Adding upstream version 1:115.7.0.upstream/1%115.7.0upstream

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

48 files changed, 6902 insertions, 0 deletions

diff --git a/dom/promise/Promise-inl.h b/dom/promise/Promise-inl.h
new file mode 100644
index 0000000000..a7a6ebd0fd
--- /dev/null
+++ b/dom/promise/Promise-inl.h
@@ -0,0 +1,341 @@
+/* -*- 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_Promise_inl_h
+#define mozilla_dom_Promise_inl_h
+
+#include <type_traits>
+#include <utility>
+
+#include "mozilla/AlreadyAddRefed.h"
+#include "mozilla/ResultExtensions.h"
+#include "mozilla/dom/BindingUtils.h"
+#include "mozilla/dom/Promise.h"
+#include "mozilla/dom/PromiseNativeHandler.h"
+#include "nsCycleCollectionParticipant.h"
+
+namespace mozilla::dom {
+
+class PromiseNativeThenHandlerBase : public PromiseNativeHandler {
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS(PromiseNativeThenHandlerBase)
+
+  PromiseNativeThenHandlerBase(Promise* aPromise) : mPromise(aPromise) {}
+
+  virtual bool HasResolvedCallback() = 0;
+  virtual bool HasRejectedCallback() = 0;
+
+  MOZ_CAN_RUN_SCRIPT void ResolvedCallback(JSContext* aCx,
+                                           JS::Handle<JS::Value> aValue,
+                                           ErrorResult& aRv) override;
+
+  MOZ_CAN_RUN_SCRIPT void RejectedCallback(JSContext* aCx,
+                                           JS::Handle<JS::Value> aValue,
+                                           ErrorResult& aRv) override;
+
+ protected:
+  virtual ~PromiseNativeThenHandlerBase() = default;
+
+  MOZ_CAN_RUN_SCRIPT virtual already_AddRefed<Promise> CallResolveCallback(
+      JSContext* aCx, JS::Handle<JS::Value> aValue, ErrorResult& aRv) = 0;
+  MOZ_CAN_RUN_SCRIPT virtual already_AddRefed<Promise> CallRejectCallback(
+      JSContext* aCx, JS::Handle<JS::Value> aValue, ErrorResult& aRv) = 0;
+
+  virtual void Traverse(nsCycleCollectionTraversalCallback&) = 0;
+  virtual void Unlink() = 0;
+  virtual void Trace(const TraceCallbacks& aCallbacks, void* aClosure) = 0;
+
+  RefPtr<Promise> mPromise;
+};
+
+namespace {
+
+template <typename T, bool = IsRefcounted<std::remove_pointer_t<T>>::value,
+          bool = (std::is_convertible_v<T, nsISupports*> ||
+                  std::is_convertible_v<T*, nsISupports*>)>
+struct StorageTypeHelper {
+  using Type = T;
+};
+
+template <typename T>
+struct StorageTypeHelper<T, true, true> {
+  using Type = nsCOMPtr<T>;
+};
+
+template <typename T>
+struct StorageTypeHelper<nsCOMPtr<T>, true, true> {
+  using Type = nsCOMPtr<T>;
+};
+
+template <typename T>
+struct StorageTypeHelper<T*, true, false> {
+  using Type = RefPtr<T>;
+};
+
+template <typename T>
+struct StorageTypeHelper<JS::Handle<T>, false, false> {
+  using Type = JS::Heap<T>;
+};
+
+template <template <typename> class SmartPtr, typename T>
+struct StorageTypeHelper<SmartPtr<T>, true, false>
+    : std::enable_if<std::is_convertible_v<SmartPtr<T>, T*>, RefPtr<T>> {
+  using Type = typename StorageTypeHelper::enable_if::type;
+};
+
+template <typename T>
+using StorageType = typename StorageTypeHelper<std::decay_t<T>>::Type;
+
+// Helpers to choose the correct argument type based on the storage type. Smart
+// pointers are converted to the corresponding raw pointer type. Everything else
+// is passed by move reference.
+//
+// Note: We can't just use std::forward for this because the input type may be a
+// raw pointer which does not match the argument type, and while the
+// spec-compliant behavior there should still give us the expected results, MSVC
+// considers it an illegal use of std::forward.
+template <template <typename> class SmartPtr, typename T>
+decltype(std::declval<SmartPtr<T>>().get()) ArgType(SmartPtr<T>& aVal) {
+  return aVal.get();
+}
+
+template <typename T>
+T&& ArgType(T& aVal) {
+  return std::move(aVal);
+}
+
+using ::ImplCycleCollectionUnlink;
+
+template <typename ResolveCallback, typename RejectCallback, typename ArgsTuple,
+          typename JSArgsTuple>
+class NativeThenHandler;
+
+template <typename ResolveCallback, typename RejectCallback, typename... Args,
+          typename... JSArgs>
+class NativeThenHandler<ResolveCallback, RejectCallback, std::tuple<Args...>,
+                        std::tuple<JSArgs...>>
+    final : public PromiseNativeThenHandlerBase {
+ public:
+  /**
+   * @param aPromise A promise that will be settled by the result of the
+   * callbacks. Any thrown value to ErrorResult passed to those callbacks will
+   * be used to reject the promise, otherwise the promise will be resolved with
+   * the return value.
+   * @param aOnResolve A resolve callback
+   * @param aOnReject A reject callback
+   * @param aArgs The custom arguments to be passed to the both callbacks. The
+   * handler class will grab them to make them live long enough and to allow
+   * cycle collection.
+   * @param aJSArgs The JS arguments to be passed to the both callbacks, after
+   * native arguments. The handler will also grab them and allow garbage
+   * collection.
+   *
+   * XXX(krosylight): ideally there should be two signatures, with or without a
+   * promise parameter. Unfortunately doing so confuses the compiler and errors
+   * out, because nothing prevents promise from being ResolveCallback.
+   */
+  NativeThenHandler(Promise* aPromise, Maybe<ResolveCallback>&& aOnResolve,
+                    Maybe<RejectCallback>&& aOnReject,
+                    std::tuple<std::remove_reference_t<Args>...>&& aArgs,
+                    std::tuple<std::remove_reference_t<JSArgs>...>&& aJSArgs)
+      : PromiseNativeThenHandlerBase(aPromise),
+        mOnResolve(std::forward<Maybe<ResolveCallback>>(aOnResolve)),
+        mOnReject(std::forward<Maybe<RejectCallback>>(aOnReject)),
+        mArgs(std::forward<decltype(aArgs)>(aArgs)),
+        mJSArgs(std::forward<decltype(aJSArgs)>(aJSArgs)) {
+    if constexpr (std::tuple_size<decltype(mJSArgs)>::value > 0) {
+      mozilla::HoldJSObjects(this);
+    }
+  }
+
+ protected:
+  ~NativeThenHandler() override {
+    if constexpr (std::tuple_size<decltype(mJSArgs)>::value > 0) {
+      mozilla::DropJSObjects(this);
+    }
+  }
+
+  void Traverse(nsCycleCollectionTraversalCallback& cb) override {
+    auto* tmp = this;
+    NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mArgs)
+  }
+
+  void Unlink() override {
+    auto* tmp = this;
+    NS_IMPL_CYCLE_COLLECTION_UNLINK(mArgs)
+    NS_IMPL_CYCLE_COLLECTION_UNLINK(mJSArgs)
+  }
+
+  void Trace(const TraceCallbacks& aCallbacks, void* aClosure) override {
+    std::apply(
+        [&aCallbacks, aClosure](auto&&... aArgs) {
+          (aCallbacks.Trace(&aArgs, "mJSArgs[]", aClosure), ...);
+        },
+        mJSArgs);
+  }
+
+  bool HasResolvedCallback() override { return mOnResolve.isSome(); }
+  bool HasRejectedCallback() override { return mOnReject.isSome(); }
+
+  MOZ_CAN_RUN_SCRIPT already_AddRefed<Promise> CallResolveCallback(
+      JSContext* aCx, JS::Handle<JS::Value> aValue, ErrorResult& aRv) override {
+    return CallCallback(aCx, *mOnResolve, aValue, aRv);
+  }
+  MOZ_CAN_RUN_SCRIPT already_AddRefed<Promise> CallRejectCallback(
+      JSContext* aCx, JS::Handle<JS::Value> aValue, ErrorResult& aRv) override {
+    return CallCallback(aCx, *mOnReject, aValue, aRv);
+  }
+
+  // mJSArgs are marked with Trace() above, so they can be safely converted to
+  // Handles. But we should not circumvent the read barrier, so call
+  // exposeToActiveJS explicitly.
+  template <typename T>
+  static JS::Handle<T> GetJSArgHandleForCall(JS::Heap<T>& aArg) {
+    aArg.exposeToActiveJS();
+    return JS::Handle<T>::fromMarkedLocation(aArg.address());
+  }
+
+  template <typename TCallback, size_t... Indices, size_t... JSIndices>
+  MOZ_CAN_RUN_SCRIPT already_AddRefed<Promise> CallCallback(
+      JSContext* aCx, const TCallback& aHandler, JS::Handle<JS::Value> aValue,
+      ErrorResult& aRv, std::index_sequence<Indices...>,
+      std::index_sequence<JSIndices...>) {
+    return aHandler(aCx, aValue, aRv, ArgType(std::get<Indices>(mArgs))...,
+                    GetJSArgHandleForCall(std::get<JSIndices>(mJSArgs))...);
+  }
+
+  template <typename TCallback>
+  MOZ_CAN_RUN_SCRIPT already_AddRefed<Promise> CallCallback(
+      JSContext* aCx, const TCallback& aHandler, JS::Handle<JS::Value> aValue,
+      ErrorResult& aRv) {
+    return CallCallback(aCx, aHandler, aValue, aRv,
+                        std::index_sequence_for<Args...>{},
+                        std::index_sequence_for<JSArgs...>{});
+  }
+
+  Maybe<ResolveCallback> mOnResolve;
+  Maybe<RejectCallback> mOnReject;
+
+  std::tuple<StorageType<Args>...> mArgs;
+  std::tuple<StorageType<JSArgs>...> mJSArgs;
+};
+
+}  // anonymous namespace
+
+template <typename ResolveCallback, typename RejectCallback, typename... Args,
+          typename... JSArgs>
+Result<RefPtr<Promise>, nsresult>
+Promise::ThenCatchWithCycleCollectedArgsJSImpl(
+    Maybe<ResolveCallback>&& aOnResolve, Maybe<RejectCallback>&& aOnReject,
+    std::tuple<Args...>&& aArgs, std::tuple<JSArgs...>&& aJSArgs) {
+  using HandlerType =
+      NativeThenHandler<ResolveCallback, RejectCallback, std::tuple<Args...>,
+                        std::tuple<JSArgs...>>;
+
+  ErrorResult rv;
+  RefPtr<Promise> promise = Promise::Create(GetParentObject(), rv);
+  if (rv.Failed()) {
+    return Err(rv.StealNSResult());
+  }
+
+  auto* handler = new (fallible)
+      HandlerType(promise, std::forward<Maybe<ResolveCallback>>(aOnResolve),
+                  std::forward<Maybe<RejectCallback>>(aOnReject),
+                  std::forward<std::tuple<Args...>>(aArgs),
+                  std::forward<std::tuple<JSArgs...>>(aJSArgs));
+
+  if (!handler) {
+    return Err(NS_ERROR_OUT_OF_MEMORY);
+  }
+
+  AppendNativeHandler(handler);
+  return std::move(promise);
+}
+
+template <typename ResolveCallback, typename RejectCallback, typename... Args>
+Promise::ThenResult<ResolveCallback, Args...>
+Promise::ThenCatchWithCycleCollectedArgsImpl(
+    Maybe<ResolveCallback>&& aOnResolve, Maybe<RejectCallback>&& aOnReject,
+    Args&&... aArgs) {
+  return ThenCatchWithCycleCollectedArgsJSImpl(
+      std::forward<Maybe<ResolveCallback>>(aOnResolve),
+      std::forward<Maybe<RejectCallback>>(aOnReject),
+      std::make_tuple(std::forward<Args>(aArgs)...), std::make_tuple());
+}
+
+template <typename ResolveCallback, typename RejectCallback, typename... Args>
+Promise::ThenResult<ResolveCallback, Args...>
+Promise::ThenCatchWithCycleCollectedArgs(ResolveCallback&& aOnResolve,
+                                         RejectCallback&& aOnReject,
+                                         Args&&... aArgs) {
+  return ThenCatchWithCycleCollectedArgsImpl(Some(aOnResolve), Some(aOnReject),
+                                             std::forward<Args>(aArgs)...);
+}
+
+template <typename Callback, typename... Args>
+Promise::ThenResult<Callback, Args...> Promise::ThenWithCycleCollectedArgs(
+    Callback&& aOnResolve, Args&&... aArgs) {
+  return ThenCatchWithCycleCollectedArgsImpl(Some(aOnResolve),
+                                             Maybe<Callback>(Nothing()),
+                                             std::forward<Args>(aArgs)...);
+}
+
+template <typename Callback, typename... Args>
+Promise::ThenResult<Callback, Args...> Promise::CatchWithCycleCollectedArgs(
+    Callback&& aOnReject, Args&&... aArgs) {
+  return ThenCatchWithCycleCollectedArgsImpl(Maybe<Callback>(Nothing()),
+                                             Some(aOnReject),
+                                             std::forward<Args>(aArgs)...);
+}
+
+template <typename ResolveCallback, typename RejectCallback, typename ArgsTuple,
+          typename JSArgsTuple>
+Result<RefPtr<Promise>, nsresult> Promise::ThenCatchWithCycleCollectedArgsJS(
+    ResolveCallback&& aOnResolve, RejectCallback&& aOnReject, ArgsTuple&& aArgs,
+    JSArgsTuple&& aJSArgs) {
+  return ThenCatchWithCycleCollectedArgsJSImpl(
+      Some(aOnResolve), Some(aOnReject), std::forward<ArgsTuple>(aArgs),
+      std::forward<JSArgsTuple>(aJSArgs));
+}
+
+template <typename Callback, typename ArgsTuple, typename JSArgsTuple>
+Result<RefPtr<Promise>, nsresult> Promise::ThenWithCycleCollectedArgsJS(
+    Callback&& aOnResolve, ArgsTuple&& aArgs, JSArgsTuple&& aJSArgs) {
+  return ThenCatchWithCycleCollectedArgsJSImpl(
+      Some(aOnResolve), Maybe<Callback>(Nothing()),
+      std::forward<ArgsTuple>(aArgs), std::forward<JSArgsTuple>(aJSArgs));
+}
+
+template <typename ResolveCallback, typename RejectCallback, typename... Args>
+void Promise::AddCallbacksWithCycleCollectedArgs(ResolveCallback&& aOnResolve,
+                                                 RejectCallback&& aOnReject,
+                                                 Args&&... aArgs) {
+  auto onResolve =
+      [aOnResolve](JSContext* aCx, JS::Handle<JS::Value> value,
+                   ErrorResult& aRv,
+                   StorageType<Args>&&... aArgs) -> already_AddRefed<Promise> {
+    aOnResolve(aCx, value, aRv, aArgs...);
+    return nullptr;
+  };
+  auto onReject =
+      [aOnReject](JSContext* aCx, JS::Handle<JS::Value> value, ErrorResult& aRv,
+                  StorageType<Args>&&... aArgs) -> already_AddRefed<Promise> {
+    aOnReject(aCx, value, aRv, aArgs...);
+    return nullptr;
+  };
+
+  // Note: explicit template parameters for clang<7/gcc<8 without "Template
+  // argument deduction for class templates" support
+  AppendNativeHandler(
+      new NativeThenHandler<decltype(onResolve), decltype(onReject),
+                            std::tuple<Args...>, std::tuple<>>(
+          nullptr, Some(onResolve), Some(onReject),
+          std::make_tuple(std::forward<Args>(aArgs)...), std::make_tuple()));
+}
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_Promise_inl_h
diff --git a/dom/promise/Promise.cpp b/dom/promise/Promise.cpp
new file mode 100644
index 0000000000..941b2a7cc6
--- /dev/null
+++ b/dom/promise/Promise.cpp
@@ -0,0 +1,1109 @@
+/* -*- 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/Promise.h"
+#include "mozilla/dom/Promise-inl.h"
+
+#include "js/Debug.h"
+
+#include "mozilla/Atomics.h"
+#include "mozilla/BasePrincipal.h"
+#include "mozilla/CycleCollectedJSContext.h"
+#include "mozilla/HoldDropJSObjects.h"
+#include "mozilla/OwningNonNull.h"
+#include "mozilla/Preferences.h"
+#include "mozilla/ResultExtensions.h"
+#include "mozilla/Unused.h"
+
+#include "mozilla/dom/AutoEntryScript.h"
+#include "mozilla/dom/BindingUtils.h"
+#include "mozilla/dom/DOMException.h"
+#include "mozilla/dom/DOMExceptionBinding.h"
+#include "mozilla/dom/Exceptions.h"
+#include "mozilla/dom/MediaStreamError.h"
+#include "mozilla/dom/PromiseBinding.h"
+#include "mozilla/dom/ScriptSettings.h"
+#include "mozilla/dom/UserActivation.h"
+#include "mozilla/dom/WorkerPrivate.h"
+#include "mozilla/dom/WorkerRunnable.h"
+#include "mozilla/dom/WorkerRef.h"
+#include "mozilla/dom/WorkletImpl.h"
+#include "mozilla/dom/WorkletGlobalScope.h"
+
+#include "jsfriendapi.h"
+#include "js/Exception.h"  // JS::ExceptionStack
+#include "js/Object.h"     // JS::GetCompartment
+#include "js/StructuredClone.h"
+#include "nsContentUtils.h"
+#include "nsCycleCollectionParticipant.h"
+#include "nsDebug.h"
+#include "nsGlobalWindow.h"
+#include "nsIScriptObjectPrincipal.h"
+#include "nsJSEnvironment.h"
+#include "nsJSPrincipals.h"
+#include "nsJSUtils.h"
+#include "nsPIDOMWindow.h"
+#include "PromiseDebugging.h"
+#include "PromiseNativeHandler.h"
+#include "PromiseWorkerProxy.h"
+#include "WrapperFactory.h"
+#include "xpcpublic.h"
+#include "xpcprivate.h"
+
+namespace mozilla::dom {
+
+// Promise
+
+NS_IMPL_CYCLE_COLLECTION_SINGLE_ZONE_SCRIPT_HOLDER_CLASS(Promise)
+
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(Promise)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mGlobal)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK_WEAK_PTR
+  tmp->mPromiseObj = nullptr;
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(Promise)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mGlobal)
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN(Promise)
+  // If you add new JS member variables, you may need to stop using
+  // NS_IMPL_CYCLE_COLLECTION_SINGLE_ZONE_SCRIPT_HOLDER_CLASS.
+  NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBER_CALLBACK(mPromiseObj);
+NS_IMPL_CYCLE_COLLECTION_TRACE_END
+
+Promise::Promise(nsIGlobalObject* aGlobal)
+    : mGlobal(aGlobal), mPromiseObj(nullptr) {
+  MOZ_ASSERT(mGlobal);
+
+  mozilla::HoldJSObjects(this);
+}
+
+Promise::~Promise() { mozilla::DropJSObjects(this); }
+
+// static
+already_AddRefed<Promise> Promise::Create(
+    nsIGlobalObject* aGlobal, ErrorResult& aRv,
+    PropagateUserInteraction aPropagateUserInteraction) {
+  if (!aGlobal) {
+    aRv.Throw(NS_ERROR_UNEXPECTED);
+    return nullptr;
+  }
+  RefPtr<Promise> p = new Promise(aGlobal);
+  p->CreateWrapper(aRv, aPropagateUserInteraction);
+  if (aRv.Failed()) {
+    return nullptr;
+  }
+  return p.forget();
+}
+
+// static
+already_AddRefed<Promise> Promise::CreateInfallible(
+    nsIGlobalObject* aGlobal,
+    PropagateUserInteraction aPropagateUserInteraction) {
+  MOZ_ASSERT(aGlobal);
+  RefPtr<Promise> p = new Promise(aGlobal);
+  IgnoredErrorResult rv;
+  p->CreateWrapper(rv, aPropagateUserInteraction);
+  if (rv.Failed() && rv.ErrorCodeIs(NS_ERROR_OUT_OF_MEMORY)) {
+    MOZ_CRASH("Out of memory");
+  }
+
+  // We may have failed to init the wrapper here, because nsIGlobalObject had
+  // null GlobalJSObject. In that case we consider the JS realm is dead, which
+  // means:
+  // 1. This promise can't be settled.
+  // 2. Nothing can subscribe this promise anymore from that realm.
+  // Such condition makes this promise a no-op object.
+  (void)NS_WARN_IF(!p->PromiseObj());
+
+  return p.forget();
+}
+
+bool Promise::MaybePropagateUserInputEventHandling() {
+  MOZ_ASSERT(mPromiseObj,
+             "Should be called only if the wrapper is successfully created");
+  JS::PromiseUserInputEventHandlingState state =
+      UserActivation::IsHandlingUserInput()
+          ? JS::PromiseUserInputEventHandlingState::HadUserInteractionAtCreation
+          : JS::PromiseUserInputEventHandlingState::
+                DidntHaveUserInteractionAtCreation;
+  JS::Rooted<JSObject*> p(RootingCx(), mPromiseObj);
+  return JS::SetPromiseUserInputEventHandlingState(p, state);
+}
+
+// static
+already_AddRefed<Promise> Promise::Resolve(
+    nsIGlobalObject* aGlobal, JSContext* aCx, JS::Handle<JS::Value> aValue,
+    ErrorResult& aRv, PropagateUserInteraction aPropagateUserInteraction) {
+  JSAutoRealm ar(aCx, aGlobal->GetGlobalJSObject());
+  JS::Rooted<JSObject*> p(aCx, JS::CallOriginalPromiseResolve(aCx, aValue));
+  if (!p) {
+    aRv.NoteJSContextException(aCx);
+    return nullptr;
+  }
+
+  return CreateFromExisting(aGlobal, p, aPropagateUserInteraction);
+}
+
+// static
+already_AddRefed<Promise> Promise::Reject(nsIGlobalObject* aGlobal,
+                                          JSContext* aCx,
+                                          JS::Handle<JS::Value> aValue,
+                                          ErrorResult& aRv) {
+  JSAutoRealm ar(aCx, aGlobal->GetGlobalJSObject());
+  JS::Rooted<JSObject*> p(aCx, JS::CallOriginalPromiseReject(aCx, aValue));
+  if (!p) {
+    aRv.NoteJSContextException(aCx);
+    return nullptr;
+  }
+
+  // This promise will never be resolved, so we pass
+  // eDontPropagateUserInteraction for aPropagateUserInteraction
+  // unconditionally.
+  return CreateFromExisting(aGlobal, p, eDontPropagateUserInteraction);
+}
+
+// static
+already_AddRefed<Promise> Promise::All(
+    JSContext* aCx, const nsTArray<RefPtr<Promise>>& aPromiseList,
+    ErrorResult& aRv, PropagateUserInteraction aPropagateUserInteraction) {
+  JS::Rooted<JSObject*> globalObj(aCx, JS::CurrentGlobalOrNull(aCx));
+  if (!globalObj) {
+    aRv.Throw(NS_ERROR_UNEXPECTED);
+    return nullptr;
+  }
+
+  nsCOMPtr<nsIGlobalObject> global = xpc::NativeGlobal(globalObj);
+  if (!global) {
+    aRv.Throw(NS_ERROR_UNEXPECTED);
+    return nullptr;
+  }
+
+  JS::RootedVector<JSObject*> promises(aCx);
+  if (!promises.reserve(aPromiseList.Length())) {
+    aRv.NoteJSContextException(aCx);
+    return nullptr;
+  }
+
+  for (const auto& promise : aPromiseList) {
+    JS::Rooted<JSObject*> promiseObj(aCx, promise->PromiseObj());
+    if (!promiseObj) {
+      // No-op object will never settle, so we return a no-op Promise here,
+      // which is equivalent of returning the existing no-op one.
+      return do_AddRef(promise);
+    }
+    // Just in case, make sure these are all in the context compartment.
+    if (!JS_WrapObject(aCx, &promiseObj)) {
+      aRv.NoteJSContextException(aCx);
+      return nullptr;
+    }
+    promises.infallibleAppend(promiseObj);
+  }
+
+  JS::Rooted<JSObject*> result(aCx, JS::GetWaitForAllPromise(aCx, promises));
+  if (!result) {
+    aRv.NoteJSContextException(aCx);
+    return nullptr;
+  }
+
+  return CreateFromExisting(global, result, aPropagateUserInteraction);
+}
+
+void Promise::Then(JSContext* aCx,
+                   // aCalleeGlobal may not be in the compartment of aCx, when
+                   // called over Xrays.
+                   JS::Handle<JSObject*> aCalleeGlobal,
+                   AnyCallback* aResolveCallback, AnyCallback* aRejectCallback,
+                   JS::MutableHandle<JS::Value> aRetval, ErrorResult& aRv) {
+  NS_ASSERT_OWNINGTHREAD(Promise);
+
+  // Let's hope this does the right thing with Xrays...  Ensure everything is
+  // just in the caller compartment; that ought to do the trick.  In theory we
+  // should consider aCalleeGlobal, but in practice our only caller is
+  // DOMRequest::Then, which is not working with a Promise subclass, so things
+  // should be OK.
+  JS::Rooted<JSObject*> promise(aCx, PromiseObj());
+  if (!promise) {
+    // This promise is no-op, so do nothing.
+    return;
+  }
+
+  if (!JS_WrapObject(aCx, &promise)) {
+    aRv.NoteJSContextException(aCx);
+    return;
+  }
+
+  JS::Rooted<JSObject*> resolveCallback(aCx);
+  if (aResolveCallback) {
+    resolveCallback = aResolveCallback->CallbackOrNull();
+    if (!JS_WrapObject(aCx, &resolveCallback)) {
+      aRv.NoteJSContextException(aCx);
+      return;
+    }
+  }
+
+  JS::Rooted<JSObject*> rejectCallback(aCx);
+  if (aRejectCallback) {
+    rejectCallback = aRejectCallback->CallbackOrNull();
+    if (!JS_WrapObject(aCx, &rejectCallback)) {
+      aRv.NoteJSContextException(aCx);
+      return;
+    }
+  }
+
+  JS::Rooted<JSObject*> retval(aCx);
+  retval = JS::CallOriginalPromiseThen(aCx, promise, resolveCallback,
+                                       rejectCallback);
+  if (!retval) {
+    aRv.NoteJSContextException(aCx);
+    return;
+  }
+
+  aRetval.setObject(*retval);
+}
+
+static void SettlePromise(Promise* aSettlingPromise, Promise* aCallbackPromise,
+                          ErrorResult& aRv) {
+  if (!aSettlingPromise) {
+    return;
+  }
+  if (aRv.IsUncatchableException()) {
+    return;
+  }
+  if (aRv.Failed()) {
+    aSettlingPromise->MaybeReject(std::move(aRv));
+    return;
+  }
+  if (aCallbackPromise) {
+    aSettlingPromise->MaybeResolve(aCallbackPromise);
+  } else {
+    aSettlingPromise->MaybeResolveWithUndefined();
+  }
+}
+
+void PromiseNativeThenHandlerBase::ResolvedCallback(
+    JSContext* aCx, JS::Handle<JS::Value> aValue, ErrorResult& aRv) {
+  if (!HasResolvedCallback()) {
+    mPromise->MaybeResolve(aValue);
+    return;
+  }
+  RefPtr<Promise> promise = CallResolveCallback(aCx, aValue, aRv);
+  SettlePromise(mPromise, promise, aRv);
+}
+
+void PromiseNativeThenHandlerBase::RejectedCallback(
+    JSContext* aCx, JS::Handle<JS::Value> aValue, ErrorResult& aRv) {
+  if (!HasRejectedCallback()) {
+    mPromise->MaybeReject(aValue);
+    return;
+  }
+  RefPtr<Promise> promise = CallRejectCallback(aCx, aValue, aRv);
+  SettlePromise(mPromise, promise, aRv);
+}
+
+NS_IMPL_CYCLE_COLLECTION_CLASS(PromiseNativeThenHandlerBase)
+
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(PromiseNativeThenHandlerBase)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mPromise)
+  tmp->Traverse(cb);
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(PromiseNativeThenHandlerBase)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mPromise)
+  tmp->Unlink();
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(PromiseNativeThenHandlerBase)
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+NS_INTERFACE_MAP_END
+
+NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN(PromiseNativeThenHandlerBase)
+  tmp->Trace(aCallbacks, aClosure);
+NS_IMPL_CYCLE_COLLECTION_TRACE_END
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(PromiseNativeThenHandlerBase)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(PromiseNativeThenHandlerBase)
+
+Result<RefPtr<Promise>, nsresult> Promise::ThenWithoutCycleCollection(
+    const std::function<already_AddRefed<Promise>(
+        JSContext* aCx, JS::Handle<JS::Value> aValue, ErrorResult& aRv)>&
+        aCallback) {
+  return ThenWithCycleCollectedArgs(aCallback);
+}
+
+void Promise::CreateWrapper(
+    ErrorResult& aRv, PropagateUserInteraction aPropagateUserInteraction) {
+  AutoJSAPI jsapi;
+  if (!jsapi.Init(mGlobal)) {
+    aRv.Throw(NS_ERROR_UNEXPECTED);
+    return;
+  }
+  JSContext* cx = jsapi.cx();
+  mPromiseObj = JS::NewPromiseObject(cx, nullptr);
+  if (!mPromiseObj) {
+    JS_ClearPendingException(cx);
+    aRv.Throw(NS_ERROR_OUT_OF_MEMORY);
+    return;
+  }
+  if (aPropagateUserInteraction == ePropagateUserInteraction) {
+    Unused << MaybePropagateUserInputEventHandling();
+  }
+}
+
+void Promise::MaybeResolve(JSContext* aCx, JS::Handle<JS::Value> aValue) {
+  NS_ASSERT_OWNINGTHREAD(Promise);
+
+  JS::Rooted<JSObject*> p(aCx, PromiseObj());
+  if (!p || !JS::ResolvePromise(aCx, p, aValue)) {
+    // Now what?  There's nothing sane to do here.
+    JS_ClearPendingException(aCx);
+  }
+}
+
+void Promise::MaybeReject(JSContext* aCx, JS::Handle<JS::Value> aValue) {
+  NS_ASSERT_OWNINGTHREAD(Promise);
+
+  JS::Rooted<JSObject*> p(aCx, PromiseObj());
+  if (!p || !JS::RejectPromise(aCx, p, aValue)) {
+    // Now what?  There's nothing sane to do here.
+    JS_ClearPendingException(aCx);
+  }
+}
+
+#define SLOT_NATIVEHANDLER 0
+#define SLOT_NATIVEHANDLER_TASK 1
+
+enum class NativeHandlerTask : int32_t { Resolve, Reject };
+
+MOZ_CAN_RUN_SCRIPT
+static bool NativeHandlerCallback(JSContext* aCx, unsigned aArgc,
+                                  JS::Value* aVp) {
+  JS::CallArgs args = CallArgsFromVp(aArgc, aVp);
+
+  JS::Value v =
+      js::GetFunctionNativeReserved(&args.callee(), SLOT_NATIVEHANDLER);
+  MOZ_ASSERT(v.isObject());
+
+  JS::Rooted<JSObject*> obj(aCx, &v.toObject());
+  PromiseNativeHandler* handler = nullptr;
+  if (NS_FAILED(UNWRAP_OBJECT(PromiseNativeHandler, &obj, handler))) {
+    return Throw(aCx, NS_ERROR_UNEXPECTED);
+  }
+
+  v = js::GetFunctionNativeReserved(&args.callee(), SLOT_NATIVEHANDLER_TASK);
+  NativeHandlerTask task = static_cast<NativeHandlerTask>(v.toInt32());
+
+  ErrorResult rv;
+  if (task == NativeHandlerTask::Resolve) {
+    // handler is kept alive by "obj" on the stack.
+    MOZ_KnownLive(handler)->ResolvedCallback(aCx, args.get(0), rv);
+  } else {
+    MOZ_ASSERT(task == NativeHandlerTask::Reject);
+    // handler is kept alive by "obj" on the stack.
+    MOZ_KnownLive(handler)->RejectedCallback(aCx, args.get(0), rv);
+  }
+
+  return !rv.MaybeSetPendingException(aCx);
+}
+
+static JSObject* CreateNativeHandlerFunction(JSContext* aCx,
+                                             JS::Handle<JSObject*> aHolder,
+                                             NativeHandlerTask aTask) {
+  JSFunction* func = js::NewFunctionWithReserved(aCx, NativeHandlerCallback,
+                                                 /* nargs = */ 1,
+                                                 /* flags = */ 0, nullptr);
+  if (!func) {
+    return nullptr;
+  }
+
+  JS::Rooted<JSObject*> obj(aCx, JS_GetFunctionObject(func));
+
+  JS::AssertObjectIsNotGray(aHolder);
+  js::SetFunctionNativeReserved(obj, SLOT_NATIVEHANDLER,
+                                JS::ObjectValue(*aHolder));
+  js::SetFunctionNativeReserved(obj, SLOT_NATIVEHANDLER_TASK,
+                                JS::Int32Value(static_cast<int32_t>(aTask)));
+
+  return obj;
+}
+
+namespace {
+
+class PromiseNativeHandlerShim final : public PromiseNativeHandler {
+  RefPtr<PromiseNativeHandler> mInner;
+#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
+  enum InnerState{
+      NotCleared,
+      ClearedFromResolve,
+      ClearedFromReject,
+      ClearedFromCC,
+  };
+  InnerState mState = NotCleared;
+#endif
+
+  ~PromiseNativeHandlerShim() = default;
+
+ public:
+  explicit PromiseNativeHandlerShim(PromiseNativeHandler* aInner)
+      : mInner(aInner) {
+    MOZ_DIAGNOSTIC_ASSERT(mInner);
+  }
+
+  MOZ_CAN_RUN_SCRIPT
+  void ResolvedCallback(JSContext* aCx, JS::Handle<JS::Value> aValue,
+                        ErrorResult& aRv) override {
+#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
+    MOZ_DIAGNOSTIC_ASSERT(mState != ClearedFromResolve);
+    MOZ_DIAGNOSTIC_ASSERT(mState != ClearedFromReject);
+    MOZ_DIAGNOSTIC_ASSERT(mState != ClearedFromCC);
+#else
+    if (!mInner) {
+      return;
+    }
+#endif
+    RefPtr<PromiseNativeHandler> inner = std::move(mInner);
+    inner->ResolvedCallback(aCx, aValue, aRv);
+    MOZ_ASSERT(!mInner);
+#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
+    mState = ClearedFromResolve;
+#endif
+  }
+
+  MOZ_CAN_RUN_SCRIPT
+  void RejectedCallback(JSContext* aCx, JS::Handle<JS::Value> aValue,
+                        ErrorResult& aRv) override {
+#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
+    MOZ_DIAGNOSTIC_ASSERT(mState != ClearedFromResolve);
+    MOZ_DIAGNOSTIC_ASSERT(mState != ClearedFromReject);
+    MOZ_DIAGNOSTIC_ASSERT(mState != ClearedFromCC);
+#else
+    if (!mInner) {
+      return;
+    }
+#endif
+    RefPtr<PromiseNativeHandler> inner = std::move(mInner);
+    inner->RejectedCallback(aCx, aValue, aRv);
+    MOZ_ASSERT(!mInner);
+#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
+    mState = ClearedFromReject;
+#endif
+  }
+
+  bool WrapObject(JSContext* aCx, JS::Handle<JSObject*> aGivenProto,
+                  JS::MutableHandle<JSObject*> aWrapper) {
+    return PromiseNativeHandler_Binding::Wrap(aCx, this, aGivenProto, aWrapper);
+  }
+
+  NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+  NS_DECL_CYCLE_COLLECTION_CLASS(PromiseNativeHandlerShim)
+};
+
+NS_IMPL_CYCLE_COLLECTION_CLASS(PromiseNativeHandlerShim)
+NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(PromiseNativeHandlerShim)
+  NS_IMPL_CYCLE_COLLECTION_UNLINK(mInner)
+#ifdef MOZ_DIAGNOSTIC_ASSERT_ENABLED
+  tmp->mState = ClearedFromCC;
+#endif
+NS_IMPL_CYCLE_COLLECTION_UNLINK_END
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(PromiseNativeHandlerShim)
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mInner)
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+NS_IMPL_CYCLE_COLLECTING_ADDREF(PromiseNativeHandlerShim)
+NS_IMPL_CYCLE_COLLECTING_RELEASE(PromiseNativeHandlerShim)
+
+NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(PromiseNativeHandlerShim)
+  NS_INTERFACE_MAP_ENTRY(nsISupports)
+NS_INTERFACE_MAP_END
+
+}  // anonymous namespace
+
+void Promise::AppendNativeHandler(PromiseNativeHandler* aRunnable) {
+  NS_ASSERT_OWNINGTHREAD(Promise);
+
+  AutoJSAPI jsapi;
+  if (NS_WARN_IF(!mPromiseObj || !jsapi.Init(mGlobal))) {
+    // Our API doesn't allow us to return a useful error.  Not like this should
+    // happen anyway.
+    return;
+  }
+
+  // The self-hosted promise js may keep the object we pass to it alive
+  // for quite a while depending on when GC runs.  Therefore, pass a shim
+  // object instead.  The shim will free its inner PromiseNativeHandler
+  // after the promise has settled just like our previous c++ promises did.
+  RefPtr<PromiseNativeHandlerShim> shim =
+      new PromiseNativeHandlerShim(aRunnable);
+
+  JSContext* cx = jsapi.cx();
+  JS::Rooted<JSObject*> handlerWrapper(cx);
+  // Note: PromiseNativeHandler is NOT wrappercached.  So we can't use
+  // ToJSValue here, because it will try to do XPConnect wrapping on it, sadly.
+  if (NS_WARN_IF(!shim->WrapObject(cx, nullptr, &handlerWrapper))) {
+    // Again, no way to report errors.
+    jsapi.ClearException();
+    return;
+  }
+
+  JS::Rooted<JSObject*> resolveFunc(cx);
+  resolveFunc = CreateNativeHandlerFunction(cx, handlerWrapper,
+                                            NativeHandlerTask::Resolve);
+  if (NS_WARN_IF(!resolveFunc)) {
+    jsapi.ClearException();
+    return;
+  }
+
+  JS::Rooted<JSObject*> rejectFunc(cx);
+  rejectFunc = CreateNativeHandlerFunction(cx, handlerWrapper,
+                                           NativeHandlerTask::Reject);
+  if (NS_WARN_IF(!rejectFunc)) {
+    jsapi.ClearException();
+    return;
+  }
+
+  JS::Rooted<JSObject*> promiseObj(cx, PromiseObj());
+  if (NS_WARN_IF(
+          !JS::AddPromiseReactions(cx, promiseObj, resolveFunc, rejectFunc))) {
+    jsapi.ClearException();
+    return;
+  }
+}
+
+void Promise::HandleException(JSContext* aCx) {
+  JS::Rooted<JS::Value> exn(aCx);
+  if (JS_GetPendingException(aCx, &exn)) {
+    JS_ClearPendingException(aCx);
+    // Always reject even if this was called in *Resolve.
+    MaybeReject(aCx, exn);
+  }
+}
+
+// static
+already_AddRefed<Promise> Promise::RejectWithExceptionFromContext(
+    nsIGlobalObject* aGlobal, JSContext* aCx, ErrorResult& aError) {
+  JS::Rooted<JS::Value> exn(aCx);
+  if (!JS_GetPendingException(aCx, &exn)) {
+    // This is very important: if there is no pending exception here but we're
+    // ending up in this code, that means the callee threw an uncatchable
+    // exception.  Just propagate that out as-is.
+    aError.ThrowUncatchableException();
+    return nullptr;
+  }
+
+  JSAutoRealm ar(aCx, aGlobal->GetGlobalJSObject());
+  if (!JS_WrapValue(aCx, &exn)) {
+    // We just give up.
+    aError.StealExceptionFromJSContext(aCx);
+    return nullptr;
+  }
+
+  JS_ClearPendingException(aCx);
+
+  IgnoredErrorResult error;
+  RefPtr<Promise> promise = Promise::Reject(aGlobal, aCx, exn, error);
+  if (!promise) {
+    // We just give up, let's store the exception in the ErrorResult.
+    aError.ThrowJSException(aCx, exn);
+    return nullptr;
+  }
+
+  return promise.forget();
+}
+
+// static
+already_AddRefed<Promise> Promise::CreateFromExisting(
+    nsIGlobalObject* aGlobal, JS::Handle<JSObject*> aPromiseObj,
+    PropagateUserInteraction aPropagateUserInteraction) {
+  MOZ_ASSERT(JS::GetCompartment(aGlobal->GetGlobalJSObjectPreserveColor()) ==
+             JS::GetCompartment(aPromiseObj));
+  RefPtr<Promise> p = new Promise(aGlobal);
+  p->mPromiseObj = aPromiseObj;
+  if (aPropagateUserInteraction == ePropagateUserInteraction &&
+      !p->MaybePropagateUserInputEventHandling()) {
+    return nullptr;
+  }
+  return p.forget();
+}
+
+void Promise::MaybeResolveWithUndefined() {
+  NS_ASSERT_OWNINGTHREAD(Promise);
+
+  MaybeResolve(JS::UndefinedHandleValue);
+}
+
+void Promise::MaybeReject(const RefPtr<MediaStreamError>& aArg) {
+  NS_ASSERT_OWNINGTHREAD(Promise);
+
+  MaybeSomething(aArg, &Promise::MaybeReject);
+}
+
+void Promise::MaybeRejectWithUndefined() {
+  NS_ASSERT_OWNINGTHREAD(Promise);
+
+  MaybeSomething(JS::UndefinedHandleValue, &Promise::MaybeReject);
+}
+
+void Promise::ReportRejectedPromise(JSContext* aCx,
+                                    JS::Handle<JSObject*> aPromise) {
+  MOZ_ASSERT(!js::IsWrapper(aPromise));
+
+  MOZ_ASSERT(JS::GetPromiseState(aPromise) == JS::PromiseState::Rejected);
+
+  bool isChrome = false;
+  uint64_t innerWindowID = 0;
+  nsGlobalWindowInner* winForDispatch = nullptr;
+  if (MOZ_LIKELY(NS_IsMainThread())) {
+    isChrome = nsContentUtils::ObjectPrincipal(aPromise)->IsSystemPrincipal();
+
+    if (nsGlobalWindowInner* win = xpc::WindowGlobalOrNull(aPromise)) {
+      winForDispatch = win;
+      innerWindowID = win->WindowID();
+    } else if (nsGlobalWindowInner* win = xpc::SandboxWindowOrNull(
+                   JS::GetNonCCWObjectGlobal(aPromise), aCx)) {
+      // Don't dispatch rejections from the sandbox to the associated DOM
+      // window.
+      innerWindowID = win->WindowID();
+    }
+  } else if (const WorkerPrivate* wp = GetCurrentThreadWorkerPrivate()) {
+    isChrome = wp->UsesSystemPrincipal();
+    innerWindowID = wp->WindowID();
+  } else if (nsCOMPtr<nsIGlobalObject> global = xpc::NativeGlobal(aPromise)) {
+    if (nsCOMPtr<WorkletGlobalScope> workletGlobal =
+            do_QueryInterface(global)) {
+      WorkletImpl* impl = workletGlobal->Impl();
+      isChrome = impl->PrincipalInfo().type() ==
+                 mozilla::ipc::PrincipalInfo::TSystemPrincipalInfo;
+      innerWindowID = impl->LoadInfo().InnerWindowID();
+    }
+  }
+
+  JS::Rooted<JS::Value> result(aCx, JS::GetPromiseResult(aPromise));
+  // resolutionSite can be null if async stacks are disabled.
+  JS::Rooted<JSObject*> resolutionSite(aCx,
+                                       JS::GetPromiseResolutionSite(aPromise));
+
+  // We're inspecting the rejection value only to report it to the console, and
+  // we do so without side-effects, so we can safely unwrap it without regard to
+  // the privileges of the Promise object that holds it. If we don't unwrap
+  // before trying to create the error report, we wind up reporting any
+  // cross-origin objects as "uncaught exception: Object".
+  RefPtr<xpc::ErrorReport> xpcReport = new xpc::ErrorReport();
+  {
+    Maybe<JSAutoRealm> ar;
+    JS::Rooted<JS::Value> unwrapped(aCx, result);
+    if (unwrapped.isObject()) {
+      unwrapped.setObject(*js::UncheckedUnwrap(&unwrapped.toObject()));
+      ar.emplace(aCx, &unwrapped.toObject());
+    }
+
+    JS::ErrorReportBuilder report(aCx);
+    RefPtr<Exception> exn;
+    if (unwrapped.isObject() &&
+        (NS_SUCCEEDED(UNWRAP_OBJECT(DOMException, &unwrapped, exn)) ||
+         NS_SUCCEEDED(UNWRAP_OBJECT(Exception, &unwrapped, exn)))) {
+      xpcReport->Init(aCx, exn, isChrome, innerWindowID);
+    } else {
+      // Use the resolution site as the exception stack
+      JS::ExceptionStack exnStack(aCx, unwrapped, resolutionSite);
+      if (!report.init(aCx, exnStack, JS::ErrorReportBuilder::NoSideEffects)) {
+        JS_ClearPendingException(aCx);
+        return;
+      }
+
+      xpcReport->Init(report.report(), report.toStringResult().c_str(),
+                      isChrome, innerWindowID);
+    }
+  }
+
+  // Used to initialize the similarly named nsISciptError attribute.
+  xpcReport->mIsPromiseRejection = true;
+
+  // Now post an event to do the real reporting async
+  RefPtr<AsyncErrorReporter> event = new AsyncErrorReporter(xpcReport);
+  if (winForDispatch) {
+    if (!winForDispatch->IsDying()) {
+      // Exceptions from a dying window will cause the window to leak.
+      event->SetException(aCx, result);
+      if (resolutionSite) {
+        event->SerializeStack(aCx, resolutionSite);
+      }
+    }
+    winForDispatch->Dispatch(mozilla::TaskCategory::Other, event.forget());
+  } else {
+    NS_DispatchToMainThread(event);
+  }
+}
+
+void Promise::MaybeResolveWithClone(JSContext* aCx,
+                                    JS::Handle<JS::Value> aValue) {
+  JS::Rooted<JSObject*> sourceScope(aCx, JS::CurrentGlobalOrNull(aCx));
+  AutoEntryScript aes(GetParentObject(), "Promise resolution");
+  JSContext* cx = aes.cx();
+  JS::Rooted<JS::Value> value(cx, aValue);
+
+  xpc::StackScopedCloneOptions options;
+  options.wrapReflectors = true;
+  if (!StackScopedClone(cx, options, sourceScope, &value)) {
+    HandleException(cx);
+    return;
+  }
+  MaybeResolve(aCx, value);
+}
+
+void Promise::MaybeRejectWithClone(JSContext* aCx,
+                                   JS::Handle<JS::Value> aValue) {
+  JS::Rooted<JSObject*> sourceScope(aCx, JS::CurrentGlobalOrNull(aCx));
+  AutoEntryScript aes(GetParentObject(), "Promise rejection");
+  JSContext* cx = aes.cx();
+  JS::Rooted<JS::Value> value(cx, aValue);
+
+  xpc::StackScopedCloneOptions options;
+  options.wrapReflectors = true;
+  if (!StackScopedClone(cx, options, sourceScope, &value)) {
+    HandleException(cx);
+    return;
+  }
+  MaybeReject(aCx, value);
+}
+
+// A WorkerRunnable to resolve/reject the Promise on the worker thread.
+// Calling thread MUST hold PromiseWorkerProxy's mutex before creating this.
+class PromiseWorkerProxyRunnable : public WorkerRunnable {
+ public:
+  PromiseWorkerProxyRunnable(PromiseWorkerProxy* aPromiseWorkerProxy,
+                             PromiseWorkerProxy::RunCallbackFunc aFunc)
+      : WorkerRunnable(aPromiseWorkerProxy->GetWorkerPrivate(),
+                       WorkerThreadUnchangedBusyCount),
+        mPromiseWorkerProxy(aPromiseWorkerProxy),
+        mFunc(aFunc) {
+    MOZ_ASSERT(NS_IsMainThread());
+    MOZ_ASSERT(mPromiseWorkerProxy);
+  }
+
+  virtual bool WorkerRun(JSContext* aCx,
+                         WorkerPrivate* aWorkerPrivate) override {
+    MOZ_ASSERT(aWorkerPrivate);
+    aWorkerPrivate->AssertIsOnWorkerThread();
+    MOZ_ASSERT(aWorkerPrivate == mWorkerPrivate);
+
+    MOZ_ASSERT(mPromiseWorkerProxy);
+    RefPtr<Promise> workerPromise = mPromiseWorkerProxy->WorkerPromise();
+
+    // Here we convert the buffer to a JS::Value.
+    JS::Rooted<JS::Value> value(aCx);
+    if (!mPromiseWorkerProxy->Read(aCx, &value)) {
+      JS_ClearPendingException(aCx);
+      return false;
+    }
+
+    (workerPromise->*mFunc)(aCx, value);
+
+    // Release the Promise because it has been resolved/rejected for sure.
+    mPromiseWorkerProxy->CleanUp();
+    return true;
+  }
+
+ protected:
+  ~PromiseWorkerProxyRunnable() = default;
+
+ private:
+  RefPtr<PromiseWorkerProxy> mPromiseWorkerProxy;
+
+  // Function pointer for calling Promise::{ResolveInternal,RejectInternal}.
+  PromiseWorkerProxy::RunCallbackFunc mFunc;
+};
+
+/* static */
+already_AddRefed<PromiseWorkerProxy> PromiseWorkerProxy::Create(
+    WorkerPrivate* aWorkerPrivate, Promise* aWorkerPromise,
+    const PromiseWorkerProxyStructuredCloneCallbacks* aCb) {
+  MOZ_ASSERT(aWorkerPrivate);
+  aWorkerPrivate->AssertIsOnWorkerThread();
+  MOZ_ASSERT(aWorkerPromise);
+  MOZ_ASSERT_IF(aCb, !!aCb->Write && !!aCb->Read);
+
+  RefPtr<PromiseWorkerProxy> proxy =
+      new PromiseWorkerProxy(aWorkerPromise, aCb);
+
+  // Maintain a reference so that we have a valid object to clean up when
+  // removing the feature.
+  proxy.get()->AddRef();
+
+  // We do this to make sure the worker thread won't shut down before the
+  // promise is resolved/rejected on the worker thread.
+  RefPtr<StrongWorkerRef> workerRef = StrongWorkerRef::Create(
+      aWorkerPrivate, "PromiseWorkerProxy", [proxy]() { proxy->CleanUp(); });
+
+  if (NS_WARN_IF(!workerRef)) {
+    // Probably the worker is terminating. We cannot complete the operation
+    // and we have to release all the resources.  CleanUp releases the extra
+    // ref, too
+    proxy->CleanUp();
+    return nullptr;
+  }
+
+  proxy->mWorkerRef = new ThreadSafeWorkerRef(workerRef);
+
+  return proxy.forget();
+}
+
+NS_IMPL_ISUPPORTS0(PromiseWorkerProxy)
+
+PromiseWorkerProxy::PromiseWorkerProxy(
+    Promise* aWorkerPromise,
+    const PromiseWorkerProxyStructuredCloneCallbacks* aCallbacks)
+    : mWorkerPromise(aWorkerPromise),
+      mCleanedUp(false),
+      mCallbacks(aCallbacks),
+      mCleanUpLock("cleanUpLock") {}
+
+PromiseWorkerProxy::~PromiseWorkerProxy() {
+  MOZ_ASSERT(mCleanedUp);
+  MOZ_ASSERT(!mWorkerPromise);
+  MOZ_ASSERT(!mWorkerRef);
+}
+
+WorkerPrivate* PromiseWorkerProxy::GetWorkerPrivate() const {
+#ifdef DEBUG
+  if (NS_IsMainThread()) {
+    mCleanUpLock.AssertCurrentThreadOwns();
+  }
+#endif
+  // Safe to check this without a lock since we assert lock ownership on the
+  // main thread above.
+  MOZ_ASSERT(!mCleanedUp);
+  MOZ_ASSERT(mWorkerRef);
+
+  return mWorkerRef->Private();
+}
+
+bool PromiseWorkerProxy::OnWritingThread() const {
+  return IsCurrentThreadRunningWorker();
+}
+
+Promise* PromiseWorkerProxy::WorkerPromise() const {
+  MOZ_ASSERT(IsCurrentThreadRunningWorker());
+  MOZ_ASSERT(mWorkerPromise);
+  return mWorkerPromise;
+}
+
+void PromiseWorkerProxy::RunCallback(JSContext* aCx,
+                                     JS::Handle<JS::Value> aValue,
+                                     RunCallbackFunc aFunc) {
+  MOZ_ASSERT(NS_IsMainThread());
+
+  MutexAutoLock lock(Lock());
+  // If the worker thread's been cancelled we don't need to resolve the Promise.
+  if (CleanedUp()) {
+    return;
+  }
+
+  // The |aValue| is written into the StructuredCloneHolderBase.
+  if (!Write(aCx, aValue)) {
+    JS_ClearPendingException(aCx);
+    MOZ_ASSERT(false,
+               "cannot serialize the value with the StructuredCloneAlgorithm!");
+  }
+
+  RefPtr<PromiseWorkerProxyRunnable> runnable =
+      new PromiseWorkerProxyRunnable(this, aFunc);
+
+  runnable->Dispatch();
+}
+
+void PromiseWorkerProxy::ResolvedCallback(JSContext* aCx,
+                                          JS::Handle<JS::Value> aValue,
+                                          ErrorResult& aRv) {
+  RunCallback(aCx, aValue, &Promise::MaybeResolve);
+}
+
+void PromiseWorkerProxy::RejectedCallback(JSContext* aCx,
+                                          JS::Handle<JS::Value> aValue,
+                                          ErrorResult& aRv) {
+  RunCallback(aCx, aValue, &Promise::MaybeReject);
+}
+
+void PromiseWorkerProxy::CleanUp() {
+  // Can't release Mutex while it is still locked, so scope the lock.
+  {
+    MutexAutoLock lock(Lock());
+
+    if (CleanedUp()) {
+      return;
+    }
+
+    // We can be called if we failed to get a WorkerRef
+    if (mWorkerRef) {
+      mWorkerRef->Private()->AssertIsOnWorkerThread();
+    }
+
+    // Release the Promise and remove the PromiseWorkerProxy from the holders of
+    // the worker thread since the Promise has been resolved/rejected or the
+    // worker thread has been cancelled.
+    mCleanedUp = true;
+    mWorkerPromise = nullptr;
+    mWorkerRef = nullptr;
+
+    // Clear the StructuredCloneHolderBase class.
+    Clear();
+  }
+  Release();
+}
+
+JSObject* PromiseWorkerProxy::CustomReadHandler(
+    JSContext* aCx, JSStructuredCloneReader* aReader,
+    const JS::CloneDataPolicy& aCloneDataPolicy, uint32_t aTag,
+    uint32_t aIndex) {
+  if (NS_WARN_IF(!mCallbacks)) {
+    return nullptr;
+  }
+
+  return mCallbacks->Read(aCx, aReader, this, aTag, aIndex);
+}
+
+bool PromiseWorkerProxy::CustomWriteHandler(JSContext* aCx,
+                                            JSStructuredCloneWriter* aWriter,
+                                            JS::Handle<JSObject*> aObj,
+                                            bool* aSameProcessScopeRequired) {
+  if (NS_WARN_IF(!mCallbacks)) {
+    return false;
+  }
+
+  return mCallbacks->Write(aCx, aWriter, this, aObj);
+}
+
+// Specializations of MaybeRejectBrokenly we actually support.
+template <>
+void Promise::MaybeRejectBrokenly(const RefPtr<DOMException>& aArg) {
+  MaybeSomething(aArg, &Promise::MaybeReject);
+}
+template <>
+void Promise::MaybeRejectBrokenly(const nsAString& aArg) {
+  MaybeSomething(aArg, &Promise::MaybeReject);
+}
+
+Promise::PromiseState Promise::State() const {
+  JS::Rooted<JSObject*> p(RootingCx(), PromiseObj());
+  const JS::PromiseState state = JS::GetPromiseState(p);
+
+  if (state == JS::PromiseState::Fulfilled) {
+    return PromiseState::Resolved;
+  }
+
+  if (state == JS::PromiseState::Rejected) {
+    return PromiseState::Rejected;
+  }
+
+  return PromiseState::Pending;
+}
+
+bool Promise::SetSettledPromiseIsHandled() {
+  if (!mPromiseObj) {
+    // Do nothing as it's a no-op promise
+    return false;
+  }
+  AutoAllowLegacyScriptExecution exemption;
+  AutoEntryScript aes(mGlobal, "Set settled promise handled");
+  JSContext* cx = aes.cx();
+  JS::Rooted<JSObject*> promiseObj(cx, mPromiseObj);
+  return JS::SetSettledPromiseIsHandled(cx, promiseObj);
+}
+
+bool Promise::SetAnyPromiseIsHandled() {
+  if (!mPromiseObj) {
+    // Do nothing as it's a no-op promise
+    return false;
+  }
+  AutoAllowLegacyScriptExecution exemption;
+  AutoEntryScript aes(mGlobal, "Set any promise handled");
+  JSContext* cx = aes.cx();
+  JS::Rooted<JSObject*> promiseObj(cx, mPromiseObj);
+  return JS::SetAnyPromiseIsHandled(cx, promiseObj);
+}
+
+/* static */
+already_AddRefed<Promise> Promise::CreateResolvedWithUndefined(
+    nsIGlobalObject* global, ErrorResult& aRv) {
+  RefPtr<Promise> returnPromise = Promise::Create(global, aRv);
+  if (aRv.Failed()) {
+    return nullptr;
+  }
+  returnPromise->MaybeResolveWithUndefined();
+  return returnPromise.forget();
+}
+
+already_AddRefed<Promise> Promise::CreateRejected(
+    nsIGlobalObject* aGlobal, JS::Handle<JS::Value> aRejectionError,
+    ErrorResult& aRv) {
+  RefPtr<Promise> promise = Promise::Create(aGlobal, aRv);
+  if (aRv.Failed()) {
+    return nullptr;
+  }
+  promise->MaybeReject(aRejectionError);
+  return promise.forget();
+}
+
+already_AddRefed<Promise> Promise::CreateRejectedWithTypeError(
+    nsIGlobalObject* aGlobal, const nsACString& aMessage, ErrorResult& aRv) {
+  RefPtr<Promise> returnPromise = Promise::Create(aGlobal, aRv);
+  if (aRv.Failed()) {
+    return nullptr;
+  }
+  returnPromise->MaybeRejectWithTypeError(aMessage);
+  return returnPromise.forget();
+}
+
+already_AddRefed<Promise> Promise::CreateRejectedWithErrorResult(
+    nsIGlobalObject* aGlobal, ErrorResult& aRejectionError) {
+  RefPtr<Promise> returnPromise = Promise::Create(aGlobal, IgnoreErrors());
+  if (!returnPromise) {
+    return nullptr;
+  }
+  returnPromise->MaybeReject(std::move(aRejectionError));
+  return returnPromise.forget();
+}
+
+}  // namespace mozilla::dom
+
+extern "C" {
+
+// These functions are used in the implementation of ffi bindings for
+// dom::Promise from Rust.
+
+void DomPromise_AddRef(mozilla::dom::Promise* aPromise) {
+  MOZ_ASSERT(aPromise);
+  aPromise->AddRef();
+}
+
+void DomPromise_Release(mozilla::dom::Promise* aPromise) {
+  MOZ_ASSERT(aPromise);
+  aPromise->Release();
+}
+
+#define DOM_PROMISE_FUNC_WITH_VARIANT(name, func)                         \
+  void name(mozilla::dom::Promise* aPromise, nsIVariant* aVariant) {      \
+    MOZ_ASSERT(aPromise);                                                 \
+    MOZ_ASSERT(aVariant);                                                 \
+    mozilla::dom::AutoEntryScript aes(aPromise->GetGlobalObject(),        \
+                                      "Promise resolution or rejection"); \
+    JSContext* cx = aes.cx();                                             \
+                                                                          \
+    JS::Rooted<JS::Value> val(cx);                                        \
+    nsresult rv = NS_OK;                                                  \
+    if (!XPCVariant::VariantDataToJS(cx, aVariant, &rv, &val)) {          \
+      aPromise->MaybeRejectWithTypeError(                                 \
+          "Failed to convert nsIVariant to JS");                          \
+      return;                                                             \
+    }                                                                     \
+    aPromise->func(val);                                                  \
+  }
+
+DOM_PROMISE_FUNC_WITH_VARIANT(DomPromise_RejectWithVariant, MaybeReject)
+DOM_PROMISE_FUNC_WITH_VARIANT(DomPromise_ResolveWithVariant, MaybeResolve)
+
+#undef DOM_PROMISE_FUNC_WITH_VARIANT
+}
diff --git a/dom/promise/Promise.h b/dom/promise/Promise.h
new file mode 100644
index 0000000000..e10893fd73
--- /dev/null
+++ b/dom/promise/Promise.h
@@ -0,0 +1,453 @@
+/* -*- 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_Promise_h
+#define mozilla_dom_Promise_h
+
+#include <functional>
+#include <type_traits>
+#include <utility>
+#include "ErrorList.h"
+#include "js/RootingAPI.h"
+#include "js/TypeDecls.h"
+#include "mozilla/AlreadyAddRefed.h"
+#include "mozilla/Assertions.h"
+#include "mozilla/ErrorResult.h"
+#include "mozilla/RefPtr.h"
+#include "mozilla/Result.h"
+#include "mozilla/WeakPtr.h"
+#include "mozilla/dom/AutoEntryScript.h"
+#include "mozilla/dom/ScriptSettings.h"
+#include "mozilla/dom/ToJSValue.h"
+#include "nsCycleCollectionParticipant.h"
+#include "nsError.h"
+#include "nsISupports.h"
+#include "nsString.h"
+
+class nsCycleCollectionTraversalCallback;
+class nsIGlobalObject;
+
+namespace JS {
+class Value;
+}
+
+namespace mozilla::dom {
+
+class AnyCallback;
+class MediaStreamError;
+class PromiseInit;
+class PromiseNativeHandler;
+class PromiseDebugging;
+
+class Promise : public SupportsWeakPtr {
+  friend class PromiseTask;
+  friend class PromiseWorkerProxy;
+  friend class PromiseWorkerProxyRunnable;
+
+ public:
+  NS_INLINE_DECL_CYCLE_COLLECTING_NATIVE_REFCOUNTING(Promise)
+  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_NATIVE_CLASS(Promise)
+
+  enum PropagateUserInteraction {
+    eDontPropagateUserInteraction,
+    ePropagateUserInteraction
+  };
+
+  // Promise creation tries to create a JS reflector for the Promise, so is
+  // fallible.  Furthermore, we don't want to do JS-wrapping on a 0-refcount
+  // object, so we addref before doing that and return the addrefed pointer
+  // here.
+  // Pass ePropagateUserInteraction for aPropagateUserInteraction if you want
+  // the promise resolve handler to be called as if we were handling user
+  // input events in case we are currently handling user input events.
+  static already_AddRefed<Promise> Create(
+      nsIGlobalObject* aGlobal, ErrorResult& aRv,
+      PropagateUserInteraction aPropagateUserInteraction =
+          eDontPropagateUserInteraction);
+
+  // Same as Promise::Create but never throws, but instead:
+  // 1. Causes crash on OOM (as nearly every other web APIs do)
+  // 2. Silently creates a no-op Promise if the JS context is shut down
+  // This can be useful for implementations that produce promises but do not
+  // care whether the current global is alive to consume them.
+  // Note that PromiseObj() can return a nullptr if created this way.
+  static already_AddRefed<Promise> CreateInfallible(
+      nsIGlobalObject* aGlobal,
+      PropagateUserInteraction aPropagateUserInteraction =
+          eDontPropagateUserInteraction);
+
+  // Reports a rejected Promise by sending an error report.
+  static void ReportRejectedPromise(JSContext* aCx,
+                                    JS::Handle<JSObject*> aPromise);
+
+  using MaybeFunc = void (Promise::*)(JSContext*, JS::Handle<JS::Value>);
+
+  // Helpers for using Promise from C++.
+  // Most DOM objects are handled already.  To add a new type T, add a
+  // ToJSValue overload in ToJSValue.h.
+  // aArg is a const reference so we can pass rvalues like integer constants
+  template <typename T>
+  void MaybeResolve(T&& aArg) {
+    MaybeSomething(std::forward<T>(aArg), &Promise::MaybeResolve);
+  }
+
+  void MaybeResolveWithUndefined();
+
+  void MaybeReject(JS::Handle<JS::Value> aValue) {
+    MaybeSomething(aValue, &Promise::MaybeReject);
+  }
+
+  // This method is deprecated.  Consumers should MaybeRejectWithDOMException if
+  // they are rejecting with a DOMException, or use one of the other
+  // MaybeReject* methods otherwise.  If they have a random nsresult which may
+  // or may not correspond to a DOMException type, they should consider using an
+  // appropriate DOMException-type nsresult with an informative message and
+  // calling MaybeRejectWithDOMException.
+  inline void MaybeReject(nsresult aArg) {
+    MOZ_ASSERT(NS_FAILED(aArg));
+    MaybeSomething(aArg, &Promise::MaybeReject);
+  }
+
+  inline void MaybeReject(ErrorResult&& aArg) {
+    MOZ_ASSERT(aArg.Failed());
+    MaybeSomething(std::move(aArg), &Promise::MaybeReject);
+    // That should have consumed aArg.
+    MOZ_ASSERT(!aArg.Failed());
+  }
+
+  void MaybeReject(const RefPtr<MediaStreamError>& aArg);
+
+  void MaybeRejectWithUndefined();
+
+  void MaybeResolveWithClone(JSContext* aCx, JS::Handle<JS::Value> aValue);
+  void MaybeRejectWithClone(JSContext* aCx, JS::Handle<JS::Value> aValue);
+
+  // Facilities for rejecting with various spec-defined exception values.
+#define DOMEXCEPTION(name, err)                                   \
+  inline void MaybeRejectWith##name(const nsACString& aMessage) { \
+    ErrorResult res;                                              \
+    res.Throw##name(aMessage);                                    \
+    MaybeReject(std::move(res));                                  \
+  }                                                               \
+  template <int N>                                                \
+  void MaybeRejectWith##name(const char(&aMessage)[N]) {          \
+    MaybeRejectWith##name(nsLiteralCString(aMessage));            \
+  }
+
+#include "mozilla/dom/DOMExceptionNames.h"
+
+#undef DOMEXCEPTION
+
+  template <ErrNum errorNumber, typename... Ts>
+  void MaybeRejectWithTypeError(Ts&&... aMessageArgs) {
+    ErrorResult res;
+    res.ThrowTypeError<errorNumber>(std::forward<Ts>(aMessageArgs)...);
+    MaybeReject(std::move(res));
+  }
+
+  inline void MaybeRejectWithTypeError(const nsACString& aMessage) {
+    ErrorResult res;
+    res.ThrowTypeError(aMessage);
+    MaybeReject(std::move(res));
+  }
+
+  template <int N>
+  void MaybeRejectWithTypeError(const char (&aMessage)[N]) {
+    MaybeRejectWithTypeError(nsLiteralCString(aMessage));
+  }
+
+  template <ErrNum errorNumber, typename... Ts>
+  void MaybeRejectWithRangeError(Ts&&... aMessageArgs) {
+    ErrorResult res;
+    res.ThrowRangeError<errorNumber>(std::forward<Ts>(aMessageArgs)...);
+    MaybeReject(std::move(res));
+  }
+
+  inline void MaybeRejectWithRangeError(const nsACString& aMessage) {
+    ErrorResult res;
+    res.ThrowRangeError(aMessage);
+    MaybeReject(std::move(res));
+  }
+
+  template <int N>
+  void MaybeRejectWithRangeError(const char (&aMessage)[N]) {
+    MaybeRejectWithRangeError(nsLiteralCString(aMessage));
+  }
+
+  // DO NOT USE MaybeRejectBrokenly with in new code.  Promises should be
+  // rejected with Error instances.
+  // Note: MaybeRejectBrokenly is a template so we can use it with DOMException
+  // without instantiating the DOMException specialization of MaybeSomething in
+  // every translation unit that includes this header, because that would
+  // require use to include DOMException.h either here or in all those
+  // translation units.
+  template <typename T>
+  void MaybeRejectBrokenly(const T& aArg);  // Not implemented by default; see
+                                            // specializations in the .cpp for
+                                            // the T values we support.
+
+  // Mark a settled promise as already handled so that rejections will not
+  // be reported as unhandled.
+  bool SetSettledPromiseIsHandled();
+
+  // Mark a promise as handled so that rejections will not be reported as
+  // unhandled. Consider using SetSettledPromiseIsHandled if this promise is
+  // expected to be settled.
+  [[nodiscard]] bool SetAnyPromiseIsHandled();
+
+  // WebIDL
+
+  nsIGlobalObject* GetParentObject() const { return GetGlobalObject(); }
+
+  // Do the equivalent of Promise.resolve in the compartment of aGlobal.  The
+  // compartment of aCx is ignored.  Errors are reported on the ErrorResult; if
+  // aRv comes back !Failed(), this function MUST return a non-null value.
+  // Pass ePropagateUserInteraction for aPropagateUserInteraction if you want
+  // the promise resolve handler to be called as if we were handling user
+  // input events in case we are currently handling user input events.
+  static already_AddRefed<Promise> Resolve(
+      nsIGlobalObject* aGlobal, JSContext* aCx, JS::Handle<JS::Value> aValue,
+      ErrorResult& aRv,
+      PropagateUserInteraction aPropagateUserInteraction =
+          eDontPropagateUserInteraction);
+
+  // Do the equivalent of Promise.reject in the compartment of aGlobal.  The
+  // compartment of aCx is ignored.  Errors are reported on the ErrorResult; if
+  // aRv comes back !Failed(), this function MUST return a non-null value.
+  static already_AddRefed<Promise> Reject(nsIGlobalObject* aGlobal,
+                                          JSContext* aCx,
+                                          JS::Handle<JS::Value> aValue,
+                                          ErrorResult& aRv);
+
+  template <typename T>
+  static already_AddRefed<Promise> Reject(nsIGlobalObject* aGlobal, T&& aValue,
+                                          ErrorResult& aError) {
+    AutoJSAPI jsapi;
+    if (!jsapi.Init(aGlobal)) {
+      aError.Throw(NS_ERROR_UNEXPECTED);
+      return nullptr;
+    }
+
+    JSContext* cx = jsapi.cx();
+    JS::Rooted<JS::Value> val(cx);
+    if (!ToJSValue(cx, std::forward<T>(aValue), &val)) {
+      return Promise::RejectWithExceptionFromContext(aGlobal, cx, aError);
+    }
+
+    return Reject(aGlobal, cx, val, aError);
+  }
+
+  static already_AddRefed<Promise> RejectWithExceptionFromContext(
+      nsIGlobalObject* aGlobal, JSContext* aCx, ErrorResult& aError);
+
+  // Do the equivalent of Promise.all in the current compartment of aCx.  Errors
+  // are reported on the ErrorResult; if aRv comes back !Failed(), this function
+  // MUST return a non-null value.
+  // Pass ePropagateUserInteraction for aPropagateUserInteraction if you want
+  // the promise resolve handler to be called as if we were handling user
+  // input events in case we are currently handling user input events.
+  static already_AddRefed<Promise> All(
+      JSContext* aCx, const nsTArray<RefPtr<Promise>>& aPromiseList,
+      ErrorResult& aRv,
+      PropagateUserInteraction aPropagateUserInteraction =
+          eDontPropagateUserInteraction);
+
+  void Then(JSContext* aCx,
+            // aCalleeGlobal may not be in the compartment of aCx, when called
+            // over Xrays.
+            JS::Handle<JSObject*> aCalleeGlobal, AnyCallback* aResolveCallback,
+            AnyCallback* aRejectCallback, JS::MutableHandle<JS::Value> aRetval,
+            ErrorResult& aRv);
+
+  template <typename Callback, typename... Args>
+  using IsHandlerCallback =
+      std::is_same<already_AddRefed<Promise>,
+                   decltype(std::declval<Callback>()(
+                       (JSContext*)(nullptr),
+                       std::declval<JS::Handle<JS::Value>>(),
+                       std::declval<ErrorResult&>(), std::declval<Args>()...))>;
+
+  template <typename Callback, typename... Args>
+  using ThenResult =
+      std::enable_if_t<IsHandlerCallback<Callback, Args...>::value,
+                       Result<RefPtr<Promise>, nsresult>>;
+
+  // Similar to the JavaScript then() function. Accepts two lambda function
+  // arguments, which it attaches as native resolve/reject handlers, and
+  // returns a new promise which:
+  // 1. if the ErrorResult contains an error value, rejects with it.
+  // 2. else, resolves with a return value.
+  //
+  // Any additional arguments passed after the callback functions are stored and
+  // passed as additional arguments to the functions when it is called. These
+  // values will participate in cycle collection for the promise handler, and
+  // therefore may safely form reference cycles with the promise chain.
+  //
+  // Any strong references required by the callbacks should be passed in this
+  // manner, rather than using lambda capture, lambda captures do not support
+  // cycle collection, and can easily lead to leaks.
+  template <typename ResolveCallback, typename RejectCallback, typename... Args>
+  ThenResult<ResolveCallback, Args...> ThenCatchWithCycleCollectedArgs(
+      ResolveCallback&& aOnResolve, RejectCallback&& aOnReject,
+      Args&&... aArgs);
+
+  // Same as ThenCatchWithCycleCollectedArgs, except the rejection error will
+  // simply be propagated.
+  template <typename Callback, typename... Args>
+  ThenResult<Callback, Args...> ThenWithCycleCollectedArgs(
+      Callback&& aOnResolve, Args&&... aArgs);
+
+  // Same as ThenCatchWithCycleCollectedArgs, except the resolved value will
+  // simply be propagated.
+  template <typename Callback, typename... Args>
+  ThenResult<Callback, Args...> CatchWithCycleCollectedArgs(
+      Callback&& aOnReject, Args&&... aArgs);
+
+  // Same as Then[Catch]CycleCollectedArgs but the arguments are gathered into
+  // an `std::tuple` and there is an additional `std::tuple` for JS arguments
+  // after that.
+  template <typename ResolveCallback, typename RejectCallback,
+            typename ArgsTuple, typename JSArgsTuple>
+  Result<RefPtr<Promise>, nsresult> ThenCatchWithCycleCollectedArgsJS(
+      ResolveCallback&& aOnResolve, RejectCallback&& aOnReject,
+      ArgsTuple&& aArgs, JSArgsTuple&& aJSArgs);
+  template <typename Callback, typename ArgsTuple, typename JSArgsTuple>
+  Result<RefPtr<Promise>, nsresult> ThenWithCycleCollectedArgsJS(
+      Callback&& aOnResolve, ArgsTuple&& aArgs, JSArgsTuple&& aJSArgs);
+
+  Result<RefPtr<Promise>, nsresult> ThenWithoutCycleCollection(
+      const std::function<already_AddRefed<Promise>(
+          JSContext*, JS::Handle<JS::Value>, ErrorResult& aRv)>& aCallback);
+
+  // Similar to ThenCatchWithCycleCollectedArgs but doesn't care with return
+  // values of the callbacks and does not return a new promise.
+  template <typename ResolveCallback, typename RejectCallback, typename... Args>
+  void AddCallbacksWithCycleCollectedArgs(ResolveCallback&& aOnResolve,
+                                          RejectCallback&& aOnReject,
+                                          Args&&... aArgs);
+
+  // This can be null if this promise is made after the corresponding JSContext
+  // is dead.
+  JSObject* PromiseObj() const { return mPromiseObj; }
+
+  void AppendNativeHandler(PromiseNativeHandler* aRunnable);
+
+  nsIGlobalObject* GetGlobalObject() const { return mGlobal; }
+
+  // Create a dom::Promise from a given SpiderMonkey Promise object.
+  // aPromiseObj MUST be in the compartment of aGlobal's global JS object.
+  // Pass ePropagateUserInteraction for aPropagateUserInteraction if you want
+  // the promise resolve handler to be called as if we were handling user
+  // input events in case we are currently handling user input events.
+  static already_AddRefed<Promise> CreateFromExisting(
+      nsIGlobalObject* aGlobal, JS::Handle<JSObject*> aPromiseObj,
+      PropagateUserInteraction aPropagateUserInteraction =
+          eDontPropagateUserInteraction);
+
+  enum class PromiseState { Pending, Resolved, Rejected };
+
+  PromiseState State() const;
+
+  static already_AddRefed<Promise> CreateResolvedWithUndefined(
+      nsIGlobalObject* aGlobal, ErrorResult& aRv);
+
+  static already_AddRefed<Promise> CreateRejected(
+      nsIGlobalObject* aGlobal, JS::Handle<JS::Value> aRejectionError,
+      ErrorResult& aRv);
+
+  static already_AddRefed<Promise> CreateRejectedWithTypeError(
+      nsIGlobalObject* aGlobal, const nsACString& aMessage, ErrorResult& aRv);
+
+  // The rejection error will be consumed if the promise is successfully
+  // created, else the error will remain and rv.Failed() will keep being true.
+  // This intentionally is not an overload of CreateRejected to prevent
+  // accidental omission of the second argument. (See also bug 1762233 about
+  // removing its third argument.)
+  static already_AddRefed<Promise> CreateRejectedWithErrorResult(
+      nsIGlobalObject* aGlobal, ErrorResult& aRejectionError);
+
+ protected:
+  template <typename ResolveCallback, typename RejectCallback, typename... Args,
+            typename... JSArgs>
+  Result<RefPtr<Promise>, nsresult> ThenCatchWithCycleCollectedArgsJSImpl(
+      Maybe<ResolveCallback>&& aOnResolve, Maybe<RejectCallback>&& aOnReject,
+      std::tuple<Args...>&& aArgs, std::tuple<JSArgs...>&& aJSArgs);
+  template <typename ResolveCallback, typename RejectCallback, typename... Args>
+  ThenResult<ResolveCallback, Args...> ThenCatchWithCycleCollectedArgsImpl(
+      Maybe<ResolveCallback>&& aOnResolve, Maybe<RejectCallback>&& aOnReject,
+      Args&&... aArgs);
+
+  // Legacy method for throwing DOMExceptions.  Only used by media code at this
+  // point, via DetailedPromise.  Do NOT add new uses!  When this is removed,
+  // remove the friend declaration in ErrorResult.h.
+  inline void MaybeRejectWithDOMException(nsresult rv,
+                                          const nsACString& aMessage) {
+    ErrorResult res;
+    res.ThrowDOMException(rv, aMessage);
+    MaybeReject(std::move(res));
+  }
+
+  struct PromiseCapability;
+
+  // Do NOT call this unless you're Promise::Create or
+  // Promise::CreateFromExisting.  I wish we could enforce that from inside this
+  // class too, somehow.
+  explicit Promise(nsIGlobalObject* aGlobal);
+
+  virtual ~Promise();
+
+  // Do JS-wrapping after Promise creation.
+  // Pass ePropagateUserInteraction for aPropagateUserInteraction if you want
+  // the promise resolve handler to be called as if we were handling user
+  // input events in case we are currently handling user input events.
+  void CreateWrapper(ErrorResult& aRv,
+                     PropagateUserInteraction aPropagateUserInteraction =
+                         eDontPropagateUserInteraction);
+
+ private:
+  void MaybeResolve(JSContext* aCx, JS::Handle<JS::Value> aValue);
+  void MaybeReject(JSContext* aCx, JS::Handle<JS::Value> aValue);
+
+  template <typename T>
+  void MaybeSomething(T&& aArgument, MaybeFunc aFunc) {
+    MOZ_ASSERT(PromiseObj());  // It was preserved!
+
+    AutoAllowLegacyScriptExecution exemption;
+    AutoEntryScript aes(mGlobal, "Promise resolution or rejection");
+    JSContext* cx = aes.cx();
+
+    JS::Rooted<JS::Value> val(cx);
+    if (!ToJSValue(cx, std::forward<T>(aArgument), &val)) {
+      HandleException(cx);
+      return;
+    }
+
+    (this->*aFunc)(cx, val);
+  }
+
+  void HandleException(JSContext* aCx);
+
+  bool MaybePropagateUserInputEventHandling();
+
+  RefPtr<nsIGlobalObject> mGlobal;
+
+  JS::Heap<JSObject*> mPromiseObj;
+};
+
+}  // namespace mozilla::dom
+
+extern "C" {
+// These functions are used in the implementation of ffi bindings for
+// dom::Promise from Rust in xpcom crate.
+void DomPromise_AddRef(mozilla::dom::Promise* aPromise);
+void DomPromise_Release(mozilla::dom::Promise* aPromise);
+void DomPromise_RejectWithVariant(mozilla::dom::Promise* aPromise,
+                                  nsIVariant* aVariant);
+void DomPromise_ResolveWithVariant(mozilla::dom::Promise* aPromise,
+                                   nsIVariant* aVariant);
+}
+
+#endif  // mozilla_dom_Promise_h
diff --git a/dom/promise/PromiseDebugging.cpp b/dom/promise/PromiseDebugging.cpp
new file mode 100644
index 0000000000..b27661ef5e
--- /dev/null
+++ b/dom/promise/PromiseDebugging.cpp
@@ -0,0 +1,296 @@
+/* -*- 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/Value.h"
+#include "nsThreadUtils.h"
+
+#include "mozilla/CycleCollectedJSContext.h"
+#include "mozilla/RefPtr.h"
+#include "mozilla/SchedulerGroup.h"
+#include "mozilla/ThreadLocal.h"
+#include "mozilla/TimeStamp.h"
+
+#include "mozilla/dom/BindingDeclarations.h"
+#include "mozilla/dom/ContentChild.h"
+#include "mozilla/dom/Promise.h"
+#include "mozilla/dom/PromiseBinding.h"
+#include "mozilla/dom/PromiseDebugging.h"
+#include "mozilla/dom/PromiseDebuggingBinding.h"
+
+namespace mozilla::dom {
+
+class FlushRejections : public DiscardableRunnable {
+ public:
+  FlushRejections() : DiscardableRunnable("dom::FlushRejections") {}
+
+  static void Init() {
+    if (!sDispatched.init()) {
+      MOZ_CRASH("Could not initialize FlushRejections::sDispatched");
+    }
+    sDispatched.set(false);
+  }
+
+  static void DispatchNeeded() {
+    if (sDispatched.get()) {
+      // An instance of `FlushRejections` has already been dispatched
+      // and not run yet. No need to dispatch another one.
+      return;
+    }
+    sDispatched.set(true);
+
+    // Dispatch the runnable to the current thread where
+    // the Promise was rejected, e.g. workers or worklets.
+    NS_DispatchToCurrentThread(new FlushRejections());
+  }
+
+  static void FlushSync() {
+    sDispatched.set(false);
+
+    // Call the callbacks if necessary.
+    // Note that these callbacks may in turn cause Promise to turn
+    // uncaught or consumed. Since `sDispatched` is `false`,
+    // `FlushRejections` will be called once again, on an ulterior
+    // tick.
+    PromiseDebugging::FlushUncaughtRejectionsInternal();
+  }
+
+  NS_IMETHOD Run() override {
+    FlushSync();
+    return NS_OK;
+  }
+
+ private:
+  // `true` if an instance of `FlushRejections` is currently dispatched
+  // and has not been executed yet.
+  static MOZ_THREAD_LOCAL(bool) sDispatched;
+};
+
+/* static */ MOZ_THREAD_LOCAL(bool) FlushRejections::sDispatched;
+
+/* static */
+void PromiseDebugging::GetState(GlobalObject& aGlobal,
+                                JS::Handle<JSObject*> aPromise,
+                                PromiseDebuggingStateHolder& aState,
+                                ErrorResult& aRv) {
+  JSContext* cx = aGlobal.Context();
+  // CheckedUnwrapStatic is fine, since we're looking for promises only.
+  JS::Rooted<JSObject*> obj(cx, js::CheckedUnwrapStatic(aPromise));
+  if (!obj || !JS::IsPromiseObject(obj)) {
+    aRv.ThrowTypeError<MSG_IS_NOT_PROMISE>();
+    return;
+  }
+  switch (JS::GetPromiseState(obj)) {
+    case JS::PromiseState::Pending:
+      aState.mState = PromiseDebuggingState::Pending;
+      break;
+    case JS::PromiseState::Fulfilled:
+      aState.mState = PromiseDebuggingState::Fulfilled;
+      aState.mValue = JS::GetPromiseResult(obj);
+      break;
+    case JS::PromiseState::Rejected:
+      aState.mState = PromiseDebuggingState::Rejected;
+      aState.mReason = JS::GetPromiseResult(obj);
+      break;
+  }
+}
+
+/* static */
+void PromiseDebugging::GetPromiseID(GlobalObject& aGlobal,
+                                    JS::Handle<JSObject*> aPromise,
+                                    nsString& aID, ErrorResult& aRv) {
+  JSContext* cx = aGlobal.Context();
+  // CheckedUnwrapStatic is fine, since we're looking for promises only.
+  JS::Rooted<JSObject*> obj(cx, js::CheckedUnwrapStatic(aPromise));
+  if (!obj || !JS::IsPromiseObject(obj)) {
+    aRv.ThrowTypeError<MSG_IS_NOT_PROMISE>();
+    return;
+  }
+  uint64_t promiseID = JS::GetPromiseID(obj);
+  aID = sIDPrefix;
+  aID.AppendInt(promiseID);
+}
+
+/* static */
+void PromiseDebugging::GetAllocationStack(GlobalObject& aGlobal,
+                                          JS::Handle<JSObject*> aPromise,
+                                          JS::MutableHandle<JSObject*> aStack,
+                                          ErrorResult& aRv) {
+  JSContext* cx = aGlobal.Context();
+  // CheckedUnwrapStatic is fine, since we're looking for promises only.
+  JS::Rooted<JSObject*> obj(cx, js::CheckedUnwrapStatic(aPromise));
+  if (!obj || !JS::IsPromiseObject(obj)) {
+    aRv.ThrowTypeError<MSG_IS_NOT_PROMISE>();
+    return;
+  }
+  aStack.set(JS::GetPromiseAllocationSite(obj));
+}
+
+/* static */
+void PromiseDebugging::GetRejectionStack(GlobalObject& aGlobal,
+                                         JS::Handle<JSObject*> aPromise,
+                                         JS::MutableHandle<JSObject*> aStack,
+                                         ErrorResult& aRv) {
+  JSContext* cx = aGlobal.Context();
+  // CheckedUnwrapStatic is fine, since we're looking for promises only.
+  JS::Rooted<JSObject*> obj(cx, js::CheckedUnwrapStatic(aPromise));
+  if (!obj || !JS::IsPromiseObject(obj)) {
+    aRv.ThrowTypeError<MSG_IS_NOT_PROMISE>();
+    return;
+  }
+  aStack.set(JS::GetPromiseResolutionSite(obj));
+}
+
+/* static */
+void PromiseDebugging::GetFullfillmentStack(GlobalObject& aGlobal,
+                                            JS::Handle<JSObject*> aPromise,
+                                            JS::MutableHandle<JSObject*> aStack,
+                                            ErrorResult& aRv) {
+  JSContext* cx = aGlobal.Context();
+  // CheckedUnwrapStatic is fine, since we're looking for promises only.
+  JS::Rooted<JSObject*> obj(cx, js::CheckedUnwrapStatic(aPromise));
+  if (!obj || !JS::IsPromiseObject(obj)) {
+    aRv.ThrowTypeError<MSG_IS_NOT_PROMISE>();
+    return;
+  }
+  aStack.set(JS::GetPromiseResolutionSite(obj));
+}
+
+/*static */
+nsString PromiseDebugging::sIDPrefix;
+
+/* static */
+void PromiseDebugging::Init() {
+  FlushRejections::Init();
+
+  // Generate a prefix for identifiers: "PromiseDebugging.$processid."
+  sIDPrefix = u"PromiseDebugging."_ns;
+  if (XRE_IsContentProcess()) {
+    sIDPrefix.AppendInt(ContentChild::GetSingleton()->GetID());
+    sIDPrefix.Append('.');
+  } else {
+    sIDPrefix.AppendLiteral("0.");
+  }
+}
+
+/* static */
+void PromiseDebugging::Shutdown() { sIDPrefix.SetIsVoid(true); }
+
+/* static */
+void PromiseDebugging::FlushUncaughtRejections() {
+  MOZ_ASSERT(!NS_IsMainThread());
+  FlushRejections::FlushSync();
+}
+
+/* static */
+void PromiseDebugging::AddUncaughtRejectionObserver(
+    GlobalObject&, UncaughtRejectionObserver& aObserver) {
+  CycleCollectedJSContext* storage = CycleCollectedJSContext::Get();
+  nsTArray<nsCOMPtr<nsISupports>>& observers =
+      storage->mUncaughtRejectionObservers;
+  observers.AppendElement(&aObserver);
+}
+
+/* static */
+bool PromiseDebugging::RemoveUncaughtRejectionObserver(
+    GlobalObject&, UncaughtRejectionObserver& aObserver) {
+  CycleCollectedJSContext* storage = CycleCollectedJSContext::Get();
+  nsTArray<nsCOMPtr<nsISupports>>& observers =
+      storage->mUncaughtRejectionObservers;
+  for (size_t i = 0; i < observers.Length(); ++i) {
+    UncaughtRejectionObserver* observer =
+        static_cast<UncaughtRejectionObserver*>(observers[i].get());
+    if (*observer == aObserver) {
+      observers.RemoveElementAt(i);
+      return true;
+    }
+  }
+  return false;
+}
+
+/* static */
+void PromiseDebugging::AddUncaughtRejection(JS::Handle<JSObject*> aPromise) {
+  // This might OOM, but won't set a pending exception, so we'll just ignore it.
+  if (CycleCollectedJSContext::Get()->mUncaughtRejections.append(aPromise)) {
+    FlushRejections::DispatchNeeded();
+  }
+}
+
+/* void */
+void PromiseDebugging::AddConsumedRejection(JS::Handle<JSObject*> aPromise) {
+  // If the promise is in our list of uncaught rejections, we haven't yet
+  // reported it as unhandled. In that case, just remove it from the list
+  // and don't add it to the list of consumed rejections.
+  auto& uncaughtRejections =
+      CycleCollectedJSContext::Get()->mUncaughtRejections;
+  for (size_t i = 0; i < uncaughtRejections.length(); i++) {
+    if (uncaughtRejections[i] == aPromise) {
+      // To avoid large amounts of memmoves, we don't shrink the vector here.
+      // Instead, we filter out nullptrs when iterating over the vector later.
+      uncaughtRejections[i].set(nullptr);
+      return;
+    }
+  }
+  // This might OOM, but won't set a pending exception, so we'll just ignore it.
+  if (CycleCollectedJSContext::Get()->mConsumedRejections.append(aPromise)) {
+    FlushRejections::DispatchNeeded();
+  }
+}
+
+/* static */
+void PromiseDebugging::FlushUncaughtRejectionsInternal() {
+  CycleCollectedJSContext* storage = CycleCollectedJSContext::Get();
+
+  auto& uncaught = storage->mUncaughtRejections;
+  auto& consumed = storage->mConsumedRejections;
+
+  AutoJSAPI jsapi;
+  jsapi.Init();
+  JSContext* cx = jsapi.cx();
+
+  // Notify observers of uncaught Promise.
+  auto& observers = storage->mUncaughtRejectionObservers;
+
+  for (size_t i = 0; i < uncaught.length(); i++) {
+    JS::Rooted<JSObject*> promise(cx, uncaught[i]);
+    // Filter out nullptrs which might've been added by
+    // PromiseDebugging::AddConsumedRejection.
+    if (!promise) {
+      continue;
+    }
+
+    bool suppressReporting = false;
+    for (size_t j = 0; j < observers.Length(); ++j) {
+      RefPtr<UncaughtRejectionObserver> obs =
+          static_cast<UncaughtRejectionObserver*>(observers[j].get());
+
+      if (obs->OnLeftUncaught(promise, IgnoreErrors())) {
+        suppressReporting = true;
+      }
+    }
+
+    if (!suppressReporting) {
+      JSAutoRealm ar(cx, promise);
+      Promise::ReportRejectedPromise(cx, promise);
+    }
+  }
+  storage->mUncaughtRejections.clear();
+
+  // Notify observers of consumed Promise.
+
+  for (size_t i = 0; i < consumed.length(); i++) {
+    JS::Rooted<JSObject*> promise(cx, consumed[i]);
+
+    for (size_t j = 0; j < observers.Length(); ++j) {
+      RefPtr<UncaughtRejectionObserver> obs =
+          static_cast<UncaughtRejectionObserver*>(observers[j].get());
+
+      obs->OnConsumed(promise, IgnoreErrors());
+    }
+  }
+  storage->mConsumedRejections.clear();
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/promise/PromiseDebugging.h b/dom/promise/PromiseDebugging.h
new file mode 100644
index 0000000000..ed14e2215b
--- /dev/null
+++ b/dom/promise/PromiseDebugging.h
@@ -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/. */
+
+#ifndef mozilla_dom_PromiseDebugging_h
+#define mozilla_dom_PromiseDebugging_h
+
+#include "js/TypeDecls.h"
+#include "nsTArray.h"
+#include "mozilla/RefPtr.h"
+
+namespace mozilla {
+
+class ErrorResult;
+
+namespace dom {
+class Promise;
+struct PromiseDebuggingStateHolder;
+class GlobalObject;
+class UncaughtRejectionObserver;
+class FlushRejections;
+class WorkerPrivate;
+
+void TriggerFlushRejections();
+
+class PromiseDebugging {
+ public:
+  static void Init();
+  static void Shutdown();
+
+  static void GetState(GlobalObject&, JS::Handle<JSObject*> aPromise,
+                       PromiseDebuggingStateHolder& aState, ErrorResult& aRv);
+
+  static void GetPromiseID(GlobalObject&, JS::Handle<JSObject*>, nsString&,
+                           ErrorResult&);
+
+  static void GetAllocationStack(GlobalObject&, JS::Handle<JSObject*> aPromise,
+                                 JS::MutableHandle<JSObject*> aStack,
+                                 ErrorResult& aRv);
+  static void GetRejectionStack(GlobalObject&, JS::Handle<JSObject*> aPromise,
+                                JS::MutableHandle<JSObject*> aStack,
+                                ErrorResult& aRv);
+  static void GetFullfillmentStack(GlobalObject&,
+                                   JS::Handle<JSObject*> aPromise,
+                                   JS::MutableHandle<JSObject*> aStack,
+                                   ErrorResult& aRv);
+
+  // Mechanism for watching uncaught instances of Promise.
+  static void AddUncaughtRejectionObserver(
+      GlobalObject&, UncaughtRejectionObserver& aObserver);
+  static bool RemoveUncaughtRejectionObserver(
+      GlobalObject&, UncaughtRejectionObserver& aObserver);
+
+  // Mark a Promise as having been left uncaught at script completion.
+  static void AddUncaughtRejection(JS::Handle<JSObject*>);
+  // Mark a Promise previously added with `AddUncaughtRejection` as
+  // eventually consumed.
+  static void AddConsumedRejection(JS::Handle<JSObject*>);
+  // Propagate the informations from AddUncaughtRejection
+  // and AddConsumedRejection to observers.
+  static void FlushUncaughtRejections();
+
+ protected:
+  static void FlushUncaughtRejectionsInternal();
+  friend class FlushRejections;
+  friend class mozilla::dom::WorkerPrivate;
+
+ private:
+  // Identity of the process.
+  // This property is:
+  // - set during initialization of the layout module,
+  // prior to any Worker using it;
+  // - read by both the main thread and the Workers;
+  // - unset during shutdown of the layout module,
+  // after any Worker has been shutdown.
+  static nsString sIDPrefix;
+};
+
+}  // namespace dom
+}  // namespace mozilla
+
+#endif  // mozilla_dom_PromiseDebugging_h
diff --git a/dom/promise/PromiseNativeHandler.cpp b/dom/promise/PromiseNativeHandler.cpp
new file mode 100644
index 0000000000..88f7edef3a
--- /dev/null
+++ b/dom/promise/PromiseNativeHandler.cpp
@@ -0,0 +1,63 @@
+/* -*- 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 "PromiseNativeHandler.h"
+#include "mozilla/dom/BindingUtils.h"
+#include "mozilla/dom/Promise.h"
+#include "mozilla/dom/DOMException.h"
+#include "mozilla/dom/DOMExceptionBinding.h"
+#include "nsISupportsImpl.h"
+
+namespace mozilla::dom {
+
+NS_IMPL_ISUPPORTS0(DomPromiseListener)
+
+DomPromiseListener::DomPromiseListener(CallbackTypeResolved&& aResolve,
+                                       CallbackTypeRejected&& aReject)
+    : mResolve(std::move(aResolve)), mReject(std::move(aReject)) {}
+
+DomPromiseListener::~DomPromiseListener() {
+  if (mReject) {
+    mReject(NS_BINDING_ABORTED);
+  }
+}
+
+void DomPromiseListener::ResolvedCallback(JSContext* aCx,
+                                          JS::Handle<JS::Value> aValue,
+                                          ErrorResult& aRv) {
+  if (mResolve) {
+    mResolve(aCx, aValue);
+  }
+  // Let's clear the lambdas in case we have a cycle to ourselves.
+  Clear();
+}
+
+void DomPromiseListener::RejectedCallback(JSContext* aCx,
+                                          JS::Handle<JS::Value> aValue,
+                                          ErrorResult& aRv) {
+  if (mReject) {
+    nsresult errorCode = NS_ERROR_DOM_NOT_NUMBER_ERR;
+    if (aValue.isInt32()) {
+      errorCode = nsresult(aValue.toInt32());
+    } else if (aValue.isObject()) {
+      RefPtr<::mozilla::dom::DOMException> domException;
+      UNWRAP_OBJECT(DOMException, aValue, domException);
+      if (domException) {
+        errorCode = domException->GetResult();
+      }
+    }
+    mReject(errorCode);
+  }
+  // Let's clear the lambdas in case we have a cycle to ourselves.
+  Clear();
+}
+
+void DomPromiseListener::Clear() {
+  mResolve = nullptr;
+  mReject = nullptr;
+}
+
+}  // namespace mozilla::dom
diff --git a/dom/promise/PromiseNativeHandler.h b/dom/promise/PromiseNativeHandler.h
new file mode 100644
index 0000000000..0867e7f75d
--- /dev/null
+++ b/dom/promise/PromiseNativeHandler.h
@@ -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/. */
+
+#ifndef mozilla_dom_PromiseNativeHandler_h
+#define mozilla_dom_PromiseNativeHandler_h
+
+#include <functional>
+#include "js/TypeDecls.h"
+#include "js/Value.h"
+#include "mozilla/ErrorResult.h"
+#include "mozilla/Maybe.h"
+#include "nsISupports.h"
+
+namespace mozilla::dom {
+
+/*
+ * PromiseNativeHandler allows C++ to react to a Promise being
+ * rejected/resolved. A PromiseNativeHandler can be appended to a Promise using
+ * Promise::AppendNativeHandler().
+ */
+class PromiseNativeHandler : public nsISupports {
+ protected:
+  virtual ~PromiseNativeHandler() = default;
+
+ public:
+  MOZ_CAN_RUN_SCRIPT
+  virtual void ResolvedCallback(JSContext* aCx, JS::Handle<JS::Value> aValue,
+                                ErrorResult& aRv) = 0;
+
+  MOZ_CAN_RUN_SCRIPT
+  virtual void RejectedCallback(JSContext* aCx, JS::Handle<JS::Value> aValue,
+                                ErrorResult& aRv) = 0;
+};
+
+// This class is used to set C++ callbacks once a dom Promise a resolved or
+// rejected.
+class DomPromiseListener final : public PromiseNativeHandler {
+  NS_DECL_ISUPPORTS
+
+ public:
+  using CallbackTypeResolved =
+      std::function<void(JSContext*, JS::Handle<JS::Value>)>;
+  using CallbackTypeRejected = std::function<void(nsresult)>;
+
+  DomPromiseListener(CallbackTypeResolved&& aResolve,
+                     CallbackTypeRejected&& aReject);
+
+  void Clear();
+
+  void ResolvedCallback(JSContext* aCx, JS::Handle<JS::Value> aValue,
+                        ErrorResult& aRv) override;
+  void RejectedCallback(JSContext* aCx, JS::Handle<JS::Value> aValue,
+                        ErrorResult& aRv) override;
+
+ private:
+  ~DomPromiseListener();
+  CallbackTypeResolved mResolve;
+  CallbackTypeRejected mReject;
+};
+
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_PromiseNativeHandler_h
diff --git a/dom/promise/PromiseWorkerProxy.h b/dom/promise/PromiseWorkerProxy.h
new file mode 100644
index 0000000000..92ebd5eaf2
--- /dev/null
+++ b/dom/promise/PromiseWorkerProxy.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_PromiseWorkerProxy_h
+#define mozilla_dom_PromiseWorkerProxy_h
+
+#include <cstdint>
+#include "js/TypeDecls.h"
+#include "mozilla/AlreadyAddRefed.h"
+#include "mozilla/Mutex.h"
+#include "mozilla/RefPtr.h"
+#include "mozilla/dom/Promise.h"
+#include "mozilla/dom/PromiseNativeHandler.h"
+#include "mozilla/dom/StructuredCloneHolder.h"
+#include "nsISupports.h"
+
+struct JSStructuredCloneReader;
+struct JSStructuredCloneWriter;
+
+namespace JS {
+class CloneDataPolicy;
+}  // namespace JS
+
+namespace mozilla::dom {
+
+class ThreadSafeWorkerRef;
+class WorkerPrivate;
+
+// A proxy to (eventually) mirror a resolved/rejected Promise's result from the
+// main thread to a Promise on the worker thread.
+//
+// How to use:
+//
+//   1. Create a Promise on the worker thread and return it to the content
+//      script:
+//
+//        RefPtr<Promise> promise =
+//          Promise::Create(workerPrivate->GlobalScope(), aRv);
+//        if (aRv.Failed()) {
+//          return nullptr;
+//        }
+//
+//   2. Create a PromiseWorkerProxy wrapping the Promise. If this fails, the
+//      worker is shutting down and you should fail the original call. This is
+//      only likely to happen in (Gecko-specific) worker onclose handlers.
+//
+//        RefPtr<PromiseWorkerProxy> proxy =
+//          PromiseWorkerProxy::Create(workerPrivate, promise);
+//        if (!proxy) {
+//          // You may also reject the Promise with an AbortError or similar.
+//          return nullptr;
+//        }
+//
+//   3. Dispatch a runnable to the main thread, with a reference to the proxy to
+//      perform the main thread operation. PromiseWorkerProxy is thread-safe
+//      refcounted.
+//
+//   4. Return the worker thread promise to the JS caller:
+//
+//        return promise.forget();
+//
+//   5. In your main thread runnable Run(), obtain a Promise on
+//      the main thread and call its AppendNativeHandler(PromiseNativeHandler*)
+//      to bind the PromiseWorkerProxy created at #2.
+//
+//   4. Then the Promise results returned by ResolvedCallback/RejectedCallback
+//      will be dispatched as a WorkerRunnable to the worker thread to
+//      resolve/reject the Promise created at #1.
+//
+// PromiseWorkerProxy can also be used in situations where there is no main
+// thread Promise, or where special handling is required on the worker thread
+// for promise resolution. Create a PromiseWorkerProxy as in steps 1 to 3
+// above. When the main thread is ready to resolve the worker thread promise:
+//
+//   1. Acquire the mutex before attempting to access the worker private.
+//
+//        AssertIsOnMainThread();
+//        MutexAutoLock lock(proxy->Lock());
+//        if (proxy->CleanedUp()) {
+//          // Worker has already shut down, can't access worker private.
+//          return;
+//        }
+//
+//   2. Dispatch a runnable to the worker. Use GetWorkerPrivate() to acquire the
+//      worker.
+//
+//        RefPtr<FinishTaskWorkerRunnable> runnable =
+//          new FinishTaskWorkerRunnable(proxy->GetWorkerPrivate(), proxy,
+//                                       result);
+//        if (!r->Dispatch()) {
+//          // Worker is alive but not Running any more, so the Promise can't
+//          // be resolved, give up. The proxy will get Release()d at some
+//          // point.
+//
+//          // Usually do nothing, but you may want to log the fact.
+//        }
+//
+//   3. In the WorkerRunnable's WorkerRun() use WorkerPromise() to access the
+//      Promise and resolve/reject it. Then call CleanUp().
+//
+//        bool
+//        WorkerRun(JSContext* aCx, WorkerPrivate* aWorkerPrivate) override
+//        {
+//          aWorkerPrivate->AssertIsOnWorkerThread();
+//          RefPtr<Promise> promise = mProxy->WorkerPromise();
+//          promise->MaybeResolve(mResult);
+//          mProxy->CleanUp();
+//        }
+//
+// Note: If a PromiseWorkerProxy is not cleaned up by a WorkerRunnable - this
+// can happen if the main thread Promise is never fulfilled - it will
+// stay alive till the worker reaches a Canceling state, even if all external
+// references to it are dropped.
+
+class PromiseWorkerProxy : public PromiseNativeHandler,
+                           public StructuredCloneHolderBase,
+                           public SingleWriterLockOwner {
+  friend class PromiseWorkerProxyRunnable;
+
+  NS_DECL_THREADSAFE_ISUPPORTS
+
+ public:
+  typedef JSObject* (*ReadCallbackOp)(JSContext* aCx,
+                                      JSStructuredCloneReader* aReader,
+                                      const PromiseWorkerProxy* aProxy,
+                                      uint32_t aTag, uint32_t aData);
+  typedef bool (*WriteCallbackOp)(JSContext* aCx,
+                                  JSStructuredCloneWriter* aWorker,
+                                  PromiseWorkerProxy* aProxy,
+                                  JS::Handle<JSObject*> aObj);
+
+  bool OnWritingThread() const override;
+
+  struct PromiseWorkerProxyStructuredCloneCallbacks {
+    ReadCallbackOp Read;
+    WriteCallbackOp Write;
+  };
+
+  static already_AddRefed<PromiseWorkerProxy> Create(
+      WorkerPrivate* aWorkerPrivate, Promise* aWorkerPromise,
+      const PromiseWorkerProxyStructuredCloneCallbacks* aCallbacks = nullptr);
+
+  // Main thread callers must hold Lock() and check CleanUp() before calling
+  // this. Worker thread callers, this will assert that the proxy has not been
+  // cleaned up.
+  WorkerPrivate* GetWorkerPrivate() const MOZ_NO_THREAD_SAFETY_ANALYSIS;
+
+  // This should only be used within WorkerRunnable::WorkerRun() running on the
+  // worker thread! Do not call this after calling CleanUp().
+  Promise* WorkerPromise() const;
+
+  // Worker thread only. Calling this invalidates several assumptions, so be
+  // sure this is the last thing you do.
+  // 1. WorkerPrivate() will no longer return a valid worker.
+  // 2. WorkerPromise() will crash!
+  void CleanUp();
+
+  Mutex& Lock() MOZ_RETURN_CAPABILITY(mCleanUpLock) { return mCleanUpLock; }
+
+  bool CleanedUp() const MOZ_REQUIRES(mCleanUpLock) {
+    mCleanUpLock.AssertCurrentThreadOwns();
+    return mCleanedUp;
+  }
+
+  // StructuredCloneHolderBase
+
+  JSObject* CustomReadHandler(JSContext* aCx, JSStructuredCloneReader* aReader,
+                              const JS::CloneDataPolicy& aCloneDataPolicy,
+                              uint32_t aTag, uint32_t aIndex) override;
+
+  bool CustomWriteHandler(JSContext* aCx, JSStructuredCloneWriter* aWriter,
+                          JS::Handle<JSObject*> aObj,
+                          bool* aSameProcessScopeRequired) override;
+
+ protected:
+  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:
+  explicit PromiseWorkerProxy(
+      Promise* aWorkerPromise,
+      const PromiseWorkerProxyStructuredCloneCallbacks* aCallbacks = nullptr);
+
+  virtual ~PromiseWorkerProxy();
+
+  // Function pointer for calling Promise::{ResolveInternal,RejectInternal}.
+  typedef void (Promise::*RunCallbackFunc)(JSContext*, JS::Handle<JS::Value>);
+
+  void RunCallback(JSContext* aCx, JS::Handle<JS::Value> aValue,
+                   RunCallbackFunc aFunc);
+
+  // Any thread with appropriate checks.
+  RefPtr<ThreadSafeWorkerRef> mWorkerRef;
+
+  // Worker thread only.
+  RefPtr<Promise> mWorkerPromise;
+
+  // 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.
+
+  const PromiseWorkerProxyStructuredCloneCallbacks* mCallbacks;
+
+  // 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;
+};
+}  // namespace mozilla::dom
+
+#endif  // mozilla_dom_PromiseWorkerProxy_h
diff --git a/dom/promise/gtest/NativeThenHandler.cpp b/dom/promise/gtest/NativeThenHandler.cpp
new file mode 100644
index 0000000000..13ed6d2c11
--- /dev/null
+++ b/dom/promise/gtest/NativeThenHandler.cpp
@@ -0,0 +1,160 @@
+/* -*- 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 "gtest/gtest.h"
+
+#include "js/TypeDecls.h"
+#include "js/Value.h"
+#include "mozilla/dom/Promise.h"
+#include "mozilla/dom/Promise-inl.h"
+#include "xpcpublic.h"
+
+using namespace mozilla;
+using namespace mozilla::dom;
+
+struct TraceCounts {
+  int32_t mValue = 0;
+  int32_t mId = 0;
+  int32_t mObject = 0;
+  int32_t mWrapperCache = 0;
+  int32_t mTenuredHeapObject = 0;
+  int32_t mString = 0;
+  int32_t mScript = 0;
+  int32_t mFunction = 0;
+};
+
+struct DummyCallbacks final : public TraceCallbacks {
+  void Trace(JS::Heap<JS::Value>*, const char*, void* aClosure) const override {
+    static_cast<TraceCounts*>(aClosure)->mValue++;
+  }
+
+  void Trace(JS::Heap<jsid>*, const char*, void* aClosure) const override {
+    static_cast<TraceCounts*>(aClosure)->mId++;
+  }
+
+  void Trace(JS::Heap<JSObject*>*, const char*, void* aClosure) const override {
+    static_cast<TraceCounts*>(aClosure)->mObject++;
+  }
+
+  void Trace(nsWrapperCache*, const char* aName,
+             void* aClosure) const override {
+    static_cast<TraceCounts*>(aClosure)->mWrapperCache++;
+  }
+
+  void Trace(JS::TenuredHeap<JSObject*>*, const char*,
+             void* aClosure) const override {
+    static_cast<TraceCounts*>(aClosure)->mTenuredHeapObject++;
+  }
+
+  void Trace(JS::Heap<JSString*>*, const char*, void* aClosure) const override {
+    static_cast<TraceCounts*>(aClosure)->mString++;
+  }
+
+  void Trace(JS::Heap<JSScript*>*, const char*, void* aClosure) const override {
+    static_cast<TraceCounts*>(aClosure)->mScript++;
+  }
+
+  void Trace(JS::Heap<JSFunction*>*, const char*,
+             void* aClosure) const override {
+    static_cast<TraceCounts*>(aClosure)->mFunction++;
+  }
+};
+
+TEST(NativeThenHandler, TraceValue)
+{
+  auto onResolve = [](JSContext*, JS::Handle<JS::Value>, ErrorResult&,
+                      JS::Handle<JS::Value>) -> already_AddRefed<Promise> {
+    return nullptr;
+  };
+  auto onReject = [](JSContext*, JS::Handle<JS::Value>, ErrorResult&,
+                     JS::Handle<JS::Value>) -> already_AddRefed<Promise> {
+    return nullptr;
+  };
+
+  // Explicit type for backward compatibility with clang<7 / gcc<8
+  using HandlerType =
+      NativeThenHandler<decltype(onResolve), decltype(onReject), std::tuple<>,
+                        std::tuple<JS::HandleValue>>;
+  RefPtr<HandlerType> handler = new HandlerType(
+      nullptr, Some(onResolve), Some(onReject), std::make_tuple(),
+      std::make_tuple(JS::UndefinedHandleValue));
+
+  TraceCounts counts;
+  NS_CYCLE_COLLECTION_PARTICIPANT(HandlerType)
+      ->Trace(handler.get(), DummyCallbacks(), &counts);
+
+  EXPECT_EQ(counts.mValue, 1);
+}
+
+TEST(NativeThenHandler, TraceObject)
+{
+  auto onResolve = [](JSContext*, JS::Handle<JS::Value>, ErrorResult&,
+                      JS::Handle<JSObject*>) -> already_AddRefed<Promise> {
+    return nullptr;
+  };
+  auto onReject = [](JSContext*, JS::Handle<JS::Value>, ErrorResult&,
+                     JS::Handle<JSObject*>) -> already_AddRefed<Promise> {
+    return nullptr;
+  };
+
+  AutoJSAPI jsapi;
+  MOZ_ALWAYS_TRUE(jsapi.Init(xpc::PrivilegedJunkScope()));
+  JSContext* cx = jsapi.cx();
+  JS::Rooted<JSObject*> obj(cx, JS_NewPlainObject(cx));
+
+  // Explicit type for backward compatibility with clang<7 / gcc<8
+  using HandlerType =
+      NativeThenHandler<decltype(onResolve), decltype(onReject), std::tuple<>,
+                        std::tuple<JS::HandleObject>>;
+  RefPtr<HandlerType> handler = new HandlerType(
+      nullptr, Some(onResolve), Some(onReject), std::make_tuple(),
+      std::make_tuple(JS::HandleObject(obj)));
+
+  TraceCounts counts;
+  NS_CYCLE_COLLECTION_PARTICIPANT(HandlerType)
+      ->Trace(handler.get(), DummyCallbacks(), &counts);
+
+  EXPECT_EQ(counts.mObject, 1);
+}
+
+TEST(NativeThenHandler, TraceMixed)
+{
+  auto onResolve = [](JSContext*, JS::Handle<JS::Value>, ErrorResult&,
+                      nsIGlobalObject*, Promise*, JS::Handle<JS::Value>,
+                      JS::Handle<JSObject*>) -> already_AddRefed<Promise> {
+    return nullptr;
+  };
+  auto onReject = [](JSContext*, JS::Handle<JS::Value>, ErrorResult&,
+                     nsIGlobalObject*, Promise*, JS::Handle<JS::Value>,
+                     JS::Handle<JSObject*>) -> already_AddRefed<Promise> {
+    return nullptr;
+  };
+
+  AutoJSAPI jsapi;
+  MOZ_ALWAYS_TRUE(jsapi.Init(xpc::PrivilegedJunkScope()));
+  JSContext* cx = jsapi.cx();
+  nsCOMPtr<nsIGlobalObject> global = xpc::CurrentNativeGlobal(cx);
+  JS::Rooted<JSObject*> obj(cx, JS_NewPlainObject(cx));
+
+  RefPtr<Promise> promise = Promise::Create(global, IgnoreErrors());
+
+  // Explicit type for backward compatibility with clang<7 / gcc<8
+  using HandlerType =
+      NativeThenHandler<decltype(onResolve), decltype(onReject),
+                        std::tuple<nsCOMPtr<nsIGlobalObject>, RefPtr<Promise>>,
+                        std::tuple<JS::HandleValue, JS::HandleObject>>;
+  RefPtr<HandlerType> handler = new HandlerType(
+      nullptr, Some(onResolve), Some(onReject),
+      std::make_tuple(global, promise),
+      std::make_tuple(JS::UndefinedHandleValue, JS::HandleObject(obj)));
+
+  TraceCounts counts;
+  NS_CYCLE_COLLECTION_PARTICIPANT(HandlerType)
+      ->Trace(handler.get(), DummyCallbacks(), &counts);
+
+  EXPECT_EQ(counts.mValue, 1);
+  EXPECT_EQ(counts.mObject, 1);
+}
diff --git a/dom/promise/gtest/ThenWithCycleCollectedArgsJS.cpp b/dom/promise/gtest/ThenWithCycleCollectedArgsJS.cpp
new file mode 100644
index 0000000000..31b9fde3ca
--- /dev/null
+++ b/dom/promise/gtest/ThenWithCycleCollectedArgsJS.cpp
@@ -0,0 +1,158 @@
+/* -*- 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 "gtest/gtest.h"
+
+#include "mozilla/dom/Promise.h"
+#include "mozilla/dom/Promise-inl.h"
+#include "xpcpublic.h"
+
+using namespace mozilla;
+using namespace mozilla::dom;
+
+TEST(ThenWithCycleCollectedArgsJS, Empty)
+{
+  nsCOMPtr<nsIGlobalObject> global =
+      xpc::NativeGlobal(xpc::PrivilegedJunkScope());
+
+  RefPtr<Promise> promise = Promise::Create(global, IgnoreErrors());
+  auto result = promise->ThenWithCycleCollectedArgsJS(
+      [](JSContext*, JS::Handle<JS::Value>, ErrorResult&) { return nullptr; },
+      std::make_tuple(), std::make_tuple());
+}
+
+TEST(ThenWithCycleCollectedArgsJS, nsCOMPtr)
+{
+  nsCOMPtr<nsIGlobalObject> global =
+      xpc::NativeGlobal(xpc::PrivilegedJunkScope());
+
+  RefPtr<Promise> promise = Promise::Create(global, IgnoreErrors());
+  auto result = promise->ThenWithCycleCollectedArgsJS(
+      [](JSContext*, JS::Handle<JS::Value>, ErrorResult&, nsIGlobalObject*) {
+        return nullptr;
+      },
+      std::make_tuple(global), std::make_tuple());
+}
+
+TEST(ThenWithCycleCollectedArgsJS, RefPtr)
+{
+  nsCOMPtr<nsIGlobalObject> global =
+      xpc::NativeGlobal(xpc::PrivilegedJunkScope());
+
+  RefPtr<Promise> promise = Promise::Create(global, IgnoreErrors());
+  auto result = promise->ThenWithCycleCollectedArgsJS(
+      [](JSContext*, JS::Handle<JS::Value>, ErrorResult&, Promise*) {
+        return nullptr;
+      },
+      std::make_tuple(promise), std::make_tuple());
+}
+
+TEST(ThenWithCycleCollectedArgsJS, RefPtrAndJSHandle)
+{
+  nsCOMPtr<nsIGlobalObject> global =
+      xpc::NativeGlobal(xpc::PrivilegedJunkScope());
+
+  RefPtr<Promise> promise = Promise::Create(global, IgnoreErrors());
+  auto result = promise->ThenWithCycleCollectedArgsJS(
+      [](JSContext*, JS::Handle<JS::Value> v, ErrorResult&, Promise*,
+         JS::Handle<JS::Value>) { return nullptr; },
+      std::make_tuple(promise), std::make_tuple(JS::UndefinedHandleValue));
+}
+
+TEST(ThenWithCycleCollectedArgsJS, Mixed)
+{
+  AutoJSAPI jsapi;
+  MOZ_ALWAYS_TRUE(jsapi.Init(xpc::PrivilegedJunkScope()));
+  JSContext* cx = jsapi.cx();
+  nsCOMPtr<nsIGlobalObject> global = xpc::CurrentNativeGlobal(cx);
+  JS::Rooted<JSObject*> obj(cx, JS_NewPlainObject(cx));
+
+  RefPtr<Promise> promise = Promise::Create(global, IgnoreErrors());
+  auto result = promise->ThenWithCycleCollectedArgsJS(
+      [](JSContext*, JS::Handle<JS::Value>, ErrorResult&, nsIGlobalObject*,
+         Promise*, JS::Handle<JS::Value>,
+         JS::Handle<JSObject*>) { return nullptr; },
+      std::make_tuple(global, promise),
+      std::make_tuple(JS::UndefinedHandleValue, JS::HandleObject(obj)));
+}
+
+TEST(ThenCatchWithCycleCollectedArgsJS, Empty)
+{
+  nsCOMPtr<nsIGlobalObject> global =
+      xpc::NativeGlobal(xpc::PrivilegedJunkScope());
+
+  RefPtr<Promise> promise = Promise::Create(global, IgnoreErrors());
+  auto result = promise->ThenCatchWithCycleCollectedArgsJS(
+      [](JSContext*, JS::Handle<JS::Value>, ErrorResult&) { return nullptr; },
+      [](JSContext*, JS::Handle<JS::Value>, ErrorResult&) { return nullptr; },
+      std::make_tuple(), std::make_tuple());
+}
+
+TEST(ThenCatchWithCycleCollectedArgsJS, nsCOMPtr)
+{
+  nsCOMPtr<nsIGlobalObject> global =
+      xpc::NativeGlobal(xpc::PrivilegedJunkScope());
+
+  RefPtr<Promise> promise = Promise::Create(global, IgnoreErrors());
+  auto result = promise->ThenCatchWithCycleCollectedArgsJS(
+      [](JSContext*, JS::Handle<JS::Value>, ErrorResult&, nsIGlobalObject*) {
+        return nullptr;
+      },
+      [](JSContext*, JS::Handle<JS::Value>, ErrorResult&, nsIGlobalObject*) {
+        return nullptr;
+      },
+      std::make_tuple(global), std::make_tuple());
+}
+
+TEST(ThenCatchWithCycleCollectedArgsJS, RefPtr)
+{
+  nsCOMPtr<nsIGlobalObject> global =
+      xpc::NativeGlobal(xpc::PrivilegedJunkScope());
+
+  RefPtr<Promise> promise = Promise::Create(global, IgnoreErrors());
+  auto result = promise->ThenCatchWithCycleCollectedArgsJS(
+      [](JSContext*, JS::Handle<JS::Value>, ErrorResult&, Promise*) {
+        return nullptr;
+      },
+      [](JSContext*, JS::Handle<JS::Value>, ErrorResult&, Promise*) {
+        return nullptr;
+      },
+      std::make_tuple(promise), std::make_tuple());
+}
+
+TEST(ThenCatchWithCycleCollectedArgsJS, RefPtrAndJSHandle)
+{
+  nsCOMPtr<nsIGlobalObject> global =
+      xpc::NativeGlobal(xpc::PrivilegedJunkScope());
+
+  RefPtr<Promise> promise = Promise::Create(global, IgnoreErrors());
+  auto result = promise->ThenCatchWithCycleCollectedArgsJS(
+      [](JSContext*, JS::Handle<JS::Value> v, ErrorResult&, Promise*,
+         JS::Handle<JS::Value>) { return nullptr; },
+      [](JSContext*, JS::Handle<JS::Value> v, ErrorResult&, Promise*,
+         JS::Handle<JS::Value>) { return nullptr; },
+      std::make_tuple(promise), std::make_tuple(JS::UndefinedHandleValue));
+}
+
+TEST(ThenCatchWithCycleCollectedArgsJS, Mixed)
+{
+  AutoJSAPI jsapi;
+  MOZ_ALWAYS_TRUE(jsapi.Init(xpc::PrivilegedJunkScope()));
+  JSContext* cx = jsapi.cx();
+  nsCOMPtr<nsIGlobalObject> global = xpc::CurrentNativeGlobal(cx);
+  JS::Rooted<JSObject*> obj(cx, JS_NewPlainObject(cx));
+
+  RefPtr<Promise> promise = Promise::Create(global, IgnoreErrors());
+  auto result = promise->ThenCatchWithCycleCollectedArgsJS(
+      [](JSContext*, JS::Handle<JS::Value>, ErrorResult&, nsIGlobalObject*,
+         Promise*, JS::Handle<JS::Value>,
+         JS::Handle<JSObject*>) { return nullptr; },
+      [](JSContext*, JS::Handle<JS::Value>, ErrorResult&, nsIGlobalObject*,
+         Promise*, JS::Handle<JS::Value>,
+         JS::Handle<JSObject*>) { return nullptr; },
+      std::make_tuple(global, promise),
+      std::make_tuple(JS::UndefinedHandleValue, JS::HandleObject(obj)));
+}
diff --git a/dom/promise/gtest/moz.build b/dom/promise/gtest/moz.build
new file mode 100644
index 0000000000..a220822834
--- /dev/null
+++ b/dom/promise/gtest/moz.build
@@ -0,0 +1,14 @@
+# -*- 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/.
+
+UNIFIED_SOURCES += [
+    "NativeThenHandler.cpp",
+    "ThenWithCycleCollectedArgsJS.cpp",
+]
+
+LOCAL_INCLUDES += ["/dom/promise"]
+
+FINAL_LIBRARY = "xul-gtest"
diff --git a/dom/promise/moz.build b/dom/promise/moz.build
new file mode 100644
index 0000000000..c317f1fae0
--- /dev/null
+++ b/dom/promise/moz.build
@@ -0,0 +1,42 @@
+# -*- 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: Core & HTML")
+
+EXPORTS.mozilla.dom += [
+    "Promise-inl.h",
+    "Promise.h",
+    "PromiseDebugging.h",
+    "PromiseNativeHandler.h",
+    "PromiseWorkerProxy.h",
+]
+
+UNIFIED_SOURCES += [
+    "Promise.cpp",
+    "PromiseDebugging.cpp",
+    "PromiseNativeHandler.cpp",
+]
+
+LOCAL_INCLUDES += [
+    "../base",
+    "../ipc",
+    "/js/xpconnect/src",
+]
+
+TEST_DIRS += [
+    "gtest",
+]
+
+include("/ipc/chromium/chromium-config.mozbuild")
+
+FINAL_LIBRARY = "xul"
+
+MOCHITEST_MANIFESTS += ["tests/mochitest.ini"]
+
+MOCHITEST_CHROME_MANIFESTS += ["tests/chrome.ini"]
+
+XPCSHELL_TESTS_MANIFESTS += ["tests/unit/xpcshell.ini"]
diff --git a/dom/promise/tests/chrome.ini b/dom/promise/tests/chrome.ini
new file mode 100644
index 0000000000..1df9608c38
--- /dev/null
+++ b/dom/promise/tests/chrome.ini
@@ -0,0 +1,15 @@
+[DEFAULT]
+
+[test_on_new_promise.html]
+[test_on_promise_settled.html]
+[test_on_promise_settled_duplicates.html]
+[test_promise_xrays.html]
+support-files = file_promise_xrays.html
+[test_promise_argument_xrays.html]
+support-files = file_promise_xrays.html file_promise_argument_tests.js
+skip-if = debug == false
+[test_promise_retval_xrays.html]
+support-files = file_promise_xrays.html file_promise_retval_tests.js
+skip-if = debug == false
+[test_promise_job_with_bind_from_discarded_iframe.html]
+support-files = file_promise_job_with_bind_from_discarded_iframe.html
diff --git a/dom/promise/tests/file_promise_and_timeout_ordering.js b/dom/promise/tests/file_promise_and_timeout_ordering.js
new file mode 100644
index 0000000000..734621eae0
--- /dev/null
+++ b/dom/promise/tests/file_promise_and_timeout_ordering.js
@@ -0,0 +1,18 @@
+var log = [];
+var resolvedPromise = Promise.resolve(null);
+function schedulePromiseTask(f) {
+  resolvedPromise.then(f);
+}
+
+setTimeout(function () {
+  log.push("t1start");
+  schedulePromiseTask(function () {
+    log.push("promise");
+  });
+  log.push("t1end");
+}, 10);
+
+setTimeout(function () {
+  log.push("t2");
+  postMessage(log.join(", "));
+}, 10);
diff --git a/dom/promise/tests/file_promise_argument_tests.js b/dom/promise/tests/file_promise_argument_tests.js
new file mode 100644
index 0000000000..2a3b4e78c9
--- /dev/null
+++ b/dom/promise/tests/file_promise_argument_tests.js
@@ -0,0 +1,175 @@
+/*
+ * This file is meant to provide common infrastructure for several consumers.
+ * The consumer is expected to define the following things:
+ *
+ * 1) An verifyPromiseGlobal function which does whatever test the consumer
+ *    wants.
+ * 2) An isXrayArgumentTest global boolean, because some of these tests act
+ *    differenly based on that boolean.
+ * 3) A function named getPromise.  This function is given a global object and a
+ *    single argument to use for getting the promise.  The getPromise function
+ *    is expected to trigger the canonical Promise.resolve for the given global
+ *    with the given argument in some way that depends on the test, and return
+ *    the result.
+ * 4) A subframe (frames[0]) which can be used as a second global for creating
+ *    promises.
+ */
+
+/* global verifyPromiseGlobal, getPromise, isXrayArgumentTest */
+
+var label = "parent";
+
+function passBasicPromise() {
+  var p1 = Promise.resolve();
+  verifyPromiseGlobal(p1, window, "Promise.resolve return value 1");
+  var p2 = getPromise(window, p1);
+  is(p1, p2, "Basic promise should just pass on through");
+  return p2;
+}
+
+function passPrimitive(global) {
+  var p = getPromise(global, 5);
+  verifyPromiseGlobal(p, global, "Promise wrapping primitive");
+  return p.then(function (arg) {
+    is(arg, 5, "Should have the arg we passed in");
+  });
+}
+
+function passThenable(global) {
+  var called = false;
+  var thenable = {
+    then(f) {
+      called = true;
+      f(7);
+    },
+  };
+  var p = getPromise(global, thenable);
+  verifyPromiseGlobal(p, global, "Promise wrapping thenable");
+  return p.then(function (arg) {
+    ok(called, "Thenable should have been called");
+    is(arg, 7, "Should have the arg our thenable passed in");
+  });
+}
+
+function passWrongPromiseWithMatchingConstructor() {
+  var p1 = Promise.resolve();
+  verifyPromiseGlobal(p1, window, "Promise.resolve() return value 2");
+  p1.constructor = frames[0].Promise;
+  var p2 = getPromise(frames[0], p1);
+  // The behavior here will depend on whether we're touching frames[0] via Xrays
+  // or not.  If we are not, the current compartment while getting our promise
+  // will be that of frames[0].  If we are, it will be our window's compartment.
+  if (isXrayArgumentTest) {
+    isnot(
+      p1,
+      p2,
+      "Should have wrapped the Promise in a new promise, because its constructor is not matching the current-compartment Promise constructor"
+    );
+    verifyPromiseGlobal(
+      p2,
+      window,
+      "Promise wrapping xrayed promise with therefore non-matching constructor"
+    );
+  } else {
+    is(
+      p1,
+      p2,
+      "Should have left the Promise alone because its constructor matched"
+    );
+  }
+  return p2;
+}
+
+function passCorrectPromiseWithMismatchedConstructor() {
+  var p1 = Promise.resolve(9);
+  verifyPromiseGlobal(p1, window, "Promise.resolve() return value 3");
+  p1.constructor = frames[0].Promise;
+  var p2 = getPromise(window, p1);
+  isnot(
+    p1,
+    p2,
+    "Should have wrapped promise in a new promise, since its .constructor was wrong"
+  );
+  verifyPromiseGlobal(
+    p2,
+    window,
+    "Promise wrapping passed-in promise with mismatched constructor"
+  );
+  return p2.then(function (arg) {
+    is(arg, 9, "Should have propagated along our resolution value");
+  });
+}
+
+function passPromiseToOtherGlobal() {
+  var p1 = Promise.resolve();
+  verifyPromiseGlobal(p1, window, "Promise.resolve() return value 4");
+  var p2 = getPromise(frames[0], p1);
+  // The behavior here will depend on whether we're touching frames[0] via Xrays
+  // or not.  If we are not, the current compartment while getting our promise
+  // will be that of frames[0].  If we are, it will be our window's compartment.
+  if (isXrayArgumentTest) {
+    is(
+      p1,
+      p2,
+      "Should have left the Promise alone, because its constructor matches the current compartment's constructor"
+    );
+  } else {
+    isnot(
+      p1,
+      p2,
+      "Should have wrapped promise in a promise from the other global"
+    );
+    verifyPromiseGlobal(
+      p2,
+      frames[0],
+      "Promise wrapping passed-in basic promise"
+    );
+  }
+  return p2;
+}
+
+function passPromiseSubclass() {
+  class PromiseSubclass extends Promise {
+    constructor(func) {
+      super(func);
+    }
+  }
+
+  var p1 = PromiseSubclass.resolve(11);
+  verifyPromiseGlobal(p1, window, "PromiseSubclass.resolve() return value");
+  var p2 = getPromise(window, p1);
+  isnot(p1, p2, "Should have wrapped promise subclass in a new promise");
+  verifyPromiseGlobal(
+    p2,
+    window,
+    "Promise wrapping passed-in promise subclass"
+  );
+  return p2.then(function (arg) {
+    is(
+      arg,
+      11,
+      "Should have propagated along our resolution value from subclass"
+    );
+  });
+}
+
+function runPromiseArgumentTests(finishFunc) {
+  Promise.resolve()
+    .then(passBasicPromise)
+    .then(passPrimitive.bind(undefined, window))
+    .then(passPrimitive.bind(undefined, frames[0]))
+    .then(passThenable.bind(undefined, window))
+    .then(passThenable.bind(undefined, frames[0]))
+    .then(passWrongPromiseWithMatchingConstructor)
+    .then(passCorrectPromiseWithMismatchedConstructor)
+    .then(passPromiseToOtherGlobal)
+    .then(passPromiseSubclass)
+    .then(finishFunc)
+    .catch(function (e) {
+      ok(
+        false,
+        `Exception thrown: ${e}@${location.pathname}:${e.lineNumber}:${e.columnNumber}`
+      );
+      finishFunc();
+    });
+}
diff --git a/dom/promise/tests/file_promise_job_with_bind_from_discarded_iframe.html b/dom/promise/tests/file_promise_job_with_bind_from_discarded_iframe.html
new file mode 100644
index 0000000000..352cf6623e
--- /dev/null
+++ b/dom/promise/tests/file_promise_job_with_bind_from_discarded_iframe.html
@@ -0,0 +1,14 @@
+<!DOCTYPE html>
+<html>
+<head>
+<title>iframe in http</title>
+</head>
+<body>
+<div id="result"></div>
+<script type="text/javascript">
+if (typeof SpecialPowers !== "undefined") {
+  document.getElementById("result").textContent = "ok";
+}
+</script>
+</body>
+</html>
diff --git a/dom/promise/tests/file_promise_retval_tests.js b/dom/promise/tests/file_promise_retval_tests.js
new file mode 100644
index 0000000000..37ede9e514
--- /dev/null
+++ b/dom/promise/tests/file_promise_retval_tests.js
@@ -0,0 +1,56 @@
+/*
+ * This file is meant to provide common infrastructure for several consumers.
+ * The consumer is expected to define the following things:
+ *
+ * 1) A verifyPromiseGlobal function which does whatever test the consumer
+ *    wants.  This function is passed a promise and the global whose
+ *    TestFunctions was used to get the promise.
+ * 2) A expectedExceptionGlobal function which is handed the global whose
+ *    TestFunctions was used to trigger the exception and should return the
+ *    global the exception is expected to live in.
+ * 3) A subframe (frames[0]) which can be used as a second global for creating
+ *    promises.
+ */
+
+/* global verifyPromiseGlobal, expectedExceptionGlobal */
+
+var label = "parent";
+
+function testThrownException(global) {
+  var p = global.TestFunctions.throwToRejectPromise();
+  verifyPromiseGlobal(p, global, "throwToRejectPromise return value");
+  return p
+    .then(() => {})
+    .catch(err => {
+      var expected = expectedExceptionGlobal(global);
+      is(
+        SpecialPowers.unwrap(SpecialPowers.Cu.getGlobalForObject(err)),
+        expected,
+        "Should have an exception object from the right global too"
+      );
+      ok(
+        err instanceof expected.DOMException,
+        "Should have a DOMException here"
+      );
+      is(
+        Object.getPrototypeOf(err),
+        expected.DOMException.prototype,
+        "Should have a DOMException from the right global"
+      );
+      is(err.name, "InvalidStateError", "Should have the right DOMException");
+    });
+}
+
+function runPromiseRetvalTests(finishFunc) {
+  Promise.resolve()
+    .then(testThrownException.bind(undefined, window))
+    .then(testThrownException.bind(undefined, frames[0]))
+    .then(finishFunc)
+    .catch(function (e) {
+      ok(
+        false,
+        `Exception thrown: ${e}@${location.pathname}:${e.lineNumber}:${e.columnNumber}`
+      );
+      finishFunc();
+    });
+}
diff --git a/dom/promise/tests/file_promise_xrays.html b/dom/promise/tests/file_promise_xrays.html
new file mode 100644
index 0000000000..e08014a337
--- /dev/null
+++ b/dom/promise/tests/file_promise_xrays.html
@@ -0,0 +1,34 @@
+<!DOCTYPE html>
+<html>
+  <script>
+    function vendGetter(name) {
+      // eslint-disable-next-line no-throw-literal
+      return function() { throw "Getting " + String(name); };
+    }
+    function vendSetter(name) {
+      // eslint-disable-next-line no-throw-literal
+      return function() { throw "Setting " + String(name); };
+    }
+    var setupThrew = false;
+    try {
+      // Neuter everything we can think of on Promise.
+      for (var obj of [Promise, Promise.prototype]) {
+        let propNames = Object.getOwnPropertyNames(obj);
+        propNames = propNames.concat(Object.getOwnPropertySymbols(obj));
+        for (var propName of propNames) {
+          if ((propName == "prototype" ||
+               propName == Symbol.hasInstance) &&
+              obj == Promise) {
+            // They're not configurable.
+            continue;
+          }
+          Object.defineProperty(obj, propName,
+            { get: vendGetter(propName), set: vendSetter(propName) });
+        }
+      }
+    } catch (e) {
+      // Something went wrong.  Save that info so the test can check for it.
+      setupThrew = e;
+    }
+  </script>
+</html>
diff --git a/dom/promise/tests/mochitest.ini b/dom/promise/tests/mochitest.ini
new file mode 100644
index 0000000000..bc3c3e4787
--- /dev/null
+++ b/dom/promise/tests/mochitest.ini
@@ -0,0 +1,28 @@
+[DEFAULT]
+support-files =
+  promise_uncatchable_exception.js
+
+[test_bug883683.html]
+[test_promise.html]
+[test_promise_uncatchable_exception.html]
+skip-if = debug == false
+[test_promise_utils.html]
+[test_resolve.html]
+[test_resolver_return_value.html]
+[test_thenable_vs_promise_ordering.html]
+[test_promise_and_timeout_ordering.html]
+support-files = file_promise_and_timeout_ordering.js
+[test_promise_and_timeout_ordering_workers.html]
+support-files = file_promise_and_timeout_ordering.js
+[test_species_getter.html]
+[test_webassembly_compile.html]
+support-files = test_webassembly_compile_sample.wasm test_webassembly_compile_worker.js test_webassembly_compile_worker_terminate.js
+[test_promise_argument.html]
+support-files = file_promise_argument_tests.js
+skip-if = debug == false
+[test_promise_callback_retval.html]
+support-files = file_promise_argument_tests.js
+skip-if = debug == false
+[test_promise_retval.html]
+support-files = file_promise_retval_tests.js
+skip-if = debug == false
diff --git a/dom/promise/tests/promise_uncatchable_exception.js b/dom/promise/tests/promise_uncatchable_exception.js
new file mode 100644
index 0000000000..eafc9e5448
--- /dev/null
+++ b/dom/promise/tests/promise_uncatchable_exception.js
@@ -0,0 +1,11 @@
+/* global TestFunctions */
+
+postMessage("Done", "*");
+
+var p = new Promise(function (resolve, reject) {
+  TestFunctions.throwUncatchableException();
+  ok(false, "Shouldn't get here!");
+}).catch(function (exception) {
+  ok(false, "Shouldn't get here!");
+});
+ok(false, "Shouldn't get here!");
diff --git a/dom/promise/tests/test_bug883683.html b/dom/promise/tests/test_bug883683.html
new file mode 100644
index 0000000000..1b31e32330
--- /dev/null
+++ b/dom/promise/tests/test_bug883683.html
@@ -0,0 +1,41 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<html>
+<head>
+  <title>Promise - bug 883683</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="application/javascript"><!--
+
+function runTest() {
+  [{}, {}, {}, {}, {}].reduce(Promise.reject.bind(Promise));
+  ok(true, "No leaks with reject?");
+
+  [{}, {}, {}, {}, {}].reduce(Promise.resolve.bind(Promise));
+  ok(true, "No leaks with resolve?");
+
+  [{}, {}, {}, {}, {}].reduce(function(a, b, c, d) { return new Promise(function(r1, r2) { throw a; }); });
+  ok(true, "No leaks with exception?");
+
+  [{}, {}, {}, {}, {}].reduce(function(a, b, c, d) { return new Promise(function(r1, r2) { }); });
+  ok(true, "No leaks with empty promise?");
+
+  SimpleTest.finish();
+}
+
+SimpleTest.waitForExplicitFinish();
+runTest();
+// -->
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/promise/tests/test_on_new_promise.html b/dom/promise/tests/test_on_new_promise.html
new file mode 100644
index 0000000000..195707f1d7
--- /dev/null
+++ b/dom/promise/tests/test_on_new_promise.html
@@ -0,0 +1,45 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+
+<!--
+Bug 1083210 - Sanity test for interaction between DOM promises and
+Debugger.prototype.onNewPromise.
+-->
+
+<html>
+<head>
+  <title>Test for interaction with SpiderMonkey's Debugger.prototype.onNewPromise</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>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+  <script type="application/javascript">
+  is(Object.prototype.toString.call(new Promise(function() {})),
+     "[object Promise]",
+     "We should have the native DOM promise implementation.");
+
+  const {addDebuggerToGlobal} = ChromeUtils.importESModule("resource://gre/modules/jsdebugger.sys.mjs");
+  var dbgGlobal = new Cu.Sandbox(document.nodePrincipal,
+                                 {freshCompartment: true});
+  addDebuggerToGlobal(dbgGlobal);
+  var dbg = new dbgGlobal.Debugger(this);
+
+  var wrappedPromise;
+  dbg.onNewPromise = function(wp) { wrappedPromise = wp; };
+
+  var promise = new Promise(function() {});
+  // eslint-disable-next-line no-debugger
+  debugger;
+  ok(wrappedPromise);
+  is(wrappedPromise.unsafeDereference(), promise);
+  </script>
+</pre>
+</body>
+</html>
diff --git a/dom/promise/tests/test_on_promise_settled.html b/dom/promise/tests/test_on_promise_settled.html
new file mode 100644
index 0000000000..b40475206b
--- /dev/null
+++ b/dom/promise/tests/test_on_promise_settled.html
@@ -0,0 +1,53 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+
+<!--
+Bug 1084065 - Sanity test for interaction between DOM promises and
+Debugger.prototype.onPromiseResolved.
+-->
+
+<html>
+<head>
+  <title>Test for interaction with SpiderMonkey's Debugger.prototype.onNewPromise</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>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+  <script type="application/javascript">
+  SimpleTest.waitForExplicitFinish();
+
+  is(Object.prototype.toString.call(new Promise(function() {})),
+     "[object Promise]",
+     "We should have the native DOM promise implementation.");
+
+  const {addDebuggerToGlobal} = ChromeUtils.importESModule("resource://gre/modules/jsdebugger.sys.mjs");
+  var dbgGlobal = new Cu.Sandbox(document.nodePrincipal,
+                                 {freshCompartment: true});
+  addDebuggerToGlobal(dbgGlobal);
+  var dbg = new dbgGlobal.Debugger(this);
+
+  var wrappedPromise;
+  dbg.onPromiseSettled = function(wp) { wrappedPromise = wp; };
+
+  var promise = Promise.resolve();
+  promise
+    .then(function() {
+      ok(wrappedPromise);
+      is(wrappedPromise.unsafeDereference(), promise);
+      dbg.onPromiseSettled = undefined;
+    })
+    .catch(function(e) {
+      ok(false, "Got an unexpected error: " + e);
+    })
+    .then(SimpleTest.finish);
+  </script>
+</pre>
+</body>
+</html>
diff --git a/dom/promise/tests/test_on_promise_settled_duplicates.html b/dom/promise/tests/test_on_promise_settled_duplicates.html
new file mode 100644
index 0000000000..e11f4eaa60
--- /dev/null
+++ b/dom/promise/tests/test_on_promise_settled_duplicates.html
@@ -0,0 +1,58 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+
+<!--
+Bug 1084065 - Test that Debugger.prototype.onPromiseResolved doesn't get dupes.
+-->
+
+<html>
+<head>
+  <title>Test for interaction with SpiderMonkey's Debugger.prototype.onNewPromise</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>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+  <script type="application/javascript">
+  SimpleTest.waitForExplicitFinish();
+
+  is(Object.prototype.toString.call(new Promise(function() {})),
+     "[object Promise]",
+     "We should have the native DOM promise implementation.");
+
+  const {addDebuggerToGlobal} = ChromeUtils.importESModule("resource://gre/modules/jsdebugger.sys.mjs");
+  var dbgGlobal = new Cu.Sandbox(document.nodePrincipal,
+                                 {freshCompartment: true});
+  addDebuggerToGlobal(dbgGlobal);
+  var dbg = new dbgGlobal.Debugger(this);
+
+  var seen = new Set();
+  dbg.onPromiseSettled = function(wp) {
+    is(seen.has(wp), false);
+    seen.add(wp);
+  };
+
+  var promise = new Promise(function(fulfill, reject) {
+    fulfill(1);
+    fulfill(2);
+    fulfill(3);
+  });
+
+  promise
+    .then(function() {
+      dbg.onPromiseSettled = undefined;
+    })
+    .catch(function(e) {
+      ok(false, "Got an unexpected error: " + e);
+    })
+    .then(SimpleTest.finish);
+  </script>
+</pre>
+</body>
+</html>
diff --git a/dom/promise/tests/test_promise.html b/dom/promise/tests/test_promise.html
new file mode 100644
index 0000000000..7c724daf51
--- /dev/null
+++ b/dom/promise/tests/test_promise.html
@@ -0,0 +1,844 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<html>
+<head>
+  <title>Basic Promise Test</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="application/javascript"><!--
+
+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);
+  });
+  promise.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();
+  });
+  promise.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 promiseReject() {
+  var promise = new Promise(function(resolve, reject) {
+    reject(42);
+  });
+  promise.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 promiseRejectNoHandler() {
+  // This test only checks that the code that reports unhandled errors in the
+  // Promises implementation does not crash or leak.
+
+  new Promise(function(res, rej) {
+    // eslint-disable-next-line no-undef
+    noSuchMethod();
+  });
+  runTest();
+}
+
+function promiseRejectNoArg() {
+  var promise = new Promise(function(resolve, reject) {
+    reject();
+  });
+  promise.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) {
+    // eslint-disable-next-line no-throw-literal
+    throw 42;
+  });
+  promise.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 promiseGC() {
+  var resolve;
+  var promise = new Promise(function(r1, r2) {
+    resolve = r1;
+  });
+  promise.then(function(what) {
+    ok(true, "Then - promise is still alive");
+    runTest();
+  });
+
+  promise = null;
+
+  SpecialPowers.gc();
+  SpecialPowers.forceGC();
+  SpecialPowers.forceCC();
+
+  resolve(42);
+}
+
+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_SyncXHR() {
+  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.");
+}
+
+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");
+    // eslint-disable-next-line no-throw-literal
+    throw "booh";
+  }).catch(function(e) {
+    ok(true, "window.onerror 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 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 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");
+    // eslint-disable-next-line no-throw-literal
+    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 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(res, rej) {
+      ok(true, "Nested promise is executed");
+      res(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(res, rej) {
+      ok(true, "Nested promise is executed");
+      res(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(res, rej) {
+      ok(true, "Nested promise is executed");
+      res(new Promise(function(resInner, rejInner) {
+        ok(true, "Nested nested promise is executed");
+        resInner(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);
+  promise.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);
+  promise.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");
+  }));
+  promise.then(function(what) {
+    is(what, 42, "Value == 42");
+    runTest();
+  }, function() {
+    ok(false, "This should not be called");
+  });
+}
+
+function promiseSimpleThenableResolve() {
+  var thenable = { then(resolve) { resolve(5); } };
+  var promise = new Promise(function(resolve, reject) {
+    resolve(thenable);
+  });
+
+  promise.then(function(v) {
+    ok(v === 5, "promiseSimpleThenableResolve");
+    runTest();
+  }, function(e) {
+    ok(false, "promiseSimpleThenableResolve: Should not reject");
+  });
+}
+
+function promiseSimpleThenableReject() {
+  var thenable = { then(resolve, reject) { reject(5); } };
+  var promise = new Promise(function(resolve, reject) {
+    resolve(thenable);
+  });
+
+  promise.then(function() {
+    ok(false, "promiseSimpleThenableReject: Should not resolve");
+    runTest();
+  }, function(e) {
+    ok(e === 5, "promiseSimpleThenableReject");
+    runTest();
+  });
+}
+
+function promiseThenableThrowsBeforeCallback() {
+  var thenable = { then(resolve) {
+    throw new TypeError("Hi there");
+
+    // eslint-disable-next-line no-unreachable
+    resolve(5);
+  }};
+
+  var promise = Promise.resolve(thenable);
+  promise.then(function(v) {
+    ok(false, "promiseThenableThrowsBeforeCallback: Should've rejected");
+    runTest();
+  }, function(e) {
+    ok(e instanceof TypeError, "promiseThenableThrowsBeforeCallback");
+    runTest();
+  });
+}
+
+function promiseThenableThrowsAfterCallback() {
+  var thenable = { then(resolve) {
+    resolve(5);
+    throw new TypeError("Hi there");
+  }};
+
+  var promise = Promise.resolve(thenable);
+  promise.then(function(v) {
+    ok(v === 5, "promiseThenableThrowsAfterCallback");
+    runTest();
+  }, function(e) {
+    ok(false, "promiseThenableThrowsAfterCallback: Should've resolved");
+    runTest();
+  });
+}
+
+function promiseThenableRejectThenResolve() {
+  var thenable = { then(resolve, reject) {
+    reject(new TypeError("Hi there"));
+    resolve(5);
+  }};
+
+  var promise = Promise.resolve(thenable);
+  promise.then(function(v) {
+    ok(false, "promiseThenableRejectThenResolve should have rejected");
+    runTest();
+  }, function(e) {
+    ok(e instanceof TypeError, "promiseThenableRejectThenResolve");
+    runTest();
+  });
+}
+
+function promiseWithThenReplaced() {
+  // Ensure that we call the 'then' on the promise and not the internal then.
+  var promise = new Promise(function(resolve, reject) {
+    resolve(5);
+  });
+
+  // Rogue `then` always rejects.
+  promise.then = function(onFulfill, onReject) {
+    onReject(new TypeError("Foo"));
+  };
+
+  var promise2 = Promise.resolve(promise);
+  promise2.then(function(v) {
+    ok(false, "promiseWithThenReplaced: Should've rejected");
+    runTest();
+  }, function(e) {
+    ok(e instanceof TypeError, "promiseWithThenReplaced");
+    runTest();
+  });
+}
+
+function promiseStrictHandlers() {
+  var promise = Promise.resolve(5);
+  promise.then(function() {
+    "use strict";
+    ok(this === undefined, "Strict mode callback should have this === undefined.");
+    runTest();
+  });
+}
+
+function promiseStrictExecutorThisArg() {
+  new Promise(function(resolve, reject) {
+    "use strict";
+    ok(this === undefined, "thisArg should be undefined.");
+    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 1008467 - Promise fails with "too much recursion".
+// The bug was that the callbacks passed to a thenable would resolve the
+// promise synchronously when the fulfill handler returned a non-thenable.
+//
+// For example:
+// var p = new Promise(function(resolve) {
+//   resolve(5);
+// });
+// var m = Promise.resolve(p);
+//
+// At this point `m` is a Promise that is resolved with a thenable `p`, so it
+// calls `p.then()` with two callbacks, both of which would synchronously resolve
+// `m` when `p` invoked them (on account of itself being resolved, possibly
+// synchronously. A chain of these 'Promise resolved by a Promise' would lead to
+// stack overflow.
+function promiseTestAsyncThenableResolution() {
+  var k = 3000;
+  Promise.resolve().then(function next() {
+    k--;
+    if (k > 0) return Promise.resolve().then(next);
+    return undefined;
+  }).then(function() {
+    ok(true, "Resolution of a chain of thenables should not be synchronous.");
+    runTest();
+  });
+}
+
+// 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";
+                info(results);
+    ok(match, "Chained promises should resolve asynchronously.");
+    runTest();
+  }, function() {
+    ok(false, "promiseWrapperAsyncResolution: One of the promises failed.");
+    runTest();
+  });
+}
+
+var tests = [ promiseResolve, promiseReject,
+              promiseException, promiseGC,
+              promiseAsync_TimeoutResolveThen,
+              promiseAsync_ResolveTimeoutThen,
+              promiseAsync_ResolveThenTimeout,
+              promiseAsync_SyncXHR,
+              promiseDoubleThen, promiseThenException,
+              promiseThenCatchThen, promiseRejectThenCatchThen,
+              promiseRejectThenCatchThen2,
+              promiseRejectThenCatchExceptionThen,
+              promiseThenCatchOrderingResolve,
+              promiseThenCatchOrderingReject,
+              promiseNestedPromise, promiseNestedNestedPromise,
+              promiseWrongNestedPromise, promiseLoop,
+              promiseStaticReject, promiseStaticResolve,
+              promiseResolveNestedPromise,
+              promiseResolveNoArg,
+              promiseRejectNoArg,
+              promiseThenNoArg,
+              promiseThenUndefinedResolveFunction,
+              promiseThenNullResolveFunction,
+              promiseCatchNoArg,
+              promiseRejectNoHandler,
+              promiseSimpleThenableResolve,
+              promiseSimpleThenableReject,
+              promiseThenableThrowsBeforeCallback,
+              promiseThenableThrowsAfterCallback,
+              promiseThenableRejectThenResolve,
+              promiseWithThenReplaced,
+              promiseStrictHandlers,
+              promiseStrictExecutorThisArg,
+              promiseResolveArray,
+              promiseResolveThenable,
+              promiseResolvePromise,
+              promiseResolveThenableCleanStack,
+              promiseTestAsyncThenableResolution,
+              promiseWrapperAsyncResolution,
+            ];
+
+function runTest() {
+  if (!tests.length) {
+    SimpleTest.finish();
+    return;
+  }
+
+  var test = tests.shift();
+  test();
+}
+
+SimpleTest.waitForExplicitFinish();
+SimpleTest.requestFlakyTimeout("untriaged");
+runTest();
+// -->
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/promise/tests/test_promise_and_timeout_ordering.html b/dom/promise/tests/test_promise_and_timeout_ordering.html
new file mode 100644
index 0000000000..e92e928e75
--- /dev/null
+++ b/dom/promise/tests/test_promise_and_timeout_ordering.html
@@ -0,0 +1,16 @@
+<!DOCTYPE html>
+<meta charset=utf-8>
+<title>Test for promise and timeout ordering</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id="log"></div>
+<script>
+/* global async_test, assert_equals */
+var t = async_test("Promise callbacks should run immediately after the setTimeout handler that enqueues them");
+var origPostMessage = window.postMessage;
+window.postMessage = function(msg) { origPostMessage.call(window, msg, "*"); };
+window.onmessage = t.step_func_done(function(e) {
+  assert_equals(e.data, "t1start, t1end, promise, t2");
+});
+</script>
+<script src="file_promise_and_timeout_ordering.js"></script>
diff --git a/dom/promise/tests/test_promise_and_timeout_ordering_workers.html b/dom/promise/tests/test_promise_and_timeout_ordering_workers.html
new file mode 100644
index 0000000000..85fd4c0019
--- /dev/null
+++ b/dom/promise/tests/test_promise_and_timeout_ordering_workers.html
@@ -0,0 +1,14 @@
+<!DOCTYPE html>
+<meta charset=utf-8>
+<title>Test for promise and timeout ordering in workers</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id="log"></div>
+<script>
+/* global async_test, assert_equals */
+var t = async_test("Promise callbacks in workers should run immediately after the setTimeout handler that enqueues them");
+var w = new Worker("file_promise_and_timeout_ordering.js");
+w.onmessage = t.step_func_done(function(e) {
+  assert_equals(e.data, "t1start, t1end, promise, t2");
+});
+</script>
diff --git a/dom/promise/tests/test_promise_argument.html b/dom/promise/tests/test_promise_argument.html
new file mode 100644
index 0000000000..22343ef00f
--- /dev/null
+++ b/dom/promise/tests/test_promise_argument.html
@@ -0,0 +1,49 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1323324
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1323324</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  <script src="file_promise_argument_tests.js"></script>
+  <script type="application/javascript">
+  /** Test for Bug 1323324 **/
+  SimpleTest.waitForExplicitFinish();
+
+  var globalWrapper;
+  function verifyPromiseGlobal(p, global, msg) {
+    // SpecialPowers.Cu.getGlobalForObject returns a SpecialPowers wrapper for
+    // the actual global.  We want to grab the underlying object.
+    globalWrapper = SpecialPowers.Cu.getGlobalForObject(p);
+    is(SpecialPowers.unwrap(globalWrapper), global,
+       msg + " should come from " + global.label);
+  }
+
+  const isXrayArgumentTest = false;
+
+  function getPromise(global, arg) {
+    return global.TestFunctions.passThroughPromise(arg);
+  }
+
+  addLoadEvent(function() {
+    frames[0].label = "child";
+    SpecialPowers.pushPrefEnv({set: [["dom.expose_test_interfaces", true]]},
+                              runPromiseArgumentTests.bind(undefined,
+                                                           SimpleTest.finish));
+  });
+  </script>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1323324">Mozilla Bug 1323324</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+  <!-- A subframe so we have another global to work with -->
+  <iframe></iframe>
+</div>
+<pre id="test">
+</pre>
+</body>
+</html>
diff --git a/dom/promise/tests/test_promise_argument_xrays.html b/dom/promise/tests/test_promise_argument_xrays.html
new file mode 100644
index 0000000000..f3a234cf6d
--- /dev/null
+++ b/dom/promise/tests/test_promise_argument_xrays.html
@@ -0,0 +1,90 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1233324
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1233324</title>
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="chrome://global/skin"/>
+  <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1233324">Mozilla Bug 1233324</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+<iframe id="t" src="http://example.org/chrome/dom/promise/tests/file_promise_xrays.html"></iframe>
+</div>
+
+<pre id="test">
+<script src="file_promise_argument_tests.js"></script>
+<script type="application/javascript">
+
+var win = $("t").contentWindow;
+
+/** Test for Bug 1233324 **/
+SimpleTest.waitForExplicitFinish();
+
+function testLoadComplete() {
+  is(win.location.href, $("t").src, "Should have loaded the right thing");
+  nextTest();
+}
+
+function testHaveXray() {
+  is(typeof win.Promise.race, "function", "Should see a race() function");
+  var exception;
+  try {
+    win.Promise.wrappedJSObject.race;
+  } catch (e) {
+    exception = e;
+  }
+  is(exception, "Getting race", "Should have thrown the right exception");
+  is(win.wrappedJSObject.setupThrew, false, "Setup should not have thrown");
+  nextTest();
+}
+
+function verifyPromiseGlobal(p, _, msg) {
+  // SpecialPowers.Cu.getGlobalForObject returns a SpecialPowers wrapper for
+  // the actual global.  We want to grab the underlying object.
+  var global = SpecialPowers.unwrap(SpecialPowers.Cu.getGlobalForObject(p));
+
+  // We expect our global to always be "window" here, because we're working over
+  // Xrays.
+  is(global, window, msg + " should come from " + window.label);
+}
+
+const isXrayArgumentTest = true;
+
+function getPromise(global, arg) {
+  return global.TestFunctions.passThroughPromise(arg);
+}
+
+function testPromiseArgumentConversions() {
+  runPromiseArgumentTests(nextTest);
+}
+
+var tests = [
+  testLoadComplete,
+  testHaveXray,
+  testPromiseArgumentConversions,
+];
+
+function nextTest() {
+  if (!tests.length) {
+    SimpleTest.finish();
+    return;
+  }
+  tests.shift()();
+}
+
+addLoadEvent(function() {
+  frames[0].label = "child";
+  SpecialPowers.pushPrefEnv({set: [["dom.expose_test_interfaces", true]]},
+                            nextTest);
+});
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/promise/tests/test_promise_callback_retval.html b/dom/promise/tests/test_promise_callback_retval.html
new file mode 100644
index 0000000000..332c370a3e
--- /dev/null
+++ b/dom/promise/tests/test_promise_callback_retval.html
@@ -0,0 +1,53 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1323324
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1323324</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  <script src="file_promise_argument_tests.js"></script>
+  <script type="application/javascript">
+  /* global TestFunctions */
+
+  /** Test for Bug 1323324 **/
+  SimpleTest.waitForExplicitFinish();
+
+  var globalWrapper;
+  function verifyPromiseGlobal(p, global, msg) {
+    // SpecialPowers.Cu.getGlobalForObject returns a SpecialPowers wrapper for
+    // the actual global.  We want to grab the underlying object.
+    globalWrapper = SpecialPowers.Cu.getGlobalForObject(p);
+    is(SpecialPowers.unwrap(globalWrapper), global,
+       msg + " should come from " + global.label);
+  }
+
+  const isXrayArgumentTest = false;
+
+  var func;
+  function getPromise(global, arg) {
+    func = new global.Function("x", "return x").bind(undefined, arg);
+    return TestFunctions.passThroughCallbackPromise(func);
+  }
+
+  addLoadEvent(function() {
+    frames[0].label = "child";
+    SpecialPowers.pushPrefEnv({set: [["dom.expose_test_interfaces", true]]},
+                              runPromiseArgumentTests.bind(undefined,
+                                                           SimpleTest.finish));
+  });
+  </script>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1323324">Mozilla Bug 1323324</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+  <!-- A subframe so we have another global to work with -->
+  <iframe></iframe>
+</div>
+<pre id="test">
+</pre>
+</body>
+</html>
diff --git a/dom/promise/tests/test_promise_job_with_bind_from_discarded_iframe.html b/dom/promise/tests/test_promise_job_with_bind_from_discarded_iframe.html
new file mode 100644
index 0000000000..1cea250072
--- /dev/null
+++ b/dom/promise/tests/test_promise_job_with_bind_from_discarded_iframe.html
@@ -0,0 +1,63 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1723124.
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1723124.</title>
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="chrome://global/skin"/>
+  <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1723124.">Mozilla Bug 1723124.</a>
+
+<iframe id="frame" src="http://example.org/chrome/dom/promise/tests/file_promise_job_with_bind_from_discarded_iframe.html"></iframe>
+
+<pre id="test">
+<script type="text/javascript">
+/** Test for Bug 1723124. **/
+SimpleTest.waitForExplicitFinish();
+
+var frame = document.getElementById("frame");
+
+SimpleTest.waitForCondition(() => {
+  var result = frame.contentDocument.getElementById("result");
+  if (!result) {
+    return false;
+  }
+  // Wait for the iframe's script to check if it has no access to SpecialPowers.
+  return result.textContent == "ok";
+}, () => {
+  var iframe_bind = frame.contentWindow.Function.prototype.bind;
+  // Removing iframe from the tree discards the browsing context,
+  // and promise jobs in the iframe global stops working.
+  frame.remove();
+
+  Promise.resolve(10)
+    .then(function (v) {
+      // Handler in top-level realm, without bind.
+      //
+      // This job is created with the top-level realm, and should be called.
+      is(v, 10, "normal function should get the value from promise");
+      return 20;
+    }, function () {
+      ok(false, "unexpectedly rejected");
+    })
+    .then(iframe_bind.call(function (bound_arg, v) {
+      // Handler in top-level realm, with bind in discarded iframe.
+      //
+      // This job is also created with the top-level realm, and should be
+      // called.
+      is(v, 20, "bound function should get the value from promise");
+      is(bound_arg, 30, "bound function should get the arguments from bind");
+      SimpleTest.finish();
+    }, this, 30), function () {
+      ok(false, "unexpectedly rejected");
+    });
+});
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/promise/tests/test_promise_retval.html b/dom/promise/tests/test_promise_retval.html
new file mode 100644
index 0000000000..e425b8e203
--- /dev/null
+++ b/dom/promise/tests/test_promise_retval.html
@@ -0,0 +1,51 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1436276.
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1436276.</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+  <script src="file_promise_retval_tests.js"></script>
+  <script type="application/javascript">
+  /** Test for Bug 1436276. **/
+  SimpleTest.waitForExplicitFinish();
+
+  function verifyPromiseGlobal(p, global, msg) {
+    // SpecialPowers.Cu.getGlobalForObject returns a SpecialPowers wrapper for
+    // the actual global.  We want to grab the underlying object.
+    var globalWrapper = SpecialPowers.Cu.getGlobalForObject(p);
+    is(SpecialPowers.unwrap(globalWrapper), global,
+       msg + " should come from " + global.label);
+  }
+
+  function expectedExceptionGlobal(global) {
+    // We should end up with an exception from "global".
+    return global;
+  }
+
+  function getPromise(global, arg) {
+    return global.TestFunctions.passThroughPromise(arg);
+  }
+
+  addLoadEvent(function() {
+    frames[0].label = "child";
+    SpecialPowers.pushPrefEnv({set: [["dom.expose_test_interfaces", true]]},
+                              runPromiseRetvalTests.bind(undefined,
+                                                         SimpleTest.finish));
+  });
+  </script>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1323324">Mozilla Bug 1323324</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+  <!-- A subframe so we have another global to work with -->
+  <iframe></iframe>
+</div>
+<pre id="test">
+</pre>
+</body>
+</html>
diff --git a/dom/promise/tests/test_promise_retval_xrays.html b/dom/promise/tests/test_promise_retval_xrays.html
new file mode 100644
index 0000000000..1270e3a3bb
--- /dev/null
+++ b/dom/promise/tests/test_promise_retval_xrays.html
@@ -0,0 +1,94 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1436276.
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1436276.</title>
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="chrome://global/skin"/>
+  <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1436276.">Mozilla Bug 1436276.</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+<iframe id="t" src="http://example.org/chrome/dom/promise/tests/file_promise_xrays.html"></iframe>
+</div>
+
+<pre id="test">
+<script src="file_promise_retval_tests.js"></script>
+<script type="application/javascript">
+
+var win = $("t").contentWindow;
+
+/** Test for Bug 1233324 **/
+SimpleTest.waitForExplicitFinish();
+
+function testLoadComplete() {
+  is(win.location.href, $("t").src, "Should have loaded the right thing");
+  nextTest();
+}
+
+function testHaveXray() {
+  is(typeof win.Promise.race, "function", "Should see a race() function");
+  var exception;
+  try {
+    win.Promise.wrappedJSObject.race;
+  } catch (e) {
+    exception = e;
+  }
+  is(exception, "Getting race", "Should have thrown the right exception");
+  is(win.wrappedJSObject.setupThrew, false, "Setup should not have thrown");
+  nextTest();
+}
+
+function verifyPromiseGlobal(p, _, msg) {
+  // SpecialPowers.Cu.getGlobalForObject returns a SpecialPowers wrapper for
+  // the actual global.  We want to grab the underlying object.
+  var global = SpecialPowers.unwrap(SpecialPowers.Cu.getGlobalForObject(p));
+
+  // We expect our global to always be "window" here, because we're working over
+  // Xrays.
+  is(global, window, msg + " should come from " + window.label);
+}
+
+function expectedExceptionGlobal(_) {
+  // We should end up with an exception from "window" no matter what global
+  // was involved to start with, because we're working over Xrays.
+  return window;
+}
+
+function getPromise(global, arg) {
+  return global.TestFunctions.passThroughPromise(arg);
+}
+
+function testPromiseRetvals() {
+  runPromiseRetvalTests(nextTest);
+}
+
+var tests = [
+  testLoadComplete,
+  testHaveXray,
+  testPromiseRetvals,
+];
+
+function nextTest() {
+  if (!tests.length) {
+    SimpleTest.finish();
+    return;
+  }
+  tests.shift()();
+}
+
+addLoadEvent(function() {
+  frames[0].label = "child";
+  SpecialPowers.pushPrefEnv({set: [["dom.expose_test_interfaces", true]]},
+                            nextTest);
+});
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/promise/tests/test_promise_uncatchable_exception.html b/dom/promise/tests/test_promise_uncatchable_exception.html
new file mode 100644
index 0000000000..2bb6f1fe17
--- /dev/null
+++ b/dom/promise/tests/test_promise_uncatchable_exception.html
@@ -0,0 +1,35 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<html>
+<head>
+  <title>Promise - uncatchable exceptions</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="application/javascript">
+
+onmessage = function(evt) {
+  ok(true, "finished");
+  SimpleTest.finish();
+};
+
+function go() {
+  var script = document.createElement("script");
+  script.src = "promise_uncatchable_exception.js";
+  document.body.appendChild(script);
+}
+
+SimpleTest.waitForExplicitFinish();
+SpecialPowers.pushPrefEnv({set: [["dom.expose_test_interfaces", true]]}, go);
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/promise/tests/test_promise_utils.html b/dom/promise/tests/test_promise_utils.html
new file mode 100644
index 0000000000..b20d909351
--- /dev/null
+++ b/dom/promise/tests/test_promise_utils.html
@@ -0,0 +1,313 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<html>
+<head>
+  <title>Test for Promise.all, Promise.race</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="application/javascript"><!--
+
+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 promiseAllEmptyArray() {
+  var p = Promise.all([]);
+  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, 0, "Resolved array length should match iterable's length.");
+    runTest();
+  }, function() {
+    ok(false, "Promise.all shouldn't fail when iterable has no rejected Promises.");
+    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 promiseAllIterable() {
+  function* promiseGen() {
+    var i = 3;
+    while (--i) {
+      yield Promise.resolve(i);
+    }
+
+    yield new Promise(function(resolve) {
+      setTimeout(resolve, 10);
+    });
+  }
+
+  Promise.all(promiseGen()).then(function(values) {
+    is(values.length, 3, "Resolved array length should match iterable's length.");
+    is(values[0], 2, "Array values should match.");
+    is(values[1], 1, "Array values should match.");
+    is(values[2], undefined, "Array values should match.");
+    runTest();
+  }, function(e) {
+    ok(false, "Promise.all shouldn't fail when an iterable is passed.");
+    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 promiseAllCastError() {
+  var p = Promise.all([Promise.resolve(2), { then() {
+    throw new ReferenceError("placeholder for nonexistent function call");
+  } }]);
+  ok(p instanceof Promise, "Should cast to a Promise.");
+  p.then(function(v) {
+    ok(false, "promiseAllCastError: should've rejected.");
+    runTest();
+  }, function(e) {
+    ok(e instanceof ReferenceError, "promiseCastThenableError");
+    runTest();
+  });
+}
+
+// Check that the resolved array is enumerable.
+function promiseAllEnumerable() {
+  var p = Promise.all([1, new Date(), Promise.resolve("firefox")]);
+  p.then(function(v) {
+    var count = 0;
+    for (let key in v) {
+      ++count;
+      ok(v[key] === 1 || v[key] instanceof Date || v[key] === "firefox",
+         "Enumerated properties don't match.");
+    }
+    is(count, 3, "Resolved array from Promise.all should be enumerable");
+    runTest();
+  }, function(e) {
+    ok(false, "promiseAllEnumerable: should've resolved.");
+    runTest();
+  });
+}
+
+function promiseRaceEmpty() {
+  var p = Promise.race([]);
+  ok(p instanceof Promise, "Should return a Promise.");
+  p.then(function() {
+    ok(false, "Should not resolve");
+  }, function() {
+    ok(false, "Should not reject");
+  });
+  // Per spec, An empty race never resolves or rejects.
+  setTimeout(function() {
+    ok(true);
+    runTest();
+  }, 50);
+}
+
+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 promiseRaceIterable() {
+  function* participants() {
+    yield new Promise(function(resolve) {
+      setTimeout(resolve, 10, 10);
+    });
+    yield new Promise(function(resolve) {
+      setTimeout(resolve, 20, 20);
+    });
+  }
+
+  Promise.race(participants()).then(function(winner) {
+    is(winner, 10, "Winner should be the one that finished earlier.");
+    runTest();
+  }, function(e) {
+    ok(false, "Promise.race shouldn't throw when an iterable is passed!");
+    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) {
+      throw new ReferenceError("placeholder for nonexistent function call");
+    }),
+    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();
+  });
+}
+
+var tests = [
+              promiseUtilitiesDefined,
+              promiseAllEmptyArray,
+              promiseAllArray,
+              promiseAllIterable,
+              promiseAllWaitsForAllPromises,
+              promiseAllRejectFails,
+              promiseAllCastError,
+              promiseAllEnumerable,
+
+              promiseRaceEmpty,
+              promiseRaceValuesArray,
+              promiseRacePromiseArray,
+              promiseRaceIterable,
+              promiseRaceReject,
+              promiseRaceThrow,
+            ];
+
+function runTest() {
+  if (!tests.length) {
+    SimpleTest.finish();
+    return;
+  }
+
+  var test = tests.shift();
+  test();
+}
+
+SimpleTest.waitForExplicitFinish();
+SimpleTest.requestFlakyTimeout("untriaged");
+runTest();
+// -->
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/promise/tests/test_promise_xrays.html b/dom/promise/tests/test_promise_xrays.html
new file mode 100644
index 0000000000..8559dbb2a4
--- /dev/null
+++ b/dom/promise/tests/test_promise_xrays.html
@@ -0,0 +1,365 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1170760
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1170760</title>
+  <script src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="chrome://global/skin"/>
+  <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1170760">Mozilla Bug 1170760</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+<iframe id="t" src="http://example.org/chrome/dom/promise/tests/file_promise_xrays.html"></iframe>
+</div>
+
+<pre id="test">
+<script type="application/javascript">
+
+var win = $("t").contentWindow;
+
+/** Test for Bug 1170760 **/
+SimpleTest.waitForExplicitFinish();
+
+function testLoadComplete() {
+  is(win.location.href, $("t").src, "Should have loaded the right thing");
+  nextTest();
+}
+
+function testHaveXray() {
+  is(typeof win.Promise.race, "function", "Should see a race() function");
+  var exception;
+  try {
+    win.Promise.wrappedJSObject.race;
+  } catch (e) {
+    exception = e;
+  }
+  is(exception, "Getting race", "Should have thrown the right exception");
+  is(win.wrappedJSObject.setupThrew, false, "Setup should not have thrown");
+  nextTest();
+}
+
+function testConstructor1() {
+  var p = new win.Promise(function(resolve, reject) { resolve(win.Promise.resolve(5)); });
+  p.then(
+    function(arg) {
+      is(arg, 5, "Content Promise constructor resolved with content promise should work");
+    },
+    function(e) {
+      ok(false, "Content Promise constructor resolved with content promise should not fail");
+    }
+  ).then(nextTest);
+}
+
+function testConstructor2() {
+  var p = new win.Promise(function(resolve, reject) { resolve(Promise.resolve(5)); });
+  p.then(
+    function(arg) {
+      is(arg, 5, "Content Promise constructor resolved with chrome promise should work");
+    },
+    function(e) {
+      ok(false, "Content Promise constructor resolved with chrome promise should not fail");
+    }
+  ).then(nextTest);
+}
+
+function testRace1() {
+  var p = win.Promise.race(new win.Array(1, 2));
+  p.then(
+    function(arg) {
+      ok(arg == 1 || arg == 2,
+         "Should get the right value when racing content-side array");
+    },
+    function(e) {
+      ok(false, "testRace1 threw exception: " + e);
+    }
+  ).then(nextTest);
+}
+
+function testRace2() {
+  var p = win.Promise.race(
+    [win.Promise.resolve(1), win.Promise.resolve(2)]);
+  p.then(
+    function(arg) {
+      ok(arg == 1 || arg == 2,
+         "Should get the right value when racing content-side array of explicit Promises");
+    },
+    function(e) {
+      ok(false, "testRace2 threw exception: " + e);
+    }
+  ).then(nextTest);
+}
+
+function testRace3() {
+  // This works with a chrome-side array because we do the iteration
+  // while still in the Xray compartment.
+  var p = win.Promise.race([1, 2]);
+  p.then(
+    function(arg) {
+      ok(arg == 1 || arg == 2,
+         "Should get the right value when racing chrome-side array");
+    },
+    function(e) {
+      ok(false, "testRace3 threw exception: " + e);
+    }
+  ).then(nextTest);
+}
+
+function testRace4() {
+  // This works with both content-side and chrome-side Promises because we want
+  // it to and go to some lengths to make it work.
+  var p = win.Promise.race([Promise.resolve(1), win.Promise.resolve(2)]);
+  p.then(
+    function(arg) {
+      ok(arg == 1 || arg == 2,
+         "Should get the right value when racing chrome-side promises");
+    },
+    function(e) {
+      ok(false, "testRace4 threw exception: " + e);
+    }
+  ).then(nextTest);
+}
+
+function testAll1() {
+  var p = win.Promise.all(new win.Array(1, 2));
+  p.then(
+    function(arg) {
+      ok(arg instanceof win.Array, "Should get an Array from Promise.all (1)");
+      is(arg[0], 1, "First entry of Promise.all return value should be correct (1)");
+      is(arg[1], 2, "Second entry of Promise.all return value should be correct (1)");
+    },
+    function(e) {
+      ok(false, "testAll1 threw exception: " + e);
+    }
+  ).then(nextTest);
+}
+
+function testAll2() {
+  var p = win.Promise.all(
+    [win.Promise.resolve(1), win.Promise.resolve(2)]);
+  p.then(
+    function(arg) {
+      ok(arg instanceof win.Array, "Should get an Array from Promise.all (2)");
+      is(arg[0], 1, "First entry of Promise.all return value should be correct (2)");
+      is(arg[1], 2, "Second entry of Promise.all return value should be correct (2)");
+    },
+    function(e) {
+      ok(false, "testAll2 threw exception: " + e);
+    }
+  ).then(nextTest);
+}
+
+function testAll3() {
+  // This works with a chrome-side array because we do the iteration
+  // while still in the Xray compartment.
+  var p = win.Promise.all([1, 2]);
+  p.then(
+    function(arg) {
+      ok(arg instanceof win.Array, "Should get an Array from Promise.all (3)");
+      is(arg[0], 1, "First entry of Promise.all return value should be correct (3)");
+      is(arg[1], 2, "Second entry of Promise.all return value should be correct (3)");
+    },
+    function(e) {
+      ok(false, "testAll3 threw exception: " + e);
+    }
+  ).then(nextTest);
+}
+
+function testAll4() {
+  // This works with both content-side and chrome-side Promises because we want
+  // it to and go to some lengths to make it work.
+  var p = win.Promise.all([Promise.resolve(1), win.Promise.resolve(2)]);
+  p.then(
+    function(arg) {
+      ok(arg instanceof win.Array, "Should get an Array from Promise.all (4)");
+      is(arg[0], 1, "First entry of Promise.all return value should be correct (4)");
+      is(arg[1], 2, "Second entry of Promise.all return value should be correct (4)");
+    },
+    function(e) {
+      ok(false, "testAll4 threw exception: " + e);
+    }
+  ).then(nextTest);
+}
+
+function testAll5() {
+  var p = win.Promise.all(new win.Array());
+  p.then(
+    function(arg) {
+      ok(arg instanceof win.Array, "Should get an Array from Promise.all (5)");
+    },
+    function(e) {
+      ok(false, "testAll5 threw exception: " + e);
+    }
+  ).then(nextTest);
+}
+
+function testResolve1() {
+  var p = win.Promise.resolve(5);
+  ok(p instanceof win.Promise, "Promise.resolve should return a promise");
+  p.then(
+    function(arg) {
+      is(arg, 5, "Should get correct Promise.resolve value");
+    },
+    function(e) {
+      ok(false, "testAll5 threw exception: " + e);
+    }
+  ).then(nextTest);
+}
+
+function testResolve2() {
+  var p = win.Promise.resolve(5);
+  var q = win.Promise.resolve(p);
+  is(q, p, "Promise.resolve should just pass through Promise values");
+  nextTest();
+}
+
+function testResolve3() {
+  var p = win.Promise.resolve(Promise.resolve(5));
+  p.then(
+    function(arg) {
+      is(arg, 5, "Promise.resolve with chrome Promise should work");
+    },
+    function(e) {
+      ok(false, "Promise.resolve with chrome Promise should not fail");
+    }
+  ).then(nextTest);
+}
+
+function testResolve4() {
+  var p = new win.Promise((res, rej) => {});
+  Cu.getJSTestingFunctions().resolvePromise(p, 42);
+  p.then(
+    function(arg) {
+      is(arg, 42, "Resolving an Xray to a promise with TestingFunctions resolvePromise should work");
+    },
+    function(e) {
+      ok(false, "Resolving an Xray to a promise with TestingFunctions resolvePromise should not fail");
+    }
+  ).then(nextTest);
+}
+
+function testReject1() {
+  var p = win.Promise.reject(5);
+  ok(p instanceof win.Promise, "Promise.reject should return a promise");
+  p.then(
+    function(arg) {
+      ok(false, "Promise should be rejected");
+    },
+    function(e) {
+      is(e, 5, "Should get correct Promise.reject value");
+    }
+  ).then(nextTest);
+}
+
+function testReject2() {
+  var p = new win.Promise((res, rej) => {});
+  Cu.getJSTestingFunctions().rejectPromise(p, 42);
+  p.then(
+    function(arg) {
+      ok(false, "Rejecting an Xray to a promise with TestingFunctions rejectPromise should trigger catch handler");
+    },
+    function(e) {
+      is(e, 42, "Rejecting an Xray to a promise with TestingFunctions rejectPromise should work");
+    }
+  ).then(nextTest);
+}
+
+function testThen1() {
+  var p = win.Promise.resolve(5);
+  var q = p.then((x) => x * x);
+  ok(q instanceof win.Promise,
+     "Promise.then should return a promise from the right global");
+  q.then(
+    function(arg) {
+      is(arg, 25, "Promise.then should work");
+    },
+    function(e) {
+      ok(false, "Promise.then should not fail");
+    }
+  ).then(nextTest);
+}
+
+function testThen2() {
+  var p = win.Promise.resolve(5);
+  var q = p.then((x) => Promise.resolve(x * x));
+  ok(q instanceof win.Promise,
+     "Promise.then should return a promise from the right global");
+  q.then(
+    function(arg) {
+      is(arg, 25, "Promise.then resolved with chrome promise should work");
+    },
+    function(e) {
+      ok(false, "Promise.then resolved with chrome promise should not fail");
+    }
+  ).then(nextTest);
+}
+
+function testCatch1() {
+  var p = win.Promise.reject(5);
+  ok(p instanceof win.Promise, "Promise.reject should return a promise");
+  var q = p.catch((x) => x * x);
+  ok(q instanceof win.Promise,
+     "Promise.catch should return a promise from the right global");
+  q.then(
+    function(arg) {
+      is(arg, 25, "Promise.catch should work");
+    },
+    function(e) {
+      ok(false, "Promise.catch should not fail");
+    }
+  ).then(nextTest);
+}
+
+function testToStringTag1() {
+  is(win.Promise.prototype[Symbol.toStringTag], "Promise", "@@toStringTag was incorrect");
+  var p = win.Promise.resolve();
+  is(String(p), "[object Promise]", "String() result was incorrect");
+  is(p.toString(), "[object Promise]", "toString result was incorrect");
+  is(Object.prototype.toString.call(p), "[object Promise]", "second toString result was incorrect");
+  nextTest();
+}
+
+var tests = [
+  testLoadComplete,
+  testHaveXray,
+  testConstructor1,
+  testConstructor2,
+  testRace1,
+  testRace2,
+  testRace3,
+  testRace4,
+  testAll1,
+  testAll2,
+  testAll3,
+  testAll4,
+  testAll5,
+  testResolve1,
+  testResolve2,
+  testResolve3,
+  testResolve4,
+  testReject1,
+  testReject2,
+  testThen1,
+  testThen2,
+  testCatch1,
+  testToStringTag1,
+];
+
+function nextTest() {
+  if (!tests.length) {
+    SimpleTest.finish();
+    return;
+  }
+  tests.shift()();
+}
+
+addLoadEvent(nextTest);
+
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/promise/tests/test_resolve.html b/dom/promise/tests/test_resolve.html
new file mode 100644
index 0000000000..7e4745b47a
--- /dev/null
+++ b/dom/promise/tests/test_resolve.html
@@ -0,0 +1,66 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<html>
+<head>
+  <title>Promise.resolve(anything) Test</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="application/javascript"><!--
+
+var tests = [
+  null,
+  42,
+  "hello world",
+  true,
+  false,
+  {},
+  { a: 42 },
+  [ 1, 2, 3, 4, null, true, "hello world" ],
+  function() {},
+  window,
+  undefined,
+  document.createElement("input"),
+  new Date(),
+];
+
+function cbError() {
+  ok(false, "Nothing should arrive here!");
+}
+
+function runTest() {
+  if (!tests.length) {
+    SimpleTest.finish();
+    return;
+  }
+
+  var test = tests.pop();
+
+  new Promise(function(resolve, reject) {
+    resolve(test);
+  }).then(function(what) {
+    ok(test === what, "What is: " + what);
+  }, cbError).then(function() {
+    new Promise(function(resolve, reject) {
+      reject(test);
+    }).then(cbError, function(what) {
+      ok(test === what, "What is: " + what);
+    }).then(runTest, cbError);
+  });
+}
+
+SimpleTest.waitForExplicitFinish();
+runTest();
+// -->
+</script>
+</pre>
+</body>
+</html>
diff --git a/dom/promise/tests/test_resolver_return_value.html b/dom/promise/tests/test_resolver_return_value.html
new file mode 100644
index 0000000000..82e8793824
--- /dev/null
+++ b/dom/promise/tests/test_resolver_return_value.html
@@ -0,0 +1,40 @@
+<!DOCTYPE HTML>
+<html>
+<!--
+https://bugzilla.mozilla.org/show_bug.cgi?id=1120235
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Test for Bug 1120235</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 1120235 **/
+  var res, rej;
+  var p = new Promise(function(resolve, reject) { res = resolve; rej = reject; });
+  is(res(1), undefined, "Resolve function should return undefined");
+  is(rej(2), undefined, "Reject function should return undefined");
+
+  var thenable = {
+    then(resolve, reject) {
+      is(resolve(3), undefined, "Thenable resolve argument should return undefined");
+      is(reject(4), undefined, "Thenable reject argument should return undefined");
+      SimpleTest.finish();
+    },
+  };
+
+  SimpleTest.waitForExplicitFinish();
+  p = Promise.resolve(thenable);
+  </script>
+</head>
+<body>
+<a target="_blank" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1120235">Mozilla Bug 1120235</a>
+<p id="display"></p>
+<div id="content" style="display: none">
+
+</div>
+<pre id="test">
+</pre>
+</body>
+</html>
diff --git a/dom/promise/tests/test_species_getter.html b/dom/promise/tests/test_species_getter.html
new file mode 100644
index 0000000000..23cb7d8ae0
--- /dev/null
+++ b/dom/promise/tests/test_species_getter.html
@@ -0,0 +1,25 @@
+<!DOCTYPE html>
+<meta charset=utf-8>
+<title>Test for ...</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id="log"></div>
+<script>
+test(function() {
+  /* global test, assert_not_equals, assert_equals */
+
+  var desc = Object.getOwnPropertyDescriptor(Promise, Symbol.species);
+  assert_not_equals(desc, undefined, "Should have a property");
+
+  assert_equals(desc.configurable, true, "Property should be configurable");
+  assert_equals(desc.enumerable, false, "Property should not be enumerable");
+  assert_equals(desc.set, undefined, "Should not have a setter");
+  var getter = desc.get;
+
+  var things = [undefined, null, 5, "xyz", Promise, Object];
+  for (var thing of things) {
+    assert_equals(getter.call(thing), thing,
+                  "Getter should return its this value");
+  }
+}, "Promise should have an @@species getter that works per spec");
+</script>
diff --git a/dom/promise/tests/test_thenable_vs_promise_ordering.html b/dom/promise/tests/test_thenable_vs_promise_ordering.html
new file mode 100644
index 0000000000..a537490b16
--- /dev/null
+++ b/dom/promise/tests/test_thenable_vs_promise_ordering.html
@@ -0,0 +1,29 @@
+<!DOCTYPE html>
+<meta charset=utf-8>
+<title>Test for promise resolution ordering with thenables and promises</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<div id="log"></div>
+<script>
+/* global async_test, assert_true, assert_equals */
+
+var t = async_test("A promise resolved first (with a thenable) should trigger its callbacks before a promise resolved second (with a promise).");
+t.step(function() {
+  var customThenCalled = false;
+  var p0 = Promise.resolve();
+  p0.then = function(resolved, rejected) {
+    customThenCalled = true;
+    Promise.prototype.then.call(this, resolved, rejected);
+  };
+  var p1 = new Promise(function(r) { r(p0); });
+  delete p0.then;
+  var p2 = new Promise(function(r) { r(p0); });
+  var resolutionOrder = "";
+  Promise.all([ p1.then(function() { resolutionOrder += "1"; }),
+                p2.then(function() { resolutionOrder += "2"; }) ])
+         .then(t.step_func_done(function() {
+           assert_true(customThenCalled, "Should have called custom then");
+           assert_equals(resolutionOrder, "12");
+         }));
+});
+</script>
diff --git a/dom/promise/tests/test_webassembly_compile.html b/dom/promise/tests/test_webassembly_compile.html
new file mode 100644
index 0000000000..351f0f4ae4
--- /dev/null
+++ b/dom/promise/tests/test_webassembly_compile.html
@@ -0,0 +1,446 @@
+<!--
+  Any copyright is dedicated to the Public Domain.
+  http://creativecommons.org/publicdomain/zero/1.0/
+-->
+<html>
+<head>
+  <title>WebAssembly.compile Test</title>
+  <script src="/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="/tests/SimpleTest/test.css"/>
+</head>
+<body>
+<script>
+const testingFunctions = SpecialPowers.Cu.getJSTestingFunctions();
+const wasmIsSupported = SpecialPowers.unwrap(testingFunctions.wasmIsSupported);
+const wasmHasTier2CompilationCompleted = SpecialPowers.unwrap(testingFunctions.wasmHasTier2CompilationCompleted);
+const wasmLoadedFromCache = SpecialPowers.unwrap(testingFunctions.wasmLoadedFromCache);
+const isCachingEnabled = SpecialPowers.getBoolPref("javascript.options.wasm_caching");
+
+// The test_webassembly_compile_sample.wasm is a medium-sized module with 100
+// functions that call each other recursively, returning a computed sum.
+// Any other non-trivial module could be generated and used.
+var sampleCode;
+const sampleURL = "test_webassembly_compile_sample.wasm";
+const sampleFileSize = 16053;
+const sampleURLWithRandomQuery = () => sampleURL + "?id=" + String(Math.ceil(Math.random()*100000));
+const sampleExportName = "run";
+const sampleResult = 1275;
+
+function checkSampleModule(m) {
+  ok(m instanceof WebAssembly.Module, "got a module");
+  var i = new WebAssembly.Instance(m);
+  ok(i instanceof WebAssembly.Instance, "got an instance");
+  ok(i.exports[sampleExportName]() === sampleResult, "got result");
+}
+
+function checkSampleInstance(i) {
+  ok(i instanceof WebAssembly.Instance, "got a module");
+  ok(i.exports[sampleExportName]() === sampleResult, "got result");
+}
+
+function fetchSampleModuleCode() {
+  fetch(sampleURL)
+  .then(response => response.arrayBuffer())
+  .then(buffer => { sampleCode = buffer; runTest(); })
+  .catch(err => ok(false, String(err)));
+}
+
+function propertiesExist() {
+  if (!wasmIsSupported()) {
+    ok(!this.WebAssembly, "If the device doesn't support, there will be no WebAssembly object");
+    SimpleTest.finish();
+    return;
+  }
+
+  ok(WebAssembly, "WebAssembly object should exist");
+  ok(WebAssembly.compile, "WebAssembly.compile function should exist");
+  runTest();
+}
+
+function compileFail() {
+  WebAssembly.compile().then(
+    () => { ok(false, "should have failed"); runTest(); }
+  ).catch(
+    err => { ok(err instanceof TypeError, "empty compile failed"); runTest(); }
+  );
+}
+
+function compileSuccess() {
+  WebAssembly.compile(sampleCode).then(
+    m => { checkSampleModule(m); runTest(); }
+  ).catch(
+    err => { ok(false, String(err)); runTest(); }
+  );
+}
+
+function compileManySuccess() {
+  const N = 100;
+
+  var arr = [];
+  for (var i = 0; i < N; i++)
+    arr.push(WebAssembly.compile(sampleCode));
+
+  SpecialPowers.gc();
+
+  Promise.all(arr).then(ms => {
+    ok(ms.length === N, "got the right number");
+    for (var j = 0; j < N; j++)
+      checkSampleModule(ms[j]);
+    runTest();
+  }).catch(
+    err => { ok(false, String(err)); runTest(); }
+  );
+}
+
+function terminateCompileInWorker() {
+    var w = new Worker(`data:text/plain,
+      var sampleCode;
+      function spawnWork() {
+        const N = 100;
+        var arr = [];
+        for (var i = 0; i < N; i++)
+          arr.push(WebAssembly.compile(sampleCode));
+        Promise.all(arr).then(spawnWork);
+      }
+      onmessage = e => {
+        sampleCode = e.data;
+        spawnWork();
+        postMessage("ok");
+      }
+    `);
+    w.postMessage(sampleCode);
+    w.onmessage = e => {
+      ok(e.data === "ok", "worker finished first step");
+      w.terminate();
+      runTest();
+    };
+}
+
+function instantiateFail() {
+  WebAssembly.instantiate().then(
+    () => { ok(false, "should have failed"); runTest(); }
+  ).catch(
+    err => { ok(err instanceof TypeError, "empty compile failed"); runTest(); }
+  );
+}
+
+function instantiateSuccess() {
+  WebAssembly.instantiate(sampleCode).then(
+    r => { checkSampleModule(r.module); checkSampleInstance(r.instance); runTest(); }
+  ).catch(
+    err => { ok(false, String(err)); runTest(); }
+  );
+}
+
+function chainSuccess() {
+  WebAssembly.compile(sampleCode).then(
+    m => WebAssembly.instantiate(m)
+  ).then(
+    i => { checkSampleInstance(i); runTest(); }
+  ).catch(
+    err => { ok(false, String(err)); runTest(); }
+  );
+}
+
+function compileStreamingNonResponse() {
+  WebAssembly.compileStreaming({})
+  .then(() => { ok(false); })
+  .catch(err => { ok(err instanceof TypeError, "rejected {}"); runTest(); });
+}
+
+function compileStreamingNoMime() {
+  WebAssembly.compileStreaming(new Response(new ArrayBuffer()))
+  .then(() => { ok(false); })
+  .catch(err => { ok(err instanceof TypeError, "rejected no MIME type"); runTest(); });
+}
+
+function compileStreamingBadMime() {
+  var badMimes = [
+    "",
+    "application/js",
+    "application/js;application/wasm",
+    "application/wasm;application/js",
+    "application/wasm;",
+    "application/wasm1",
+  ];
+  var promises = [];
+  for (let mimeType of badMimes) {
+    var init = { headers: { "Content-Type": mimeType } };
+    promises.push(
+      WebAssembly.compileStreaming(new Response(sampleCode, init))
+      .then(() => Promise.reject(), err => {
+        is(err.message,
+          `WebAssembly: Response has unsupported MIME type '${mimeType}' expected 'application/wasm'`,
+          "correct MIME type error message");
+        return Promise.resolve();
+      })
+    );
+  }
+  Promise.all(promises)
+  .then(() => { ok(true, "all bad MIME types rejected"); runTest(); });
+}
+
+function compileStreamingGoodMime() {
+  var badMimes = [
+    "application/wasm",
+    "   application/wasm ",
+    "application/wasm   ",
+  ];
+  var promises = [];
+  for (let mimeType of badMimes) {
+    var init = { headers: { "Content-Type": mimeType } };
+    promises.push(
+      WebAssembly.compileStreaming(new Response(sampleCode, init))
+    );
+  }
+  Promise.all(promises)
+  .then(() => { ok(true, "all good MIME types accepted"); runTest(); });
+}
+
+function compileStreamingDoubleUseFail() {
+  fetch(sampleURL)
+  .then(response => {
+      WebAssembly.compileStreaming(response)
+      .then(m => {
+        checkSampleModule(m);
+        return WebAssembly.compileStreaming(response);
+      })
+      .then(
+        () => ok(false, "should have failed on second use"),
+        err => { ok(true, "failed on second use"); runTest(); }
+      );
+  });
+}
+
+function compileStreamingNullBody() {
+  var init = { headers: { "Content-Type": "application/wasm" } };
+  WebAssembly.compileStreaming(new Response(undefined, init))
+  .then(() => { ok(false); })
+  .catch(err => { ok(err instanceof WebAssembly.CompileError, "null body"); runTest(); });
+}
+
+function compileStreamingFetch() {
+  WebAssembly.compileStreaming(fetch(sampleURL))
+  .then(m => { checkSampleModule(m); runTest(); })
+  .catch(err => { ok(false, String(err)); });
+}
+
+function compileCachedBasic() {
+  const url = sampleURLWithRandomQuery();
+  WebAssembly.compileStreaming(fetch(url))
+  .then(module => {
+    checkSampleModule(module);
+    ok(!wasmLoadedFromCache(module), "not cached yet");
+    while(!wasmHasTier2CompilationCompleted(module));
+    return WebAssembly.compileStreaming(fetch(url));
+  })
+  .then(module => {
+    checkSampleModule(module);
+    ok(wasmLoadedFromCache(module), "loaded from cache");
+  })
+  .then(() => runTest())
+  .catch(err => { ok(false, String(err)) });
+}
+
+function compileCachedCompressed() {
+  const url = sampleURLWithRandomQuery();
+
+  // It is a rough estimate that compilation code is about
+  // 2-4 times of the wasm file size. After it compression
+  // it will be less (about 60% ?)
+  const EstimatedCompilationArtifactSize = 2 * sampleFileSize;
+  const EstimatedCompressedArtifactSize = 0.6 * EstimatedCompilationArtifactSize;
+
+  // Set limit on cache entry so it will fail if it is not
+  // compressed.
+  const cleanup = () => {
+    SpecialPowers.clearUserPref("browser.cache.disk.max_entry_size")
+  };
+  Promise.resolve(SpecialPowers.setIntPref("browser.cache.disk.max_entry_size",
+    Math.round(EstimatedCompressedArtifactSize / 1024) /* kb */))
+  .then(() => WebAssembly.compileStreaming(fetch(url)))
+  .then(module => {
+    checkSampleModule(module);
+    ok(!wasmLoadedFromCache(module), "not cached yet");
+    while(!wasmHasTier2CompilationCompleted(module));
+    return WebAssembly.compileStreaming(fetch(url));
+  })
+  .then(module => {
+    checkSampleModule(module);
+    ok(wasmLoadedFromCache(module), "loaded from cache");
+  })
+  .then(() => { cleanup(); runTest() })
+  .catch(err => { cleanup(); ok(false, String(err)) });
+}
+
+function compileCachedTooLargeForCache() {
+  const url = sampleURLWithRandomQuery();
+  // Set unreasonable limit, caching will fail.
+  // Bug 1719508 can change name of pref, this and
+  // compileCachedCompressed tests will become invalid.
+  const cleanup = () => {
+    SpecialPowers.clearUserPref("browser.cache.disk.max_entry_size")
+  };
+  Promise.resolve(SpecialPowers.setIntPref("browser.cache.disk.max_entry_size", 1 /* kb */))
+  .then(() => WebAssembly.compileStreaming(fetch(url)))
+  .then(module => {
+    console.log(module)
+    checkSampleModule(module);
+    ok(!wasmLoadedFromCache(module), "not cached yet");
+    while(!wasmHasTier2CompilationCompleted(module));
+    return WebAssembly.compileStreaming(fetch(url));
+  })
+  .then(module => {
+    checkSampleModule(module);
+    ok(!wasmLoadedFromCache(module), "not cached (size limit)");
+  })
+  .then(() => { cleanup(); runTest() })
+  .catch(err => { cleanup(); ok(false, String(err)) });
+}
+
+const Original = "original";
+const Clone = "clone";
+
+function compileCachedBothClonesHitCache(which) {
+  const url = sampleURLWithRandomQuery();
+  WebAssembly.compileStreaming(fetch(url))
+  .then(module => {
+    checkSampleModule(module);
+    ok(!wasmLoadedFromCache(module), "not cached yet");
+    while(!wasmHasTier2CompilationCompleted(module));
+    return fetch(url);
+  })
+  .then(original => {
+    let clone = original.clone();
+    if (which === Clone) [clone, original] = [original, clone];
+    return Promise.all([
+      WebAssembly.compileStreaming(original),
+      WebAssembly.compileStreaming(clone)
+    ]);
+  })
+  .then(([m1, m2]) => {
+    checkSampleModule(m1);
+    ok(wasmLoadedFromCache(m1), "clone loaded from cache");
+    checkSampleModule(m2);
+    ok(wasmLoadedFromCache(m2), "original loaded from cache");
+  })
+  .then(() => runTest())
+  .catch(err => { ok(false, String(err)) });
+}
+
+function compileCachedCacheThroughClone(which) {
+  const url = sampleURLWithRandomQuery();
+  fetch(url)
+  .then(original => {
+    ok(true, "fun time");
+    let clone = original.clone();
+    if (which === Clone) [clone, original] = [original, clone];
+    return Promise.all([
+      WebAssembly.compileStreaming(original),
+      clone.arrayBuffer()
+    ]);
+  })
+  .then(([module, buffer]) => {
+    ok(!wasmLoadedFromCache(module), "not cached yet");
+    ok(buffer instanceof ArrayBuffer);
+    while(!wasmHasTier2CompilationCompleted(module));
+    return WebAssembly.compileStreaming(fetch(url));
+  })
+  .then(m => {
+    ok(wasmLoadedFromCache(m), "cache hit of " + which);
+  })
+  .then(() => runTest())
+  .catch(err => { ok(false, String(err)) });
+}
+
+function instantiateStreamingFetch() {
+  WebAssembly.instantiateStreaming(fetch(sampleURL))
+  .then(({module, instance}) => { checkSampleModule(module); checkSampleInstance(instance); runTest(); })
+  .catch(err => { ok(false, String(err)); });
+}
+
+function compileManyStreamingFetch() {
+  const N = 20;
+
+  var arr = [];
+  for (var i = 0; i < N; i++)
+    arr.push(WebAssembly.compileStreaming(fetch(sampleURL)));
+
+  SpecialPowers.gc();
+
+  Promise.all(arr).then(ms => {
+    ok(ms.length === N, "got the right number");
+    for (var j = 0; j < N; j++)
+      checkSampleModule(ms[j]);
+    runTest();
+  }).catch(
+    err => { ok(false, String(err)); runTest(); }
+  );
+}
+
+function runWorkerTests() {
+  var w = new Worker("test_webassembly_compile_worker.js");
+  w.postMessage(sampleCode);
+  w.onmessage = e => {
+    ok(e.data === "ok", "worker test: " + e.data);
+    runTest();
+  };
+}
+
+function terminateCompileStreamingInWorker() {
+  var w = new Worker("test_webassembly_compile_worker_terminate.js");
+  w.onmessage = e => {
+    ok(e.data === "ok", "worker streaming terminate test: " + e.data);
+    w.terminate();
+    runTest();
+  };
+}
+
+var tests = [ propertiesExist,
+              compileFail,
+              compileSuccess,
+              compileManySuccess,
+              terminateCompileInWorker,
+              instantiateFail,
+              instantiateSuccess,
+              chainSuccess,
+              compileStreamingNonResponse,
+              compileStreamingNoMime,
+              compileStreamingBadMime,
+              compileStreamingGoodMime,
+              compileStreamingDoubleUseFail,
+              compileStreamingNullBody,
+              compileStreamingFetch,
+              ...(isCachingEnabled ? [
+                compileCachedBasic,
+                compileCachedCompressed,
+                compileCachedTooLargeForCache,
+                compileCachedBothClonesHitCache.bind(Original),
+                compileCachedBothClonesHitCache.bind(Clone),
+                compileCachedCacheThroughClone.bind(Original),
+                compileCachedCacheThroughClone.bind(Clone),
+              ]: []),
+              instantiateStreamingFetch,
+              compileManyStreamingFetch,
+              runWorkerTests,
+              terminateCompileStreamingInWorker,
+            ];
+
+// This initialization must always run
+tests.unshift(fetchSampleModuleCode);
+
+function runTest() {
+  if (!tests.length) {
+    SimpleTest.finish();
+    return;
+  }
+
+  var test = tests.shift();
+  test();
+}
+
+SimpleTest.waitForExplicitFinish();
+runTest();
+</script>
+</body>
+</html>
diff --git a/dom/promise/tests/test_webassembly_compile_sample.wasm b/dom/promise/tests/test_webassembly_compile_sample.wasm
new file mode 100644
index 0000000000..787e19a5df
--- /dev/null
+++ b/dom/promise/tests/test_webassembly_compile_sample.wasm
diff --git a/dom/promise/tests/test_webassembly_compile_worker.js b/dom/promise/tests/test_webassembly_compile_worker.js
new file mode 100644
index 0000000000..90c3551137
--- /dev/null
+++ b/dom/promise/tests/test_webassembly_compile_worker.js
@@ -0,0 +1,55 @@
+const sampleURL = "test_webassembly_compile_sample.wasm";
+const sampleExportName = "run";
+const sampleResult = 1275;
+
+/* eslint-disable no-throw-literal */
+
+function checkSampleModule(m) {
+  if (!(m instanceof WebAssembly.Module)) {
+    throw "not a module";
+  }
+  var i = new WebAssembly.Instance(m);
+  if (!(i instanceof WebAssembly.Instance)) {
+    throw "not an instance";
+  }
+  if (i.exports[sampleExportName]() !== sampleResult) {
+    throw "wrong result";
+  }
+}
+
+function checkSampleInstance(i) {
+  if (!(i instanceof WebAssembly.Instance)) {
+    throw "not an instance";
+  }
+  if (i.exports[sampleExportName]() !== sampleResult) {
+    throw "wrong result";
+  }
+}
+
+const initObj = { headers: { "Content-Type": "application/wasm" } };
+
+onmessage = e => {
+  WebAssembly.compile(e.data)
+    .then(m => checkSampleModule(m))
+    .then(() => WebAssembly.instantiate(e.data))
+    .then(({ module, instance }) => {
+      checkSampleModule(module);
+      checkSampleInstance(instance);
+    })
+    .then(() => WebAssembly.compileStreaming(new Response(e.data, initObj)))
+    .then(m => checkSampleModule(m))
+    .then(() => WebAssembly.instantiateStreaming(new Response(e.data, initObj)))
+    .then(({ module, instance }) => {
+      checkSampleModule(module);
+      checkSampleInstance(instance);
+    })
+    .then(() => WebAssembly.compileStreaming(fetch(sampleURL)))
+    .then(m => checkSampleModule(m))
+    .then(() => WebAssembly.instantiateStreaming(fetch(sampleURL)))
+    .then(({ module, instance }) => {
+      checkSampleModule(module);
+      checkSampleInstance(instance);
+    })
+    .then(() => postMessage("ok"))
+    .catch(err => postMessage("fail: " + err));
+};
diff --git a/dom/promise/tests/test_webassembly_compile_worker_terminate.js b/dom/promise/tests/test_webassembly_compile_worker_terminate.js
new file mode 100644
index 0000000000..5b96c9034b
--- /dev/null
+++ b/dom/promise/tests/test_webassembly_compile_worker_terminate.js
@@ -0,0 +1,13 @@
+const sampleURL = "test_webassembly_compile_sample.wasm";
+
+function spawnWork() {
+  const N = 50;
+  var arr = [];
+  for (var i = 0; i < N; i++) {
+    arr.push(WebAssembly.compileStreaming(fetch(sampleURL)));
+  }
+  Promise.all(arr).then(spawnWork);
+}
+
+spawnWork();
+postMessage("ok");
diff --git a/dom/promise/tests/unit/test_monitor_uncaught.js b/dom/promise/tests/unit/test_monitor_uncaught.js
new file mode 100644
index 0000000000..afa328cb97
--- /dev/null
+++ b/dom/promise/tests/unit/test_monitor_uncaught.js
@@ -0,0 +1,322 @@
+/* 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 { setTimeout } = ChromeUtils.importESModule(
+  "resource://gre/modules/Timer.sys.mjs"
+);
+const { PromiseTestUtils } = ChromeUtils.importESModule(
+  "resource://testing-common/PromiseTestUtils.sys.mjs"
+);
+
+// Prevent test failures due to the unhandled rejections in this test file.
+PromiseTestUtils.disableUncaughtRejectionObserverForSelfTest();
+
+add_task(async function test_globals() {
+  Assert.notEqual(
+    PromiseDebugging,
+    undefined,
+    "PromiseDebugging is available."
+  );
+});
+
+add_task(async function test_promiseID() {
+  let p1 = new Promise(resolve => {});
+  let p2 = new Promise(resolve => {});
+  let p3 = p2.catch(null);
+  let promise = [p1, p2, p3];
+
+  let identifiers = promise.map(PromiseDebugging.getPromiseID);
+  info("Identifiers: " + JSON.stringify(identifiers));
+  let idSet = new Set(identifiers);
+  Assert.equal(
+    idSet.size,
+    identifiers.length,
+    "PromiseDebugging.getPromiseID returns a distinct id per promise"
+  );
+
+  let identifiers2 = promise.map(PromiseDebugging.getPromiseID);
+  Assert.equal(
+    JSON.stringify(identifiers),
+    JSON.stringify(identifiers2),
+    "Successive calls to PromiseDebugging.getPromiseID return the same id for the same promise"
+  );
+});
+
+add_task(async function test_observe_uncaught() {
+  // The names of Promise instances
+  let names = new Map();
+
+  // The results for UncaughtPromiseObserver callbacks.
+  let CallbackResults = function (name) {
+    this.name = name;
+    this.expected = new Set();
+    this.observed = new Set();
+    this.blocker = new Promise(resolve => (this.resolve = resolve));
+  };
+  CallbackResults.prototype = {
+    observe(promise) {
+      info(this.name + " observing Promise " + names.get(promise));
+      Assert.equal(
+        PromiseDebugging.getState(promise).state,
+        "rejected",
+        this.name + " observed a rejected Promise"
+      );
+      if (!this.expected.has(promise)) {
+        Assert.ok(
+          false,
+          this.name +
+            " observed a Promise that it expected to observe, " +
+            names.get(promise) +
+            " (" +
+            PromiseDebugging.getPromiseID(promise) +
+            ", " +
+            PromiseDebugging.getAllocationStack(promise) +
+            ")"
+        );
+      }
+      Assert.ok(
+        this.expected.delete(promise),
+        this.name +
+          " observed a Promise that it expected to observe, " +
+          names.get(promise) +
+          " (" +
+          PromiseDebugging.getPromiseID(promise) +
+          ")"
+      );
+      Assert.ok(
+        !this.observed.has(promise),
+        this.name + " observed a Promise that it has not observed yet"
+      );
+      this.observed.add(promise);
+      if (this.expected.size == 0) {
+        this.resolve();
+      } else {
+        info(
+          this.name +
+            " is still waiting for " +
+            this.expected.size +
+            " observations:"
+        );
+        info(
+          JSON.stringify(Array.from(this.expected.values(), x => names.get(x)))
+        );
+      }
+    },
+  };
+
+  let onLeftUncaught = new CallbackResults("onLeftUncaught");
+  let onConsumed = new CallbackResults("onConsumed");
+
+  let observer = {
+    onLeftUncaught(promise, data) {
+      onLeftUncaught.observe(promise);
+    },
+    onConsumed(promise) {
+      onConsumed.observe(promise);
+    },
+  };
+
+  let resolveLater = function (delay = 20) {
+    // eslint-disable-next-line mozilla/no-arbitrary-setTimeout
+    return new Promise((resolve, reject) => setTimeout(resolve, delay));
+  };
+  let rejectLater = function (delay = 20) {
+    // eslint-disable-next-line mozilla/no-arbitrary-setTimeout
+    return new Promise((resolve, reject) => setTimeout(reject, delay));
+  };
+  let makeSamples = function* () {
+    yield {
+      promise: Promise.resolve(0),
+      name: "Promise.resolve",
+    };
+    yield {
+      promise: Promise.resolve(resolve => resolve(0)),
+      name: "Resolution callback",
+    };
+    yield {
+      promise: Promise.resolve(0).catch(null),
+      name: "`catch(null)`",
+    };
+    yield {
+      promise: Promise.reject(0).catch(() => {}),
+      name: "Reject and catch immediately",
+    };
+    yield {
+      promise: resolveLater(),
+      name: "Resolve later",
+    };
+    yield {
+      promise: Promise.reject("Simple rejection"),
+      leftUncaught: true,
+      consumed: false,
+      name: "Promise.reject",
+    };
+
+    // Reject a promise now, consume it later.
+    let p = Promise.reject("Reject now, consume later");
+
+    // eslint-disable-next-line mozilla/no-arbitrary-setTimeout
+    setTimeout(
+      () =>
+        p.catch(() => {
+          info("Consumed promise");
+        }),
+      200
+    );
+    yield {
+      promise: p,
+      leftUncaught: true,
+      consumed: true,
+      name: "Reject now, consume later",
+    };
+
+    yield {
+      promise: Promise.all([Promise.resolve("Promise.all"), rejectLater()]),
+      leftUncaught: true,
+      name: "Rejecting through Promise.all",
+    };
+    yield {
+      promise: Promise.race([resolveLater(500), Promise.reject()]),
+      leftUncaught: true, // The rejection wins the race.
+      name: "Rejecting through Promise.race",
+    };
+    yield {
+      promise: Promise.race([Promise.resolve(), rejectLater(500)]),
+      leftUncaught: false, // The resolution wins the race.
+      name: "Resolving through Promise.race",
+    };
+
+    let boom = new Error("`throw` in the constructor");
+    yield {
+      promise: new Promise(() => {
+        throw boom;
+      }),
+      leftUncaught: true,
+      name: "Throwing in the constructor",
+    };
+
+    let rejection = Promise.reject("`reject` during resolution");
+    yield {
+      promise: rejection,
+      leftUncaught: false,
+      consumed: false, // `rejection` is consumed immediately (see below)
+      name: "Promise.reject, again",
+    };
+
+    yield {
+      promise: new Promise(resolve => resolve(rejection)),
+      leftUncaught: true,
+      consumed: false,
+      name: "Resolving with a rejected promise",
+    };
+
+    yield {
+      promise: Promise.resolve(0).then(() => rejection),
+      leftUncaught: true,
+      consumed: false,
+      name: "Returning a rejected promise from success handler",
+    };
+
+    yield {
+      promise: Promise.resolve(0).then(() => {
+        throw new Error();
+      }),
+      leftUncaught: true,
+      consumed: false,
+      name: "Throwing during the call to the success callback",
+    };
+  };
+  let samples = [];
+  for (let s of makeSamples()) {
+    samples.push(s);
+    info(
+      "Promise '" +
+        s.name +
+        "' has id " +
+        PromiseDebugging.getPromiseID(s.promise)
+    );
+  }
+
+  PromiseDebugging.addUncaughtRejectionObserver(observer);
+
+  for (let s of samples) {
+    names.set(s.promise, s.name);
+    if (s.leftUncaught || false) {
+      onLeftUncaught.expected.add(s.promise);
+    }
+    if (s.consumed || false) {
+      onConsumed.expected.add(s.promise);
+    }
+  }
+
+  info("Test setup, waiting for callbacks.");
+  await onLeftUncaught.blocker;
+
+  info("All calls to onLeftUncaught are complete.");
+  if (onConsumed.expected.size != 0) {
+    info("onConsumed is still waiting for the following Promise:");
+    info(
+      JSON.stringify(
+        Array.from(onConsumed.expected.values(), x => names.get(x))
+      )
+    );
+    await onConsumed.blocker;
+  }
+
+  info("All calls to onConsumed are complete.");
+  let removed = PromiseDebugging.removeUncaughtRejectionObserver(observer);
+  Assert.ok(removed, "removeUncaughtRejectionObserver succeeded");
+  removed = PromiseDebugging.removeUncaughtRejectionObserver(observer);
+  Assert.ok(
+    !removed,
+    "second call to removeUncaughtRejectionObserver didn't remove anything"
+  );
+});
+
+add_task(async function test_uninstall_observer() {
+  let Observer = function () {
+    this.blocker = new Promise(resolve => (this.resolve = resolve));
+    this.active = true;
+  };
+  Observer.prototype = {
+    set active(x) {
+      this._active = x;
+      if (x) {
+        PromiseDebugging.addUncaughtRejectionObserver(this);
+      } else {
+        PromiseDebugging.removeUncaughtRejectionObserver(this);
+      }
+    },
+    onLeftUncaught() {
+      Assert.ok(this._active, "This observer is active.");
+      this.resolve();
+    },
+    onConsumed() {
+      Assert.ok(false, "We should not consume any Promise.");
+    },
+  };
+
+  info("Adding an observer.");
+  let deactivate = new Observer();
+  Promise.reject("I am an uncaught rejection.");
+  await deactivate.blocker;
+  Assert.ok(true, "The observer has observed an uncaught Promise.");
+  deactivate.active = false;
+  info(
+    "Removing the observer, it should not observe any further uncaught Promise."
+  );
+
+  info(
+    "Rejecting a Promise and waiting a little to give a chance to observers."
+  );
+  let wait = new Observer();
+  Promise.reject("I am another uncaught rejection.");
+  await wait.blocker;
+  // eslint-disable-next-line mozilla/no-arbitrary-setTimeout
+  await new Promise(resolve => setTimeout(resolve, 100));
+  // Normally, `deactivate` should not be notified of the uncaught rejection.
+  wait.active = false;
+});
diff --git a/dom/promise/tests/unit/test_promise_job_across_sandbox.js b/dom/promise/tests/unit/test_promise_job_across_sandbox.js
new file mode 100644
index 0000000000..ff1d1575e3
--- /dev/null
+++ b/dom/promise/tests/unit/test_promise_job_across_sandbox.js
@@ -0,0 +1,221 @@
+function createSandbox() {
+  const uri = Services.io.newURI("https://example.com");
+  const principal = Services.scriptSecurityManager.createContentPrincipal(
+    uri,
+    {}
+  );
+  return new Cu.Sandbox(principal, {});
+}
+
+add_task(async function testReactionJob() {
+  const sandbox = createSandbox();
+
+  sandbox.eval(`
+var testPromise = Promise.resolve(10);
+`);
+
+  // Calling `Promise.prototype.then` from sandbox performs GetFunctionRealm
+  // on wrapped `resolve` in sandbox realm, and it fails to unwrap the security
+  // wrapper. The reaction job should be created with sandbox realm.
+  const p = new Promise(resolve => {
+    sandbox.resolve = resolve;
+
+    sandbox.eval(`
+testPromise.then(resolve);
+`);
+  });
+
+  const result = await p;
+
+  equal(result, 10);
+});
+
+add_task(async function testReactionJobNuked() {
+  const sandbox = createSandbox();
+
+  sandbox.eval(`
+var testPromise = Promise.resolve(10);
+`);
+
+  // Calling `Promise.prototype.then` from sandbox performs GetFunctionRealm
+  // on wrapped `resolve` in sandbox realm, and it fails to unwrap the security
+  // wrapper. The reaction job should be created with sandbox realm.
+  const p1 = new Promise(resolve => {
+    sandbox.resolve = resolve;
+
+    sandbox.eval(`
+testPromise.then(resolve);
+`);
+
+    // Given the reaction job is created with the sandbox realm, nuking the
+    // sandbox prevents the job gets executed.
+    Cu.nukeSandbox(sandbox);
+  });
+
+  const p2 = Promise.resolve(11);
+
+  // Given the p1 doesn't get resolved, p2 should win.
+  const result = await Promise.race([p1, p2]);
+
+  equal(result, 11);
+});
+
+add_task(async function testReactionJobWithXray() {
+  const sandbox = createSandbox();
+
+  sandbox.eval(`
+var testPromise = Promise.resolve(10);
+`);
+
+  // Calling `Promise.prototype.then` from privileged realm via Xray uses
+  // privileged `Promise.prototype.then` function, and GetFunctionRealm
+  // performed there successfully gets top-level realm. The reaction job
+  // should be created with top-level realm.
+  const result = await new Promise(resolve => {
+    sandbox.testPromise.then(resolve);
+
+    // Given the reaction job is created with the top-level realm, nuking the
+    // sandbox doesn't affect the reaction job.
+    Cu.nukeSandbox(sandbox);
+  });
+
+  equal(result, 10);
+});
+
+add_task(async function testBoundReactionJob() {
+  const sandbox = createSandbox();
+
+  sandbox.eval(`
+var resolve = undefined;
+var callbackPromise = new Promise(r => { resolve = r; });
+var callback = function (v) { resolve(v + 1); };
+`);
+
+  // Create a bound function where its realm is privileged realm, and
+  // its target is from sandbox realm.
+  sandbox.bound_callback = Function.prototype.bind.call(
+    sandbox.callback,
+    sandbox
+  );
+
+  // Calling `Promise.prototype.then` from sandbox performs GetFunctionRealm
+  // and it fails. The reaction job should be created with sandbox realm.
+  sandbox.eval(`
+Promise.resolve(10).then(bound_callback);
+`);
+
+  const result = await sandbox.callbackPromise;
+  equal(result, 11);
+});
+
+add_task(async function testThenableJob() {
+  const sandbox = createSandbox();
+
+  const p = new Promise(resolve => {
+    // Create a bound function where its realm is privileged realm, and
+    // its target is from sandbox realm.
+    sandbox.then = function (onFulfilled, onRejected) {
+      resolve(10);
+    };
+  });
+
+  // Creating a promise thenable job in the following `Promise.resolve` performs
+  // GetFunctionRealm on the bound thenable.then and fails. The reaction job
+  // should be created with sandbox realm.
+  sandbox.eval(`
+var thenable = {
+  then: then,
+};
+
+Promise.resolve(thenable);
+`);
+
+  const result = await p;
+  equal(result, 10);
+});
+
+add_task(async function testThenableJobNuked() {
+  const sandbox = createSandbox();
+
+  let called = false;
+  sandbox.then = function (onFulfilled, onRejected) {
+    called = true;
+  };
+
+  // Creating a promise thenable job in the following `Promise.resolve` performs
+  // GetFunctionRealm on the bound thenable.then and fails. The reaction job
+  // should be created with sandbox realm.
+  sandbox.eval(`
+var thenable = {
+  then: then,
+};
+
+Promise.resolve(thenable);
+`);
+
+  Cu.nukeSandbox(sandbox);
+
+  // Drain the job queue, to make sure we hit dead object error inside the
+  // thenable job.
+  await Promise.resolve(10);
+
+  equal(
+    Services.console.getMessageArray().find(x => {
+      return x.toString().includes("can't access dead object");
+    }) !== undefined,
+    true
+  );
+  equal(called, false);
+});
+
+add_task(async function testThenableJobAccessError() {
+  const sandbox = createSandbox();
+
+  let accessed = false;
+  sandbox.thenable = {
+    get then() {
+      accessed = true;
+    },
+  };
+
+  // The following operation silently fails when accessing `then` property.
+  sandbox.eval(`
+var x = typeof thenable.then;
+
+Promise.resolve(thenable);
+`);
+
+  equal(accessed, false);
+});
+
+add_task(async function testBoundThenableJob() {
+  const sandbox = createSandbox();
+
+  sandbox.eval(`
+var resolve = undefined;
+var callbackPromise = new Promise(r => { resolve = r; });
+var callback = function (v) { resolve(v + 1); };
+
+var then = function(onFulfilled, onRejected) {
+  onFulfilled(10);
+};
+`);
+
+  // Create a bound function where its realm is privileged realm, and
+  // its target is from sandbox realm.
+  sandbox.bound_then = Function.prototype.bind.call(sandbox.then, sandbox);
+
+  // Creating a promise thenable job in the following `Promise.resolve` performs
+  // GetFunctionRealm on the bound thenable.then and fails. The reaction job
+  // should be created with sandbox realm.
+  sandbox.eval(`
+var thenable = {
+  then: bound_then,
+};
+
+Promise.resolve(thenable).then(callback);
+`);
+
+  const result = await sandbox.callbackPromise;
+  equal(result, 11);
+});
diff --git a/dom/promise/tests/unit/test_promise_unhandled_rejection.js b/dom/promise/tests/unit/test_promise_unhandled_rejection.js
new file mode 100644
index 0000000000..68471569ec
--- /dev/null
+++ b/dom/promise/tests/unit/test_promise_unhandled_rejection.js
@@ -0,0 +1,139 @@
+"use strict";
+
+// Tests that unhandled promise rejections generate the appropriate
+// console messages.
+
+const { AddonTestUtils } = ChromeUtils.importESModule(
+  "resource://testing-common/AddonTestUtils.sys.mjs"
+);
+const { PromiseTestUtils } = ChromeUtils.importESModule(
+  "resource://testing-common/PromiseTestUtils.sys.mjs"
+);
+
+PromiseTestUtils.expectUncaughtRejection(/could not be cloned/);
+PromiseTestUtils.expectUncaughtRejection(/An exception was thrown/);
+PromiseTestUtils.expectUncaughtRejection(/Bleah/);
+
+const filename = "resource://foo/Bar.jsm";
+
+async function getSandboxMessages(sandbox, code) {
+  let { messages } = await AddonTestUtils.promiseConsoleOutput(async () => {
+    Cu.evalInSandbox(code, sandbox, null, filename, 1);
+
+    // We need two trips through the event loop for this error to be reported.
+    await new Promise(executeSoon);
+    await new Promise(executeSoon);
+  });
+
+  // xpcshell tests on OS-X sometimes include an extra warning, which we
+  // unfortunately need to ignore:
+  return messages.filter(
+    msg =>
+      !msg.message.includes(
+        "No chrome package registered for chrome://branding/locale/brand.properties"
+      )
+  );
+}
+
+add_task(async function test_unhandled_dom_exception() {
+  let sandbox = Cu.Sandbox(Services.scriptSecurityManager.getSystemPrincipal());
+  sandbox.StructuredCloneHolder = StructuredCloneHolder;
+
+  let messages = await getSandboxMessages(
+    sandbox,
+    `new Promise(() => {
+      new StructuredCloneHolder("", "", () => {});
+    });`
+  );
+
+  equal(messages.length, 1, "Got one console message");
+
+  let [msg] = messages;
+  ok(msg instanceof Ci.nsIScriptError, "Message is a script error");
+  equal(msg.sourceName, filename, "Got expected filename");
+  equal(msg.lineNumber, 2, "Got expected line number");
+  equal(
+    msg.errorMessage,
+    "DataCloneError: Function object could not be cloned.",
+    "Got expected error message"
+  );
+});
+
+add_task(async function test_unhandled_dom_exception_wrapped() {
+  let sandbox = Cu.Sandbox(
+    Services.scriptSecurityManager.createContentPrincipalFromOrigin(
+      "http://example.com/"
+    )
+  );
+  Cu.exportFunction(
+    function frick() {
+      throw new Components.Exception(
+        "Bleah.",
+        Cr.NS_ERROR_FAILURE,
+        Components.stack.caller
+      );
+    },
+    sandbox,
+    { defineAs: "frick" }
+  );
+
+  let messages = await getSandboxMessages(
+    sandbox,
+    `new Promise(() => {
+      frick();
+    });`
+  );
+
+  equal(messages.length, 2, "Got two console messages");
+
+  let [msg1, msg2] = messages;
+  ok(msg1 instanceof Ci.nsIScriptError, "Message is a script error");
+  equal(msg1.sourceName, filename, "Got expected filename");
+  equal(msg1.lineNumber, 2, "Got expected line number");
+  equal(
+    msg1.errorMessage,
+    "NS_ERROR_FAILURE: Bleah.",
+    "Got expected error message"
+  );
+
+  ok(msg2 instanceof Ci.nsIScriptError, "Message is a script error");
+  equal(msg2.sourceName, filename, "Got expected filename");
+  equal(msg2.lineNumber, 2, "Got expected line number");
+  equal(
+    msg2.errorMessage,
+    "InvalidStateError: An exception was thrown",
+    "Got expected error message"
+  );
+});
+
+add_task(async function test_unhandled_dom_exception_from_sandbox() {
+  let sandbox = Cu.Sandbox(
+    Services.scriptSecurityManager.createContentPrincipalFromOrigin(
+      "http://example.com/"
+    ),
+    { wantGlobalProperties: ["DOMException"] }
+  );
+  let ctor = Cu.evalInSandbox("DOMException", sandbox);
+  Cu.exportFunction(
+    function frick() {
+      throw new ctor("Bleah.");
+    },
+    sandbox,
+    { defineAs: "frick" }
+  );
+
+  let messages = await getSandboxMessages(
+    sandbox,
+    `new Promise(() => {
+      frick();
+    });`
+  );
+
+  equal(messages.length, 1, "Got one console messages");
+
+  let [msg] = messages;
+  ok(msg instanceof Ci.nsIScriptError, "Message is a script error");
+  equal(msg.sourceName, filename, "Got expected filename");
+  equal(msg.lineNumber, 2, "Got expected line number");
+  equal(msg.errorMessage, "Error: Bleah.", "Got expected error message");
+});
diff --git a/dom/promise/tests/unit/xpcshell.ini b/dom/promise/tests/unit/xpcshell.ini
new file mode 100644
index 0000000000..4da333a9b2
--- /dev/null
+++ b/dom/promise/tests/unit/xpcshell.ini
@@ -0,0 +1,6 @@
+[DEFAULT]
+head =
+
+[test_monitor_uncaught.js]
+[test_promise_unhandled_rejection.js]
+[test_promise_job_across_sandbox.js]