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diff --git a/dom/workers/WorkerRef.h b/dom/workers/WorkerRef.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef mozilla_dom_workers_WorkerRef_h
+#define mozilla_dom_workers_WorkerRef_h
+
+#include "mozilla/dom/WorkerStatus.h"
+#include "mozilla/MoveOnlyFunction.h"
+#include "mozilla/RefPtr.h"
+#include "nsISupports.h"
+#include "nsTString.h"
+
+#ifdef DEBUG
+#  include "mozilla/Mutex.h"
+#endif
+
+namespace mozilla::dom {
+
+/*
+ * If you want to play with a DOM Worker, you must know that it can go away
+ * at any time if nothing prevents its shutting down. This documentation helps
+ * to understand how to play with DOM Workers correctly.
+ *
+ * There are several reasons why a DOM Worker could go away. Here is the
+ * complete list:
+ *
+ * a. GC/CC - If the DOM Worker thread is idle and the Worker object is garbage
+ *    collected, it goes away.
+ * b. The worker script can call self.close()
+ * c. The Worker object calls worker.terminate()
+ * d. Firefox is shutting down.
+ *
+ * When a DOM Worker goes away, it does several steps. See more in
+ * WorkerStatus.h. The DOM Worker thread will basically stop scheduling
+ * WorkerRunnables, and eventually WorkerControlRunnables. But if there is
+ * something preventing the shutting down, it will always possible to dispatch
+ * WorkerControlRunnables.  Of course, at some point, the worker _must_ be
+ * released, otherwise firefox will leak it and the browser shutdown will hang.
+ *
+ * WeakWorkerRef is a refcounted, NON thread-safe object.
+ *
+ * From this object, you can obtain a WorkerPrivate, calling
+ * WeakWorkerRef::GetPrivate(). It returns nullptr if the worker is shutting
+ * down or if it is already gone away.
+ *
+ * If you want to know when a DOM Worker starts the shutting down procedure,
+ * pass a callback to the mozilla::dom::WeakWorkerRef::Create() method.
+ * Your function will be called. Note that _after_ the callback,
+ * WeakWorkerRef::GetPrivate() will return nullptr.
+ *
+ * How to keep a DOM Worker alive?
+ * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ *
+ * If you need to keep the worker alive, you must use StrongWorkerRef.
+ * You can have this refcounted, NON thread-safe object, calling
+ * mozilla::dom::StrongWorkerRef::Create(WorkerPrivate* aWorkerPrivate);
+ *
+ * If you have a StrongWorkerRef:
+ * a. the DOM Worker is kept alive.
+ * b. you can have access to the WorkerPrivate, calling: Private().
+ * c. WorkerControlRunnable can be dispatched.
+ *
+ * Note that the DOM Worker shutdown can start at any time, but having a
+ * StrongWorkerRef prevents the full shutdown. Also with StrongWorkerRef, you
+ * can pass a callback when calling mozilla::dom::StrongWorkerRef::Create().
+ *
+ * When the DOM Worker shutdown starts, WorkerRunnable cannot be dispatched
+ * anymore. At this point, you should dispatch WorkerControlRunnable just to
+ * release resources.
+ *
+ * How to have a thread-safe DOM Worker reference?
+ * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ *
+ * Sometimes you need to play with threads and you need a thread-safe worker
+ * reference. ThreadSafeWorkerRef is what you want.
+ *
+ * Just because this object can be sent to different threads, we don't allow the
+ * setting of a callback. It would be confusing.
+ *
+ * ThreadSafeWorkerRef can be destroyed in any thread. Internally it keeps a
+ * reference to its StrongWorkerRef creator and this ref will be dropped on the
+ * correct thread when the ThreadSafeWorkerRef is deleted.
+ *
+ * IPC WorkerRef
+ * ~~~~~~~~~~~~~
+ *
+ * IPDL protocols require a correct shutdown sequence. Because of this, they
+ * need a special configuration:
+ * 1. they need to be informed when the Worker starts the shutting down
+ * 2. they don't want to prevent the shutdown
+ * 3. but at the same time, they need to block the shutdown until the WorkerRef
+ *    is not longer alive.
+ *
+ * Point 1 is a standard feature of WorkerRef; point 2 is similar to
+ * WeakWorkerRef; point 3 is similar to StrongWorkerRef.
+ *
+ * You can create a special IPC WorkerRef using this static method:
+ * mozilla::dom::IPCWorkerRef::Create(WorkerPrivate* aWorkerPrivate,
+ *                                    const char* * aName);
+ */
+
+class WorkerPrivate;
+class StrongWorkerRef;
+class ThreadSafeWorkerRef;
+
+#ifdef DEBUG  // In debug mode, provide a way for clients to annotate WorkerRefs
+#  define SET_WORKERREF_DEBUG_STATUS(workerref, str) \
+    ((workerref)->DebugSetWorkerRefStatus(str))
+#  define GET_WORKERREF_DEBUG_STATUS(workerref) \
+    ((workerref)->DebugGetWorkerRefStatus())
+#else
+#  define SET_WORKERREF_DEBUG_STATUS(workerref, str) (void())
+#  define GET_WORKERREF_DEBUG_STATUS(workerref) (EmptyCString())
+#endif
+
+class WorkerRef {
+  friend class WorkerPrivate;
+
+ public:
+  NS_INLINE_DECL_REFCOUNTING(WorkerRef)
+
+#ifdef DEBUG
+  mutable Mutex mDebugMutex;
+  nsCString mDebugStatus MOZ_GUARDED_BY(mDebugMutex);
+
+  void DebugSetWorkerRefStatus(const nsCString& aStatus) {
+    MutexAutoLock lock(mDebugMutex);
+    mDebugStatus = aStatus;
+  }
+
+  const nsCString DebugGetWorkerRefStatus() const {
+    MutexAutoLock lock(mDebugMutex);
+    return mDebugStatus;
+  }
+#endif
+
+ protected:
+  WorkerRef(WorkerPrivate* aWorkerPrivate, const char* aName,
+            bool aIsPreventingShutdown);
+  virtual ~WorkerRef();
+
+  virtual void Notify();
+
+  bool HoldWorker(WorkerStatus aStatus);
+  void ReleaseWorker();
+
+  bool IsPreventingShutdown() const { return mIsPreventingShutdown; }
+
+  const char* Name() const { return mName; }
+
+  WorkerPrivate* mWorkerPrivate;
+
+  MoveOnlyFunction<void()> mCallback;
+  const char* const mName;
+  const bool mIsPreventingShutdown;
+
+  // True if this WorkerRef has been added to a WorkerPrivate.
+  bool mHolding;
+};
+
+class WeakWorkerRef final : public WorkerRef {
+ public:
+  static already_AddRefed<WeakWorkerRef> Create(
+      WorkerPrivate* aWorkerPrivate,
+      MoveOnlyFunction<void()>&& aCallback = nullptr);
+
+  WorkerPrivate* GetPrivate() const;
+
+  // This can be called on any thread. It's racy and, in general, the wrong
+  // choice.
+  WorkerPrivate* GetUnsafePrivate() const;
+
+ private:
+  explicit WeakWorkerRef(WorkerPrivate* aWorkerPrivate);
+  ~WeakWorkerRef();
+
+  void Notify() override;
+};
+
+class StrongWorkerRef final : public WorkerRef {
+ public:
+  static already_AddRefed<StrongWorkerRef> Create(
+      WorkerPrivate* aWorkerPrivate, const char* aName,
+      MoveOnlyFunction<void()>&& aCallback = nullptr);
+
+  // This function creates a StrongWorkerRef even when in the Canceling state of
+  // the worker's lifecycle. It's intended to be used by system code, e.g. code
+  // that needs to perform IPC.
+  //
+  // This method should only be used in cases where the StrongWorkerRef will be
+  // used for an extremely bounded duration that cannot be impacted by content.
+  // For example, IPCStreams use this type of ref in order to immediately
+  // migrate to an actor on another thread. Whether the IPCStream ever actually
+  // is streamed does not matter; the ref will be dropped once the new actor is
+  // created. For this reason, this method does not take a callback. It's
+  // expected and required that callers will drop the reference when they are
+  // done.
+  static already_AddRefed<StrongWorkerRef> CreateForcibly(
+      WorkerPrivate* aWorkerPrivate, const char* aName);
+
+  WorkerPrivate* Private() const;
+
+ private:
+  friend class WeakWorkerRef;
+  friend class ThreadSafeWorkerRef;
+
+  static already_AddRefed<StrongWorkerRef> CreateImpl(
+      WorkerPrivate* aWorkerPrivate, const char* aName,
+      WorkerStatus aFailStatus);
+
+  StrongWorkerRef(WorkerPrivate* aWorkerPrivate, const char* aName);
+  ~StrongWorkerRef();
+};
+
+class ThreadSafeWorkerRef final {
+ public:
+  NS_INLINE_DECL_THREADSAFE_REFCOUNTING(ThreadSafeWorkerRef)
+
+  explicit ThreadSafeWorkerRef(StrongWorkerRef* aRef);
+
+  WorkerPrivate* Private() const;
+
+#ifdef DEBUG
+  RefPtr<StrongWorkerRef>& Ref() { return mRef; }
+#endif
+
+ private:
+  friend class StrongWorkerRef;
+
+  ~ThreadSafeWorkerRef();
+
+  RefPtr<StrongWorkerRef> mRef;
+};
+
+class IPCWorkerRef final : public WorkerRef {
+ public:
+  static already_AddRefed<IPCWorkerRef> Create(
+      WorkerPrivate* aWorkerPrivate, const char* aName,
+      MoveOnlyFunction<void()>&& aCallback = nullptr);
+
+  WorkerPrivate* Private() const;
+
+  void SetActorCount(uint32_t aCount);
+
+ private:
+  IPCWorkerRef(WorkerPrivate* aWorkerPrivate, const char* aName);
+  ~IPCWorkerRef();
+
+  // The count of background actors which binding with this IPCWorkerRef.
+  uint32_t mActorCount;
+};
+
+// Template class to keep an Actor pointer, as a raw pointer, in a ref-counted
+// way when passed to lambdas.
+template <class ActorPtr>
+class IPCWorkerRefHelper final {
+ public:
+  NS_INLINE_DECL_REFCOUNTING(IPCWorkerRefHelper);
+
+  explicit IPCWorkerRefHelper(ActorPtr* aActor) : mActor(aActor) {}
+
+  ActorPtr* Actor() const { return mActor; }
+
+ private:
+  ~IPCWorkerRefHelper() = default;
+
+  // Raw pointer
+  ActorPtr* mActor;
+};
+
+}  // namespace mozilla::dom
+
+#endif /* mozilla_dom_workers_WorkerRef_h */