Merging upstream version 126.0.

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

32 files changed, 891 insertions, 260 deletions

diff --git a/dom/workers/RuntimeService.cpp b/dom/workers/RuntimeService.cpp
index 02efb12053..321895e700 100644
--- a/dom/workers/RuntimeService.cpp
+++ b/dom/workers/RuntimeService.cpp
@@ -372,6 +372,9 @@ void LoadJSGCMemoryOptions(const char* aPrefName, void* /* aClosure */) {
       PREF("gc_parallel_marking", JSGC_PARALLEL_MARKING_ENABLED),
       PREF("gc_parallel_marking_threshold_mb",
            JSGC_PARALLEL_MARKING_THRESHOLD_MB),
+#ifdef NIGHTLY_BUILD
+      PREF("gc_experimental_semispace_nursery", JSGC_SEMISPACE_NURSERY_ENABLED),
+#endif
       // Note: Workers do not currently trigger eager minor GC, but if that is
       // desired the following parameters should be added:
       // javascript.options.mem.nursery_eager_collection_threshold_kb
@@ -426,6 +429,9 @@ void LoadJSGCMemoryOptions(const char* aPrefName, void* /* aClosure */) {
       }
       case JSGC_COMPACTING_ENABLED:
       case JSGC_PARALLEL_MARKING_ENABLED:
+#ifdef NIGHTLY_BUILD
+      case JSGC_SEMISPACE_NURSERY_ENABLED:
+#endif
       case JSGC_BALANCED_HEAP_LIMITS_ENABLED: {
         bool present;
         bool prefValue = GetPref(pref->fullName, false, &present);
diff --git a/dom/workers/ScriptLoader.cpp b/dom/workers/ScriptLoader.cpp
index 73997b2725..9dcb1d0c9a 100644
--- a/dom/workers/ScriptLoader.cpp
+++ b/dom/workers/ScriptLoader.cpp
@@ -517,9 +517,7 @@ already_AddRefed<WorkerScriptLoader> WorkerScriptLoader::Create(
   }
 
   // Set up the module loader, if it has not been initialzied yet.
-  if (!aWorkerPrivate->IsServiceWorker()) {
-    self->InitModuleLoader();
-  }
+  self->InitModuleLoader();
 
   return self.forget();
 }
@@ -1065,8 +1063,8 @@ nsresult WorkerScriptLoader::LoadScript(
     // 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());
+    loadInfo->SetIsInThirdPartyContext(
+        mWorkerRef->Private()->IsThirdPartyContext());
 
     Maybe<ClientInfo> clientInfo;
     clientInfo.emplace(loadContext->mClientInfo.ref());
@@ -1856,12 +1854,6 @@ void ReportLoadError(ErrorResult& aRv, nsresult aLoadResult,
                       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);
@@ -1877,7 +1869,7 @@ void ReportLoadError(ErrorResult& aRv, nsresult aLoadResult,
       // make it impossible for consumers to realize that our error was
       // NS_BINDING_ABORTED.
       aRv.Throw(aLoadResult);
-      return;
+      break;
 
     case NS_ERROR_DOM_BAD_URI:
       // This is actually a security error.
@@ -1885,15 +1877,16 @@ void ReportLoadError(ErrorResult& aRv, nsresult aLoadResult,
       aRv.ThrowSecurityError(err);
       break;
 
+    case NS_ERROR_FILE_NOT_FOUND:
+    case NS_ERROR_NOT_AVAILABLE:
+    case NS_ERROR_CORRUPTED_CONTENT:
+    case NS_ERROR_DOM_NETWORK_ERR:
+    // 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.
     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;
+      aRv.Throw(NS_ERROR_DOM_NETWORK_ERR);
+      break;
   }
 }
 
diff --git a/dom/workers/Worker.cpp b/dom/workers/Worker.cpp
index 2348572e65..88df53b877 100644
--- a/dom/workers/Worker.cpp
+++ b/dom/workers/Worker.cpp
@@ -83,6 +83,12 @@ JSObject* Worker::WrapObject(JSContext* aCx,
   return wrapper;
 }
 
+bool Worker::IsEligibleForMessaging() {
+  NS_ASSERT_OWNINGTHREAD(Worker);
+
+  return mWorkerPrivate && mWorkerPrivate->ParentStatusProtected() <= Running;
+}
+
 void Worker::PostMessage(JSContext* aCx, JS::Handle<JS::Value> aMessage,
                          const Sequence<JSObject*>& aTransferable,
                          ErrorResult& aRv) {
diff --git a/dom/workers/Worker.h b/dom/workers/Worker.h
index 14d0630f28..6a0e295fc2 100644
--- a/dom/workers/Worker.h
+++ b/dom/workers/Worker.h
@@ -42,6 +42,31 @@ class Worker : public DOMEventTargetHelper, public SupportsWeakPtr {
     return Some(EventCallbackDebuggerNotificationType::Worker);
   }
 
+  // True if the worker is not yet closing from the perspective of this, the
+  // owning thread, and therefore it's okay to post a message to the worker.
+  // This is not a guarantee that the worker will process the message.
+  //
+  // This method will return false if `globalThis.close()` is invoked on the
+  // worker before that method returns control to the caller and without waiting
+  // for any task to be queued on this thread and run; this biases us to avoid
+  // doing wasteful work but does mean if you are exposing something to content
+  // that is specified to only transition as the result of a task, then you
+  // should not use this method.
+  //
+  // The method name comes from
+  // https://html.spec.whatwg.org/multipage/web-messaging.html#eligible-for-messaging
+  // and is intended to convey whether it's okay to begin to take the steps to
+  // create an `EventWithOptionsRunnable` to pass to `PostEventWithOptions`.
+  // Note that early returning based on calling this method without performing
+  // the structured serialization steps that would otherwise run is potentially
+  // observable to content if content is in control of any of the payload in
+  // such a way that an object with getters or a proxy could be provided.
+  //
+  // There is an identically named method on nsIGlobalObject and the semantics
+  // are intentionally similar but please make sure you document your
+  // assumptions when calling either method.
+  bool IsEligibleForMessaging();
+
   void PostMessage(JSContext* aCx, JS::Handle<JS::Value> aMessage,
                    const Sequence<JSObject*>& aTransferable, ErrorResult& aRv);
 
@@ -49,6 +74,8 @@ class Worker : public DOMEventTargetHelper, public SupportsWeakPtr {
                    const StructuredSerializeOptions& aOptions,
                    ErrorResult& aRv);
 
+  // Callers must call `IsEligibleForMessaging` before constructing an
+  // `EventWithOptionsRunnable` subclass.
   void PostEventWithOptions(JSContext* aCx, JS::Handle<JS::Value> aOptions,
                             const Sequence<JSObject*>& aTransferable,
                             EventWithOptionsRunnable* aRunnable,
diff --git a/dom/workers/WorkerLoadInfo.cpp b/dom/workers/WorkerLoadInfo.cpp
index 0dec07a675..29fb69c212 100644
--- a/dom/workers/WorkerLoadInfo.cpp
+++ b/dom/workers/WorkerLoadInfo.cpp
@@ -101,7 +101,7 @@ WorkerLoadInfoData::WorkerLoadInfoData()
       mUsingStorageAccess(false),
       mServiceWorkersTestingInWindow(false),
       mShouldResistFingerprinting(false),
-      mIsThirdPartyContextToTopWindow(true),
+      mIsThirdPartyContext(true),
       mSecureContext(eNotSet) {}
 
 nsresult WorkerLoadInfo::SetPrincipalsAndCSPOnMainThread(
diff --git a/dom/workers/WorkerLoadInfo.h b/dom/workers/WorkerLoadInfo.h
index 722e71d6f3..c86538145c 100644
--- a/dom/workers/WorkerLoadInfo.h
+++ b/dom/workers/WorkerLoadInfo.h
@@ -147,7 +147,7 @@ struct WorkerLoadInfoData {
   bool mShouldResistFingerprinting;
   Maybe<RFPTarget> mOverriddenFingerprintingSettings;
   OriginAttributes mOriginAttributes;
-  bool mIsThirdPartyContextToTopWindow;
+  bool mIsThirdPartyContext;
 
   enum {
     eNotSet,
diff --git a/dom/workers/WorkerPrivate.cpp b/dom/workers/WorkerPrivate.cpp
index a8643981aa..df248acda4 100644
--- a/dom/workers/WorkerPrivate.cpp
+++ b/dom/workers/WorkerPrivate.cpp
@@ -1443,8 +1443,8 @@ nsresult WorkerPrivate::SetCSPFromHeaderValues(
   }
   MOZ_ASSERT(selfURI, "need a self URI for CSP");
 
-  rv = csp->SetRequestContextWithPrincipal(mLoadInfo.mPrincipal, selfURI,
-                                           u""_ns, 0);
+  rv = csp->SetRequestContextWithPrincipal(mLoadInfo.mPrincipal, selfURI, ""_ns,
+                                           0);
   NS_ENSURE_SUCCESS(rv, rv);
 
   csp->EnsureEventTarget(mMainThreadEventTarget);
@@ -1574,8 +1574,6 @@ nsresult WorkerPrivate::DispatchLockHeld(
   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!");
@@ -1624,6 +1622,7 @@ nsresult WorkerPrivate::DispatchLockHeld(
   }
 
   if (NS_WARN_IF(NS_FAILED(rv))) {
+    LOGV(("WorkerPrivate::Dispatch Failed [%p]", this));
     return rv;
   }
 
@@ -2792,8 +2791,7 @@ nsresult WorkerPrivate::GetLoadInfo(
     loadInfo.mOriginAttributes = aParent->GetOriginAttributes();
     loadInfo.mServiceWorkersTestingInWindow =
         aParent->ServiceWorkersTestingInWindow();
-    loadInfo.mIsThirdPartyContextToTopWindow =
-        aParent->IsThirdPartyContextToTopWindow();
+    loadInfo.mIsThirdPartyContext = aParent->IsThirdPartyContext();
     loadInfo.mShouldResistFingerprinting = aParent->ShouldResistFingerprinting(
         RFPTarget::IsAlwaysEnabledForPrecompute);
     loadInfo.mOverriddenFingerprintingSettings =
@@ -2954,7 +2952,7 @@ nsresult WorkerPrivate::GetLoadInfo(
           StorageAllowedForDocument(document) != StorageAccess::eAllow) {
         loadInfo.mUsingStorageAccess = false;
       }
-      loadInfo.mIsThirdPartyContextToTopWindow =
+      loadInfo.mIsThirdPartyContext =
           AntiTrackingUtils::IsThirdPartyWindow(globalWindow, nullptr);
       loadInfo.mCookieJarSettings = document->CookieJarSettings();
       if (loadInfo.mCookieJarSettings) {
@@ -3022,7 +3020,7 @@ nsresult WorkerPrivate::GetLoadInfo(
       cookieJarSettings->Serialize(loadInfo.mCookieJarSettingsArgs);
 
       loadInfo.mOriginAttributes = OriginAttributes();
-      loadInfo.mIsThirdPartyContextToTopWindow = false;
+      loadInfo.mIsThirdPartyContext = false;
     }
 
     MOZ_ASSERT(loadInfo.mLoadingPrincipal);
@@ -3104,10 +3102,33 @@ void WorkerPrivate::OverrideLoadInfoLoadGroup(WorkerLoadInfo& aLoadInfo,
 
 void WorkerPrivate::RunLoopNeverRan() {
   LOG(WorkerLog(), ("WorkerPrivate::RunLoopNeverRan [%p]", this));
+  // RunLoopNeverRan is only called in WorkerThreadPrimaryRunnable::Run() to
+  // handle cases
+  //   1. Fail to get BackgroundChild for the worker thread or
+  //   2. Fail to initialize the worker's JS context
+  // However, mPreStartRunnables had already dispatched in
+  // WorkerThread::SetWorkerPrivateInWorkerThread() where beforing above jobs
+  // start. So we need to clean up these dispatched runnables for the worker
+  // thread.
+
+  auto data = mWorkerThreadAccessible.Access();
+  RefPtr<WorkerThread> thread;
   {
     MutexAutoLock lock(mMutex);
-
+    // WorkerPrivate::DoRunLoop() is never called, so CompileScriptRunnable
+    // should not execute yet. However, the Worker is going to "Dead", flip the
+    // mCancelBeforeWorkerScopeConstructed to true for the dispatched runnables
+    // to indicate runnables there is no valid WorkerGlobalScope for executing.
+    MOZ_ASSERT(!data->mCancelBeforeWorkerScopeConstructed);
+    data->mCancelBeforeWorkerScopeConstructed.Flip();
+    // Switch State to Dead
     mStatus = Dead;
+    thread = mThread;
+  }
+
+  // Clear the dispatched mPreStartRunnables.
+  if (thread && NS_HasPendingEvents(thread)) {
+    NS_ProcessPendingEvents(nullptr);
   }
 
   // After mStatus is set to Dead there can be no more
@@ -3230,11 +3251,6 @@ void WorkerPrivate::DoRunLoop(JSContext* aCx) {
 
     {
       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.
@@ -3270,6 +3286,25 @@ void WorkerPrivate::DoRunLoop(JSContext* aCx) {
       currentStatus = mStatus;
     }
 
+    // Status transitions to Closing/Canceling and there are no SyncLoops,
+    // set global start dying, disconnect EventTargetObjects and
+    // WebTaskScheduler.
+    // The Worker might switch to the "Killing" immediately then directly exits
+    // DoRunLoop(). Before exiting the DoRunLoop(), explicitly disconnecting the
+    // WorkerGlobalScope's EventTargetObject here would help to fail runnable
+    // dispatching when the Worker is in the status changing.
+    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();
+        }
+      }
+    }
+
     // 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
@@ -3335,21 +3370,6 @@ void WorkerPrivate::DoRunLoop(JSContext* aCx) {
       }
     }
 
-    // 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);
@@ -4324,7 +4344,6 @@ void WorkerPrivate::AdjustNonblockingCCBackgroundActorCount(int32_t aCount) {
 }
 
 void WorkerPrivate::UpdateCCFlag(const CCFlag aFlag) {
-  LOGV(("WorkerPrivate::UpdateCCFlag [%p]", this));
   AssertIsOnWorkerThread();
 
   auto data = mWorkerThreadAccessible.Access();
@@ -4984,17 +5003,6 @@ bool WorkerPrivate::NotifyInternal(WorkerStatus aStatus) {
     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
@@ -5005,8 +5013,20 @@ bool WorkerPrivate::NotifyInternal(WorkerStatus aStatus) {
 
     // 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 >= Killing) {
+      mParentStatus = aStatus;
+    }
+  }
+
+  // Status transistion to "Canceling"/"Killing", mark the scope as dying when
+  // "Canceling," or shutdown the StorageManager when "Killing."
+  if (aStatus >= Canceling) {
+    if (data->mScope) {
+      if (aStatus == Canceling) {
+        data->mScope->NoteTerminating();
+      } else {
+        data->mScope->NoteShuttingDown();
+      }
     }
   }
 
diff --git a/dom/workers/WorkerPrivate.h b/dom/workers/WorkerPrivate.h
index a670d00975..ce754ba9f6 100644
--- a/dom/workers/WorkerPrivate.h
+++ b/dom/workers/WorkerPrivate.h
@@ -972,9 +972,7 @@ class WorkerPrivate final
   }
 
   // Determine if the worker was created under a third-party context.
-  bool IsThirdPartyContextToTopWindow() const {
-    return mLoadInfo.mIsThirdPartyContextToTopWindow;
-  }
+  bool IsThirdPartyContext() const { return mLoadInfo.mIsThirdPartyContext; }
 
   bool IsWatchedByDevTools() const { return mLoadInfo.mWatchedByDevTools; }
 
diff --git a/dom/workers/WorkerRunnable.cpp b/dom/workers/WorkerRunnable.cpp
index ff2178d16e..14a3e5e3f9 100644
--- a/dom/workers/WorkerRunnable.cpp
+++ b/dom/workers/WorkerRunnable.cpp
@@ -226,22 +226,6 @@ 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();
diff --git a/dom/workers/WorkerScope.cpp b/dom/workers/WorkerScope.cpp
index 92d6c89dca..2121a99cb3 100644
--- a/dom/workers/WorkerScope.cpp
+++ b/dom/workers/WorkerScope.cpp
@@ -721,7 +721,7 @@ void WorkerGlobalScope::GetJSTestingFunctions(
 }
 
 already_AddRefed<Promise> WorkerGlobalScope::Fetch(
-    const RequestOrUSVString& aInput, const RequestInit& aInit,
+    const RequestOrUTF8String& aInput, const RequestInit& aInit,
     CallerType aCallerType, ErrorResult& aRv) {
   return FetchRequest(this, aInput, aInit, aCallerType, aRv);
 }
diff --git a/dom/workers/WorkerScope.h b/dom/workers/WorkerScope.h
index 12a97e12c3..668755ce4a 100644
--- a/dom/workers/WorkerScope.h
+++ b/dom/workers/WorkerScope.h
@@ -68,7 +68,7 @@ template <typename T>
 class Optional;
 class Performance;
 class Promise;
-class RequestOrUSVString;
+class RequestOrUTF8String;
 template <typename T>
 class Sequence;
 class ServiceWorkerDescriptor;
@@ -326,7 +326,7 @@ class WorkerGlobalScope : public WorkerGlobalScopeBase {
                        JS::MutableHandle<JS::Value> aRetval,
                        ErrorResult& aError);
 
-  already_AddRefed<Promise> Fetch(const RequestOrUSVString& aInput,
+  already_AddRefed<Promise> Fetch(const RequestOrUTF8String& aInput,
                                   const RequestInit& aInit,
                                   CallerType aCallerType, ErrorResult& aRv);
 
diff --git a/dom/workers/WorkerThread.cpp b/dom/workers/WorkerThread.cpp
index 19cf9cb364..14d944e4d3 100644
--- a/dom/workers/WorkerThread.cpp
+++ b/dom/workers/WorkerThread.cpp
@@ -13,6 +13,7 @@
 #include "mozilla/Atomics.h"
 #include "mozilla/CycleCollectedJSContext.h"
 #include "mozilla/EventQueue.h"
+#include "mozilla/Logging.h"
 #include "mozilla/MacroForEach.h"
 #include "mozilla/NotNull.h"
 #include "mozilla/ThreadEventQueue.h"
@@ -25,8 +26,15 @@
 #include "nsIRunnable.h"
 #include "nsIThreadInternal.h"
 #include "nsString.h"
+#include "nsThreadUtils.h"
 #include "prthread.h"
 
+static mozilla::LazyLogModule gWorkerThread("WorkerThread");
+#ifdef LOGV
+#  undef LOGV
+#endif
+#define LOGV(msg) MOZ_LOG(gWorkerThread, LogLevel::Verbose, msg);
+
 namespace mozilla {
 
 using namespace ipc;
@@ -143,7 +151,11 @@ void WorkerThread::SetWorker(const WorkerThreadFriendKey& /* aKey */,
       while (mOtherThreadsDispatchingViaEventTarget) {
         mWorkerPrivateCondVar.Wait();
       }
-
+      // Need to clean up the dispatched runnables if
+      // mOtherThreadsDispatchingViaEventTarget was non-zero.
+      if (NS_HasPendingEvents(nullptr)) {
+        NS_ProcessPendingEvents(nullptr);
+      }
 #ifdef DEBUG
       mAcceptingNonWorkerRunnables = true;
 #endif
@@ -223,6 +235,8 @@ WorkerThread::Dispatch(already_AddRefed<nsIRunnable> aRunnable,
   // May be called on any thread!
   nsCOMPtr<nsIRunnable> runnable(aRunnable);  // in case we exit early
 
+  LOGV(("WorkerThread::Dispatch [%p] runnable: %p", this, runnable.get()));
+
   // Workers only support asynchronous dispatch.
   if (NS_WARN_IF(aFlags != NS_DISPATCH_NORMAL)) {
     return NS_ERROR_UNEXPECTED;
@@ -282,6 +296,8 @@ WorkerThread::Dispatch(already_AddRefed<nsIRunnable> aRunnable,
   }
 
   if (NS_WARN_IF(NS_FAILED(rv))) {
+    LOGV(("WorkerThread::Dispatch [%p] failed, runnable: %p", this,
+          runnable.get()));
     return rv;
   }
 
diff --git a/dom/workers/loader/CacheLoadHandler.cpp b/dom/workers/loader/CacheLoadHandler.cpp
index 16f992e837..7059249602 100644
--- a/dom/workers/loader/CacheLoadHandler.cpp
+++ b/dom/workers/loader/CacheLoadHandler.cpp
@@ -305,18 +305,15 @@ void CacheLoadHandler::Load(Cache* aCache) {
     return;
   }
 
-  nsAutoCString spec;
-  rv = uri->GetSpec(spec);
+  MOZ_ASSERT(loadContext->mFullURL.IsEmpty());
+  rv = uri->GetSpec(loadContext->mFullURL);
   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::RequestOrUTF8String request;
+  request.SetAsUTF8String().ShareOrDependUpon(loadContext->mFullURL);
 
   mozilla::dom::CacheQueryOptions params;
 
diff --git a/dom/workers/loader/NetworkLoadHandler.cpp b/dom/workers/loader/NetworkLoadHandler.cpp
index 9c2c243066..07398dac0a 100644
--- a/dom/workers/loader/NetworkLoadHandler.cpp
+++ b/dom/workers/loader/NetworkLoadHandler.cpp
@@ -358,10 +358,10 @@ nsresult NetworkLoadHandler::PrepareForRequest(nsIRequest* aRequest) {
   RefPtr<mozilla::dom::Response> response = new mozilla::dom::Response(
       mRequestHandle->GetCacheCreator()->Global(), std::move(ir), nullptr);
 
-  mozilla::dom::RequestOrUSVString request;
+  mozilla::dom::RequestOrUTF8String request;
 
   MOZ_ASSERT(!loadContext->mFullURL.IsEmpty());
-  request.SetAsUSVString().ShareOrDependUpon(loadContext->mFullURL);
+  request.SetAsUTF8String().ShareOrDependUpon(loadContext->mFullURL);
 
   // This JSContext will not end up executing JS code because here there are
   // no ReadableStreams involved.
diff --git a/dom/workers/loader/WorkerLoadContext.h b/dom/workers/loader/WorkerLoadContext.h
index 97362f2871..f5b107a610 100644
--- a/dom/workers/loader/WorkerLoadContext.h
+++ b/dom/workers/loader/WorkerLoadContext.h
@@ -130,7 +130,7 @@ class WorkerLoadContext : public JS::loader::LoadContextBase {
   /* TODO: Split out a ServiceWorkerLoadContext */
   // This full URL string is populated only if this object is used in a
   // ServiceWorker.
-  nsString mFullURL;
+  nsCString 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
diff --git a/dom/workers/loader/WorkerModuleLoader.cpp b/dom/workers/loader/WorkerModuleLoader.cpp
index da340c89bd..d76c61c31f 100644
--- a/dom/workers/loader/WorkerModuleLoader.cpp
+++ b/dom/workers/loader/WorkerModuleLoader.cpp
@@ -147,6 +147,15 @@ already_AddRefed<ModuleLoadRequest> WorkerModuleLoader::CreateDynamicImport(
   return request.forget();
 }
 
+bool WorkerModuleLoader::IsDynamicImportSupported() {
+  WorkerPrivate* workerPrivate = GetCurrentThreadWorkerPrivate();
+  if (workerPrivate->IsServiceWorker()) {
+    return false;
+  }
+
+  return true;
+}
+
 bool WorkerModuleLoader::CanStartLoad(ModuleLoadRequest* aRequest,
                                       nsresult* aRvOut) {
   return true;
diff --git a/dom/workers/loader/WorkerModuleLoader.h b/dom/workers/loader/WorkerModuleLoader.h
index 6ad45b42a0..f49d08743c 100644
--- a/dom/workers/loader/WorkerModuleLoader.h
+++ b/dom/workers/loader/WorkerModuleLoader.h
@@ -63,6 +63,8 @@ class WorkerModuleLoader : public JS::loader::ModuleLoaderBase {
       JS::Handle<JSString*> aSpecifier,
       JS::Handle<JSObject*> aPromise) override;
 
+  bool IsDynamicImportSupported() override;
+
   bool CanStartLoad(ModuleLoadRequest* aRequest, nsresult* aRvOut) override;
 
   // StartFetch is special for worker modules, as we need to move back to the
diff --git a/dom/workers/nsIWorkerDebugger.idl b/dom/workers/nsIWorkerDebugger.idl
index 931d01a4ac..573e7027b0 100644
--- a/dom/workers/nsIWorkerDebugger.idl
+++ b/dom/workers/nsIWorkerDebugger.idl
@@ -25,11 +25,11 @@ interface nsIWorkerDebugger : nsISupports
   const unsigned long TYPE_SHARED = 1;
   const unsigned long TYPE_SERVICE = 2;
 
-  readonly attribute bool isClosed;
+  readonly attribute boolean isClosed;
 
-  readonly attribute bool isChrome;
+  readonly attribute boolean isChrome;
 
-  readonly attribute bool isInitialized;
+  readonly attribute boolean isInitialized;
 
   readonly attribute nsIWorkerDebugger parent;
 
diff --git a/dom/workers/remoteworkers/RemoteWorkerChild.cpp b/dom/workers/remoteworkers/RemoteWorkerChild.cpp
index feb294f3fc..bf63c1729c 100644
--- a/dom/workers/remoteworkers/RemoteWorkerChild.cpp
+++ b/dom/workers/remoteworkers/RemoteWorkerChild.cpp
@@ -286,7 +286,7 @@ nsresult RemoteWorkerChild::ExecWorkerOnMainThread(RemoteWorkerData&& aData) {
   info.mStorageAccess = aData.storageAccess();
   info.mUseRegularPrincipal = aData.useRegularPrincipal();
   info.mUsingStorageAccess = aData.usingStorageAccess();
-  info.mIsThirdPartyContextToTopWindow = aData.isThirdPartyContextToTopWindow();
+  info.mIsThirdPartyContext = aData.isThirdPartyContext();
   info.mOriginAttributes =
       BasePrincipal::Cast(principal)->OriginAttributesRef();
   info.mShouldResistFingerprinting = aData.shouldResistFingerprinting();
diff --git a/dom/workers/remoteworkers/RemoteWorkerTypes.ipdlh b/dom/workers/remoteworkers/RemoteWorkerTypes.ipdlh
index 8894450b72..08fb5700fe 100644
--- a/dom/workers/remoteworkers/RemoteWorkerTypes.ipdlh
+++ b/dom/workers/remoteworkers/RemoteWorkerTypes.ipdlh
@@ -76,7 +76,7 @@ struct RemoteWorkerData
 
   StorageAccess storageAccess;
 
-  bool isThirdPartyContextToTopWindow;
+  bool isThirdPartyContext;
 
   bool shouldResistFingerprinting;
 
diff --git a/dom/workers/test/call_throws.js b/dom/workers/test/call_throws.js
new file mode 100644
index 0000000000..dfde155961
--- /dev/null
+++ b/dom/workers/test/call_throws.js
@@ -0,0 +1,4 @@
+function workerMethod() {
+  console.log("workerMethod about to throw...");
+  throw new Error("Method-Throw-Payload");
+}
diff --git a/dom/workers/test/chrome.toml b/dom/workers/test/chrome.toml
index 0b2d68da39..239394d2ea 100644
--- a/dom/workers/test/chrome.toml
+++ b/dom/workers/test/chrome.toml
@@ -89,10 +89,6 @@ support-files = [
 ["test_chromeWorkerJSM.xhtml"]
 
 ["test_file.xhtml"]
-skip-if = [
-  "os == 'linux' && bits == 64 && debug", # Bug 1765445
-  "apple_catalina && !debug", # Bug 1765445
-]
 
 ["test_fileBlobPosting.xhtml"]
 
diff --git a/dom/workers/test/crashtests/1858809.html b/dom/workers/test/crashtests/1858809.html
new file mode 100644
index 0000000000..3a5190c300
--- /dev/null
+++ b/dom/workers/test/crashtests/1858809.html
@@ -0,0 +1,14 @@
+<!DOCTYPE>
+<html>
+<head>
+<meta charset="UTF-8">
+<script>
+document.addEventListener("DOMContentLoaded", () => {
+  const a = new Worker("", {})
+  const b = new Blob([""], {})
+  a.terminate()
+  new RTCRtpScriptTransform(a, b, [{}])
+})
+</script>
+</head>
+</html>
diff --git a/dom/workers/test/crashtests/crashtests.list b/dom/workers/test/crashtests/crashtests.list
index 528f4c8a10..26a1fbbf80 100644
--- a/dom/workers/test/crashtests/crashtests.list
+++ b/dom/workers/test/crashtests/crashtests.list
@@ -6,3 +6,4 @@ load 1228456.html
 load 1348882.html
 load 1821066.html
 load 1819146.html
+load 1858809.html
diff --git a/dom/workers/test/importScripts_3rdParty_worker.js b/dom/workers/test/importScripts_3rdParty_worker.js
index 326d48f77a..e55fdc514b 100644
--- a/dom/workers/test/importScripts_3rdParty_worker.js
+++ b/dom/workers/test/importScripts_3rdParty_worker.js
@@ -1,18 +1,113 @@
 const workerURL =
   "http://mochi.test:8888/tests/dom/workers/test/importScripts_3rdParty_worker.js";
 
+/**
+ * An Error can be a JS Error or a DOMException.  The primary difference is that
+ * JS Errors have a SpiderMonkey specific `fileName` for the filename and
+ * DOMEXCEPTION uses `filename`.
+ */
+function normalizeError(err) {
+  if (!err) {
+    return null;
+  }
+
+  const isDOMException = "filename" in err;
+
+  return {
+    message: err.message,
+    name: err.name,
+    isDOMException,
+    code: err.code,
+    // normalize to fileName
+    fileName: isDOMException ? err.filename : err.fileName,
+    hasFileName: !!err.fileName,
+    hasFilename: !!err.filename,
+    lineNumber: err.lineNumber,
+    columnNumber: err.columnNumber,
+    stack: err.stack,
+    stringified: err.toString(),
+  };
+}
+
+function normalizeErrorEvent(event) {
+  if (!event) {
+    return null;
+  }
+
+  return {
+    message: event.message,
+    filename: event.filename,
+    lineno: event.lineno,
+    colno: event.colno,
+    error: normalizeError(event.error),
+    stringified: event.toString(),
+  };
+}
+
+/**
+ * Normalize the `OnErrorEventHandlerNonNull onerror` invocation.  The
+ * special handling in JSEventHandler::HandleEvent ends up spreading out the
+ * contents of the ErrorEvent into discrete arguments.  The one thing lost is
+ * we can't toString the ScriptEvent itself, but this should be the same as the
+ * message anyways.
+ *
+ * The spec for the invocation is the "special error event handling" logic
+ * described in step 4 at:
+ * https://html.spec.whatwg.org/multipage/webappapis.html#the-event-handler-processing-algorithm
+ * noting that the step somewhat glosses over that it's only "onerror" that is
+ * OnErrorEventHandlerNonNull and capable of processing 5 arguments and that's
+ * why an addEventListener "error" listener doesn't get this handling.
+ *
+ * Argument names here are made to match the call-site in JSEventHandler.
+ */
+function normalizeOnError(
+  msgOrEvent,
+  fileName,
+  lineNumber,
+  columnNumber,
+  error
+) {
+  return {
+    message: msgOrEvent,
+    filename: fileName,
+    lineno: lineNumber,
+    colno: columnNumber,
+    error: normalizeError(error),
+    stringified: null,
+  };
+}
+
+/**
+ * Helper to postMessage the provided data after a setTimeout(0) so that any
+ * error event currently being dispatched that will bubble to our parent will
+ * be delivered before our postMessage.
+ */
+function delayedPostMessage(data) {
+  setTimeout(() => {
+    postMessage(data);
+  }, 0);
+}
+
 onmessage = function (a) {
+  const args = a.data;
+  // Messages are either nested (forward to a nested worker) or should be
+  // processed locally.
   if (a.data.nested) {
-    var worker = new Worker(workerURL);
+    const worker = new Worker(workerURL);
+    let firstErrorEvent;
+
+    // When the test mode is "catch"
+
     worker.onmessage = function (event) {
-      postMessage(event.data);
+      delayedPostMessage({
+        nestedMessage: event.data,
+        errorEvent: firstErrorEvent,
+      });
     };
 
     worker.onerror = function (event) {
+      firstErrorEvent = normalizeErrorEvent(event);
       event.preventDefault();
-      postMessage({
-        error: event instanceof ErrorEvent && event.filename == workerURL,
-      });
     };
 
     a.data.nested = false;
@@ -20,69 +115,47 @@ onmessage = function (a) {
     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;
+  // Local test.
+  if (a.data.mode === "catch") {
     try {
-      importScripts(crossOriginURL.href);
-    } catch (e) {
-      fileName2 = e.filename;
-      exception = e;
+      importScripts(a.data.url);
+      workerMethod();
+    } catch (ex) {
+      delayedPostMessage({
+        args,
+        error: normalizeError(ex),
+      });
     }
-
-    postMessage({
-      result:
-        fileName2 == workerURL &&
-        exception.name == "NetworkError" &&
-        exception.code == DOMException.NETWORK_ERR,
+  } else if (a.data.mode === "uncaught") {
+    const onerrorPromise = new Promise(resolve => {
+      self.onerror = (...onerrorArgs) => {
+        resolve(normalizeOnError(...onerrorArgs));
+      };
     });
-    return;
-  }
-
-  if (a.data.test == "eventListener") {
-    addEventListener("error", function (event) {
-      event.preventDefault();
-      postMessage({
-        result: event instanceof ErrorEvent && event.filename == workerURL,
+    const listenerPromise = new Promise(resolve => {
+      self.addEventListener("error", evt => {
+        resolve(normalizeErrorEvent(evt));
       });
     });
-  }
 
-  if (a.data.test == "onerror") {
-    onerror = function (...args) {
-      postMessage({ result: args[1] == workerURL });
-    };
-  }
+    Promise.all([onerrorPromise, listenerPromise]).then(
+      ([onerrorEvent, listenerEvent]) => {
+        delayedPostMessage({
+          args,
+          onerrorEvent,
+          listenerEvent,
+        });
+      }
+    );
 
-  importScripts(crossOriginURL.href);
+    importScripts(a.data.url);
+    workerMethod();
+    // we will have thrown by this point, which will trigger an "error" event
+    // on our global and then will propagate to our parent (which could be a
+    // window or a worker, if nested).
+    //
+    // To avoid hangs, throw a different error here that will fail equivalence
+    // tests.
+    throw new Error("We expected an error and this is a failsafe for hangs.");
+  }
 };
diff --git a/dom/workers/test/mime_type_is_csv.js b/dom/workers/test/mime_type_is_csv.js
new file mode 100644
index 0000000000..54d3b70689
--- /dev/null
+++ b/dom/workers/test/mime_type_is_csv.js
@@ -0,0 +1 @@
+throw new Error("This file has a CSV mime type and should not load.");
diff --git a/dom/workers/test/mime_type_is_csv.js^headers^ b/dom/workers/test/mime_type_is_csv.js^headers^
new file mode 100644
index 0000000000..0d848b02c2
--- /dev/null
+++ b/dom/workers/test/mime_type_is_csv.js^headers^
@@ -0,0 +1 @@
+Content-Type: text/csv
diff --git a/dom/workers/test/mochitest.toml b/dom/workers/test/mochitest.toml
index 5ae8094b58..a32dbf3bf6 100644
--- a/dom/workers/test/mochitest.toml
+++ b/dom/workers/test/mochitest.toml
@@ -12,6 +12,7 @@ support-files = [
   "bug998474_worker.js",
   "bug1063538_worker.js",
   "bug1063538.sjs",
+  "call_throws.js",
   "clearTimeouts_worker.js",
   "clearTimeoutsImplicit_worker.js",
   "content_worker.js",
@@ -42,6 +43,8 @@ support-files = [
   "loadEncoding_worker.js",
   "location_worker.js",
   "longThread_worker.js",
+  "mime_type_is_csv.js",
+  "mime_type_is_csv.js^headers^",
   "multi_sharedWorker_frame.html",
   "multi_sharedWorker_sharedWorker.js",
   "navigator_languages_worker.js",
@@ -58,6 +61,7 @@ support-files = [
   "recursion_worker.js",
   "recursiveOnerror_worker.js",
   "redirect_to_foreign.sjs",
+  "redirect_with_query_args.sjs",
   "rvals_worker.js",
   "sharedWorker_sharedWorker.js",
   "simpleThread_worker.js",
@@ -66,6 +70,7 @@ support-files = [
   "terminate_worker.js",
   "test_csp.html^headers^",
   "test_csp.js",
+  "toplevel_throws.js",
   "referrer_worker.html",
   "sourcemap_header_iframe.html",
   "sourcemap_header_worker.js",
diff --git a/dom/workers/test/redirect_with_query_args.sjs b/dom/workers/test/redirect_with_query_args.sjs
new file mode 100644
index 0000000000..3359367ee0
--- /dev/null
+++ b/dom/workers/test/redirect_with_query_args.sjs
@@ -0,0 +1,22 @@
+/**
+ * This file expects a query string that's the upper-cased version of a file to
+ * be redirected to in the same directory.  The redirect will also include
+ * added "secret data" as a query string.
+ *
+ * So if the request is `/path/redirect_with_query_args.sjs?FOO.JS` the redirect
+ * will be to `/path/foo.js?SECRET_DATA`.
+ **/
+
+function handleRequest(request, response) {
+  // The secret data to include in the redirect to make the redirect URL
+  // easily detectable.
+  const secretData = "SECRET_DATA";
+
+  let pathBase = request.path.split("/").slice(0, -1).join("/");
+  let targetFile = request.queryString.toLowerCase();
+  let newUrl = `${pathBase}/${targetFile}?${secretData}`;
+
+  response.setStatusLine(request.httpVersion, 302, "Found");
+  response.setHeader("Cache-Control", "no-cache");
+  response.setHeader("Location", newUrl, false);
+}
diff --git a/dom/workers/test/test_importScripts_3rdparty.html b/dom/workers/test/test_importScripts_3rdparty.html
index 7f10f23faf..b1e4913eea 100644
--- a/dom/workers/test/test_importScripts_3rdparty.html
+++ b/dom/workers/test/test_importScripts_3rdparty.html
@@ -14,123 +14,576 @@
 
 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'
+const sameOriginBaseURL = 'http://mochi.test:8888/tests/dom/workers/test';
+const crossOriginBaseURL = "https://example.com/tests/dom/workers/test";
 
-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();
-    };
+const workerRelativeUrl = 'importScripts_3rdParty_worker.js';
+const workerAbsoluteUrl = `${sameOriginBaseURL}/${workerRelativeUrl}`
 
-    worker.postMessage({ url: sameOriginURL, test: 'try', nested: false });
-  },
+/**
+ * This file tests cross-origin error muting in importScripts for workers.  In
+ * particular, we want to test:
+ * - The errors thrown by the parsing phase of importScripts().
+ * - The errors thrown by the top-level evaluation phase of importScripts().
+ * - If the error is reported to the parent's Worker binding, including through
+ *   nested workers, as well as the contents of the error.
+ * - For errors:
+ *   - What type of exception is reported?
+ *   - What fileName is reported on the exception?
+ *   - What are the contents of the stack on the exception?
+ *
+ * Relevant specs:
+ * - https://html.spec.whatwg.org/multipage/webappapis.html#fetch-a-classic-worker-imported-script
+ * - https://html.spec.whatwg.org/multipage/webappapis.html#creating-a-classic-script
+ *
+ * The situation and motivation for error muting is:
+ * - JS scripts are allowed to be loaded cross-origin without CORS for legacy
+ *   reasons.  If a script is cross-origin, its "muted errors" is set to true.
+ *   - The fetch will set the "use-URL-credentials" flag
+ *     https://fetch.spec.whatwg.org/#concept-request-use-url-credentials-flag
+ *     but will have the default "credentials" mode of "omit"
+ *     https://fetch.spec.whatwg.org/#concept-request-credentials-mode which
+ *     means that username/password will be propagated.
+ * - For legacy reasons, JS scripts aren't required to have an explicit JS MIME
+ *   type which allows attacks that attempt to load a known-non JS file as JS
+ *   in order to derive information from the errors or from side-effects to the
+ *   global for code that does parse and evaluate as legal JS.
+ **/
 
-  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 });
+ /**
+  * - `sameOrigin`: Describes the exception we expect to see for a same-origin
+  *   import.
+  * - `crossOrigin`: Describes the exception we expect to see for a cross-origin
+  *   import (from example.com while the worker is the mochitest origin).
+  *
+  * The exception fields are:
+  * - `exceptionName`: The `name` of the Error object.
+  * - `thrownFile`: Describes the filename we expect to see on the error:
+  *   - `importing-worker-script`: The worker script that's doing the importing
+  *     will be the source of the exception, not the imported script.
+  *   - `imported-script-no-redirect`: The (absolute-ified) script as passed to
+  *     importScript(s), regardless of any redirects that occur.
+  *   - `post-redirect-imported-script`: The name of the actual URL that was
+  *     loaded following any redirects.
+  */
+const scriptPermutations = [
+  {
+    name: 'Invalid script that generates a syntax error',
+    script: 'invalid.js',
+    sameOrigin: {
+      exceptionName: 'SyntaxError',
+      thrownFile: 'post-redirect-imported-script',
+      isDOMException: false,
+      message: "expected expression, got end of script"
+    },
+    crossOrigin: {
+      exceptionName: 'NetworkError',
+      thrownFile: 'importing-worker-script',
+      isDOMException: true,
+      code: DOMException.NETWORK_ERR,
+      message: "A network error occurred."
+    }
   },
+  {
+    name: 'Non-JS MIME Type',
+    script: 'mime_type_is_csv.js',
+    sameOrigin: {
+      exceptionName: 'NetworkError',
+      thrownFile: 'importing-worker-script',
+      isDOMException: true,
+      code: DOMException.NETWORK_ERR,
+      message: "A network error occurred."
+    },
+    crossOrigin: {
+      exceptionName: 'NetworkError',
+      thrownFile: 'importing-worker-script',
+      isDOMException: true,
+      code: DOMException.NETWORK_ERR,
+      message: "A network error occurred."
+    }
+  },
+  {
+    // What happens if the script is a 404?
+    name: 'Nonexistent script',
+    script: 'script_does_not_exist.js',
+    sameOrigin: {
+      exceptionName: 'NetworkError',
+      thrownFile: 'importing-worker-script',
+      isDOMException: true,
+      code: DOMException.NETWORK_ERR,
+      message: "A network error occurred."
+    },
+    crossOrigin: {
+      exceptionName: 'NetworkError',
+      thrownFile: 'importing-worker-script',
+      isDOMException: true,
+      code: DOMException.NETWORK_ERR,
+      message: "A network error occurred."
+    }
+  },
+  {
+    name: 'Script that throws during toplevel execution',
+    script: 'toplevel_throws.js',
+    sameOrigin: {
+      exceptionName: 'Error',
+      thrownFile: 'post-redirect-imported-script',
+      isDOMException: false,
+      message: "Toplevel-Throw-Payload",
+    },
+    crossOrigin: {
+      exceptionName: 'NetworkError',
+      thrownFile: 'importing-worker-script',
+      isDOMException: true,
+      code: DOMException.NETWORK_ERR,
+      message: "A network error occurred."
+    }
+  },
+  {
+    name: 'Script that exposes a method that throws',
+    script: 'call_throws.js',
+    sameOrigin: {
+      exceptionName: 'Error',
+      thrownFile: 'post-redirect-imported-script',
+      isDOMException: false,
+      message: "Method-Throw-Payload"
+    },
+    crossOrigin: {
+      exceptionName: 'Error',
+      thrownFile: 'imported-script-no-redirect',
+      isDOMException: false,
+      message: "Method-Throw-Payload"
+    }
+  },
+];
 
-  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 });
+/**
+ * Special fields:
+ * - `transformScriptImport`: A function that takes the script name as input and
+ *   produces the actual path to use for import purposes, allowing the addition
+ *   of a redirect.
+ * - `expectedURLAfterRedirect`: A function that takes the script name as
+ *   input and produces the expected script name post-redirect (if there is a
+ *   redirect).  In particular, our `redirect_with_query_args.sjs` helper will
+ *   perform a same-origin redirect and append "?SECRET_DATA" onto the end of
+ *   the redirected URL at this time.
+ * - `partOfTheURLToNotExposeToJS`: A string snippet that is present in the
+ *   post-redirect contents that should absolutely not show up in the error's
+ *   stack if the redirect isn't exposed.  This is a secondary check to the
+ *   result of expectedURLAfterRedirect.
+ */
+const urlPermutations = [
+  {
+    name: 'No Redirect',
+    transformScriptImport: x => x,
+    expectedURLAfterRedirect: x => x,
+    // No redirect means nothing to be paranoid about.
+    partOfTheURLToNotExposeToJS: null,
   },
+  {
+    name: 'Same-Origin Redirect With Query Args',
+    // We mangle the script into uppercase and the redirector undoes this in
+    // order to minimize the similarity of the pre-redirect and post-redirect
+    // strings.
+    transformScriptImport: x => `redirect_with_query_args.sjs?${x.toUpperCase()}`,
+    expectedURLAfterRedirect: x => `${x}?SECRET_DATA`,
+    // The redirect will add this when it formulates the redirected URL, and the
+    // test wants to make sure this doesn't show up in filenames or stacks
+    // unless the thrownFile is set to 'post-redirect-imported-script'.
+    partOfTheURLToNotExposeToJS: 'SECRET_DATA',
+  }
+];
+const nestedPermutations = [
+  {
+    name: 'Window Parent',
+    nested: false,
+  },
+  {
+    name: 'Worker Parent',
+    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 in nested workers via eventListener!");
-      next();
-    };
+ // NOTE: These implementations are copied from importScripts_3rdParty_worker.js
+ // for reasons of minimizing the number of calls to importScripts for
+ // debugging.
+ function normalizeError(err) {
+  if (!err) {
+    return null;
+  }
 
-    worker.postMessage({ url: sameOriginURL, test: 'eventListener', nested: true });
-  },
+  const isDOMException = "filename" in err;
 
-  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();
+  return {
+    message: err.message,
+    name: err.name,
+    isDOMException,
+    code: err.code,
+    // normalize to fileName
+    fileName: isDOMException ? err.filename : err.fileName,
+    hasFileName: !!err.fileName,
+    hasFilename: !!err.filename,
+    lineNumber: err.lineNumber,
+    columnNumber: err.columnNumber,
+    stack: err.stack,
+    stringified: err.toString(),
+  };
+}
+
+function normalizeErrorEvent(event) {
+  if (!event) {
+    return null;
+  }
+
+  return {
+    message: event.message,
+    filename: event.filename,
+    lineno: event.lineno,
+    colno: event.colno,
+    error: normalizeError(event.error),
+    stringified: event.toString(),
+  };
+}
+// End duplicated code.
+
+
+/**
+ * Validate the received error against our expectations and provided context.
+ *
+ * For `expectation`, see the `scriptPermutations` doc-block which documents
+ * its `sameOrigin` and `crossOrigin` properties which are what we expect here.
+ *
+ * The `context` should include:
+ * - `workerUrl`: The absolute URL of the toplevel worker script that the worker
+ *   is running which is the code that calls `importScripts`.
+ * - `importUrl`: The absolute URL provided to the call to `importScripts`.
+ *   This is the pre-redirect URL if a redirect is involved.
+ * - `postRedirectUrl`: The same as `importUrl` unless a redirect is involved,
+ *   in which case this will be a different URL.
+ * - `isRedirected`: Boolean indicating whether a redirect was involved.  This
+ *   is a convenience variable that's derived from the above 2 URL's for now.
+ * - `shouldNotInclude`: Provided by the URL permutation, this is used to check
+ *   that post-redirect data does not creep into the exception unless the
+ *   expected `thrownFile` is `post-redirect-imported-script`.
+ */
+function checkError(label, expectation, context, err) {
+  info(`## Checking error: ${JSON.stringify(err)}`);
+  is(err.name, expectation.exceptionName,
+     `${label}: Error name matches "${expectation.exceptionName}"?`);
+  is(err.isDOMException, expectation.isDOMException,
+     `${label}: Is a DOM Exception == ${expectation.isDOMException}?`);
+  if (expectation.code) {
+    is(err.code, expectation.code,
+       `${label}: Code matches ${expectation.code}?`);
+  }
+
+  let expectedFile;
+  switch (expectation.thrownFile) {
+    case 'importing-worker-script':
+      expectedFile = context.workerUrl;
+      break;
+    case 'imported-script-no-redirect':
+      expectedFile = context.importUrl;
+      break;
+    case 'post-redirect-imported-script':
+      expectedFile = context.postRedirectUrl;
+      break;
+    default:
+      ok(false, `Unexpected thrownFile parameter: ${expectation.thrownFile}`);
+      return;
+  }
+
+  is(err.fileName, expectedFile,
+     `${label}: Filename from ${expectation.thrownFile} is ${expectedFile}`);
+
+
+  let expMessage = expectation.message;
+  if (typeof(expMessage) === "function") {
+    expMessage = expectation.message(context);
+  }
+  is(err.message, expMessage,
+      `${label}: Message is ${expMessage}`);
+
+  // If this is a redirect and we expect the error to not be surfacing any
+  // post-redirect information and there's a `shouldNotInclude` string, then
+  // check to make sure it's not present.
+  if (context.isRedirected && context.shouldNotInclude) {
+    if (expectation.thrownFile !== 'post-redirect-imported-script') {
+      ok(!err.stack.includes(context.shouldNotInclude),
+        `${label}: Stack should not include ${context.shouldNotInclude}:\n${err.stack}`);
+      ok(!err.stringified.includes(context.shouldNotInclude),
+        `${label}: Stringified error should not include ${context.shouldNotInclude}:\n${err.stringified}`);
+    } else if (expectation.exceptionName !== 'SyntaxError') {
+      // We do expect the shouldNotInclude to be present for
+      // 'post-redirect-imported-script' as long as the exception isn't a
+      // SyntaxError.  SyntaxError stacks inherently do not include the filename
+      // of the file with the syntax problem as a stack frame.
+      ok(err.stack.includes(context.shouldNotInclude),
+         `${label}: Stack should include ${context.shouldNotInclude}:\n${err.stack}`);
     }
+  }
+  let expStringified = `${err.name}: ${expMessage}`;
+  is(err.stringified, expStringified,
+    `${label}: Stringified error should be: ${expStringified}`);
 
-    worker.postMessage({ url: sameOriginURL, test: 'onerror', nested: false });
-  },
+  // Add some whitespace in our output.
+  info("");
+}
 
-  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();
-    };
+function checkErrorEvent(label, expectation, context, event, viaTask=false) {
+  info(`## Checking error event: ${JSON.stringify(event)}`);
 
-    worker.postMessage({ url: sameOriginURL, test: 'none', nested: false });
-  },
+  let expectedFile;
+  switch (expectation.thrownFile) {
+    case 'importing-worker-script':
+      expectedFile = context.workerUrl;
+      break;
+    case 'imported-script-no-redirect':
+      expectedFile = context.importUrl;
+      break;
+    case 'post-redirect-imported-script':
+      expectedFile = context.postRedirectUrl;
+      break;
+    default:
+      ok(false, `Unexpected thrownFile parameter: ${expectation.thrownFile}`);
+      return;
+  }
 
-  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();
-    });
+  is(event.filename, expectedFile,
+     `${label}: Filename from ${expectation.thrownFile} is ${expectedFile}`);
 
-    worker.postMessage({ url: sameOriginURL, test: 'none', nested: false });
-  },
+  let expMessage = expectation.message;
+  if (typeof(expMessage) === "function") {
+    expMessage = expectation.message(context);
+  }
+  // The error event message prepends the exception name to the Error's message.
+  expMessage = `${expectation.exceptionName}: ${expMessage}`;
 
-  function() {
-    var worker = new Worker("importScripts_3rdParty_worker.js");
-    worker.onerror = function(event) {
-      ok(false, "No error should be received!");
-    };
+  is(event.message, expMessage,
+      `${label}: Message is ${expMessage}`);
+
+  // If this is a redirect and we expect the error to not be surfacing any
+  // post-redirect information and there's a `shouldNotInclude` string, then
+  // check to make sure it's not present.
+  //
+  // Note that `stringified` may not be present for the "onerror" case.
+  if (context.isRedirected &&
+      expectation.thrownFile !== 'post-redirect-imported-script' &&
+      context.shouldNotInclude &&
+      event.stringified) {
+    ok(!event.stringified.includes(context.shouldNotInclude),
+       `${label}: Stringified error should not include ${context.shouldNotInclude}:\n${event.stringified}`);
+  }
+  if (event.stringified) {
+    is(event.stringified, "[object ErrorEvent]",
+      `${label}: Stringified event should be "[object ErrorEvent]"`);
+  }
+
+  // If we received the error via a task queued because it was not handled in
+  // the worker, then per
+  // https://html.spec.whatwg.org/multipage/workers.html#runtime-script-errors-2
+  // the error will be null.
+  if (viaTask) {
+    is(event.error, null,
+      `${label}: Error is null because it came from an HTML 10.2.5 task.`);
+  } else {
+    checkError(label, expectation, context, event.error);
+  }
+}
+
+/**
+ * Helper to spawn a worker, postMessage it the given args, and return the
+ * worker's response payload and the first "error" received on the Worker
+ * binding by the time the message handler resolves.  The worker logic makes
+ * sure to delay its postMessage using setTimeout(0) so error events will always
+ * arrive before any message that is sent.
+ *
+ * If args includes a truthy `nested` value, then the `message` and
+ * `bindingErrorEvent` are as perceived by the parent worker.
+ */
+function asyncWorkerImport(args) {
+  const worker = new Worker(workerRelativeUrl);
+  const promise = new Promise((resolve, reject) => {
+    // The first "error" received on the Worker binding.
+    let firstErrorEvent = null;
 
     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 });
-  },
+      let message = event.data;
+      // For the nested case, unwrap and normalize things.
+      if (args.nested) {
+        firstErrorEvent = message.errorEvent;
+        message = message.nestedMessage;
+        // We need to re-set the argument to be nested because it was set to
+        // false so that only a single level of nesting occurred.
+        message.args.nested = true;
+      }
+
+      // Make sure the args we receive from the worker are the same as the ones
+      // we sent.
+      is(JSON.stringify(message.args), JSON.stringify(args),
+         "Worker re-transmitted args match sent args.");
 
-  function() {
-    var url = URL.createObjectURL(new Blob(["%&%^&%^"]));
-    var worker = new Worker(url);
+      resolve({
+        message,
+        bindingErrorEvent: firstErrorEvent
+      });
+      worker.terminate();
+    };
     worker.onerror = function(event) {
+      // We don't want this to bubble to the window and cause a test failure.
       event.preventDefault();
-      ok(event instanceof Event, "Event received.");
-      next();
-    };
-  }
-];
 
-function next() {
-  if (!tests.length) {
-    SimpleTest.finish();
-    return;
-  }
+      if (firstErrorEvent) {
+        ok(false, "Worker binding received more than one error");
+        reject(new Error("multiple error events received"));
+        return;
+      }
+      firstErrorEvent = normalizeErrorEvent(event);
+    }
+  });
+  info("Sending args to worker: " + JSON.stringify(args));
+  worker.postMessage(args);
 
-  var test = tests.shift();
-  test();
+  return promise;
 }
 
-SimpleTest.waitForExplicitFinish();
-next();
+function makeTestPermutations() {
+  for (const urlPerm of urlPermutations) {
+    for (const scriptPerm of scriptPermutations) {
+      for (const nestedPerm of nestedPermutations) {
+        const testName =
+          `${nestedPerm.name}: ${urlPerm.name}: ${scriptPerm.name}`;
+        const caseFunc = async () => {
+          // Make the test name much more obvious when viewing logs.
+          info(`#############################################################`);
+          info(`### ${testName}`);
+          let result, errorEvent;
+
+          const scriptName = urlPerm.transformScriptImport(scriptPerm.script);
+          const redirectedUrl = urlPerm.expectedURLAfterRedirect(scriptPerm.script);
+
+          // ### Same-Origin Import
+          // ## What does the error look like when caught?
+          ({ message, bindingErrorEvent } = await asyncWorkerImport(
+            {
+              url: `${sameOriginBaseURL}/${scriptName}`,
+              mode: "catch",
+              nested: nestedPerm.nested,
+            }));
+
+          const sameOriginContext = {
+            workerUrl: workerAbsoluteUrl,
+            importUrl: message.args.url,
+            postRedirectUrl: `${sameOriginBaseURL}/${redirectedUrl}`,
+            isRedirected: message.args.url !== redirectedUrl,
+            shouldNotInclude: urlPerm.partOfTheURLToNotExposeToJS,
+          };
 
+          checkError(
+            `${testName}: Same-Origin Thrown`,
+            scriptPerm.sameOrigin,
+            sameOriginContext,
+            message.error);
+
+          // ## What does the error events look like when not caught?
+          ({ message, bindingErrorEvent } = await asyncWorkerImport(
+            {
+              url: `${sameOriginBaseURL}/${scriptName}`,
+              mode: "uncaught",
+              nested: nestedPerm.nested,
+            }));
+
+          // The worker will have captured the error event twice, once via
+          // onerror and once via an "error" event listener.  It will have not
+          // invoked preventDefault(), so the worker's parent will also have
+          // received a copy of the error event as well.
+          checkErrorEvent(
+            `${testName}: Same-Origin Worker global onerror handler`,
+            scriptPerm.sameOrigin,
+            sameOriginContext,
+            message.onerrorEvent);
+          checkErrorEvent(
+            `${testName}: Same-Origin Worker global error listener`,
+            scriptPerm.sameOrigin,
+            sameOriginContext,
+            message.listenerEvent);
+          // Binding events
+          checkErrorEvent(
+            `${testName}: Same-Origin Parent binding onerror`,
+            scriptPerm.sameOrigin,
+            sameOriginContext,
+            bindingErrorEvent, "via-task");
+
+          // ### Cross-Origin Import
+          // ## What does the error look like when caught?
+          ({ message, bindingErrorEvent } = await asyncWorkerImport(
+            {
+              url: `${crossOriginBaseURL}/${scriptName}`,
+              mode: "catch",
+              nested: nestedPerm.nested,
+            }));
+
+          const crossOriginContext = {
+            workerUrl: workerAbsoluteUrl,
+            importUrl: message.args.url,
+            postRedirectUrl: `${crossOriginBaseURL}/${redirectedUrl}`,
+            isRedirected: message.args.url !== redirectedUrl,
+            shouldNotInclude: urlPerm.partOfTheURLToNotExposeToJS,
+          };
+
+          checkError(
+            `${testName}: Cross-Origin Thrown`,
+            scriptPerm.crossOrigin,
+            crossOriginContext,
+            message.error);
+
+          // ## What does the error events look like when not caught?
+          ({ message, bindingErrorEvent } = await asyncWorkerImport(
+            {
+              url: `${crossOriginBaseURL}/${scriptName}`,
+              mode: "uncaught",
+              nested: nestedPerm.nested,
+            }));
+
+          // The worker will have captured the error event twice, once via
+          // onerror and once via an "error" event listener.  It will have not
+          // invoked preventDefault(), so the worker's parent will also have
+          // received a copy of the error event as well.
+          checkErrorEvent(
+            `${testName}: Cross-Origin Worker global onerror handler`,
+            scriptPerm.crossOrigin,
+            crossOriginContext,
+            message.onerrorEvent);
+          checkErrorEvent(
+            `${testName}: Cross-Origin Worker global error listener`,
+            scriptPerm.crossOrigin,
+            crossOriginContext,
+            message.listenerEvent);
+          // Binding events
+          checkErrorEvent(
+            `${testName}: Cross-Origin Parent binding onerror`,
+            scriptPerm.crossOrigin,
+            crossOriginContext,
+            bindingErrorEvent, "via-task");
+        };
+
+        // The mochitest framework uses the name of the caseFunc, which by default
+        // will be inferred and set on the configurable `name` property.  It's not
+        // writable though, so we need to clobber the property.  Devtools will
+        // xray through this name but this works for the test framework.
+        Object.defineProperty(
+          caseFunc,
+          'name',
+          {
+            value: testName,
+            writable: false
+          });
+        add_task(caseFunc);
+      }
+    }
+  }
+}
+makeTestPermutations();
 </script>
 </body>
 </html>
diff --git a/dom/workers/test/test_worker_interfaces.js b/dom/workers/test/test_worker_interfaces.js
index efd108f85c..c53c0b2b0f 100644
--- a/dom/workers/test/test_worker_interfaces.js
+++ b/dom/workers/test/test_worker_interfaces.js
@@ -138,6 +138,8 @@ let interfaceNamesInGlobalScope = [
   // IMPORTANT: Do not change this list without review from a DOM peer!
   { name: "AudioDecoder", nightly: true },
   // IMPORTANT: Do not change this list without review from a DOM peer!
+  { name: "AudioEncoder", nightly: 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 },
diff --git a/dom/workers/test/toplevel_throws.js b/dom/workers/test/toplevel_throws.js
new file mode 100644
index 0000000000..3efe29d5af
--- /dev/null
+++ b/dom/workers/test/toplevel_throws.js
@@ -0,0 +1 @@
+throw new Error("Toplevel-Throw-Payload");