new Worker(url);
+    w.onmessage = onmessage;
+  }
+
+  function resistFingerprinting(value) {
+    return SpecialPowers.pushPrefEnv({"set": [["privacy.resistFingerprinting", value]]});
+  }
+
+  getWorkerHardwareConcurrency(e => {
+    var x = e.data;
+    is(typeof x, "number", "hardwareConcurrency should be a number.");
+    ok(x > 0, "hardwareConcurrency should be greater than 0.");
+
+    resistFingerprinting(true).then(() => {
+      getWorkerHardwareConcurrency(msg => {
+        const y = msg.data;
+        ok(y === 2, "hardwareConcurrency should always be 2 when we're resisting fingerprinting.");
+
+        resistFingerprinting(false).then(() => {
+          getWorkerHardwareConcurrency(msg1 => {
+            const z = msg1.data;
+            ok(z === x, "hardwareConcurrency should be the same as before we were resisting fingerprinting.");
+
+            SimpleTest.finish();
+          });
+        });
+      });
+    });
+  });
+
+  </script>
+</head>
+<body>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_newError.html b/dom/workers/test/test_newError.html
new file mode 100644
index 0000000000..9dd0889df8
--- /dev/null
+++ b/dom/workers/test/test_newError.html
@@ -0,0 +1,33 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<html>
+<head>
+  <title>Test for DOM Worker Threads</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<pre id="test">
+<script class="testbody" type="text/javascript">
+
+  var worker = new Worker("newError_worker.js");
+
+  worker.onmessage = function(event) {
+    ok(false, "Shouldn't get a message!");
+    SimpleTest.finish();
+  }
+
+  worker.onerror = function(event) {
+    is(event.message, "Error: foo!", "Got wrong error message!");
+    event.preventDefault();
+    SimpleTest.finish();
+  }
+
+  SimpleTest.waitForExplicitFinish();
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_notification.html b/dom/workers/test/test_notification.html
new file mode 100644
index 0000000000..0171dea0f2
--- /dev/null
+++ b/dom/workers/test/test_notification.html
@@ -0,0 +1,47 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=916893
+-->
+<head>
+  <title>Bug 916893</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <script type="text/javascript" src="/tests/dom/notification/test/mochitest/MockServices.js"></script>
+  <script type="text/javascript" src="/tests/dom/notification/test/mochitest/NotificationTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=916893">Bug 916893</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+</div>
+<pre id="test">
+</pre>
+<script type="text/javascript">
+  SimpleTest.requestFlakyTimeout("Mock alert service dispatches show and click events.");
+
+  function runTest() {
+    MockServices.register();
+    var w = new Worker("notification_worker.js");
+    w.onmessage = function(e) {
+      if (e.data.type === 'finish') {
+        MockServices.unregister();
+        SimpleTest.finish();
+      } else if (e.data.type === 'ok') {
+        ok(e.data.test, e.data.message);
+      } else if (e.data.type === 'is') {
+        is(e.data.test1, e.data.test2, e.data.message);
+      }
+    }
+
+    SimpleTest.waitForExplicitFinish();
+    // turn on testing pref (used by notification.cpp, and mock the alerts
+    SpecialPowers.setBoolPref("notification.prompt.testing", true);
+    w.postMessage('start')
+  }
+
+  SimpleTest.waitForExplicitFinish();
+  runTest();
+</script>
+</body>
+</html>
diff --git a/dom/workers/test/test_notification_child.html b/dom/workers/test/test_notification_child.html
new file mode 100644
index 0000000000..4f9523a03f
--- /dev/null
+++ b/dom/workers/test/test_notification_child.html
@@ -0,0 +1,46 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=916893
+-->
+<head>
+  <title>Bug 916893 - Test Notifications in child workers.</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <script type="text/javascript" src="/tests/dom/notification/test/mochitest/MockServices.js"></script>
+  <script type="text/javascript" src="/tests/dom/notification/test/mochitest/NotificationTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=916893">Bug 916893</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+</div>
+<pre id="test">
+</pre>
+<script type="text/javascript">
+  SimpleTest.requestFlakyTimeout("Mock alert service dispatches show event.");
+  function runTest() {
+    MockServices.register();
+    var w = new Worker("notification_worker_child-parent.js");
+    w.onmessage = function(e) {
+      if (e.data.type === 'finish') {
+        MockServices.unregister();
+        SimpleTest.finish();
+      } else if (e.data.type === 'ok') {
+        ok(e.data.test, e.data.message);
+      } else if (e.data.type === 'is') {
+        is(e.data.test1, e.data.test2, e.data.message);
+      }
+    }
+
+    SimpleTest.waitForExplicitFinish();
+    // turn on testing pref (used by notification.cpp, and mock the alerts
+    SpecialPowers.setBoolPref("notification.prompt.testing", true);
+    w.postMessage('start')
+  }
+
+  SimpleTest.waitForExplicitFinish();
+  runTest();
+</script>
+</body>
+</html>
diff --git a/dom/workers/test/test_notification_permission.html b/dom/workers/test/test_notification_permission.html
new file mode 100644
index 0000000000..904cfcdef2
--- /dev/null
+++ b/dom/workers/test/test_notification_permission.html
@@ -0,0 +1,48 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=916893
+-->
+<head>
+  <title>Bug 916893 - Make sure error is fired on Notification if permission is denied.</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <script type="text/javascript" src="/tests/dom/notification/test/mochitest/MockServices.js"></script>
+  <script type="text/javascript" src="/tests/dom/notification/test/mochitest/NotificationTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=916893">Bug 916893</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+</div>
+<pre id="test">
+</pre>
+<script type="text/javascript">
+  SimpleTest.requestFlakyTimeout("Mock alert service dispatches show event.");
+  function runTest() {
+    MockServices.register();
+    var w = new Worker("notification_permission_worker.js");
+    w.onmessage = function(e) {
+      if (e.data.type === 'finish') {
+        SpecialPowers.setBoolPref("notification.prompt.testing.allow", true);
+        MockServices.unregister();
+        SimpleTest.finish();
+      } else if (e.data.type === 'ok') {
+        ok(e.data.test, e.data.message);
+      } else if (e.data.type === 'is') {
+        is(e.data.test1, e.data.test2, e.data.message);
+      }
+    }
+
+    SimpleTest.waitForExplicitFinish();
+    // turn on testing pref (used by notification.cpp, and mock the alerts
+    SpecialPowers.setBoolPref("notification.prompt.testing", true);
+    SpecialPowers.setBoolPref("notification.prompt.testing.allow", false);
+    w.postMessage('start')
+  }
+
+  SimpleTest.waitForExplicitFinish();
+  runTest();
+</script>
+</body>
+</html>
diff --git a/dom/workers/test/test_onLine.html b/dom/workers/test/test_onLine.html
new file mode 100644
index 0000000000..b0429e7d96
--- /dev/null
+++ b/dom/workers/test/test_onLine.html
@@ -0,0 +1,73 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+Bug 925437: online/offline events tests.
+
+Any copyright is dedicated to the Public Domain.
+http://creativecommons.org/licenses/publicdomain/
+-->
+<head>
+  <title>Test for Bug 925437 (worker online/offline events)</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=925437">Mozilla Bug 925437</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+</pre>
+
+<script class="testbody" type="text/javascript">
+
+addLoadEvent(function() {
+  var w = new Worker("onLine_worker.js");
+
+  w.onmessage = function(e) {
+    if (e.data.type === 'ready') {
+      // XXX Important trick here.
+      //
+      // Setting iosvc.offline would trigger a sync notifyObservers call, and if
+      // there exists a preloaded about:newtab (see tabbrowser._handleNewTab),
+      // that tab will be notified.
+      //
+      // This implies a sync call across different tabGroups, and will hit the
+      // assertion in SchedulerGroup::ValidateAccess(). So use executeSoon to
+      // re-dispatch an unlabeled runnable to the event queue.
+      SpecialPowers.executeSoon(doTest);
+    } else if (e.data.type === 'ok') {
+      ok(e.data.test, e.data.message);
+    } else if (e.data.type === 'finished') {
+      SimpleTest.finish();
+    }
+  }
+
+  function doTest() {
+    var iosvc = SpecialPowers.Cc["@mozilla.org/network/io-service;1"]
+                             .getService(SpecialPowers.Ci.nsIIOService);
+    iosvc.manageOfflineStatus = false;
+
+    info("setting iosvc.offline = true");
+    iosvc.offline = true;
+
+    info("setting iosvc.offline = false");
+    iosvc.offline = false;
+
+    info("setting iosvc.offline = true");
+    iosvc.offline = true;
+
+    for (var i = 0; i < 10; ++i) {
+        iosvc.offline = !iosvc.offline;
+    }
+
+    info("setting iosvc.offline = false");
+    w.postMessage('lastTest');
+    iosvc.offline = false;
+  }
+});
+
+SimpleTest.waitForExplicitFinish();
+</script>
+</body>
+</html>
diff --git a/dom/workers/test/test_promise.html b/dom/workers/test/test_promise.html
new file mode 100644
index 0000000000..7c3ef09a98
--- /dev/null
+++ b/dom/workers/test/test_promise.html
@@ -0,0 +1,43 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test for Promise object in workers</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<p id="display"></p>
+<div id="content" style="display: none"></div>
+<pre id="test"></pre>
+<script class="testbody" type="text/javascript">
+
+  function runTest() {
+    var worker = new Worker("promise_worker.js");
+
+    worker.onmessage = function(event) {
+
+      if (event.data.type == 'finish') {
+        SimpleTest.finish();
+      } else if (event.data.type == 'status') {
+        ok(event.data.status, event.data.msg);
+      }
+    }
+
+    worker.onerror = function(event) {
+      ok(false, "Worker had an error: " + event.message);
+      SimpleTest.finish();
+    };
+
+    worker.postMessage(true);
+  }
+
+  SimpleTest.waitForExplicitFinish();
+  runTest();
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_promise_resolved_with_string.html b/dom/workers/test/test_promise_resolved_with_string.html
new file mode 100644
index 0000000000..8c0b0aca49
--- /dev/null
+++ b/dom/workers/test/test_promise_resolved_with_string.html
@@ -0,0 +1,41 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1027221
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1027221</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  <script type="application/javascript">
+
+  /** Test for Bug 1027221 **/
+    // Set up a permanent atom
+    SimpleTest.waitForExplicitFinish();
+    var x = "x";
+    // Trigger some incremental gc
+    SpecialPowers.Cu.getJSTestingFunctions().gcslice(1);
+
+    // Kick off a worker that uses this same atom
+    var w = new Worker("data:text/plain,Promise.resolve('x').then(function() { postMessage(1); });");
+    // Maybe trigger some more incremental gc
+    SpecialPowers.Cu.getJSTestingFunctions().gcslice(1);
+
+    w.onmessage = function() {
+      ok(true, "Got here");
+      SimpleTest.finish();
+    };
+
+  </script>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1027221">Mozilla Bug 1027221</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_readableStream_when_closing.html b/dom/workers/test/test_readableStream_when_closing.html
new file mode 100644
index 0000000000..24d5bf3821
--- /dev/null
+++ b/dom/workers/test/test_readableStream_when_closing.html
@@ -0,0 +1,61 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <meta charset="utf-8">
+  <title>Test for ReadableStream+fetch when the worker is closing</title>
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css"?>
+</head>
+<body>
+  <script>
+
+function workerCode() {
+  onmessage = () => {
+    const BIG_BUFFER_SIZE = 1000000;
+    const fibStream = new ReadableStream({
+        start(controller) {},
+
+        pull(controller) {
+          const buffer = new Uint8Array(BIG_BUFFER_SIZE);
+          buffer.fill(42);
+          controller.enqueue(buffer);
+        }
+    });
+
+    const r = new Response(fibStream);
+
+    const p = r.blob();
+    self.postMessage("reading");
+
+    p.then(() => {
+      // really?
+    });
+  }
+}
+
+SimpleTest.waitForExplicitFinish();
+
+const b = new Blob([workerCode+'workerCode();']);
+const url = URL.createObjectURL(b);
+const w = new Worker(url);
+w.onmessage = function(e) {
+  ok(true, 'Worker is reading');
+
+  const wdm = Cc["@mozilla.org/dom/workers/workerdebuggermanager;1"].
+              getService(Ci.nsIWorkerDebuggerManager);
+  wdm.addListener({
+    onUnregister (dbg) {
+      if (dbg.url == url) {
+        ok(true, "Debugger with url " + url + " should be unregistered.");
+        wdm.removeListener(this);
+        SimpleTest.finish();
+      }
+    }
+  });
+
+  w.terminate();
+}
+w.postMessage("start");
+  </script>
+</body>
+</html>
diff --git a/dom/workers/test/test_recursion.html b/dom/workers/test/test_recursion.html
new file mode 100644
index 0000000000..8e38a80351
--- /dev/null
+++ b/dom/workers/test/test_recursion.html
@@ -0,0 +1,69 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<!--
+Tests of DOM Worker Threads
+-->
+<head>
+  <title>Test for DOM Worker Threads Recursion</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script class="testbody" type="text/javascript">
+
+  // Intermittently triggers one assertion on Mac (bug 848098).
+  if (navigator.platform.indexOf("Mac") == 0) {
+    SimpleTest.expectAssertions(0, 1);
+  }
+
+  const testCount = 2;
+  var errorCount = 0;
+
+  var worker = new Worker("recursion_worker.js");
+
+  function done() {
+    worker.terminate();
+    SimpleTest.finish();
+  }
+
+  worker.onmessage = function(event) {
+    if (event.data == "Done") {
+      ok(true, "correct message");
+    }
+    else {
+      ok(false, "Bad message: " + event.data);
+    }
+    done();
+  }
+
+  worker.onerror = function(event) {
+    event.preventDefault();
+    if (event.message == "too much recursion") {
+      ok(true, "got correct error message");
+      ++errorCount;
+    }
+    else {
+      ok(false, "got bad error message: " + event.message);
+      done();
+    }
+  }
+
+  for (var i = 0; i < testCount; i++) {
+    worker.postMessage("");
+  }
+
+  SimpleTest.waitForExplicitFinish();
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_recursiveOnerror.html b/dom/workers/test/test_recursiveOnerror.html
new file mode 100644
index 0000000000..e6c040439d
--- /dev/null
+++ b/dom/workers/test/test_recursiveOnerror.html
@@ -0,0 +1,44 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+  <head>
+    <script src="/tests/SimpleTest/SimpleTest.js">
+    </script>
+    <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  </head>
+  <body>
+    <script type="text/javascript">
+      const filename = "http://mochi.test:8888/tests/dom/workers/test/" +
+                       "recursiveOnerror_worker.js";
+      const errors = [
+        { message: "Error: 2", lineno: 6 },
+        { message: "Error: 1", lineno: 10 }
+      ]
+
+      var errorCount = 0;
+
+      var worker = new Worker("recursiveOnerror_worker.js");
+      worker.postMessage("go");
+
+      worker.onerror = function(event) {
+        event.preventDefault();
+
+        ok(errorCount < errors.length, "Correct number of error events");
+        const error = errors[errorCount++];
+
+        is(event.message, error.message, "Correct message");
+        is(event.filename, filename, "Correct filename");
+        is(event.lineno, error.lineno, "Correct lineno");
+
+        if (errorCount == errors.length) {
+          SimpleTest.finish();
+        }
+      }
+
+      SimpleTest.waitForExplicitFinish();
+    </script>
+  </body>
+</html>
diff --git a/dom/workers/test/test_referrer.html b/dom/workers/test/test_referrer.html
new file mode 100644
index 0000000000..a95fe91809
--- /dev/null
+++ b/dom/workers/test/test_referrer.html
@@ -0,0 +1,58 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test the referrer of workers</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<p id="display"></p>
+<div id="content" style="display: none"></div>
+<pre id="test"></pre>
+<script class="testbody" type="text/javascript">
+
+  function test_mainScript() {
+    var worker = new Worker("referrer.sjs?worker");
+    worker.onmessage = function() {
+      var xhr = new XMLHttpRequest();
+      xhr.open('GET', 'referrer.sjs?result', true);
+      xhr.onload = function() {
+        is(xhr.responseText, location.href, "The referrer has been sent.");
+        next();
+      }
+      xhr.send();
+    }
+    worker.postMessage(42);
+  }
+
+  function test_importScript() {
+    var worker = new Worker("worker_referrer.js");
+    worker.onmessage = function(e) {
+      is(e.data, location.href.replace("test_referrer.html", "worker_referrer.js").split("?")[0], "The referrer has been sent.");
+      next();
+    }
+    worker.postMessage(42);
+  }
+
+  var tests = [ test_mainScript, test_importScript ];
+  function next() {
+    if (!tests.length) {
+      SimpleTest.finish();
+      return;
+    }
+
+    var test = tests.shift();
+    test();
+  }
+
+  SimpleTest.waitForExplicitFinish();
+  next();
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_referrer_header_worker.html b/dom/workers/test/test_referrer_header_worker.html
new file mode 100644
index 0000000000..6d350801cb
--- /dev/null
+++ b/dom/workers/test/test_referrer_header_worker.html
@@ -0,0 +1,39 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<head>
+  <meta charset="utf-8">
+  <title>Test the referrer of workers</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+  <script class="testbody" type="text/javascript">
+    SimpleTest.waitForExplicitFinish();
+
+    SpecialPowers.pushPrefEnv(
+      {"set": [
+         ['security.mixed_content.block_display_content', false],
+         ['security.mixed_content.block_active_content', false]
+      ]},
+      function() {
+        SpecialPowers.pushPermissions([{'type': 'systemXHR', 'allow': true, 'context': document}], test);
+    });
+
+    function test() {
+      function messageListener(event) {
+        // eslint-disable-next-line no-eval
+        eval(event.data);
+      }
+      window.addEventListener("message", messageListener);
+
+      var ifr = document.createElement('iframe');
+      ifr.setAttribute('src', 'https://example.com/tests/dom/workers/test/referrer_worker.html');
+      document.body.appendChild(ifr);
+    }
+  </script>
+</body>
+</html>
diff --git a/dom/workers/test/test_resolveWorker-assignment.html b/dom/workers/test/test_resolveWorker-assignment.html
new file mode 100644
index 0000000000..2f3be19668
--- /dev/null
+++ b/dom/workers/test/test_resolveWorker-assignment.html
@@ -0,0 +1,30 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE html>
+<html>
+  <head>
+    <script src="/tests/SimpleTest/SimpleTest.js"></script>
+    <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  </head>
+  <body>
+    <script type="application/javascript">
+      window.Worker = 17; // resolve through assignment
+
+      var desc = Object.getOwnPropertyDescriptor(window, "Worker");
+      ok(typeof desc === "object" && desc !== null, "Worker property must exist");
+
+      is(desc.value, 17, "Overwrite didn't work correctly");
+      is(desc.enumerable, false,
+         "Initial descriptor was non-enumerable, and [[Put]] changes the " +
+         "property value but not its enumerability");
+      is(desc.configurable, true,
+         "Initial descriptor was configurable, and [[Put]] changes the " +
+         "property value but not its configurability");
+      is(desc.writable, true,
+         "Initial descriptor was writable, and [[Put]] changes the " +
+         "property value but not its writability");
+    </script>
+  </body>
+</html>
diff --git a/dom/workers/test/test_resolveWorker.html b/dom/workers/test/test_resolveWorker.html
new file mode 100644
index 0000000000..0d91a9f90a
--- /dev/null
+++ b/dom/workers/test/test_resolveWorker.html
@@ -0,0 +1,31 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE html>
+<html>
+  <head>
+    <script src="/tests/SimpleTest/SimpleTest.js"></script>
+    <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  </head>
+  <body>
+    <script type="application/javascript">
+      window.Worker; // resolve not through assignment
+      Worker = 17;
+
+      var desc = Object.getOwnPropertyDescriptor(window, "Worker");
+      ok(typeof desc === "object" && desc !== null, "Worker property must exist");
+
+      is(desc.value, 17, "Overwrite didn't work correctly");
+      is(desc.enumerable, false,
+         "Initial descriptor was non-enumerable, and [[Put]] changes the " +
+         "property value but not its enumerability");
+      is(desc.configurable, true,
+         "Initial descriptor was configurable, and [[Put]] changes the " +
+         "property value but not its configurability");
+      is(desc.writable, true,
+         "Initial descriptor was writable, and [[Put]] changes the " +
+         "property value but not its writability");
+    </script>
+  </body>
+</html>
diff --git a/dom/workers/test/test_rvals.html b/dom/workers/test/test_rvals.html
new file mode 100644
index 0000000000..799c42779d
--- /dev/null
+++ b/dom/workers/test/test_rvals.html
@@ -0,0 +1,35 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test for bug 911085</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<script class="testbody" type="text/javascript">
+
+  var worker = new Worker("rvals_worker.js");
+
+  worker.onmessage = function(event) {
+    if (event.data == 'ignore') return;
+
+    if (event.data == 'finished') {
+      is(worker.terminate(), undefined, "Terminate() returns 'undefined'");
+      SimpleTest.finish();
+      return;
+    }
+
+    ok(event.data, "something good returns 'undefined' in workers");
+  };
+
+  is(worker.postMessage(42), undefined, "PostMessage() returns 'undefined' on main thread");
+  SimpleTest.waitForExplicitFinish();
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_setTimeoutWith0.html b/dom/workers/test/test_setTimeoutWith0.html
new file mode 100644
index 0000000000..8685eacfe5
--- /dev/null
+++ b/dom/workers/test/test_setTimeoutWith0.html
@@ -0,0 +1,19 @@
+<html>
+<head>
+  <title>Test for DOM Worker setTimeout and strings containing 0</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<script>
+
+var a = new Worker('worker_setTimeoutWith0.js');
+a.onmessage = function(e) {
+  is(e.data, 2, "We want to see 2 here");
+  SimpleTest.finish();
+}
+
+SimpleTest.waitForExplicitFinish();
+</script>
+</body>
+</html>
diff --git a/dom/workers/test/test_sharedWorker.html b/dom/workers/test/test_sharedWorker.html
new file mode 100644
index 0000000000..0a3cde2d32
--- /dev/null
+++ b/dom/workers/test/test_sharedWorker.html
@@ -0,0 +1,71 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+  <head>
+    <title>Test for SharedWorker</title>
+    <script src="/tests/SimpleTest/SimpleTest.js">
+    </script>
+    <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css">
+  </head>
+  <body>
+    <p id="display"></p>
+    <div id="content" style="display: none"></div>
+    <pre id="test">
+      <script class="testbody">
+        "use strict";
+
+        const href = window.location.href;
+        const filename = "sharedWorker_sharedWorker.js";
+        const sentMessage = "ping";
+        const errorFilename = href.substring(0, href.lastIndexOf("/") + 1) +
+                              filename;
+        const errorLine = 98;
+        const errorColumn = 11;
+
+        var worker = new SharedWorker(filename);
+
+        ok(worker instanceof SharedWorker, "Got SharedWorker instance");
+        ok(!("postMessage" in worker), "SharedWorker has no 'postMessage'");
+        ok(worker.port instanceof MessagePort,
+          "Shared worker has MessagePort");
+
+        var receivedMessage;
+        var receivedError;
+
+        worker.port.onmessage = function(event) {
+          ok(event instanceof MessageEvent, "Got a MessageEvent");
+          ok(event.target === worker.port,
+             "MessageEvent has correct 'target' property");
+          is(event.data, sentMessage, "Got correct message");
+          ok(receivedMessage === undefined, "Haven't gotten message yet");
+          receivedMessage = event.data;
+          if (receivedError) {
+            SimpleTest.finish();
+          }
+        };
+
+        worker.onerror = function(event) {
+          ok(event instanceof ErrorEvent, "Got an ErrorEvent");
+          is(event.message, "Error: " + sentMessage, "Got correct error");
+          is(event.filename, errorFilename, "Got correct filename");
+          is(event.lineno, errorLine, "Got correct lineno");
+          is(event.colno, errorColumn, "Got correct column");
+          ok(receivedError === undefined, "Haven't gotten error yet");
+          receivedError = event.message;
+          event.preventDefault();
+          if (receivedMessage) {
+            SimpleTest.finish();
+          }
+        };
+
+        worker.port.postMessage(sentMessage);
+
+        SimpleTest.waitForExplicitFinish();
+
+      </script>
+    </pre>
+  </body>
+</html>
diff --git a/dom/workers/test/test_sharedWorker_lifetime.html b/dom/workers/test/test_sharedWorker_lifetime.html
new file mode 100644
index 0000000000..b987f0d7cf
--- /dev/null
+++ b/dom/workers/test/test_sharedWorker_lifetime.html
@@ -0,0 +1,30 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+  <head>
+    <title>Test for MessagePort and SharedWorkers</title>
+    <meta http-equiv="content-type" content="text/html; charset=UTF-8">
+    <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  </head>
+  <body>
+    <script class="testbody" type="text/javascript">
+
+var gced = false;
+
+var sw = new SharedWorker('sharedWorker_lifetime.js');
+sw.port.onmessage = function(event) {
+  ok(gced, "The SW is still alive also after GC");
+  SimpleTest.finish();
+}
+
+sw = null;
+SpecialPowers.forceGC();
+gced = true;
+
+SimpleTest.waitForExplicitFinish();
+    </script>
+  </body>
+</html>
diff --git a/dom/workers/test/test_sharedWorker_ports.html b/dom/workers/test/test_sharedWorker_ports.html
new file mode 100644
index 0000000000..6befd4920c
--- /dev/null
+++ b/dom/workers/test/test_sharedWorker_ports.html
@@ -0,0 +1,41 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+  <head>
+    <title>Test for MessagePort and SharedWorkers</title>
+    <meta http-equiv="content-type" content="text/html; charset=UTF-8">
+    <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  </head>
+  <body>
+    <script class="testbody" type="text/javascript">
+
+var sw1 = new SharedWorker('sharedWorker_ports.js');
+sw1.port.onmessage = function(event) {
+  if (event.data.type == "connected") {
+    ok(true, "The SharedWorker is alive.");
+
+    var sw2 = new SharedWorker('sharedWorker_ports.js');
+    sw1.port.postMessage("Port from the main-thread!", [sw2.port]);
+    return;
+  }
+
+  if (event.data.type == "status") {
+    ok(event.data.test, event.data.msg);
+    return;
+  }
+
+  if (event.data.type == "finish") {
+    info("Finished!");
+    ok(sw1.port, "The port still exists");
+    sw1.port.foo = sw1; // Just a test to see if we leak.
+    SimpleTest.finish();
+  }
+}
+
+SimpleTest.waitForExplicitFinish();
+    </script>
+  </body>
+</html>
diff --git a/dom/workers/test/test_sharedWorker_privateBrowsing.html b/dom/workers/test/test_sharedWorker_privateBrowsing.html
new file mode 100644
index 0000000000..e93d65b3b8
--- /dev/null
+++ b/dom/workers/test/test_sharedWorker_privateBrowsing.html
@@ -0,0 +1,104 @@
+<html xmlns="http://www.w3.org/1999/xhtml">
+<head>
+  <title>Test for SharedWorker - Private Browsing</title>
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css"?>
+</head>
+<body>
+
+<script type="application/javascript">
+const {BrowserTestUtils} = ChromeUtils.importESModule(
+  "resource://testing-common/BrowserTestUtils.sys.mjs"
+);
+var mainWindow;
+
+var contentPage = "http://mochi.test:8888/chrome/dom/workers/test/empty.html";
+
+function testOnWindow(aIsPrivate, aCallback) {
+  var win = mainWindow.OpenBrowserWindow({private: aIsPrivate});
+  win.addEventListener("load", function() {
+    win.addEventListener("DOMContentLoaded", function onInnerLoad() {
+      if (win.content.location.href != contentPage) {
+        BrowserTestUtils.startLoadingURIString(win.gBrowser, contentPage);
+        return;
+      }
+
+      win.removeEventListener("DOMContentLoaded", onInnerLoad, true);
+      SimpleTest.executeSoon(function() { aCallback(win); });
+    }, true);
+  }, {capture: true, once: true});
+}
+
+function setupWindow() {
+  mainWindow = window.browsingContext.topChromeWindow;
+  runTest();
+}
+
+var wN;
+var wP;
+
+function doTests() {
+  testOnWindow(false, function(aWin) {
+    wN = aWin;
+
+    testOnWindow(true, function(win) {
+      wP = win;
+
+      var sharedWorker1 = new wP.content.SharedWorker('sharedWorker_privateBrowsing.js');
+      sharedWorker1.port.onmessage = function(event) {
+        is(event.data, 1, "Only 1 sharedworker expected in the private window");
+
+        var sharedWorker2 = new wN.content.SharedWorker('sharedWorker_privateBrowsing.js');
+        sharedWorker2.port.onmessage = function(event1) {
+          is(event1.data, 1, "Only 1 sharedworker expected in the normal window");
+
+          var sharedWorker3 = new wP.content.SharedWorker('sharedWorker_privateBrowsing.js');
+          sharedWorker3.port.onmessage = function(event2) {
+            is(event2.data, 2, "Only 2 sharedworker expected in the private window");
+            runTest();
+          }
+        }
+      }
+    });
+  });
+}
+
+function doSystemSharedWorkerTest() {
+  try {
+    let chromeShared =
+      new wP.SharedWorker("chrome://mochitests/content/dom/workers/test/sharedWorker_privateBrowsing.js");
+    ok(true, "system SharedWorker created without throwing or crashing!");
+  } catch (_ex) {
+    ok(false, "system SharedWorker should not throw or crash");
+  }
+  runTest();
+}
+
+var steps = [
+  setupWindow,
+  doTests,
+  doSystemSharedWorkerTest,
+];
+
+function runTest() {
+  if (!steps.length) {
+    wN.close();
+    wP.close();
+
+    SimpleTest.finish();
+    return;
+  }
+
+  var step = steps.shift();
+  step();
+}
+
+SimpleTest.waitForExplicitFinish();
+SpecialPowers.pushPrefEnv({"set": [
+  ["browser.startup.page", 0],
+  ["browser.startup.homepage_override.mstone", "ignore"],
+]}, runTest);
+
+</script>
+</body>
+</html>
diff --git a/dom/workers/test/test_sharedWorker_thirdparty.html b/dom/workers/test/test_sharedWorker_thirdparty.html
new file mode 100644
index 0000000000..caeb122bba
--- /dev/null
+++ b/dom/workers/test/test_sharedWorker_thirdparty.html
@@ -0,0 +1,54 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test for SharedWorker in 3rd Party Iframes</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"> </script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css">
+</head>
+<body>
+  <script class="testbody">
+
+  function testThirdPartyFrame(name) {
+    return new Promise(resolve => {
+      // Let's use a window, loading the same origin, in order to have the new
+      // cookie-policy applied.
+      let w = window.open("sharedWorker_thirdparty_window.html?name=" + name);
+      window.addEventListener('message', function messageListener(evt) {
+        if (evt.data.name !== name) {
+          return;
+        }
+        w.close();
+        window.removeEventListener('message', messageListener);
+        resolve(evt.data.result);
+      });
+    });
+  }
+
+  const COOKIE_BEHAVIOR_ACCEPT        = 0;
+  const COOKIE_BEHAVIOR_REJECTFOREIGN = 1;
+
+  add_task(async function allowed() {
+    await SpecialPowers.pushPrefEnv({ set: [
+      ["network.cookie.cookieBehavior", COOKIE_BEHAVIOR_ACCEPT]
+    ]});
+    let result = await testThirdPartyFrame('allowed');
+    ok(result === 'allowed',
+       'SharedWorker should be allowed when 3rd party iframes can access storage');
+  });
+
+  add_task(async function blocked() {
+    await SpecialPowers.pushPrefEnv({ set: [
+      ["network.cookie.cookieBehavior", COOKIE_BEHAVIOR_REJECTFOREIGN]
+    ]});
+    let result = await testThirdPartyFrame('blocked');
+    ok(result === 'blocked',
+       'SharedWorker should not be allowed when 3rd party iframes are denied storage');
+  });
+
+  </script>
+</body>
+</html>
diff --git a/dom/workers/test/test_sharedworker_event_listener_leaks.html b/dom/workers/test/test_sharedworker_event_listener_leaks.html
new file mode 100644
index 0000000000..4016cdda48
--- /dev/null
+++ b/dom/workers/test/test_sharedworker_event_listener_leaks.html
@@ -0,0 +1,51 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Bug 1450358 - Test SharedWorker event listener leak conditions</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <script type="text/javascript" src="/tests/dom/events/test/event_leak_utils.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<script class="testbody" type="text/javascript">
+// Manipulate SharedWorker objects in the frame's context.
+// Its important here that we create a listener callback from
+// the DOM objects back to the frame's global in order to
+// exercise the leak condition.
+async function useSharedWorker(contentWindow) {
+  contentWindow.messageCount = 0;
+
+  let sw = new contentWindow.SharedWorker("data:application/javascript,self.onconnect = e => e.ports[0].postMessage({})");
+  sw.onerror = _ => {
+    contentWindow.errorCount += 1;
+  }
+  await new Promise(resolve => {
+    sw.port.onmessage = e => {
+      contentWindow.messageCount += 1;
+      resolve();
+    };
+  });
+
+  is(contentWindow.messageCount, 1, "message should be received");
+}
+
+async function runTest() {
+  try {
+    await checkForEventListenerLeaks("SharedWorker", useSharedWorker);
+  } catch (e) {
+    ok(false, e);
+  } finally {
+    SimpleTest.finish();
+  }
+}
+
+SimpleTest.waitForExplicitFinish();
+addEventListener("load", runTest, { once: true });
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_shutdownCheck.xhtml b/dom/workers/test/test_shutdownCheck.xhtml
new file mode 100644
index 0000000000..257b37fe32
--- /dev/null
+++ b/dom/workers/test/test_shutdownCheck.xhtml
@@ -0,0 +1,61 @@
+<?xml version="1.0"?>
+<?xml-stylesheet type="text/css" href="chrome://global/skin"?>
+<?xml-stylesheet type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css"?>
+
+<window title="Worker shutdown check"
+        xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"/>
+
+  <!-- test results are displayed in the html:body -->
+  <body xmlns="http://www.w3.org/1999/xhtml">
+  </body>
+
+  <!-- test code goes here -->
+  <script type="application/javascript">
+  <![CDATA[
+
+SimpleTest.waitForExplicitFinish()
+
+const URL = "worker_shutdownCheck.js";
+
+function checkWorker() {
+  const wdm = Cc["@mozilla.org/dom/workers/workerdebuggermanager;1"].
+              getService(Ci.nsIWorkerDebuggerManager);
+
+  let e = wdm.getWorkerDebuggerEnumerator();
+  while (e.hasMoreElements()) {
+    let dbg = e.getNext().QueryInterface(Ci.nsIWorkerDebugger);
+    if (dbg.url == URL) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
+new Promise(resolve => {
+  var w = new Worker(URL);
+  ok(checkWorker(), "We have the worker");
+  w.onmessage = () => { resolve(); }
+}).then(() => {
+  info("Waiting...");
+
+  // We don't know if the worker thread is able to shutdown when calling
+  // CC/GC. Better to check again in case.
+  function checkGC() {
+    Cu.forceCC();
+    Cu.forceGC();
+    if (!checkWorker()) {
+      ok(true, "We don't have the worker");
+      SimpleTest.finish();
+      return;
+    }
+    setTimeout(checkGC, 200);
+  }
+
+  checkGC();
+});
+
+  ]]>
+  </script>
+</window>
diff --git a/dom/workers/test/test_simpleThread.html b/dom/workers/test/test_simpleThread.html
new file mode 100644
index 0000000000..aee5765170
--- /dev/null
+++ b/dom/workers/test/test_simpleThread.html
@@ -0,0 +1,74 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<!--
+Tests of DOM Worker Threads (Bug 437152)
+-->
+<head>
+  <title>Test for DOM Worker Threads (Bug 437152)</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=437152">DOM Worker Threads Bug 437152</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script class="testbody" type="text/javascript">
+
+  var worker = new Worker("simpleThread_worker.js");
+
+  worker.addEventListener("message",function(event) {
+    is(event.target, worker);
+    switch (event.data) {
+      case "no-op":
+        break;
+      case "started":
+        is(gotErrors, true);
+        worker.postMessage("no-op");
+        worker.postMessage("stop");
+        break;
+      case "stopped":
+        worker.postMessage("no-op");
+        SimpleTest.finish();
+        break;
+      default:
+        ok(false, "Unexpected message:" + event.data);
+        SimpleTest.finish();
+    }
+  });
+
+  var gotErrors = false;
+  worker.onerror = function(event) {
+    event.preventDefault();
+    is(event.target, worker);
+    is(event.message, "uncaught exception: Bad message: asdf");
+
+    worker.onerror = function(otherEvent) {
+      otherEvent.preventDefault();
+      is(otherEvent.target, worker);
+      is(otherEvent.message, "ReferenceError: Components is not defined");
+      gotErrors = true;
+
+      worker.onerror = function(oneMoreEvent) {
+        ok(false, "Worker had an error:" + oneMoreEvent.message);
+        SimpleTest.finish();
+      };
+    };
+  };
+
+  worker.postMessage("asdf");
+  worker.postMessage("components");
+  worker.postMessage("start");
+
+  SimpleTest.waitForExplicitFinish();
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_sourcemap_header.html b/dom/workers/test/test_sourcemap_header.html
new file mode 100644
index 0000000000..250b30f079
--- /dev/null
+++ b/dom/workers/test/test_sourcemap_header.html
@@ -0,0 +1,22 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Test for DOM Worker + SourceMap header</title>
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js">
+  </script>
+  <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
+  <script type="application/javascript" src="dom_worker_helper.js"></script>
+</head>
+<body>
+<p id="display"></p>
+<div id="content" style="display: none"></div>
+<pre id="test"></pre>
+
+<iframe id="worker-frame"></iframe>
+</body>
+<script type="text/javascript" src="sourcemap_header.js"></script>
+</html>
diff --git a/dom/workers/test/test_subworkers_suspended.html b/dom/workers/test/test_subworkers_suspended.html
new file mode 100644
index 0000000000..01157671d7
--- /dev/null
+++ b/dom/workers/test/test_subworkers_suspended.html
@@ -0,0 +1,144 @@
+<!DOCTYPE HTML>
+<html>
+<head>
+  <meta charset="utf-8">
+  <title>Test for sub workers+bfcache behavior</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+  <script type="application/javascript">
+
+
+
+  /**
+   * - main page opens testUrl1
+   * - testUrl1 ---"onpageshow"---> to main page
+   * - main page ---"startWorker"---> testUrl1
+   * - testUrl1 starts workers, also ---"verifyCacheData"---> main page
+   * - main page ---"changeLocation"---> testUrl1
+   * - testUrl1 navigated to testUrl2
+   * - testUrl2 ---"onpageshow"---> to main page
+   * - main page ---"startWorker"---> testUrl2
+   * - testUrl2 starts workers, also ---"verifyCacheData"---> main page
+   * - main page ---"goBack"---> testUrl2
+   * - testUrl2 navigates back to testUrl1
+   * - testUrl1 ---"onpageshow"---> to main page
+   * - main page checks cache data and ---"finish"---> testUrl2
+   * - testUrl1 ---"finished"---> to main page
+   */
+  var testUrl1 = "window_suspended.html?page1Shown";
+  var counter = 0;
+  const SUB_WORKERS = 3;
+
+  function cacheData() {
+    return caches.open("test")
+           .then(function(cache) {
+             return cache.match("http://mochi.test:888/foo");
+           })
+           .then(function(response) {
+             return response.text();
+           });
+  }
+
+  function runTest() {
+    var bc1 = new BroadcastChannel("page1Shown");
+    bc1.onmessage = async (msgEvent) => {
+      var msg = msgEvent.data;
+      var command = msg.command;
+      info(`Main page, received command=${command}`);
+      if (command == "onpageshow") {
+        info("Page1Shown: " + msg.location);
+        // First time this page is shown.
+        if (counter == 0) {
+          ok(!msg.persisted, "test page should have been persisted initially");
+          var workerMessage = { type: "page1", count: SUB_WORKERS };
+          bc1.postMessage({command: "startWorker", workerMessage});
+        } else {
+          is(msg.persisted, true, "test page should have been persisted in pageshow");
+          var promise = new Promise((resolve, reject) => {
+            info("Waiting a few seconds...");
+            setTimeout(resolve, 10000);
+          });
+
+          promise.then(function() {
+            info("Retrieving data from cache...");
+            return cacheData();
+          })
+
+          .then(function(content) {
+            is(content.indexOf("page1-"), 0, "We have data from the worker");
+          })
+          .then(function() {
+            bc1.postMessage({command: "finish"});
+          });
+        }
+        counter++;
+      } else if (command == "workerMessage") {
+        is(msg.workerMessage, "ready", "We want to receive: -ready-");
+      } else if (command == "verifyCacheData") {
+        var content = await cacheData();
+        is(content.indexOf("page1-"), 0, "We have data from the worker");
+        bc1.postMessage({command: "changeLocation"});
+      } else if (command == "finished") {
+        bc1.close();
+        bc2.close();
+        SimpleTest.finish();
+      }
+    }
+    var bc2 = new BroadcastChannel("page2Shown");
+    bc2.onmessage = async (msgEvent) => {
+      var msg = msgEvent.data;
+      var command = msg.command;
+      if (command == "onpageshow") {
+        info("Page1Shown: " + msg.location);
+        var workerMessage = { type: "page2" };
+        bc2.postMessage({command: "startWorker", workerMessage});
+      } else if (command == "workerMessage") {
+        is(msg.workerMessage, "ready", "We want to receive: -ready-");
+      } else if (command == "verifyCacheData") {
+        var content = await cacheData();
+        is(content, "page2-0", "We have data from the second worker");
+        bc2.postMessage({command: "goBack"});
+      }
+    }
+
+    SpecialPowers.pushPrefEnv({ set: [
+      ["dom.caches.testing.enabled", true],
+      // If Fission is disabled, the pref is no-op.
+      ["fission.bfcacheInParent", true],
+    ] },
+    function() {
+      window.open(testUrl1, "", "noopener");
+    });
+
+  }
+
+  if (isXOrigin) {
+    // Bug 1746646: Make mochitests work with TCP enabled (cookieBehavior = 5)
+    // Acquire storage access permission here so that the BroadcastChannel used to
+    // communicate with the opened windows works in xorigin tests. Otherwise,
+    // the iframe containing this page is isolated from first-party storage access,
+    // which isolates BroadcastChannel communication.
+    SpecialPowers.wrap(document).notifyUserGestureActivation();
+    SpecialPowers.pushPrefEnv({
+      set: [["privacy.partition.always_partition_third_party_non_cookie_storage", false]],
+    }).then(() => {
+      SpecialPowers.pushPermissions([{'type': 'storageAccessAPI', 'allow': 1, 'context': document}], () =>{
+        SpecialPowers.wrap(document).requestStorageAccess().then(() => {
+          runTest();
+        }).then(() => {
+          SpecialPowers.removePermission("3rdPartyStorage^http://mochi.test:8888", "http://mochi.xorigin-test:8888");
+        });
+      });
+    });
+  } else {
+    runTest();
+  }
+
+  SimpleTest.waitForExplicitFinish();
+  SimpleTest.requestFlakyTimeout("untriaged");
+
+  </script>
+</body>
+</html>
diff --git a/dom/workers/test/test_suspend.html b/dom/workers/test/test_suspend.html
new file mode 100644
index 0000000000..9ab1a6a7ec
--- /dev/null
+++ b/dom/workers/test/test_suspend.html
@@ -0,0 +1,188 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<head>
+  <meta charset="utf-8">
+  <title>Test for DOM Worker Threads</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<p id="display"></p>
+<div id="content" style="display: none"></div>
+<pre id="test">
+<script class="testbody" type="text/javascript">
+
+  SimpleTest.waitForExplicitFinish();
+
+  /**
+   * - main page tells subpage to call startWorker()
+   * - subpage starts worker
+   * - worker calls setInterval() and keeps calling postMessage()
+   * - onmessage(), as setup by the subpage, calls messageCallback
+   * - when messageCallback gets called more than 25 times
+   *    - subpage gets navigated to blank.html
+   * - blank page posts message to main page, and main page calls suspendCallback()
+   * - suspendCallback() schedules waitInterval() to be fired off every second
+   * - after 5 times, it clears the interval and navigates subpage back
+   * - suspend_window subpage starts receiving messages again and
+   *    does a final call to messageCallback()
+   * - finishTest() is called
+   */
+
+  var lastCount;
+
+  var suspended = false;
+  var resumed = false;
+  var finished = false;
+  var suspendBlankPageCurrentlyShowing = false;
+
+  var interval;
+  var oldMessageCount;
+  var waitCount = 0;
+
+  var bcSuspendWindow, bcSuspendBlank;
+
+  function runTest() {
+    bcSuspendWindow = new BroadcastChannel("suspendWindow");
+    bcSuspendWindow.onmessage = (msgEvent) => {
+      var msg = msgEvent.data;
+      var command = msg.command;
+      var data = msg.data;
+      if (command == "loaded") {
+        if (finished) {
+          return;
+        }
+        bcSuspendWindow.postMessage({command: "startWorker"});
+      } else if (command == "messageCallback") {
+        messageCallback(data);
+      } else if (command == "errorCallback") {
+        errorCallback(data);
+      } else if (command == "finished") {
+        SimpleTest.finish();
+      }
+    }
+
+    bcSuspendBlank = new BroadcastChannel("suspendBlank");
+    bcSuspendBlank.onmessage = (msgEvent) => {
+      var msg = msgEvent.data;
+      var command = msg.command;
+      if (command == "loaded") {
+        suspendBlankPageCurrentlyShowing = true;
+        if (suspended) {
+          badOnloadCallback();
+        } else {
+          suspendCallback();
+        }
+      } else if (command == "pagehide") {
+        suspendBlankPageCurrentlyShowing = false;
+      }
+    }
+
+    // If Fission is disabled, the pref is no-op.
+    SpecialPowers.pushPrefEnv({set: [["fission.bfcacheInParent", true]]}, () => {
+      window.open("suspend_window.html", "testWin", "noopener");
+    });
+  }
+
+  function finishTest() {
+    if (finished) {
+      return;
+    }
+    finished = true;
+    bcSuspendWindow.postMessage({command: "finish"});
+  }
+
+  function waitInterval() {
+    if (finished) {
+      return;
+    }
+    ok(suspendBlankPageCurrentlyShowing, "correct page is showing");
+    is(suspended, true, "Not suspended?");
+    is(resumed, false, "Already resumed?!");
+    is(lastCount, oldMessageCount, "Received a message while suspended!");
+    if (++waitCount == 5) {
+      clearInterval(interval);
+      resumed = true;
+      bcSuspendBlank.postMessage({command: "navigateBack"});
+    }
+  }
+
+  function badOnloadCallback() {
+    if (finished) {
+      return;
+    }
+    ok(false, "We don't want suspend_window.html to fire a new load event, we want it to come out of the bfcache!");
+    finishTest();
+  }
+
+  function suspendCallback() {
+    if (finished) {
+      return;
+    }
+    ok(suspendBlankPageCurrentlyShowing, "correct page is showing");
+    is(suspended, false, "Already suspended?");
+    is(resumed, false, "Already resumed?");
+    suspended = true;
+    oldMessageCount = lastCount;
+    interval = setInterval(waitInterval, 1000);
+  }
+
+  function messageCallback(data) {
+    if (finished) {
+      return;
+    }
+
+    if (!suspended) {
+      ok(lastCount === undefined || lastCount == data - 1,
+         "Got good data, lastCount = " + lastCount + ", data = " + data);
+      lastCount = data;
+      if (lastCount == 25) {
+        bcSuspendWindow.postMessage({command: "navigate"});
+      }
+      return;
+    }
+
+    ok(!suspendBlankPageCurrentlyShowing, "correct page is showing");
+    is(resumed, true, "Got message before resumed!");
+    is(lastCount, data - 1, "Missed a message, suspend failed!");
+    finishTest();
+  }
+
+  function errorCallback(data) {
+    if (finished) {
+      return;
+    }
+    ok(false, "testWin had an error: '" + data + "'");
+    finishTest();
+  }
+
+  if (isXOrigin) {
+    // Bug 1746646: Make mochitests work with TCP enabled (cookieBehavior = 5)
+    // Acquire storage access permission here so that the BroadcastChannel used to
+    // communicate with the opened windows works in xorigin tests. Otherwise,
+    // the iframe containing this page is isolated from first-party storage access,
+    // which isolates BroadcastChannel communication.
+    SpecialPowers.wrap(document).notifyUserGestureActivation();
+    SpecialPowers.pushPrefEnv({
+      set: [["privacy.partition.always_partition_third_party_non_cookie_storage", false]],
+    }).then(() => {
+      SpecialPowers.pushPermissions([{'type': 'storageAccessAPI', 'allow': 1, 'context': document}], () =>{
+        SpecialPowers.wrap(document).requestStorageAccess().then(() => {
+          runTest();
+        }).then(() => {
+          SpecialPowers.removePermission("3rdPartyStorage^http://mochi.test:8888", "http://mochi.xorigin-test:8888");
+        });
+      });
+    });
+  } else {
+    runTest();
+  }
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_terminate.html b/dom/workers/test/test_terminate.html
new file mode 100644
index 0000000000..c19d65770b
--- /dev/null
+++ b/dom/workers/test/test_terminate.html
@@ -0,0 +1,100 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<!--
+Tests of DOM Worker terminate feature
+-->
+<head>
+  <title>Test for DOM Worker Navigator</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script class="testbody" language="javascript">
+
+
+  var messageCount = 0;
+  var intervalCount = 0;
+
+  var interval;
+
+  var worker;
+
+  function messageListener(event) {
+    is(event.data, "Still alive!", "Correct message!");
+    if (++messageCount == 20) {
+      ok(worker.onmessage === messageListener,
+         "Correct listener before terminate");
+
+      worker.terminate();
+
+      var exception = false;
+      try {
+        worker.addEventListener("message", messageListener);
+      }
+      catch (e) {
+        exception = true;
+      }
+      is(exception, false, "addEventListener didn't throw after terminate");
+
+      exception = false;
+      try {
+        worker.removeEventListener("message", messageListener);
+      }
+      catch (e) {
+        exception = true;
+      }
+      is(exception, false, "removeEventListener didn't throw after terminate");
+
+      exception = false;
+      try {
+        worker.postMessage("foo");
+      }
+      catch (e) {
+        exception = true;
+      }
+      is(exception, false, "postMessage didn't throw after terminate");
+
+      exception = false;
+      try {
+        worker.terminate();
+      }
+      catch (e) {
+        exception = true;
+      }
+      is(exception, false, "terminate didn't throw after terminate");
+
+      ok(worker.onmessage === messageListener,
+         "Correct listener after terminate");
+
+      worker.onmessage = function(msg) { }
+
+      interval = setInterval(testCount, 1000);
+    }
+  }
+
+  function testCount() {
+    is(messageCount, 20, "Received another message after terminated!");
+    if (intervalCount++ == 5) {
+      clearInterval(interval);
+      SimpleTest.finish();
+    }
+  }
+
+  worker = new Worker("terminate_worker.js");
+  worker.onmessage = messageListener;
+
+  SimpleTest.waitForExplicitFinish();
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_threadErrors.html b/dom/workers/test/test_threadErrors.html
new file mode 100644
index 0000000000..1eb33244ba
--- /dev/null
+++ b/dom/workers/test/test_threadErrors.html
@@ -0,0 +1,64 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<!--
+Tests of DOM Worker Threads (Bug 437152)
+-->
+<head>
+  <title>Test for DOM Worker Threads (Bug 437152)</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=437152">DOM Worker Threads Bug 437152</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script class="testbody" type="text/javascript">
+
+  const expectedErrorCount = 4;
+
+  function messageListener(event) {
+    ok(false, "Unexpected message: " + event.data);
+    SimpleTest.finish();
+  };
+
+  var actualErrorCount = 0;
+  var failedWorkers = [];
+
+  function errorListener(event) {
+    event.preventDefault();
+
+    if (failedWorkers.includes(event.target)) {
+      ok(false, "Seen an extra error from this worker");
+      SimpleTest.finish();
+      return;
+    }
+
+    failedWorkers.push(event.target);
+    actualErrorCount++;
+
+    if (actualErrorCount == expectedErrorCount) {
+      ok(true, "all errors correctly detected");
+      SimpleTest.finish();
+    }
+  };
+
+  for (var i = 1; i <= expectedErrorCount; i++) {
+    var worker = new Worker("threadErrors_worker" + i + ".js");
+    worker.onmessage = messageListener;
+    worker.onerror = errorListener;
+    worker.postMessage("Hi");
+  }
+
+  SimpleTest.waitForExplicitFinish();
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_threadTimeouts.html b/dom/workers/test/test_threadTimeouts.html
new file mode 100644
index 0000000000..93a8d9243c
--- /dev/null
+++ b/dom/workers/test/test_threadTimeouts.html
@@ -0,0 +1,60 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<!--
+Tests of DOM Worker Threads (Bug 437152)
+-->
+<head>
+  <title>Test for DOM Worker Threads (Bug 437152)</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=437152">DOM Worker Threads Bug 437152</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script class="testbody" type="text/javascript">
+
+  var worker = new Worker("threadTimeouts_worker.js");
+
+  worker.onmessage = function(event) {
+    is(event.target, worker);
+    switch (event.data) {
+      case "timeoutFinished":
+        event.target.postMessage("startInterval");
+        break;
+      case "intervalFinished":
+        event.target.postMessage("cancelInterval");
+        break;
+      case "intervalCanceled":
+        worker.postMessage("startExpression");
+        break;
+      case "expressionFinished":
+        SimpleTest.finish();
+        break;
+      default:
+        ok(false, "Unexpected message");
+        SimpleTest.finish();
+    }
+  };
+
+  worker.onerror = function(event) {
+    is(event.target, worker);
+    ok(false, "Worker had an error: " + event.message);
+    SimpleTest.finish();
+  };
+
+  worker.postMessage("startTimeout");
+
+  SimpleTest.waitForExplicitFinish();
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_throwingOnerror.html b/dom/workers/test/test_throwingOnerror.html
new file mode 100644
index 0000000000..0ed1f74247
--- /dev/null
+++ b/dom/workers/test/test_throwingOnerror.html
@@ -0,0 +1,54 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<!--
+Tests of DOM Worker Threads
+-->
+<head>
+  <title>Test for DOM Worker Threads Recursion</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script class="testbody" type="text/javascript">
+
+  var worker = new Worker("throwingOnerror_worker.js");
+
+  var errors = ["foo", "bar"];
+
+  worker.onerror = function(event) {
+    event.preventDefault();
+    var found = false;
+    for (var index in errors) {
+      if (event.message == "uncaught exception: " + errors[index]) {
+        errors.splice(index, 1);
+        found = true;
+        break;
+      }
+    }
+    is(found, true, "Unexpected error!");
+  };
+
+  worker.onmessage = function(event) {
+    is(errors.length, 0, "Didn't see expected errors!");
+    SimpleTest.finish();
+  };
+
+  for (var i = 0; i < 2; i++) {
+    worker.postMessage("");
+  }
+
+  SimpleTest.waitForExplicitFinish();
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_timeoutTracing.html b/dom/workers/test/test_timeoutTracing.html
new file mode 100644
index 0000000000..8e64564b72
--- /dev/null
+++ b/dom/workers/test/test_timeoutTracing.html
@@ -0,0 +1,47 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<!--
+Tests of DOM Worker Threads
+-->
+<head>
+  <title>Test for DOM Worker Threads</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<pre id="test">
+<script class="testbody" type="text/javascript">
+
+  var worker = new Worker("timeoutTracing_worker.js");
+
+  worker.onmessage = function(event) {
+    // begin
+    worker.onmessage = null;
+
+    // 1 second should be enough to crash.
+    window.setTimeout(function() {
+      ok(true, "Didn't crash!");
+      SimpleTest.finish();
+    }, 1000);
+
+    var os = SpecialPowers.Cc["@mozilla.org/observer-service;1"]
+                          .getService(SpecialPowers.Ci.nsIObserverService);
+    os.notifyObservers(null, "memory-pressure", "heap-minimize");
+  }
+
+  worker.onerror = function(event) {
+    ok(false, "I was expecting a crash, not an error");
+    SimpleTest.finish();
+  };
+
+  SimpleTest.waitForExplicitFinish();
+  SimpleTest.requestFlakyTimeout("untriaged");
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_transferable.html b/dom/workers/test/test_transferable.html
new file mode 100644
index 0000000000..ac490f369a
--- /dev/null
+++ b/dom/workers/test/test_transferable.html
@@ -0,0 +1,123 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<!DOCTYPE HTML>
+<html>
+<!--
+Tests of DOM Worker transferable objects
+-->
+<head>
+  <title>Test for DOM Worker transferable objects</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+</head>
+<body>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+<script class="testbody" language="javascript">
+
+  function test1(sizes) {
+    if (!sizes.length) {
+      runTests();
+      return;
+    }
+
+    var size = sizes.pop();
+
+    var worker = new Worker("transferable_worker.js");
+    worker.onmessage = function(event) {
+      ok(event.data.status, event.data.event);
+      if (!event.data.status) {
+        runTests();
+        return;
+      }
+
+      if ("notEmpty" in event.data && "byteLength" in event.data.notEmpty) {
+        ok(event.data.notEmpty.byteLength != 0,
+           "P: NotEmpty object received: " + event.data.notEmpty.byteLength);
+      }
+
+      if (!event.data.last)
+        return;
+
+      test1(sizes);
+    }
+    worker.onerror = function(event) {
+      ok(false, "No errors!");
+    }
+
+    try {
+      worker.postMessage(42, true);
+      ok(false, "P: PostMessage - Exception for wrong type");
+    } catch(e) {
+      ok(true, "P: PostMessage - Exception for wrong type");
+    }
+
+    try {
+      ab = new ArrayBuffer(size);
+      worker.postMessage(42,[ab, ab]);
+      ok(false, "P: PostMessage - Exception for duplicate");
+    } catch(e) {
+      ok(true, "P: PostMessage - Exception for duplicate");
+    }
+
+    var ab = new ArrayBuffer(size);
+    ok(ab.byteLength == size, "P: The size is: " + size + " == " + ab.byteLength);
+    worker.postMessage({ data: 0, timeout: 0, ab, cb: ab, size }, [ab]);
+    ok(ab.byteLength == 0, "P: PostMessage - The size is: 0 == " + ab.byteLength)
+  }
+
+  function test2() {
+    var worker = new Worker("transferable_worker.js");
+    worker.onmessage = function(event) {
+      ok(event.data.status, event.data.event);
+      if (!event.data.status) {
+        runTests();
+        return;
+      }
+
+      if ("notEmpty" in event.data && "byteLength" in event.data.notEmpty) {
+        ok(event.data.notEmpty.byteLength != 0,
+           "P: NotEmpty object received: " + event.data.notEmpty.byteLength);
+      }
+
+      if (event.data.last) {
+        runTests();
+      }
+    }
+    worker.onerror = function(event) {
+      ok(false, "No errors!");
+    }
+
+    var f = new Float32Array([0,1,2,3]);
+    ok(f.byteLength != 0, "P: The size is: " + f.byteLength + " is not 0");
+    worker.postMessage({ event: "P: postMessage with Float32Array", status: true,
+                         size: 4, notEmpty: f, bc: [ f, f, { dd: f } ] }, [f.buffer]);
+    ok(f.byteLength == 0, "P: The size is: " + f.byteLength + " is 0");
+  }
+
+  var tests = [
+    function() { test1([1024 * 1024 * 32, 128, 4]); },
+    test2
+  ];
+  function runTests() {
+    if (!tests.length) {
+      SimpleTest.finish();
+      return;
+    }
+
+    var test = tests.shift();
+    test();
+  }
+
+  SimpleTest.waitForExplicitFinish();
+  runTests();
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/workers/test/test_worker_interfaces.html b/dom/workers/test/test_worker_interfaces.html
new file mode 100644
index 0000000000..b051e01242
--- /dev/null
+++ b/dom/workers/test/test_worker_interfaces.html
@@ -0,0 +1,19 @@
+<!-- Any copyright is dedicated to the Public Domain.
+   - http://creativecommons.org/publicdomain/zero/1.0/ -->
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Validate Interfaces Exposed to Workers</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+  <script type="text/javascript" src="worker_driver.js"></script>
+</head>
+<body>
+<script>
+  ok(!self.isSecureContext, "This test should not be running in a secure context");
+</script>
+<script class="testbody" type="text/javascript">
+workerTestExec("test_worker_interfaces.js");
+</script>
+</body>
+</html>
diff --git a/dom/workers/test/test_worker_interfaces.js b/dom/workers/test/test_worker_interfaces.js
new file mode 100644
index 0000000000..3ea89ad6b5
--- /dev/null
+++ b/dom/workers/test/test_worker_interfaces.js
@@ -0,0 +1,563 @@
+// This is a list of all interfaces that are exposed to workers.
+// Please only add things to this list with great care and proper review
+// from the associated module peers.
+
+// This file lists global interfaces we want exposed and verifies they
+// are what we intend. Each entry in the arrays below can either be a
+// simple string with the interface name, or an object with a 'name'
+// property giving the interface name as a string, and additional
+// properties which qualify the exposure of that interface. For example:
+//
+// [
+//   "AGlobalInterface", // secure context only
+//   { name: "ExperimentalThing", release: false },
+//   { name: "ReallyExperimentalThing", nightly: true },
+//   { name: "DesktopOnlyThing", desktop: true },
+//   { name: "FancyControl", xbl: true },
+//   { name: "DisabledEverywhere", disabled: true },
+// ];
+//
+// See createInterfaceMap() below for a complete list of properties.
+//
+// The values of the properties need to be literal true/false
+// (e.g. indicating whether something is enabled on a particular
+// channel/OS).  If we ever end up in a situation where a propert
+// value needs to depend on channel or OS, we will need to make sure
+// we have that information before setting up the property lists.
+
+// IMPORTANT: Do not change this list without review from
+//            a JavaScript Engine peer!
+let wasmGlobalEntry = {
+  name: "WebAssembly",
+  insecureContext: true,
+  disabled: !getJSTestingFunctions().wasmIsSupportedByHardware(),
+};
+let wasmGlobalInterfaces = [
+  { name: "Module", insecureContext: true },
+  { name: "Instance", insecureContext: true },
+  { name: "Memory", insecureContext: true },
+  { name: "Table", insecureContext: true },
+  { name: "Global", insecureContext: true },
+  { name: "CompileError", insecureContext: true },
+  { name: "LinkError", insecureContext: true },
+  { name: "RuntimeError", insecureContext: true },
+  { name: "Function", insecureContext: true, nightly: true },
+  { name: "Exception", insecureContext: true },
+  { name: "Tag", insecureContext: true },
+  { name: "compile", insecureContext: true },
+  { name: "compileStreaming", insecureContext: true },
+  { name: "instantiate", insecureContext: true },
+  { name: "instantiateStreaming", insecureContext: true },
+  { name: "validate", insecureContext: true },
+];
+// IMPORTANT: Do not change this list without review from
+//            a JavaScript Engine peer!
+let ecmaGlobals = [
+  { name: "AggregateError", insecureContext: true },
+  { name: "Array", insecureContext: true },
+  { name: "ArrayBuffer", insecureContext: true },
+  { name: "Atomics", insecureContext: true },
+  { name: "BigInt", insecureContext: true },
+  { name: "BigInt64Array", insecureContext: true },
+  { name: "BigUint64Array", insecureContext: true },
+  { name: "Boolean", insecureContext: true },
+  { name: "DataView", insecureContext: true },
+  { name: "Date", insecureContext: true },
+  { name: "Error", insecureContext: true },
+  { name: "EvalError", insecureContext: true },
+  { name: "FinalizationRegistry", insecureContext: true },
+  { name: "Float32Array", insecureContext: true },
+  { name: "Float64Array", insecureContext: true },
+  { name: "Function", insecureContext: true },
+  { name: "Infinity", insecureContext: true },
+  { name: "Int16Array", insecureContext: true },
+  { name: "Int32Array", insecureContext: true },
+  { name: "Int8Array", insecureContext: true },
+  { name: "InternalError", insecureContext: true },
+  { name: "Intl", insecureContext: true },
+  { name: "JSON", insecureContext: true },
+  { name: "Map", insecureContext: true },
+  { name: "MediaCapabilities", insecureContext: true },
+  { name: "MediaCapabilitiesInfo", insecureContext: true },
+  { name: "Math", insecureContext: true },
+  { name: "NaN", insecureContext: true },
+  { name: "Number", insecureContext: true },
+  { name: "Object", insecureContext: true },
+  { name: "Promise", insecureContext: true },
+  { name: "Proxy", insecureContext: true },
+  { name: "RangeError", insecureContext: true },
+  { name: "ReferenceError", insecureContext: true },
+  { name: "Reflect", insecureContext: true },
+  { name: "RegExp", insecureContext: true },
+  { name: "Set", insecureContext: true },
+  {
+    name: "SharedArrayBuffer",
+    insecureContext: true,
+    crossOringinIsolated: true,
+  },
+  { name: "String", insecureContext: true },
+  { name: "Symbol", insecureContext: true },
+  { name: "SyntaxError", insecureContext: true },
+  { name: "TypeError", insecureContext: true },
+  { name: "Uint16Array", insecureContext: true },
+  { name: "Uint32Array", insecureContext: true },
+  { name: "Uint8Array", insecureContext: true },
+  { name: "Uint8ClampedArray", insecureContext: true },
+  { name: "URIError", insecureContext: true },
+  { name: "WeakMap", insecureContext: true },
+  { name: "WeakRef", insecureContext: true },
+  { name: "WeakSet", insecureContext: true },
+  wasmGlobalEntry,
+  { name: "decodeURI", insecureContext: true },
+  { name: "decodeURIComponent", insecureContext: true },
+  { name: "encodeURI", insecureContext: true },
+  { name: "encodeURIComponent", insecureContext: true },
+  { name: "escape", insecureContext: true },
+  { name: "eval", insecureContext: true },
+  { name: "globalThis", insecureContext: true },
+  { name: "isFinite", insecureContext: true },
+  { name: "isNaN", insecureContext: true },
+  { name: "parseFloat", insecureContext: true },
+  { name: "parseInt", insecureContext: true },
+  { name: "undefined", insecureContext: true },
+  { name: "unescape", insecureContext: true },
+];
+// IMPORTANT: Do not change the list above without review from
+//            a JavaScript Engine peer!
+
+// IMPORTANT: Do not change the list below without review from a DOM peer!
+let interfaceNamesInGlobalScope = [
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "AbortController", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "AbortSignal", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "Blob", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "BroadcastChannel", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "ByteLengthQueuingStrategy", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  "Cache",
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  "CacheStorage",
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "CanvasGradient", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "CanvasPattern", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "CloseEvent", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "CompressionStream", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "CountQueuingStrategy", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "Crypto", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "CryptoKey" },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "CustomEvent", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "DecompressionStream", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "DedicatedWorkerGlobalScope", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "Directory", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "DOMException", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "DOMMatrix", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "DOMMatrixReadOnly", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "DOMPoint", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "DOMPointReadOnly", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "DOMQuad", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "DOMRect", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "DOMRectReadOnly", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "DOMRequest", insecureContext: true, disabled: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "DOMStringList", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "EncodedVideoChunk", insecureContext: true, nightly: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "ErrorEvent", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "Event", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "EventSource", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "EventTarget", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "File", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "FileList", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "FileReader", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "FileReaderSync", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "FileSystemDirectoryHandle" },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "FileSystemFileHandle" },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "FileSystemHandle" },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "FileSystemSyncAccessHandle" },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "FileSystemWritableFileStream" },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "FontFace", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "FontFaceSet", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "FontFaceSetLoadEvent", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "FormData", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "Headers", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "IDBCursor", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "IDBCursorWithValue", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "IDBDatabase", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "IDBFactory", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "IDBIndex", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "IDBKeyRange", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "IDBObjectStore", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "IDBOpenDBRequest", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "IDBRequest", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "IDBTransaction", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "IDBVersionChangeEvent", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "ImageBitmap", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "ImageBitmapRenderingContext", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "ImageData", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  "Lock",
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  "LockManager",
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "MessageChannel", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "MessageEvent", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "MessagePort", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "NetworkInformation", insecureContext: true, disabled: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "Notification", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "OffscreenCanvas", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "OffscreenCanvasRenderingContext2D", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "Path2D", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "Performance", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "PerformanceEntry", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "PerformanceMark", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "PerformanceMeasure", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "PerformanceObserver", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "PerformanceObserverEntryList", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "PerformanceResourceTiming", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "PerformanceServerTiming", insecureContext: false },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "ProgressEvent", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "PromiseRejectionEvent", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "ReadableByteStreamController", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "ReadableStream", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "ReadableStreamBYOBReader", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "ReadableStreamBYOBRequest", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "ReadableStreamDefaultController", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "ReadableStreamDefaultReader", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "Request", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "Response", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "RTCEncodedAudioFrame", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "RTCEncodedVideoFrame", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "RTCRtpScriptTransformer", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "RTCTransformEvent", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "Scheduler", insecureContext: true, nightly: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "StorageManager", fennec: false },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "SubtleCrypto" },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "TaskController", insecureContext: true, nightly: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "TaskPriorityChangeEvent", insecureContext: true, nightly: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "TaskSignal", insecureContext: true, nightly: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "TextDecoder", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "TextDecoderStream", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "TextEncoder", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "TextEncoderStream", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "TextMetrics", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "TransformStream", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  {
+    name: "TransformStreamDefaultController",
+    insecureContext: true,
+  },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "XMLHttpRequest", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "XMLHttpRequestEventTarget", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "XMLHttpRequestUpload", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "URL", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "URLSearchParams", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "VideoColorSpace", insecureContext: true, nightly: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "VideoDecoder", nightly: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "VideoEncoder", nightly: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "VideoFrame", insecureContext: true, nightly: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "WebGL2RenderingContext", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "WebGLActiveInfo", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "WebGLBuffer", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "WebGLContextEvent", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "WebGLFramebuffer", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "WebGLProgram", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "WebGLQuery", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "WebGLRenderbuffer", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "WebGLRenderingContext", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "WebGLSampler", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "WebGLShader", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "WebGLShaderPrecisionFormat", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "WebGLSync", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "WebGLTexture", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "WebGLTransformFeedback", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "WebGLUniformLocation", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "WebGLVertexArrayObject", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "WebSocket", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "WebTransport", insecureContext: false },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "WebTransportBidirectionalStream", insecureContext: false },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "WebTransportDatagramDuplexStream", insecureContext: false },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "WebTransportError", insecureContext: false },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "WebTransportReceiveStream", insecureContext: false },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "WebTransportSendStream", insecureContext: false },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "Worker", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "WorkerGlobalScope", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "WorkerLocation", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "WorkerNavigator", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "WritableStream", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "WritableStreamDefaultController", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "WritableStreamDefaultWriter", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "cancelAnimationFrame", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "close", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "console", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "name", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "onmessage", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "onmessageerror", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "onrtctransform", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "postMessage", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "requestAnimationFrame", insecureContext: true },
+  // IMPORTANT: Do not change this list without review from a DOM peer!
+];
+// IMPORTANT: Do not change the list above without review from a DOM peer!
+
+// List of functions defined on the global by the test harness or this test
+// file.
+let testFunctions = [
+  "ok",
+  "is",
+  "workerTestArrayEquals",
+  "workerTestDone",
+  "workerTestGetPermissions",
+  "workerTestGetHelperData",
+  "entryDisabled",
+  "createInterfaceMap",
+  "runTest",
+];
+
+function entryDisabled(
+  entry,
+  {
+    isNightly,
+    isEarlyBetaOrEarlier,
+    isRelease,
+    isDesktop,
+    isAndroid,
+    isInsecureContext,
+    isFennec,
+    isCrossOringinIsolated,
+  }
+) {
+  return (
+    entry.nightly === !isNightly ||
+    (entry.nightlyAndroid === !(isAndroid && isNightly) && isAndroid) ||
+    entry.desktop === !isDesktop ||
+    (entry.android === !isAndroid && !entry.nightlyAndroid) ||
+    entry.fennecOrDesktop === (isAndroid && !isFennec) ||
+    entry.fennec === !isFennec ||
+    entry.release === !isRelease ||
+    // The insecureContext test is very purposefully converting
+    // entry.insecureContext to boolean, so undefined will convert to
+    // false.  That way entries without an insecureContext annotation
+    // will get treated as "insecureContext: false", which means exposed
+    // only in secure contexts.
+    (isInsecureContext && !entry.insecureContext) ||
+    entry.earlyBetaOrEarlier === !isEarlyBetaOrEarlier ||
+    entry.crossOringinIsolated === !isCrossOringinIsolated ||
+    entry.disabled
+  );
+}
+
+function createInterfaceMap(data, ...interfaceGroups) {
+  var interfaceMap = {};
+
+  function addInterfaces(interfaces) {
+    for (var entry of interfaces) {
+      if (typeof entry === "string") {
+        ok(!(entry in interfaceMap), "duplicate entry for " + entry);
+        interfaceMap[entry] = !data.isInsecureContext;
+      } else {
+        ok(!(entry.name in interfaceMap), "duplicate entry for " + entry.name);
+        ok(!("pref" in entry), "Bogus pref annotation for " + entry.name);
+        interfaceMap[entry.name] = !entryDisabled(entry, data);
+      }
+    }
+  }
+
+  for (let interfaceGroup of interfaceGroups) {
+    addInterfaces(interfaceGroup);
+  }
+
+  return interfaceMap;
+}
+
+function runTest(parentName, parent, data, ...interfaceGroups) {
+  var interfaceMap = createInterfaceMap(data, ...interfaceGroups);
+  for (var name of Object.getOwnPropertyNames(parent)) {
+    // Ignore functions on the global that are part of the test (harness).
+    if (parent === self && testFunctions.includes(name)) {
+      continue;
+    }
+    ok(
+      interfaceMap[name],
+      "If this is failing: DANGER, are you sure you want to expose the new interface " +
+        name +
+        " to all webpages as a property of " +
+        parentName +
+        "? Do not make a change to this file without a " +
+        " review from a DOM peer for that specific change!!! (or a JS peer for changes to ecmaGlobals)"
+    );
+    delete interfaceMap[name];
+  }
+  for (var name of Object.keys(interfaceMap)) {
+    ok(
+      name in parent === interfaceMap[name],
+      name +
+        " should " +
+        (interfaceMap[name] ? "" : " NOT") +
+        " be defined on " +
+        parentName
+    );
+    if (!interfaceMap[name]) {
+      delete interfaceMap[name];
+    }
+  }
+  is(
+    Object.keys(interfaceMap).length,
+    0,
+    "The following interface(s) are not enumerated: " +
+      Object.keys(interfaceMap).join(", ")
+  );
+}
+
+workerTestGetHelperData(function (data) {
+  runTest("self", self, data, ecmaGlobals, interfaceNamesInGlobalScope);
+  if (WebAssembly && !entryDisabled(wasmGlobalEntry, data)) {
+    runTest("WebAssembly", WebAssembly, data, wasmGlobalInterfaces);
+  }
+  workerTestDone();
+});
diff --git a/dom/workers/test/test_worker_interfaces_secureContext.html b/dom/workers/test/test_worker_interfaces_secureContext.html
new file mode 100644
index 0000000000..7d26cd2131
--- /dev/null
+++ b/dom/workers/test/test_worker_interfaces_secureContext.html
@@ -0,0 +1,19 @@
+<!-- Any copyright is dedicated to the Public Domain.
+   - http://creativecommons.org/publicdomain/zero/1.0/ -->
+<!DOCTYPE HTML>
+<html>
+<head>
+  <title>Validate Interfaces Exposed to Workers</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css" />
+  <script type="text/javascript" src="worker_driver.js"></script>
+</head>
+<body>
+<script>
+  ok(self.isSecureContext, "This test should be running in a secure context");
+</script>
+<script class="testbody" type="text/javascript">
+workerTestExec("test_worker_interfaces.js");
+</script>
+</body>
+</html>
diff --git a/dom/workers/test/threadErrors_worker1.js b/dom/workers/test/threadErrors_worker1.js
new file mode 100644
index 0000000000..c0ddade82c
--- /dev/null
+++ b/dom/workers/test/threadErrors_worker1.js
@@ -0,0 +1,8 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+// Syntax error
+onmessage = function(event) {
+  for (var i = 0; i < 10) { }
+}
diff --git a/dom/workers/test/threadErrors_worker2.js b/dom/workers/test/threadErrors_worker2.js
new file mode 100644
index 0000000000..da79569def
--- /dev/null
+++ b/dom/workers/test/threadErrors_worker2.js
@@ -0,0 +1,8 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+// Bad function error
+onmessage = function (event) {
+  foopy();
+};
diff --git a/dom/workers/test/threadErrors_worker3.js b/dom/workers/test/threadErrors_worker3.js
new file mode 100644
index 0000000000..e470680981
--- /dev/null
+++ b/dom/workers/test/threadErrors_worker3.js
@@ -0,0 +1,8 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+// Unhandled exception in body
+onmessage = function (event) {};
+
+throw new Error("Bah!");
diff --git a/dom/workers/test/threadErrors_worker4.js b/dom/workers/test/threadErrors_worker4.js
new file mode 100644
index 0000000000..88b089aa3b
--- /dev/null
+++ b/dom/workers/test/threadErrors_worker4.js
@@ -0,0 +1,8 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+// Throwing message listener
+onmessage = function (event) {
+  throw new Error("Bah!");
+};
diff --git a/dom/workers/test/threadTimeouts_worker.js b/dom/workers/test/threadTimeouts_worker.js
new file mode 100644
index 0000000000..27e514b391
--- /dev/null
+++ b/dom/workers/test/threadTimeouts_worker.js
@@ -0,0 +1,45 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+var gTimeoutId;
+var gTimeoutCount = 0;
+var gIntervalCount = 0;
+
+function timeoutFunc() {
+  if (++gTimeoutCount > 1) {
+    throw new Error("Timeout called more than once!");
+  }
+  postMessage("timeoutFinished");
+}
+
+function intervalFunc() {
+  if (++gIntervalCount == 2) {
+    postMessage("intervalFinished");
+  }
+}
+
+function messageListener(event) {
+  switch (event.data) {
+    case "startTimeout":
+      gTimeoutId = setTimeout(timeoutFunc, 2000);
+      clearTimeout(gTimeoutId);
+      gTimeoutId = setTimeout(timeoutFunc, 2000);
+      break;
+    case "startInterval":
+      gTimeoutId = setInterval(intervalFunc, 2000);
+      break;
+    case "cancelInterval":
+      clearInterval(gTimeoutId);
+      postMessage("intervalCanceled");
+      break;
+    case "startExpression":
+      // eslint-disable-next-line no-implied-eval
+      setTimeout("this.postMessage('expressionFinished');", 2000);
+      break;
+    default:
+      throw "Bad message: " + event.data;
+  }
+}
+
+addEventListener("message", messageListener, false);
diff --git a/dom/workers/test/throwingOnerror_worker.js b/dom/workers/test/throwingOnerror_worker.js
new file mode 100644
index 0000000000..47b727f56a
--- /dev/null
+++ b/dom/workers/test/throwingOnerror_worker.js
@@ -0,0 +1,15 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+onerror = function (event) {
+  throw "bar";
+};
+
+var count = 0;
+onmessage = function (event) {
+  if (!count++) {
+    throw "foo";
+  }
+  postMessage("");
+};
diff --git a/dom/workers/test/timeoutTracing_worker.js b/dom/workers/test/timeoutTracing_worker.js
new file mode 100644
index 0000000000..2eac367535
--- /dev/null
+++ b/dom/workers/test/timeoutTracing_worker.js
@@ -0,0 +1,16 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+onmessage = function (event) {
+  throw "No messages should reach me!";
+};
+
+setInterval(function () {
+  postMessage("Still alive!");
+}, 20);
+// eslint-disable-next-line no-implied-eval
+setInterval(";", 20);
+
+postMessage("Begin!");
diff --git a/dom/workers/test/transferable_worker.js b/dom/workers/test/transferable_worker.js
new file mode 100644
index 0000000000..d0fa41cad1
--- /dev/null
+++ b/dom/workers/test/transferable_worker.js
@@ -0,0 +1,40 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+
+onmessage = function (event) {
+  if ("notEmpty" in event.data && "byteLength" in event.data.notEmpty) {
+    postMessage({
+      event: "W: NotEmpty object received: " + event.data.notEmpty.byteLength,
+      status: event.data.notEmpty.byteLength != 0,
+      last: false,
+    });
+  }
+
+  var ab = new ArrayBuffer(event.data.size);
+  postMessage({
+    event: "W: The size is: " + event.data.size + " == " + ab.byteLength,
+    status: ab.byteLength == event.data.size,
+    last: false,
+  });
+
+  postMessage(
+    {
+      event: "W: postMessage with arrayBuffer",
+      status: true,
+      notEmpty: ab,
+      ab,
+      bc: [ab, ab, { dd: ab }],
+    },
+    [ab]
+  );
+
+  postMessage({
+    event: "W: The size is: 0 == " + ab.byteLength,
+    status: ab.byteLength == 0,
+    last: false,
+  });
+
+  postMessage({ event: "W: last one!", status: true, last: true });
+};
diff --git a/dom/workers/test/window_suspended.html b/dom/workers/test/window_suspended.html
new file mode 100644
index 0000000000..ae5d25df58
--- /dev/null
+++ b/dom/workers/test/window_suspended.html
@@ -0,0 +1,71 @@
+<script>
+const WORKER_URL = "worker_suspended.js";
+var testUrl2 = "window_suspended.html?page2Shown";
+
+let cacheDataPromise = {};
+cacheDataPromise.promise = new Promise(resolve => {
+  cacheDataPromise.resolve = resolve;
+});
+var bcName = location.search.split('?')[1];
+var bc = new BroadcastChannel(bcName);
+if (bcName == "page1Shown") {
+  bc.onmessage = async (msgEvent) => {
+    var msg = msgEvent.data;
+    var command = msg.command;
+    if (command == "startWorker") {
+      // Create a worker and subworkers
+      let { worker, promise } = postMessageWorker(msg.workerMessage);
+      promise.then(function() {
+        bc.postMessage({command: "verifyCacheData"});
+        return cacheDataPromise.promise;
+      })
+      .then(function() {
+        location.href = testUrl2;
+      });
+    } else if (command == "changeLocation") {
+      cacheDataPromise.resolve();
+    } else if (command == "finish") {
+      bc.postMessage({command: "finished"});
+      bc.close();
+      window.close();
+    }
+  }
+} else if (bcName == "page2Shown") {
+  bc.onmessage = (msgEvent) => {
+    var msg = msgEvent.data;
+    var command = msg.command;
+    if (command == "startWorker") {
+      let { worker, promise } = postMessageWorker(msg.workerMessage);
+      promise.then(function() {
+        bc.postMessage({command: "verifyCacheData"});
+        return cacheDataPromise.promise;
+      })
+      .then(function() {
+        bc.close();
+        history.back();
+      });
+    } else if (command == "goBack") {
+      cacheDataPromise.resolve();
+    }
+  }
+}
+
+function postMessageWorker(message) {
+  let worker = new window.Worker(WORKER_URL);
+
+  var promise = new Promise((resolve, reject) => {
+    // Waiting until workers are ready
+    worker.addEventListener("message", function onmessage(msg) {
+      bc.postMessage({command: "workerMessage", workerMessage: msg.data});
+      worker.removeEventListener("message", onmessage);
+      resolve();
+    });
+    worker.postMessage(message);
+  });
+  return { worker, promise };
+}
+
+onpageshow = function(e) {
+  bc.postMessage({command: "onpageshow", persisted: e.persisted, location: location.href});
+}
+</script>
diff --git a/dom/workers/test/worker_bug1278777.js b/dom/workers/test/worker_bug1278777.js
new file mode 100644
index 0000000000..f596ee978b
--- /dev/null
+++ b/dom/workers/test/worker_bug1278777.js
@@ -0,0 +1,9 @@
+var xhr = new XMLHttpRequest();
+xhr.responseType = "blob";
+xhr.open("GET", "worker_bug1278777.js");
+
+xhr.onload = function () {
+  postMessage(xhr.response instanceof Blob);
+};
+
+xhr.send();
diff --git a/dom/workers/test/worker_bug1301094.js b/dom/workers/test/worker_bug1301094.js
new file mode 100644
index 0000000000..90fbe178b5
--- /dev/null
+++ b/dom/workers/test/worker_bug1301094.js
@@ -0,0 +1,11 @@
+onmessage = function (e) {
+  var xhr = new XMLHttpRequest();
+  xhr.open("POST", "worker_bug1301094.js", false);
+  xhr.onload = function () {
+    self.postMessage("OK");
+  };
+
+  var fd = new FormData();
+  fd.append("file", e.data);
+  xhr.send(fd);
+};
diff --git a/dom/workers/test/worker_bug1824498.mjs b/dom/workers/test/worker_bug1824498.mjs
new file mode 100644
index 0000000000..932bb530ac
--- /dev/null
+++ b/dom/workers/test/worker_bug1824498.mjs
@@ -0,0 +1,4 @@
+/* eslint-disable import/no-unassigned-import */
+/* eslint-disable import/no-unresolved */
+import {} from "./foo";
+import {} from "./bar";
diff --git a/dom/workers/test/worker_consoleAndBlobs.js b/dom/workers/test/worker_consoleAndBlobs.js
new file mode 100644
index 0000000000..e95a87fb83
--- /dev/null
+++ b/dom/workers/test/worker_consoleAndBlobs.js
@@ -0,0 +1,8 @@
+/**
+ * Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/
+ */
+"use strict";
+
+var b = new Blob(["123"], { type: "foo/bar" });
+console.log({ msg: "consoleAndBlobs", blob: b });
diff --git a/dom/workers/test/worker_driver.js b/dom/workers/test/worker_driver.js
new file mode 100644
index 0000000000..29a0d50025
--- /dev/null
+++ b/dom/workers/test/worker_driver.js
@@ -0,0 +1,84 @@
+// Any copyright is dedicated to the Public Domain.
+// http://creativecommons.org/publicdomain/zero/1.0/
+//
+// Utility script for writing worker tests.  In your main document do:
+//
+//  <script type="text/javascript" src="worker_driver.js"></script>
+//  <script type="text/javascript">
+//    workerTestExec('myWorkerTestCase.js')
+//  </script>
+//
+// This will then spawn a worker, define some utility functions, and then
+// execute the code in myWorkerTestCase.js.  You can then use these
+// functions in your worker-side test:
+//
+//  ok() - like the SimpleTest assert
+//  is() - like the SimpleTest assert
+//  workerTestDone() - like SimpleTest.finish() indicating the test is complete
+//
+// There are also some functions for requesting information that requires
+// SpecialPowers or other main-thread-only resources:
+//
+//  workerTestGetVersion() - request the current version string from the MT
+//  workerTestGetUserAgent() - request the user agent string from the MT
+//  workerTestGetOSCPU() - request the navigator.oscpu string from the MT
+//
+// For an example see test_worker_interfaces.html and test_worker_interfaces.js.
+
+function workerTestExec(script) {
+  SimpleTest.waitForExplicitFinish();
+  var worker = new Worker("worker_wrapper.js");
+  worker.onmessage = function (event) {
+    if (event.data.type == "finish") {
+      SimpleTest.finish();
+    } else if (event.data.type == "status") {
+      ok(event.data.status, event.data.msg);
+    } else if (event.data.type == "getHelperData") {
+      const { AppConstants } = SpecialPowers.ChromeUtils.importESModule(
+        "resource://gre/modules/AppConstants.sys.mjs"
+      );
+      const isNightly = AppConstants.NIGHTLY_BUILD;
+      const isEarlyBetaOrEarlier = AppConstants.EARLY_BETA_OR_EARLIER;
+      const isRelease = AppConstants.RELEASE_OR_BETA;
+      const isDesktop = !/Mobile|Tablet/.test(navigator.userAgent);
+      const isMac = AppConstants.platform == "macosx";
+      const isWindows = AppConstants.platform == "win";
+      const isAndroid = AppConstants.platform == "android";
+      const isLinux = AppConstants.platform == "linux";
+      const isInsecureContext = !window.isSecureContext;
+      // Currently, MOZ_APP_NAME is always "fennec" for all mobile builds, so we can't use AppConstants for this
+      const isFennec =
+        isAndroid &&
+        SpecialPowers.Cc["@mozilla.org/android/bridge;1"].getService(
+          SpecialPowers.Ci.nsIAndroidBridge
+        ).isFennec;
+      const isCrossOriginIsolated = window.crossOriginIsolated;
+
+      const result = {
+        isNightly,
+        isEarlyBetaOrEarlier,
+        isRelease,
+        isDesktop,
+        isMac,
+        isWindows,
+        isAndroid,
+        isLinux,
+        isInsecureContext,
+        isFennec,
+        isCrossOriginIsolated,
+      };
+
+      worker.postMessage({
+        type: "returnHelperData",
+        result,
+      });
+    }
+  };
+
+  worker.onerror = function (event) {
+    ok(false, "Worker had an error: " + event.data);
+    SimpleTest.finish();
+  };
+
+  worker.postMessage({ script });
+}
diff --git a/dom/workers/test/worker_dynamicImport.mjs b/dom/workers/test/worker_dynamicImport.mjs
new file mode 100644
index 0000000000..b5c50d30f7
--- /dev/null
+++ b/dom/workers/test/worker_dynamicImport.mjs
@@ -0,0 +1,2 @@
+/* eslint-disable import/no-unresolved */
+const { o } = await import("./404.js");
diff --git a/dom/workers/test/worker_referrer.js b/dom/workers/test/worker_referrer.js
new file mode 100644
index 0000000000..ec9fb1f8a0
--- /dev/null
+++ b/dom/workers/test/worker_referrer.js
@@ -0,0 +1,9 @@
+onmessage = function () {
+  importScripts(["referrer.sjs?import"]);
+  var xhr = new XMLHttpRequest();
+  xhr.open("GET", "referrer.sjs?result", true);
+  xhr.onload = function () {
+    postMessage(xhr.responseText);
+  };
+  xhr.send();
+};
diff --git a/dom/workers/test/worker_setTimeoutWith0.js b/dom/workers/test/worker_setTimeoutWith0.js
new file mode 100644
index 0000000000..91de9c5a73
--- /dev/null
+++ b/dom/workers/test/worker_setTimeoutWith0.js
@@ -0,0 +1,4 @@
+/* eslint-disable no-implied-eval */
+var x = 0;
+setTimeout("x++; '\x00'; x++;");
+setTimeout("postMessage(x);");
diff --git a/dom/workers/test/worker_shutdownCheck.js b/dom/workers/test/worker_shutdownCheck.js
new file mode 100644
index 0000000000..f51279daf6
--- /dev/null
+++ b/dom/workers/test/worker_shutdownCheck.js
@@ -0,0 +1 @@
+postMessage("Ok!");
diff --git a/dom/workers/test/worker_suspended.js b/dom/workers/test/worker_suspended.js
new file mode 100644
index 0000000000..f2b4146cba
--- /dev/null
+++ b/dom/workers/test/worker_suspended.js
@@ -0,0 +1,39 @@
+var count = 0;
+
+function do_magic(data) {
+  caches
+    .open("test")
+    .then(function (cache) {
+      return cache.put(
+        "http://mochi.test:888/foo",
+        new Response(data.type + "-" + count++)
+      );
+    })
+    .then(function () {
+      if (count == 1) {
+        postMessage("ready");
+      }
+
+      if (data.loop) {
+        setTimeout(function () {
+          do_magic(data);
+        }, 500);
+      }
+    });
+}
+
+onmessage = function (e) {
+  if (e.data.type == "page1") {
+    if (e.data.count > 0) {
+      var a = new Worker("worker_suspended.js");
+      a.postMessage({ type: "page1", count: e.data - 1 });
+      a.onmessage = function () {
+        postMessage("ready");
+      };
+    } else {
+      do_magic({ type: e.data.type, loop: true });
+    }
+  } else if (e.data.type == "page2") {
+    do_magic({ type: e.data.type, loop: false });
+  }
+};
diff --git a/dom/workers/test/worker_wrapper.js b/dom/workers/test/worker_wrapper.js
new file mode 100644
index 0000000000..6a630d92d0
--- /dev/null
+++ b/dom/workers/test/worker_wrapper.js
@@ -0,0 +1,79 @@
+// Any copyright is dedicated to the Public Domain.
+// http://creativecommons.org/publicdomain/zero/1.0/
+//
+// Worker-side wrapper script for the worker_driver.js helper code.  See
+// the comments at the top of worker_driver.js for more information.
+
+function ok(a, msg) {
+  dump("OK: " + !!a + "  =>  " + a + ": " + msg + "\n");
+  postMessage({ type: "status", status: !!a, msg: a + ": " + msg });
+}
+
+function is(a, b, msg) {
+  dump("IS: " + (a === b) + "  =>  " + a + " | " + b + ": " + msg + "\n");
+  postMessage({
+    type: "status",
+    status: a === b,
+    msg: a + " === " + b + ": " + msg,
+  });
+}
+
+function workerTestArrayEquals(a, b) {
+  if (!Array.isArray(a) || !Array.isArray(b) || a.length != b.length) {
+    return false;
+  }
+  for (var i = 0, n = a.length; i < n; ++i) {
+    if (a[i] !== b[i]) {
+      return false;
+    }
+  }
+  return true;
+}
+
+function workerTestDone() {
+  postMessage({ type: "finish" });
+}
+
+function workerTestGetPermissions(permissions, cb) {
+  addEventListener("message", function workerTestGetPermissionsCB(e) {
+    if (
+      e.data.type != "returnPermissions" ||
+      !workerTestArrayEquals(permissions, e.data.permissions)
+    ) {
+      return;
+    }
+    removeEventListener("message", workerTestGetPermissionsCB);
+    cb(e.data.result);
+  });
+  postMessage({
+    type: "getPermissions",
+    permissions,
+  });
+}
+
+function workerTestGetHelperData(cb) {
+  addEventListener("message", function workerTestGetHelperDataCB(e) {
+    if (e.data.type !== "returnHelperData") {
+      return;
+    }
+    removeEventListener("message", workerTestGetHelperDataCB);
+    cb(e.data.result);
+  });
+  postMessage({
+    type: "getHelperData",
+  });
+}
+
+addEventListener("message", function workerWrapperOnMessage(e) {
+  removeEventListener("message", workerWrapperOnMessage);
+  var data = e.data;
+  try {
+    importScripts(data.script);
+  } catch (ex) {
+    postMessage({
+      type: "status",
+      status: false,
+      msg: "worker failed to import " + data.script + "; error: " + ex.message,
+    });
+  }
+});
diff --git a/dom/workers/test/xpcshell/data/base_uri_module.mjs b/dom/workers/test/xpcshell/data/base_uri_module.mjs
new file mode 100644
index 0000000000..7604baed82
--- /dev/null
+++ b/dom/workers/test/xpcshell/data/base_uri_module.mjs
@@ -0,0 +1,23 @@
+// This file is for testing the module loader's path handling.
+// ESLint rules that modifies path shouldn't be applied.
+
+export const obj = {};
+
+export async function doImport() {
+  // This file is loaded as resource://test/data/base_uri_module.mjs
+  // Relative/absolute paths should be resolved based on the URI, instead of
+  // file: path.
+
+  const namespaceWithURI = await import(
+    "resource://test/data/base_uri_module2.mjs"
+  );
+  const namespaceWithCurrentDir = await import("./base_uri_module2.mjs");
+  const namespaceWithParentDir = await import("../data/base_uri_module2.mjs");
+  const namespaceWithAbsoluteDir = await import("/data/base_uri_module2.mjs");
+
+  return {
+    equal1: namespaceWithURI.obj2 == namespaceWithCurrentDir.obj2,
+    equal2: namespaceWithURI.obj2 == namespaceWithParentDir.obj2,
+    equal3: namespaceWithURI.obj2 == namespaceWithAbsoluteDir.obj2,
+  };
+}
diff --git a/dom/workers/test/xpcshell/data/base_uri_module2.mjs b/dom/workers/test/xpcshell/data/base_uri_module2.mjs
new file mode 100644
index 0000000000..2358d27a83
--- /dev/null
+++ b/dom/workers/test/xpcshell/data/base_uri_module2.mjs
@@ -0,0 +1 @@
+export const obj2 = {};
diff --git a/dom/workers/test/xpcshell/data/base_uri_worker.js b/dom/workers/test/xpcshell/data/base_uri_worker.js
new file mode 100644
index 0000000000..74137cc20b
--- /dev/null
+++ b/dom/workers/test/xpcshell/data/base_uri_worker.js
@@ -0,0 +1,27 @@
+// This file is for testing the module loader's path handling.
+// ESLint rules that modifies path shouldn't be applied.
+
+onmessage = async event => {
+  // This file is loaded as resource://test/data/base_uri_worker.js
+  // Relative/absolute paths should be resolved based on the URI, instead of
+  // file: path.
+
+  const namespaceWithURI = await import(
+    "resource://test/data/base_uri_module.mjs"
+  );
+  const namespaceWithCurrentDir = await import("./base_uri_module.mjs");
+  const namespaceWithParentDir = await import("../data/base_uri_module.mjs");
+  const namespaceWithAbsoluteDir = await import("/data/base_uri_module.mjs");
+
+  postMessage({
+    scriptToModule: {
+      equal1: namespaceWithURI.obj == namespaceWithCurrentDir.obj,
+      equal2: namespaceWithURI.obj == namespaceWithParentDir.obj,
+      equal3: namespaceWithURI.obj == namespaceWithAbsoluteDir.obj,
+    },
+    moduleToModuleURI: await namespaceWithURI.doImport(),
+    moduleToModuleCurrent: await namespaceWithCurrentDir.doImport(),
+    moduleToModuleParent: await namespaceWithParentDir.doImport(),
+    moduleToModuleAbsolute: await namespaceWithAbsoluteDir.doImport(),
+  });
+};
diff --git a/dom/workers/test/xpcshell/data/chrome.manifest b/dom/workers/test/xpcshell/data/chrome.manifest
new file mode 100644
index 0000000000..611e81fd4e
--- /dev/null
+++ b/dom/workers/test/xpcshell/data/chrome.manifest
@@ -0,0 +1 @@
+content workers ./
diff --git a/dom/workers/test/xpcshell/data/worker.js b/dom/workers/test/xpcshell/data/worker.js
new file mode 100644
index 0000000000..0a455f51c3
--- /dev/null
+++ b/dom/workers/test/xpcshell/data/worker.js
@@ -0,0 +1,6 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+self.onmessage = function (msg) {
+  self.postMessage("OK");
+};
diff --git a/dom/workers/test/xpcshell/data/worker_fileReader.js b/dom/workers/test/xpcshell/data/worker_fileReader.js
new file mode 100644
index 0000000000..44e7e6499b
--- /dev/null
+++ b/dom/workers/test/xpcshell/data/worker_fileReader.js
@@ -0,0 +1,7 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+self.onmessage = function (msg) {
+  var fr = new FileReader();
+  self.postMessage("OK");
+};
diff --git a/dom/workers/test/xpcshell/test_ext_redirects_sw_scripts.js b/dom/workers/test/xpcshell/test_ext_redirects_sw_scripts.js
new file mode 100644
index 0000000000..3028e5d539
--- /dev/null
+++ b/dom/workers/test/xpcshell/test_ext_redirects_sw_scripts.js
@@ -0,0 +1,558 @@
+/* -*- Mode: indent-tabs-mode: nil; js-indent-level: 2 -*- */
+/* vim: set sts=2 sw=2 et tw=80: */
+"use strict";
+
+const { TestUtils } = ChromeUtils.importESModule(
+  "resource://testing-common/TestUtils.sys.mjs"
+);
+
+const { AddonTestUtils } = ChromeUtils.importESModule(
+  "resource://testing-common/AddonTestUtils.sys.mjs"
+);
+
+const { ExtensionTestUtils } = ChromeUtils.importESModule(
+  "resource://testing-common/ExtensionXPCShellUtils.sys.mjs"
+);
+
+const { createHttpServer } = AddonTestUtils;
+
+// Force ServiceWorkerRegistrar to init by calling do_get_profile.
+// (This has to be called before AddonTestUtils.init, because it does
+// also call do_get_profile internally but it doesn't notify
+// profile-after-change).
+do_get_profile(true);
+
+AddonTestUtils.init(this);
+ExtensionTestUtils.init(this);
+
+const server = createHttpServer({ hosts: ["localhost"] });
+
+server.registerPathHandler("/page.html", (request, response) => {
+  info(`/page.html is being requested: ${JSON.stringify(request)}`);
+  response.write(`<!DOCTYPE html>`);
+});
+
+server.registerPathHandler("/sw.js", (request, response) => {
+  info(`/sw.js is being requested: ${JSON.stringify(request)}`);
+  response.setHeader("Content-Type", "application/javascript");
+  response.write(`
+    dump('Executing http://localhost/sw.js\\n');
+    importScripts('sw-imported.js');
+    dump('Executed importScripts from http://localhost/sw.js\\n');
+  `);
+});
+
+server.registerPathHandler("/sw-imported.js", (request, response) => {
+  info(`/sw-imported.js is being requested: ${JSON.stringify(request)}`);
+  response.setHeader("Content-Type", "application/javascript");
+  response.write(`
+    dump('importScript loaded from http://localhost/sw-imported.js\\n');
+    self.onmessage = evt => evt.ports[0].postMessage('original-imported-script');
+  `);
+});
+
+Services.prefs.setBoolPref("dom.serviceWorkers.testing.enabled", true);
+// Make sure this test file doesn't run with the legacy behavior by
+// setting explicitly the expected default value.
+Services.prefs.setBoolPref(
+  "extensions.filterResponseServiceWorkerScript.disabled",
+  false
+);
+Services.prefs.setBoolPref("extensions.dnr.enabled", true);
+registerCleanupFunction(() => {
+  Services.prefs.clearUserPref("dom.serviceWorkers.testing.enabled");
+  Services.prefs.clearUserPref(
+    "extensions.filterResponseServiceWorkerScript.disabled"
+  );
+  Services.prefs.clearUserPref("extensions.dnr.enabled");
+});
+
+// Helper function used to be sure to clear any data that a previous test case
+// may have left (e.g. service worker registration, cached service worker
+// scripts).
+//
+// NOTE: Given that xpcshell test are running isolated from each other (unlike
+// mochitests), we can just clear every storage type supported by clear data
+// (instead of cherry picking what we want to clear based on the test cases
+// part of this test file).
+async function ensureDataCleanup() {
+  info("Clear any service worker or data previous test cases may have left");
+  await new Promise(resolve =>
+    Services.clearData.deleteData(Ci.nsIClearDataService.CLEAR_ALL, resolve)
+  );
+}
+
+// Note that the update algorithm (https://w3c.github.io/ServiceWorker/#update-algorithm)
+// builds an "updatedResourceMap" as part of its check process. This means that only a
+// single fetch will be performed for "sw-imported.js" as part of the update check and its
+// resulting install invocation. The installation's call to importScripts when evaluated
+// will load the script directly out of the Cache API.
+function testSWUpdate(contentPage) {
+  return contentPage.spawn([], async () => {
+    const oldReg = await this.content.navigator.serviceWorker.ready;
+    const reg = await oldReg.update();
+    const sw = reg.installing || reg.waiting || reg.active;
+    return new Promise(resolve => {
+      const { MessageChannel } = this.content;
+      const { port1, port2 } = new MessageChannel();
+      port1.onmessage = evt => resolve(evt.data);
+      sw.postMessage("worker-message", [port2]);
+    });
+  });
+}
+
+add_task(async function test_extension_invalid_sw_scripts_redirect_ignored() {
+  const extension = ExtensionTestUtils.loadExtension({
+    manifest: {
+      permissions: ["<all_urls>", "webRequest", "webRequestBlocking"],
+      // In this test task, the extension resource is not expected to be
+      // requested at all, so it does not really matter whether the file is
+      // listed in web_accessible_resources. Regardless, add it to make sure
+      // that any load failure is not caused by the lack of being listed here.
+      web_accessible_resources: ["sw-unexpected-redirect.js"],
+    },
+    background() {
+      browser.webRequest.onBeforeRequest.addListener(
+        req => {
+          if (req.url == "http://localhost/sw.js") {
+            const filter = browser.webRequest.filterResponseData(req.requestId);
+            filter.ondata = event => filter.write(event.data);
+            filter.onstop = event => filter.disconnect();
+            filter.onerror = () => {
+              browser.test.sendMessage(
+                "filter-response-error:mainscript",
+                filter.error
+              );
+            };
+            return {
+              redirectUrl: browser.runtime.getURL("sw-unexpected-redirect.js"),
+            };
+          }
+
+          if (req.url == "http://localhost/sw-imported.js") {
+            const filter = browser.webRequest.filterResponseData(req.requestId);
+            filter.ondata = event => filter.write(event.data);
+            filter.onstop = event => filter.disconnect();
+            filter.onerror = () => {
+              browser.test.sendMessage(
+                "filter-response-error:importscript",
+                filter.error
+              );
+            };
+            return { redirectUrl: "about:blank" };
+          }
+
+          return {};
+        },
+        { urls: ["http://localhost/sw.js", "http://localhost/sw-imported.js"] },
+        ["blocking"]
+      );
+    },
+    files: {
+      "sw-unexpected-redirect.js": `
+        dump('main worker redirected to moz-extension://UUID/sw-unexpected-redirect.js\\n');
+        self.onmessage = evt => evt.ports[0].postMessage('sw-unexpected-redirect');
+      `,
+    },
+  });
+
+  // Start the test extension to redirect importScripts requests.
+  await extension.startup();
+
+  function awaitConsoleMessage(regexp) {
+    return new Promise(resolve => {
+      Services.console.registerListener(function listener(message) {
+        if (regexp.test(message.message)) {
+          Services.console.unregisterListener(listener);
+          resolve(message);
+        }
+      });
+    });
+  }
+
+  const awaitIgnoredMainScriptRedirect = awaitConsoleMessage(
+    /Invalid redirectUrl .* on service worker main script/
+  );
+  const awaitIgnoredImportScriptRedirect = awaitConsoleMessage(
+    /Invalid redirectUrl .* on service worker imported script/
+  );
+
+  let contentPage = await ExtensionTestUtils.loadContentPage(
+    "http://localhost/page.html"
+  );
+
+  // Register the worker after loading the test extension, which should not be
+  // able to intercept and redirect the importedScripts requests because of
+  // invalid destinations.
+  info("Register service worker from a content webpage");
+  let workerMessage = await contentPage.spawn([], async () => {
+    const reg = await this.content.navigator.serviceWorker.register("/sw.js");
+    return new Promise(resolve => {
+      const { MessageChannel } = this.content;
+      const { port1, port2 } = new MessageChannel();
+      port1.onmessage = evt => resolve(evt.data);
+      const sw = reg.active || reg.waiting || reg.installing;
+      sw.postMessage("worker-message", [port2]);
+    });
+  });
+
+  equal(
+    workerMessage,
+    "original-imported-script",
+    "Got expected worker reply (importScripts not intercepted)"
+  );
+
+  info("Wait for the expected error message on main script redirect");
+  const errorMsg = await awaitIgnoredMainScriptRedirect;
+  ok(errorMsg?.message, `Got error message: ${errorMsg?.message}`);
+  ok(
+    errorMsg?.message?.includes(extension.id),
+    "error message should include the addon id"
+  );
+  ok(
+    errorMsg?.message?.includes("http://localhost/sw.js"),
+    "error message should include the sw main script url"
+  );
+
+  info("Wait for the expected error message on import script redirect");
+  const errorMsg2 = await awaitIgnoredImportScriptRedirect;
+  ok(errorMsg2?.message, `Got error message: ${errorMsg2?.message}`);
+  ok(
+    errorMsg2?.message?.includes(extension.id),
+    "error message should include the addon id"
+  );
+  ok(
+    errorMsg2?.message?.includes("http://localhost/sw-imported.js"),
+    "error message should include the sw main script url"
+  );
+
+  info("Wait filterResponse error on main script");
+  equal(
+    await extension.awaitMessage("filter-response-error:mainscript"),
+    "Invalid request ID",
+    "Got expected error on main script"
+  );
+  info("Wait filterResponse error on import script");
+  equal(
+    await extension.awaitMessage("filter-response-error:importscript"),
+    "Invalid request ID",
+    "Got expected error on import script"
+  );
+
+  await extension.unload();
+  await contentPage.close();
+});
+
+add_task(async function test_filter_sw_script() {
+  const extension = ExtensionTestUtils.loadExtension({
+    manifest: {
+      permissions: [
+        "<all_urls>",
+        "webRequest",
+        "webRequestBlocking",
+        "webRequestFilterResponse.serviceWorkerScript",
+      ],
+    },
+    background() {
+      browser.webRequest.onBeforeRequest.addListener(
+        req => {
+          if (req.url == "http://localhost/sw.js") {
+            const filter = browser.webRequest.filterResponseData(req.requestId);
+            let decoder = new TextDecoder("utf-8");
+            let encoder = new TextEncoder();
+            filter.ondata = event => {
+              let str = decoder.decode(event.data, { stream: true });
+              browser.test.log(`Got filter ondata event: ${str}\n`);
+              str = `
+                dump('Executing filterResponse script for http://localhost/sw.js\\n');
+                self.onmessage = evt => evt.ports[0].postMessage('filter-response-script');
+                dump('Executed firlterResponse script for http://localhost/sw.js\\n');
+              `;
+              filter.write(encoder.encode(str));
+              filter.disconnect();
+            };
+          }
+
+          return {};
+        },
+        { urls: ["http://localhost/sw.js", "http://localhost/sw-imported.js"] },
+        ["blocking"]
+      );
+    },
+  });
+
+  // Start the test extension to redirect importScripts requests.
+  await extension.startup();
+
+  await ensureDataCleanup();
+  let contentPage = await ExtensionTestUtils.loadContentPage(
+    "http://localhost/page.html"
+  );
+
+  let workerMessage = await contentPage.spawn([], async () => {
+    const reg = await this.content.navigator.serviceWorker.register("/sw.js");
+    return new Promise(resolve => {
+      const { MessageChannel } = this.content;
+      const { port1, port2 } = new MessageChannel();
+      port1.onmessage = evt => resolve(evt.data);
+      const sw = reg.active || reg.waiting || reg.installing;
+      sw.postMessage("worker-message", [port2]);
+    });
+  });
+
+  equal(
+    workerMessage,
+    "filter-response-script",
+    "Got expected worker reply (filterResponse script)"
+  );
+
+  await extension.unload();
+  workerMessage = await testSWUpdate(contentPage);
+  equal(
+    workerMessage,
+    "original-imported-script",
+    "Got expected worker reply (original script)"
+  );
+
+  await contentPage.close();
+});
+
+add_task(async function test_extension_redirect_sw_imported_script() {
+  const extension = ExtensionTestUtils.loadExtension({
+    manifest: {
+      permissions: ["<all_urls>", "webRequest", "webRequestBlocking"],
+      web_accessible_resources: ["sw-imported-1.js", "sw-imported-2.js"],
+    },
+    background() {
+      let i = 1;
+      browser.webRequest.onBeforeRequest.addListener(
+        req => {
+          browser.test.log(
+            "Extension is redirecting http://localhost/sw-imported.js"
+          );
+          browser.test.sendMessage("request-redirected");
+          return {
+            redirectUrl: browser.runtime.getURL(`sw-imported-${i++}.js`),
+          };
+        },
+        { urls: ["http://localhost/sw-imported.js"] },
+        ["blocking"]
+      );
+    },
+    files: {
+      "sw-imported-1.js": `
+        dump('importScript redirected to moz-extension://UUID/sw-imported1.js \\n');
+        self.onmessage = evt => evt.ports[0].postMessage('redirected-imported-script-1');
+      `,
+      "sw-imported-2.js": `
+        dump('importScript redirected to moz-extension://UUID/sw-imported2.js \\n');
+        self.onmessage = evt => evt.ports[0].postMessage('redirected-imported-script-2');
+      `,
+    },
+  });
+
+  await ensureDataCleanup();
+  const contentPage = await ExtensionTestUtils.loadContentPage(
+    "http://localhost/page.html"
+  );
+
+  // Register the worker while the test extension isn't loaded and cannot
+  // intercept and redirect the importedScripts requests.
+  let workerMessage = await contentPage.spawn([], async () => {
+    const reg = await this.content.navigator.serviceWorker.register("/sw.js");
+    return new Promise(resolve => {
+      const { MessageChannel } = this.content;
+      const { port1, port2 } = new MessageChannel();
+      port1.onmessage = evt => resolve(evt.data);
+      const sw = reg.active || reg.waiting || reg.installing;
+      sw.postMessage("worker-message", [port2]);
+    });
+  });
+
+  equal(
+    workerMessage,
+    "original-imported-script",
+    "Got expected worker reply (importScripts not intercepted)"
+  );
+
+  // Start the test extension to redirect importScripts requests.
+  await extension.startup();
+
+  // Trigger an update on the registered service worker, then assert that the
+  // reply got is coming from the script where the extension is redirecting the
+  // request.
+  info("Update service worker and expect extension script to reply");
+  workerMessage = await testSWUpdate(contentPage);
+  await extension.awaitMessage("request-redirected");
+  equal(
+    workerMessage,
+    "redirected-imported-script-1",
+    "Got expected worker reply (importScripts redirected to moz-extension url)"
+  );
+
+  // Trigger a new update of the registered service worker, then assert that the
+  // reply got is coming from a different script where the extension is
+  // redirecting the second request (this confirms that the extension can
+  // intercept and can change the redirected imported scripts on new service
+  // worker updates).
+  info("Update service worker and expect new extension script to reply");
+  workerMessage = await testSWUpdate(contentPage);
+  await extension.awaitMessage("request-redirected");
+  equal(
+    workerMessage,
+    "redirected-imported-script-2",
+    "Got expected worker reply (importScripts redirected to moz-extension url again)"
+  );
+
+  // Uninstall the extension and trigger one more update of the registered
+  // service worker, then assert that the reply got is the one coming from the
+  // server (because difference from the one got from the cache).
+  // This verify that the service worker are updated as expected after the
+  // extension is uninstalled and the worker is not stuck on the script where
+  // the extension did redirect the request the last time.
+  info(
+    "Unload extension, update service worker and expect original script to reply"
+  );
+  await extension.unload();
+  workerMessage = await testSWUpdate(contentPage);
+  equal(
+    workerMessage,
+    "original-imported-script",
+    "Got expected worker reply (importScripts not intercepted)"
+  );
+
+  await contentPage.close();
+});
+
+// Test cases for redirects with declarativeNetRequest instead of webRequest,
+// testing the same scenarios as:
+// - test_extension_invalid_sw_scripts_redirect_ignored
+//   i.e. fail to redirect SW main script, fail to redirect SW to about:blank.
+// - test_extension_redirect_sw_imported_script
+//   i.e. allowed to redirect importScripts to moz-extension.
+add_task(async function test_dnr_redirect_sw_script_or_import() {
+  const extension = ExtensionTestUtils.loadExtension({
+    manifest: {
+      manifest_version: 3,
+      permissions: ["declarativeNetRequest"],
+      host_permissions: ["<all_urls>"],
+      granted_host_permissions: true,
+      web_accessible_resources: [
+        {
+          resources: ["sw-bad-redirect.js", "sw-dnr-redirect.js", "sw-nest.js"],
+          matches: ["*://*/*"],
+        },
+      ],
+    },
+    temporarilyInstalled: true, // <-- for granted_host_permissions
+    background: async () => {
+      await browser.declarativeNetRequest.updateSessionRules({
+        addRules: [
+          {
+            id: 1,
+            condition: { urlFilter: "|http://localhost/sw.js?dnr_redir_bad" },
+            action: {
+              type: "redirect",
+              redirect: { extensionPath: "/sw-bad-redirect.js" },
+            },
+          },
+          {
+            id: 2,
+            condition: { urlFilter: "|http://localhost/sw-imported.js|" },
+            action: {
+              type: "redirect",
+              redirect: { extensionPath: "/sw-dnr-redirect.js" },
+            },
+          },
+          {
+            id: 3,
+            condition: { urlFilter: "|http://localhost/sw-nest.js|" },
+            action: {
+              type: "redirect",
+              redirect: { extensionPath: "/sw-nest.js" },
+            },
+          },
+          {
+            id: 4,
+            condition: { urlFilter: "|http://localhost/sw-imported.js?about|" },
+            action: {
+              type: "redirect",
+              redirect: { url: "about:blank" },
+            },
+          },
+        ],
+      });
+      browser.test.sendMessage("dnr_registered");
+    },
+    files: {
+      "sw-bad-redirect.js": String.raw`
+        dump('main worker redirected to moz-extension://UUID/sw-bad-redirect.js\n');
+        self.onmessage = evt => evt.ports[0].postMessage('sw-bad-redirect');
+      `,
+      "sw-dnr-redirect.js": String.raw`
+        dump('importScript redirected to moz-extension://UUID/sw-dnr-redirect.js\n');
+        self.onmessage = evt => evt.ports[0].postMessage('sw-dnr-before-nest');
+
+        importScripts("/sw-nest.js");
+        // ^ sw-nest.js does not exist on the server, so if importScripts()
+        // succeeded, then that means that the DNR-triggered redirect worked.
+
+        self.onmessage = evt => evt.ports[0].postMessage('sw-before-about');
+        try {
+          importScripts("/sw-imported.js?about");
+          // ^ DNR redirects to about:blank, which should throw here.
+          self.onmessage = evt => evt.ports[0].postMessage('sw-dnr-about-bad');
+        } catch (e) {
+          // All is good.
+          self.onmessage = evt => evt.ports[0].postMessage('sw-dnr-redirect');
+        }
+      `,
+      "sw-nest.js": String.raw`
+        dump('importScript redirected to moz-extension://UUID/sw-nest.js\n');
+        // No other code here. The caller verifies success by confirming that
+        // the importScripts() call did not throw.
+      `,
+    },
+  });
+
+  // Start the test extension to redirect importScripts requests.
+  await extension.startup();
+  await extension.awaitMessage("dnr_registered");
+
+  await ensureDataCleanup();
+  let contentPage = await ExtensionTestUtils.loadContentPage(
+    "http://localhost/page.html"
+  );
+
+  // Register the worker after loading the test extension, which should not be
+  // able to intercept and redirect the importedScripts requests because of
+  // invalid destinations.
+  info("Register service worker from a content webpage (disallowed redirects)");
+  await contentPage.spawn([], async () => {
+    await Assert.rejects(
+      this.content.navigator.serviceWorker.register("/sw.js?dnr_redir_bad1"),
+      /SecurityError: The operation is insecure/,
+      "Redirect of main service worker script is not allowed"
+    );
+  });
+  info("Register service worker from a content webpage (with import redirect)");
+  let workerMessage = await contentPage.spawn([], async () => {
+    const reg = await this.content.navigator.serviceWorker.register("/sw.js");
+    return new Promise(resolve => {
+      const { MessageChannel } = this.content;
+      const { port1, port2 } = new MessageChannel();
+      port1.onmessage = evt => resolve(evt.data);
+      const sw = reg.active || reg.waiting || reg.installing;
+      sw.postMessage("worker-message", [port2]);
+    });
+  });
+
+  equal(
+    workerMessage,
+    "sw-dnr-redirect",
+    "Got expected worker reply (importScripts redirected to moz-extension:-URL)"
+  );
+
+  await extension.unload();
+  await contentPage.close();
+});
diff --git a/dom/workers/test/xpcshell/test_ext_worker_offline_fetch.js b/dom/workers/test/xpcshell/test_ext_worker_offline_fetch.js
new file mode 100644
index 0000000000..718093422b
--- /dev/null
+++ b/dom/workers/test/xpcshell/test_ext_worker_offline_fetch.js
@@ -0,0 +1,112 @@
+/* -*- Mode: indent-tabs-mode: nil; js-indent-level: 2 -*- */
+/* vim: set sts=2 sw=2 et tw=80: */
+"use strict";
+
+const { TestUtils } = ChromeUtils.importESModule(
+  "resource://testing-common/TestUtils.sys.mjs"
+);
+
+const { AddonTestUtils } = ChromeUtils.importESModule(
+  "resource://testing-common/AddonTestUtils.sys.mjs"
+);
+
+const { ExtensionTestUtils } = ChromeUtils.importESModule(
+  "resource://testing-common/ExtensionXPCShellUtils.sys.mjs"
+);
+
+const { createHttpServer } = AddonTestUtils;
+
+// Force ServiceWorkerRegistrar to init by calling do_get_profile.
+// (This has to be called before AddonTestUtils.init, because it does
+// also call do_get_profile internally but it doesn't notify
+// profile-after-change).
+do_get_profile(true);
+
+AddonTestUtils.init(this);
+ExtensionTestUtils.init(this);
+
+const server = createHttpServer({ hosts: ["example.com"] });
+server.registerPathHandler("/dummy", (request, response) => {
+  response.setStatusLine(request.httpVersion, 200, "OK");
+  response.setHeader("Content-Type", "text/html", false);
+  response.write("dummy page");
+});
+
+add_setup(() => {
+  info("Making sure Services.io.offline is true");
+  // Explicitly setting Services.io.offline to true makes this test able
+  // to hit on Desktop builds the same issue that test_ext_cache_api.js
+  // was hitting on Android builds (Bug 1844825).
+  Services.io.offline = true;
+});
+
+// Regression test derived from Bug 1844825.
+add_task(async function test_fetch_request_from_ext_shared_worker() {
+  if (!WebExtensionPolicy.useRemoteWebExtensions) {
+    // Ensure RemoteWorkerService has been initialized in the main
+    // process.
+    Services.obs.notifyObservers(null, "profile-after-change");
+  }
+
+  const background = async function () {
+    const testUrl = `http://example.com/dummy`;
+    const worker = new SharedWorker("worker.js");
+    const { data: result } = await new Promise(resolve => {
+      worker.port.onmessage = resolve;
+      worker.port.postMessage(["worker-fetch-test", testUrl]);
+    });
+
+    browser.test.sendMessage("test-sharedworker-fetch:done", result);
+  };
+
+  const extension = ExtensionTestUtils.loadExtension({
+    background,
+    manifest: { permissions: ["http://example.com/*"] },
+    files: {
+      "worker.js": function () {
+        self.onconnect = evt => {
+          const port = evt.ports[0];
+          port.onmessage = async evt => {
+            let result = {};
+            let message;
+            try {
+              const [msg, url] = evt.data;
+              message = msg;
+              const response = await fetch(url);
+              dump(`fetch call resolved: ${response}\n`);
+              result.fetchResolvesTo = `${response}`;
+            } catch (err) {
+              dump(`fetch call rejected: ${err}\n`);
+              result.error = err.name;
+              throw err;
+            } finally {
+              port.postMessage([`${message}:result`, result]);
+            }
+          };
+        };
+      },
+    },
+  });
+
+  await extension.startup();
+  const result = await extension.awaitMessage("test-sharedworker-fetch:done");
+  if (Services.io.offline && WebExtensionPolicy.useRemoteWebExtensions) {
+    // If the network is offline and the extensions are running in the
+    // child extension process, expect the fetch call to be rejected
+    // with an TypeError.
+    Assert.deepEqual(
+      ["worker-fetch-test:result", { error: "TypeError" }],
+      result,
+      "fetch should have been rejected with an TypeError"
+    );
+  } else {
+    // If the network is not offline or the extension are running in the
+    // parent process, we expect the fetch call to resolve to a Response.
+    Assert.deepEqual(
+      ["worker-fetch-test:result", { fetchResolvesTo: "[object Response]" }],
+      result,
+      "fetch should have been resolved to a Response instance"
+    );
+  }
+  await extension.unload();
+});
diff --git a/dom/workers/test/xpcshell/test_fileReader.js b/dom/workers/test/xpcshell/test_fileReader.js
new file mode 100644
index 0000000000..02bc3fa667
--- /dev/null
+++ b/dom/workers/test/xpcshell/test_fileReader.js
@@ -0,0 +1,33 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+// Worker must be loaded from a chrome:// uri, not a file://
+// uri, so we first need to load it.
+var WORKER_SOURCE_URI = "chrome://workers/content/worker_fileReader.js";
+do_load_manifest("data/chrome.manifest");
+
+function talk_with_worker(worker) {
+  return new Promise((resolve, reject) => {
+    worker.onmessage = function (event) {
+      let success = true;
+      if (event.data == "OK") {
+        resolve();
+      } else {
+        success = false;
+        reject(event);
+      }
+      Assert.ok(success);
+      worker.terminate();
+    };
+    worker.onerror = function (event) {
+      let error = new Error(event.message, event.filename, event.lineno);
+      worker.terminate();
+      reject(error);
+    };
+    worker.postMessage("START");
+  });
+}
+
+add_task(function test_chrome_worker() {
+  return talk_with_worker(new ChromeWorker(WORKER_SOURCE_URI));
+});
diff --git a/dom/workers/test/xpcshell/test_import_base_uri.js b/dom/workers/test/xpcshell/test_import_base_uri.js
new file mode 100644
index 0000000000..7c88a946f4
--- /dev/null
+++ b/dom/workers/test/xpcshell/test_import_base_uri.js
@@ -0,0 +1,35 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+add_task(async function testSyncImportBeforeAsyncImportDependencyInWorker() {
+  const worker = new ChromeWorker("resource://test/data/base_uri_worker.js");
+
+  const { promise, resolve } = Promise.withResolvers();
+  worker.onmessage = event => {
+    resolve(event.data);
+  };
+  worker.postMessage("");
+
+  const result = await promise;
+
+  Assert.ok(result.scriptToModule.equal1);
+  Assert.ok(result.scriptToModule.equal2);
+  Assert.ok(result.scriptToModule.equal3);
+
+  Assert.ok(result.moduleToModuleURI.equal1);
+  Assert.ok(result.moduleToModuleURI.equal2);
+  Assert.ok(result.moduleToModuleURI.equal3);
+
+  Assert.ok(result.moduleToModuleCurrent.equal1);
+  Assert.ok(result.moduleToModuleCurrent.equal2);
+  Assert.ok(result.moduleToModuleCurrent.equal3);
+
+  Assert.ok(result.moduleToModuleParent.equal1);
+  Assert.ok(result.moduleToModuleParent.equal2);
+  Assert.ok(result.moduleToModuleParent.equal3);
+
+  Assert.ok(result.moduleToModuleAbsolute.equal1);
+  Assert.ok(result.moduleToModuleAbsolute.equal2);
+  Assert.ok(result.moduleToModuleAbsolute.equal3);
+});
diff --git a/dom/workers/test/xpcshell/test_remoteworker_launch_new_process.js b/dom/workers/test/xpcshell/test_remoteworker_launch_new_process.js
new file mode 100644
index 0000000000..b95ad4bcaf
--- /dev/null
+++ b/dom/workers/test/xpcshell/test_remoteworker_launch_new_process.js
@@ -0,0 +1,88 @@
+/* -*- Mode: indent-tabs-mode: nil; js-indent-level: 2 -*- */
+/* vim: set sts=2 sw=2 et tw=80: */
+"use strict";
+
+const { TestUtils } = ChromeUtils.importESModule(
+  "resource://testing-common/TestUtils.sys.mjs"
+);
+
+const { AddonTestUtils } = ChromeUtils.importESModule(
+  "resource://testing-common/AddonTestUtils.sys.mjs"
+);
+const { createHttpServer } = AddonTestUtils;
+
+// Force ServiceWorkerRegistrar to init by calling do_get_profile.
+// (This has to be called before AddonTestUtils.init, because it does
+// also call do_get_profile internally but it doesn't notify
+// profile-after-change).
+do_get_profile(true);
+
+AddonTestUtils.init(this);
+
+const server = createHttpServer({ hosts: ["localhost"] });
+
+server.registerPathHandler("/sw.js", (request, response) => {
+  info(`/sw.js is being requested: ${JSON.stringify(request)}`);
+  response.setHeader("Content-Type", "application/javascript");
+  response.write("");
+});
+
+add_task(async function setup_prefs() {
+  // Enable nsIServiceWorkerManager.registerForTest.
+  Services.prefs.setBoolPref("dom.serviceWorkers.testing.enabled", true);
+
+  registerCleanupFunction(() => {
+    Services.prefs.clearUserPref("dom.serviceWorkers.testing.enabled");
+  });
+});
+
+/**
+ * This test installs a ServiceWorker via test API and verify that the install
+ * process spawns a new process. (Normally ServiceWorker installation won't
+ * cause a new content process to be spawned because the call to register must
+ * be coming from within an existing content process, but the registerForTest
+ * API allows us to bypass this restriction.)
+ *
+ * This models the real-world situation of a push notification being received
+ * from the network which results in a ServiceWorker being spawned without their
+ * necessarily being an existing content process to host it (especially under Fission).
+ */
+add_task(async function launch_remoteworkers_in_new_processes() {
+  const swm = Cc["@mozilla.org/serviceworkers/manager;1"].getService(
+    Ci.nsIServiceWorkerManager
+  );
+
+  const ssm = Services.scriptSecurityManager;
+
+  const initialChildCount = Services.ppmm.childCount;
+
+  // A test service worker that should spawn a regular web content child process.
+  const swRegInfoWeb = await swm.registerForTest(
+    ssm.createContentPrincipal(Services.io.newURI("http://localhost"), {}),
+    "http://localhost/scope",
+    "http://localhost/sw.js"
+  );
+  swRegInfoWeb.QueryInterface(Ci.nsIServiceWorkerRegistrationInfo);
+
+  info(
+    `web content service worker registered: ${JSON.stringify({
+      principal: swRegInfoWeb.principal.spec,
+      scope: swRegInfoWeb.scope,
+    })}`
+  );
+
+  info("Wait new process to be launched");
+  await TestUtils.waitForCondition(() => {
+    return Services.ppmm.childCount - initialChildCount >= 1;
+  }, "wait for a new child processes to be started");
+
+  // Wait both workers to become active to be sure that. besides spawning
+  // the new child processes as expected, the two remote worker have been
+  // able to run successfully (in other word their remote worker data did
+  // pass successfull the IsRemoteTypeAllowed check in RemoteworkerChild).
+  info("Wait for webcontent worker to become active");
+  await TestUtils.waitForCondition(
+    () => swRegInfoWeb.activeWorker,
+    `wait workers for scope ${swRegInfoWeb.scope} to be active`
+  );
+});
diff --git a/dom/workers/test/xpcshell/test_workers.js b/dom/workers/test/xpcshell/test_workers.js
new file mode 100644
index 0000000000..5b768f69bb
--- /dev/null
+++ b/dom/workers/test/xpcshell/test_workers.js
@@ -0,0 +1,37 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+// Worker must be loaded from a chrome:// uri, not a file://
+// uri, so we first need to load it.
+var WORKER_SOURCE_URI = "chrome://workers/content/worker.js";
+do_load_manifest("data/chrome.manifest");
+
+function talk_with_worker(worker) {
+  return new Promise((resolve, reject) => {
+    worker.onmessage = function (event) {
+      let success = true;
+      if (event.data == "OK") {
+        resolve();
+      } else {
+        success = false;
+        reject(event);
+      }
+      Assert.ok(success);
+      worker.terminate();
+    };
+    worker.onerror = function (event) {
+      let error = new Error(event.message, event.filename, event.lineno);
+      worker.terminate();
+      reject(error);
+    };
+    worker.postMessage("START");
+  });
+}
+
+add_task(function test_chrome_worker() {
+  return talk_with_worker(new ChromeWorker(WORKER_SOURCE_URI));
+});
+
+add_task(function test_worker() {
+  return talk_with_worker(new Worker(WORKER_SOURCE_URI));
+});
diff --git a/dom/workers/test/xpcshell/test_workers_clone_error.js b/dom/workers/test/xpcshell/test_workers_clone_error.js
new file mode 100644
index 0000000000..f3fd430457
--- /dev/null
+++ b/dom/workers/test/xpcshell/test_workers_clone_error.js
@@ -0,0 +1,43 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+// Worker must be loaded from a chrome:// uri, not a file://
+// uri, so we first need to load it.
+var WORKER_SOURCE_URI = "chrome://workers/content/worker.js";
+do_load_manifest("data/chrome.manifest");
+
+function talk_with_worker(worker) {
+  return new Promise((resolve, reject) => {
+    worker.onmessage = function (event) {
+      let success = true;
+      if (event.data == "OK") {
+        resolve();
+      } else {
+        success = false;
+        reject(event);
+      }
+      Assert.ok(success);
+      worker.terminate();
+    };
+    worker.onerror = function (event) {
+      let error = new Error(event.message, event.filename, event.lineno);
+      worker.terminate();
+      reject(error);
+    };
+
+    try {
+      // eslint-disable-next-line no-eval
+      eval("/");
+    } catch (e) {
+      worker.postMessage(new ClonedErrorHolder(e));
+    }
+  });
+}
+
+add_task(function test_chrome_worker() {
+  return talk_with_worker(new ChromeWorker(WORKER_SOURCE_URI));
+});
+
+add_task(function test_worker() {
+  return talk_with_worker(new Worker(WORKER_SOURCE_URI));
+});
diff --git a/dom/workers/test/xpcshell/xpcshell.toml b/dom/workers/test/xpcshell/xpcshell.toml
new file mode 100644
index 0000000000..61b1eef0c2
--- /dev/null
+++ b/dom/workers/test/xpcshell/xpcshell.toml
@@ -0,0 +1,38 @@
+[DEFAULT]
+skip-if = ["os == 'android'"]
+support-files = [
+  "data/worker.js",
+  "data/worker_fileReader.js",
+  "data/chrome.manifest",
+  "data/base_uri_worker.js",
+  "data/base_uri_module.mjs",
+  "data/base_uri_module2.mjs",
+]
+
+["test_ext_redirects_sw_scripts.js"]
+# The following firefox-appdir make sure that ExtensionTestUtils.loadExtension
+# will be able to successfully start the background page (it does fail without
+# it because there wouldn't be a global.tabTracker implementation as we would
+# expect in a real Firefox, Fenix or Thunderbird instance).
+firefox-appdir = "browser"
+
+["test_ext_worker_offline_fetch.js"]
+firefox-appdir = "browser"
+
+["test_fileReader.js"]
+
+["test_import_base_uri.js"]
+
+["test_remoteworker_launch_new_process.js"]
+# The following firefox-appdir make sure that this xpcshell test will run
+# with e10s enabled (which is needed to make sure that the test case is
+# going to launch the expected new processes)
+firefox-appdir = "browser"
+# Disable plugin loading to make it rr able to record and replay this test.
+prefs = ["plugin.disable=true"]
+skip-if = ["socketprocess_networking"] # Bug 1759035
+
+
+["test_workers.js"]
+
+["test_workers_clone_error.js"]