diff --git a/build/clang-plugin/ThreadAllows.txt b/build/clang-plugin/ThreadAllows.txt
index 934d226d4b62..b09bb32b7920 100644
--- a/build/clang-plugin/ThreadAllows.txt
+++ b/build/clang-plugin/ThreadAllows.txt
@@ -17,6 +17,7 @@ Cameras IPC
 ChainedPipePump
 ChainedPipeRecv
 Checker Test
+Compositor
 Cookie
 CrashRep Inject
 DDMediaLogs
@@ -41,6 +42,7 @@ IMAP
 IPC Launch
 IPDL Background
 IdentityCrypto
+ImageBridgeChld
 LS Thread
 LayerScope
 MDCDMThread
diff --git a/dom/media/systemservices/MediaSystemResourceManager.cpp b/dom/media/systemservices/MediaSystemResourceManager.cpp
index 8d0a797c4be2..ff02a10ed245 100644
--- a/dom/media/systemservices/MediaSystemResourceManager.cpp
+++ b/dom/media/systemservices/MediaSystemResourceManager.cpp
@@ -71,7 +71,7 @@ void MediaSystemResourceManager::Init() {
         barrier.NotifyAll();
       });
 
-  imageBridge->GetMessageLoop()->PostTask(runnable.forget());
+  imageBridge->GetThread()->Dispatch(runnable.forget());
 
   // should stop the thread until done.
   while (!done) {
@@ -178,7 +178,7 @@ void MediaSystemResourceManager::Acquire(MediaSystemResourceClient* aClient) {
     return;
   }
   aClient->mResourceState = MediaSystemResourceClient::RESOURCE_STATE_WAITING;
-  ImageBridgeChild::GetSingleton()->GetMessageLoop()->PostTask(
+  ImageBridgeChild::GetSingleton()->GetThread()->Dispatch(
       NewRunnableMethod<uint32_t>("MediaSystemResourceManager::DoAcquire", this,
                                   &MediaSystemResourceManager::DoAcquire,
                                   aClient->mId));
@@ -220,7 +220,7 @@ bool MediaSystemResourceManager::AcquireSyncNoWait(
     aClient->mResourceState = MediaSystemResourceClient::RESOURCE_STATE_WAITING;
   }
 
-  ImageBridgeChild::GetSingleton()->GetMessageLoop()->PostTask(
+  ImageBridgeChild::GetSingleton()->GetThread()->Dispatch(
       NewRunnableMethod<uint32_t>("MediaSystemResourceManager::DoAcquire", this,
                                   &MediaSystemResourceManager::DoAcquire,
                                   aClient->mId));
@@ -282,7 +282,7 @@ void MediaSystemResourceManager::ReleaseResource(
 
     aClient->mResourceState = MediaSystemResourceClient::RESOURCE_STATE_END;
 
-    ImageBridgeChild::GetSingleton()->GetMessageLoop()->PostTask(
+    ImageBridgeChild::GetSingleton()->GetThread()->Dispatch(
         NewRunnableMethod<uint32_t>(
             "MediaSystemResourceManager::DoRelease", this,
             &MediaSystemResourceManager::DoRelease, aClient->mId));
@@ -304,7 +304,7 @@ void MediaSystemResourceManager::RecvResponse(uint32_t aId, bool aSuccess) {
 void MediaSystemResourceManager::HandleAcquireResult(uint32_t aId,
                                                      bool aSuccess) {
   if (!InImageBridgeChildThread()) {
-    ImageBridgeChild::GetSingleton()->GetMessageLoop()->PostTask(
+    ImageBridgeChild::GetSingleton()->GetThread()->Dispatch(
         NewRunnableMethod<uint32_t, bool>(
             "MediaSystemResourceManager::HandleAcquireResult", this,
             &MediaSystemResourceManager::HandleAcquireResult, aId, aSuccess));
diff --git a/dom/plugins/ipc/PluginInstanceParent.cpp b/dom/plugins/ipc/PluginInstanceParent.cpp
index 1135dec4a44e..108c9b3a1f0a 100644
--- a/dom/plugins/ipc/PluginInstanceParent.cpp
+++ b/dom/plugins/ipc/PluginInstanceParent.cpp
@@ -551,7 +551,7 @@ class AsyncPluginSurfaceManager : public IGPUVideoSurfaceManager {
     if (!InImageBridgeChildThread()) {
       SynchronousTask task("AsyncPluginSurfaceManager readback sync");
       RefPtr<gfx::SourceSurface> result;
-      ImageBridgeChild::GetSingleton()->GetMessageLoop()->PostTask(
+      ImageBridgeChild::GetSingleton()->GetThread()->Dispatch(
           NewRunnableFunction("AsyncPluginSurfaceManager readback",
                               &DoSyncReadback, &pluginSD, &result, &task));
       task.Wait();
@@ -565,7 +565,7 @@ class AsyncPluginSurfaceManager : public IGPUVideoSurfaceManager {
       const SurfaceDescriptorGPUVideo& aSD) override {
     SurfaceDescriptorPlugin pluginSD = aSD;
     if (!InImageBridgeChildThread()) {
-      ImageBridgeChild::GetSingleton()->GetMessageLoop()->PostTask(
+      ImageBridgeChild::GetSingleton()->GetThread()->Dispatch(
           NewRunnableFunction("AsyncPluginSurfaceManager dealloc", &DoDealloc,
                               &pluginSD));
       return;
@@ -739,7 +739,7 @@ mozilla::ipc::IPCResult PluginInstanceParent::RecvInitDXGISurface(
   // render to.
   SurfaceDescriptorPlugin sd;
   SynchronousTask task("SendMakeAsyncPluginSurfaces sync");
-  ImageBridgeChild::GetSingleton()->GetMessageLoop()->PostTask(
+  ImageBridgeChild::GetSingleton()->GetThread()->Dispatch(
       NewRunnableFunction("SendingMakeAsyncPluginSurfaces", &InitDXGISurface,
                           format, size, &sd, &task));
   task.Wait();
@@ -781,9 +781,8 @@ mozilla::ipc::IPCResult PluginInstanceParent::RecvFinalizeDXGISurface(
   // Release the plugin surface but keep the display surface since it may
   // still be displayed.  Also let the display surface know that it should
   // not receive further requests to copy from the plugin surface.
-  ImageBridgeChild::GetSingleton()->GetMessageLoop()->PostTask(
-      NewRunnableFunction("SendingRemoveAsyncPluginSurface",
-                          &FinalizeDXGISurface, asi.mSD));
+  ImageBridgeChild::GetSingleton()->GetThread()->Dispatch(NewRunnableFunction(
+      "SendingRemoveAsyncPluginSurface", &FinalizeDXGISurface, asi.mSD));
 
   mAsyncSurfaceMap.remove(asiIt);
 #endif
@@ -897,9 +896,8 @@ mozilla::ipc::IPCResult PluginInstanceParent::RecvShowDirectDXGISurface(
 
   // Tell the ImageBridge to copy from the plugin surface to the display surface
   SynchronousTask task("SendUpdateAsyncPluginSurface sync");
-  ImageBridgeChild::GetSingleton()->GetMessageLoop()->PostTask(
-      NewRunnableFunction("SendingUpdateAsyncPluginSurface", &CopyDXGISurface,
-                          asi.mSD, &task));
+  ImageBridgeChild::GetSingleton()->GetThread()->Dispatch(NewRunnableFunction(
+      "SendingUpdateAsyncPluginSurface", &CopyDXGISurface, asi.mSD, &task));
   task.Wait();
 
   // Make sure we have an ImageContainer for SetCurrentImage.
diff --git a/gfx/ipc/VsyncBridgeParent.cpp b/gfx/ipc/VsyncBridgeParent.cpp
index 96eac4ae4dcb..9631d75b9883 100644
--- a/gfx/ipc/VsyncBridgeParent.cpp
+++ b/gfx/ipc/VsyncBridgeParent.cpp
@@ -20,7 +20,7 @@ RefPtr<VsyncBridgeParent> VsyncBridgeParent::Start(
   RefPtr<Runnable> task = NewRunnableMethod<Endpoint<PVsyncBridgeParent>&&>(
       "gfx::VsyncBridgeParent::Open", parent, &VsyncBridgeParent::Open,
       std::move(aEndpoint));
-  CompositorThreadHolder::Loop()->PostTask(task.forget());
+  CompositorThread()->Dispatch(task.forget());
 
   return parent;
 }
@@ -48,10 +48,10 @@ mozilla::ipc::IPCResult VsyncBridgeParent::RecvNotifyVsync(
 }
 
 void VsyncBridgeParent::Shutdown() {
-  MessageLoop* ccloop = CompositorThreadHolder::Loop();
-  if (MessageLoop::current() != ccloop) {
-    ccloop->PostTask(NewRunnableMethod("gfx::VsyncBridgeParent::ShutdownImpl",
-                                       this, &VsyncBridgeParent::ShutdownImpl));
+  if (!CompositorThreadHolder::IsInCompositorThread()) {
+    CompositorThread()->Dispatch(
+        NewRunnableMethod("gfx::VsyncBridgeParent::ShutdownImpl", this,
+                          &VsyncBridgeParent::ShutdownImpl));
     return;
   }
 
diff --git a/gfx/layers/TextureSync.cpp b/gfx/layers/TextureSync.cpp
index b24ac7101342..7c3847b079a0 100644
--- a/gfx/layers/TextureSync.cpp
+++ b/gfx/layers/TextureSync.cpp
@@ -111,7 +111,7 @@ static void CheckTexturesForUnlock() {
 void TextureSync::DispatchCheckTexturesForUnlock() {
   RefPtr<Runnable> task =
       NS_NewRunnableFunction("CheckTexturesForUnlock", &CheckTexturesForUnlock);
-  CompositorThreadHolder::Loop()->PostTask(task.forget());
+  CompositorThread()->Dispatch(task.forget());
 }
 
 void TextureSync::HandleWaitForTexturesMessage(MachReceiveMessage* rmsg,
diff --git a/gfx/layers/apz/src/APZUpdater.cpp b/gfx/layers/apz/src/APZUpdater.cpp
index 3a5080b7c013..91660929188c 100644
--- a/gfx/layers/apz/src/APZUpdater.cpp
+++ b/gfx/layers/apz/src/APZUpdater.cpp
@@ -373,8 +373,8 @@ void APZUpdater::RunOnUpdaterThread(LayersId aLayersId,
     return;
   }
 
-  if (MessageLoop* loop = CompositorThreadHolder::Loop()) {
-    loop->PostTask(task.forget());
+  if (CompositorThread()) {
+    CompositorThread()->Dispatch(task.forget());
   } else {
     // Could happen during startup
     NS_WARNING("Dropping task posted to updater thread");
diff --git a/gfx/layers/client/CompositableClient.cpp b/gfx/layers/client/CompositableClient.cpp
index f9e3ab25cfc4..3a15a36dc742 100644
--- a/gfx/layers/client/CompositableClient.cpp
+++ b/gfx/layers/client/CompositableClient.cpp
@@ -169,8 +169,7 @@ TextureClientRecycleAllocator* CompositableClient::GetTextureClientRecycler() {
         barrier.NotifyAll();
       });
 
-  ImageBridgeChild::GetSingleton()->GetMessageLoop()->PostTask(
-      runnable.forget());
+  ImageBridgeChild::GetSingleton()->GetThread()->Dispatch(runnable.forget());
 
   // should stop the thread until done.
   while (!done) {
diff --git a/gfx/layers/client/TextureClient.cpp b/gfx/layers/client/TextureClient.cpp
index 2d0b9df09033..dbcefb088395 100644
--- a/gfx/layers/client/TextureClient.cpp
+++ b/gfx/layers/client/TextureClient.cpp
@@ -5,57 +5,61 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 #include "mozilla/layers/TextureClient.h"
+
 #include <stdint.h>  // for uint8_t, uint32_t, etc
-#include "Layers.h"  // for Layer, etc
+
+#include "BufferTexture.h"
+#include "IPDLActor.h"
+#include "ImageContainer.h"  // for PlanarYCbCrData, etc
+#include "Layers.h"          // for Layer, etc
+#include "LayersLogging.h"   // for AppendToString
+#include "MainThreadUtils.h"
 #include "gfx2DGlue.h"
 #include "gfxPlatform.h"  // for gfxPlatform
-#include "MainThreadUtils.h"
+#include "gfxUtils.h"     // for gfxUtils::GetAsLZ4Base64Str
 #include "mozilla/Atomics.h"
+#include "mozilla/Mutex.h"
 #include "mozilla/SchedulerGroup.h"
 #include "mozilla/StaticPrefs_gfx.h"
 #include "mozilla/StaticPrefs_layers.h"
+#include "mozilla/gfx/2D.h"
+#include "mozilla/gfx/DataSurfaceHelpers.h"  // for CreateDataSourceSurfaceByCloning
+#include "mozilla/gfx/Logging.h"             // for gfxDebug
 #include "mozilla/gfx/gfxVars.h"
+#include "mozilla/ipc/CrossProcessSemaphore.h"
 #include "mozilla/ipc/SharedMemory.h"  // for SharedMemory, etc
 #include "mozilla/layers/CompositableForwarder.h"
 #include "mozilla/layers/ISurfaceAllocator.h"
 #include "mozilla/layers/ImageBridgeChild.h"
 #include "mozilla/layers/ImageDataSerializer.h"
+#include "mozilla/layers/PTextureChild.h"
 #include "mozilla/layers/PaintThread.h"
+#include "mozilla/layers/ShadowLayers.h"
+#include "mozilla/layers/TextureClientOGL.h"
 #include "mozilla/layers/TextureClientRecycleAllocator.h"
 #include "mozilla/layers/TextureRecorded.h"
-#include "mozilla/Mutex.h"
 #include "nsDebug.h"          // for NS_ASSERTION, NS_WARNING, etc
+#include "nsISerialEventTarget.h"
 #include "nsISupportsImpl.h"  // for MOZ_COUNT_CTOR, etc
-#include "ImageContainer.h"   // for PlanarYCbCrData, etc
-#include "mozilla/gfx/2D.h"
-#include "mozilla/gfx/Logging.h"  // for gfxDebug
-#include "mozilla/layers/TextureClientOGL.h"
-#include "mozilla/layers/PTextureChild.h"
-#include "mozilla/gfx/DataSurfaceHelpers.h"  // for CreateDataSourceSurfaceByCloning
-#include "nsPrintfCString.h"                 // for nsPrintfCString
-#include "LayersLogging.h"                   // for AppendToString
-#include "gfxUtils.h"                        // for gfxUtils::GetAsLZ4Base64Str
-#include "IPDLActor.h"
-#include "BufferTexture.h"
-#include "mozilla/layers/ShadowLayers.h"
-#include "mozilla/ipc/CrossProcessSemaphore.h"
+#include "nsPrintfCString.h"  // for nsPrintfCString
 
 #ifdef XP_WIN
+#  include "gfx2DGlue.h"
+#  include "gfxWindowsPlatform.h"
 #  include "mozilla/gfx/DeviceManagerDx.h"
 #  include "mozilla/layers/TextureD3D11.h"
 #  include "mozilla/layers/TextureDIB.h"
-#  include "gfxWindowsPlatform.h"
-#  include "gfx2DGlue.h"
 #endif
 #ifdef MOZ_X11
-#  include "mozilla/layers/TextureClientX11.h"
 #  include "GLXLibrary.h"
+#  include "mozilla/layers/TextureClientX11.h"
 #endif
 #ifdef MOZ_WAYLAND
 #  include <gtk/gtkx.h>
-#  include "mozilla/widget/nsWaylandDisplay.h"
-#  include "mozilla/layers/WaylandDMABUFTextureClientOGL.h"
+
 #  include "gfxPlatformGtk.h"
+#  include "mozilla/layers/WaylandDMABUFTextureClientOGL.h"
+#  include "mozilla/widget/nsWaylandDisplay.h"
 #endif
 
 #ifdef XP_MACOSX
@@ -490,12 +494,12 @@ void DeallocateTextureClient(TextureDeallocParams params) {
   }
 
   TextureChild* actor = params.actor;
-  MessageLoop* ipdlMsgLoop = nullptr;
+  nsCOMPtr<nsISerialEventTarget> ipdlThread;
 
   if (params.allocator) {
-    ipdlMsgLoop = params.allocator->GetMessageLoop();
-    if (!ipdlMsgLoop) {
-      // An allocator with no message loop means we are too late in the shutdown
+    ipdlThread = params.allocator->GetThread();
+    if (!ipdlThread) {
+      // An allocator with no thread means we are too late in the shutdown
       // sequence.
       gfxCriticalError() << "Texture deallocated too late during shutdown";
       return;
@@ -503,19 +507,19 @@ void DeallocateTextureClient(TextureDeallocParams params) {
   }
 
   // First make sure that the work is happening on the IPDL thread.
-  if (ipdlMsgLoop && MessageLoop::current() != ipdlMsgLoop) {
+  if (ipdlThread && !ipdlThread->IsOnCurrentThread()) {
     if (params.syncDeallocation) {
       bool done = false;
       ReentrantMonitor barrier("DeallocateTextureClient");
       ReentrantMonitorAutoEnter autoMon(barrier);
-      ipdlMsgLoop->PostTask(NewRunnableFunction(
+      ipdlThread->Dispatch(NewRunnableFunction(
           "DeallocateTextureClientSyncProxyRunnable",
           DeallocateTextureClientSyncProxy, params, &barrier, &done));
       while (!done) {
         barrier.Wait();
       }
     } else {
-      ipdlMsgLoop->PostTask(NewRunnableFunction(
+      ipdlThread->Dispatch(NewRunnableFunction(
           "DeallocateTextureClientRunnable", DeallocateTextureClient, params));
     }
     // The work has been forwarded to the IPDL thread, we are done.
@@ -525,8 +529,8 @@ void DeallocateTextureClient(TextureDeallocParams params) {
   // Below this line, we are either in the IPDL thread or ther is no IPDL
   // thread anymore.
 
-  if (!ipdlMsgLoop) {
-    // If we don't have a message loop we can't know for sure that we are in
+  if (!ipdlThread) {
+    // If we don't have a thread we can't know for sure that we are in
     // the IPDL thread and use the LayersIPCChannel.
     // This should ideally not happen outside of gtest, but some shutdown
     // raciness could put us in this situation.
@@ -978,15 +982,14 @@ static void CancelTextureClientNotifyNotUsed(uint64_t aTextureId,
   if (!aAllocator) {
     return;
   }
-  MessageLoop* msgLoop = nullptr;
-  msgLoop = aAllocator->GetMessageLoop();
-  if (!msgLoop) {
+  nsCOMPtr<nsISerialEventTarget> thread = aAllocator->GetThread();
+  if (!thread) {
     return;
   }
-  if (MessageLoop::current() == msgLoop) {
+  if (thread->IsOnCurrentThread()) {
     aAllocator->CancelWaitForNotifyNotUsed(aTextureId);
   } else {
-    msgLoop->PostTask(NewRunnableFunction(
+    thread->Dispatch(NewRunnableFunction(
         "CancelTextureClientNotifyNotUsedRunnable",
         CancelTextureClientNotifyNotUsed, aTextureId, aAllocator));
   }
@@ -1017,9 +1020,8 @@ void TextureClient::SetRecycleAllocator(
 }
 
 bool TextureClient::InitIPDLActor(CompositableForwarder* aForwarder) {
-  MOZ_ASSERT(aForwarder &&
-             aForwarder->GetTextureForwarder()->GetMessageLoop() ==
-                 mAllocator->GetMessageLoop());
+  MOZ_ASSERT(aForwarder && aForwarder->GetTextureForwarder()->GetThread() ==
+                               mAllocator->GetThread());
 
   if (mActor && !mActor->IPCOpen()) {
     return false;
@@ -1112,8 +1114,8 @@ bool TextureClient::InitIPDLActor(CompositableForwarder* aForwarder) {
 
 bool TextureClient::InitIPDLActor(KnowsCompositor* aKnowsCompositor) {
   MOZ_ASSERT(aKnowsCompositor &&
-             aKnowsCompositor->GetTextureForwarder()->GetMessageLoop() ==
-                 mAllocator->GetMessageLoop());
+             aKnowsCompositor->GetTextureForwarder()->GetThread() ==
+                 mAllocator->GetThread());
   TextureForwarder* fwd = aKnowsCompositor->GetTextureForwarder();
   if (mActor && !mActor->mDestroyed) {
     CompositableForwarder* currentFwd = mActor->mCompositableForwarder;
diff --git a/gfx/layers/client/TextureClientRecycleAllocator.cpp b/gfx/layers/client/TextureClientRecycleAllocator.cpp
index b7c09235bbd9..f1f1aac82233 100644
--- a/gfx/layers/client/TextureClientRecycleAllocator.cpp
+++ b/gfx/layers/client/TextureClientRecycleAllocator.cpp
@@ -153,7 +153,7 @@ already_AddRefed<TextureClient> TextureClientRecycleAllocator::CreateOrRecycle(
             new TextureClientReleaseTask(textureHolder->GetTextureClient());
         textureHolder->ClearTextureClient();
         textureHolder = nullptr;
-        mKnowsCompositor->GetTextureForwarder()->GetMessageLoop()->PostTask(
+        mKnowsCompositor->GetTextureForwarder()->GetThread()->Dispatch(
             task.forget());
       } else {
         textureHolder->GetTextureClient()->RecycleTexture(
diff --git a/gfx/layers/ipc/CanvasThread.cpp b/gfx/layers/ipc/CanvasThread.cpp
index dd2ca8a19f65..c6d66b76fae1 100644
--- a/gfx/layers/ipc/CanvasThread.cpp
+++ b/gfx/layers/ipc/CanvasThread.cpp
@@ -34,8 +34,8 @@ CanvasThreadHolder::CanvasThreadHolder(
 CanvasThreadHolder::~CanvasThreadHolder() {
   // Note we can't just use NS_IsInCompositorThread() here because
   // sCompositorThreadHolder might have already gone.
-  MOZ_ASSERT(mCompositorThreadKeepAlive->GetCompositorThread()->thread_id() ==
-             PlatformThread::CurrentId());
+  MOZ_ASSERT(
+      mCompositorThreadKeepAlive->GetCompositorThread()->IsOnCurrentThread());
 }
 
 /* static */
@@ -75,8 +75,7 @@ void CanvasThreadHolder::StaticRelease(
   RefPtr<CanvasThreadHolder> threadHolder = aCanvasThreadHolder;
   // Note we can't just use NS_IsInCompositorThread() here because
   // sCompositorThreadHolder might have already gone.
-  MOZ_ASSERT(threadHolder->mCompositorThreadKeepAlive->GetCompositorThread()
-                 ->thread_id() == PlatformThread::CurrentId());
+  MOZ_ASSERT(threadHolder->mCompositorThreadKeepAlive->IsInCompositorThread());
   threadHolder = nullptr;
 
   auto lockedCanvasThreadHolder = sCanvasThreadHolder.Lock();
@@ -89,12 +88,11 @@ void CanvasThreadHolder::StaticRelease(
 void CanvasThreadHolder::ReleaseOnCompositorThread(
     already_AddRefed<CanvasThreadHolder> aCanvasThreadHolder) {
   auto lockedCanvasThreadHolder = sCanvasThreadHolder.Lock();
-  base::Thread* compositorThread =
-      lockedCanvasThreadHolder.ref()
-          ->mCompositorThreadKeepAlive->GetCompositorThread();
-  compositorThread->message_loop()->PostTask(NewRunnableFunction(
-      "CanvasThreadHolder::StaticRelease", CanvasThreadHolder::StaticRelease,
-      std::move(aCanvasThreadHolder)));
+  lockedCanvasThreadHolder.ref()
+      ->mCompositorThreadKeepAlive->GetCompositorThread()
+      ->Dispatch(NewRunnableFunction("CanvasThreadHolder::StaticRelease",
+                                     CanvasThreadHolder::StaticRelease,
+                                     std::move(aCanvasThreadHolder)));
 }
 
 /* static */
diff --git a/gfx/layers/ipc/CompositorBridgeChild.cpp b/gfx/layers/ipc/CompositorBridgeChild.cpp
index f3ec57613d64..b972ee416506 100644
--- a/gfx/layers/ipc/CompositorBridgeChild.cpp
+++ b/gfx/layers/ipc/CompositorBridgeChild.cpp
@@ -9,7 +9,6 @@
 #include "mozilla/layers/CompositorThread.h"
 #include <stddef.h>              // for size_t
 #include "ClientLayerManager.h"  // for ClientLayerManager
-#include "base/message_loop.h"   // for MessageLoop
 #include "base/task.h"           // for NewRunnableMethod, etc
 #include "mozilla/StaticPrefs_layers.h"
 #include "mozilla/layers/CompositorManagerChild.h"
@@ -36,7 +35,6 @@
 #include "nsDebug.h"          // for NS_WARNING
 #include "nsISupportsImpl.h"  // for MOZ_COUNT_CTOR, etc
 #include "nsTArray.h"         // for nsTArray, nsTArray_Impl
-#include "nsXULAppAPI.h"      // for XRE_GetIOMessageLoop, etc
 #include "FrameLayerBuilder.h"
 #include "mozilla/dom/BrowserChild.h"
 #include "mozilla/dom/BrowserParent.h"
@@ -85,7 +83,7 @@ CompositorBridgeChild::CompositorBridgeChild(CompositorManagerChild* aManager)
       mCanSend(false),
       mActorDestroyed(false),
       mFwdTransactionId(0),
-      mMessageLoop(MessageLoop::current()),
+      mThread(NS_GetCurrentThread()),
       mProcessToken(0),
       mSectionAllocator(nullptr),
       mPaintLock("CompositorBridgeChild.mPaintLock"),
@@ -168,7 +166,7 @@ void CompositorBridgeChild::Destroy() {
     // We may have already called destroy but still have lingering references
     // or CompositorBridgeChild::ActorDestroy was called. Ensure that we do our
     // post destroy clean up no matter what. It is safe to call multiple times.
-    MessageLoop::current()->PostTask(
+    NS_GetCurrentThread()->Dispatch(
         NewRunnableMethod("CompositorBridgeChild::PrepareFinalDestroy", selfRef,
                           &CompositorBridgeChild::PrepareFinalDestroy));
     return;
@@ -225,12 +223,12 @@ void CompositorBridgeChild::Destroy() {
   // CompositorBridgeParent to the CompositorBridgeChild (e.g. caused by the
   // destruction of shared memory). We need to ensure this gets processed by the
   // CompositorBridgeChild before it gets destroyed. It suffices to ensure that
-  // events already in the MessageLoop get processed before the
-  // CompositorBridgeChild is destroyed, so we add a task to the MessageLoop to
+  // events already in the thread get processed before the
+  // CompositorBridgeChild is destroyed, so we add a task to the thread to
   // handle compositor destruction.
 
   // From now on we can't send any message message.
-  MessageLoop::current()->PostTask(
+  NS_GetCurrentThread()->Dispatch(
       NewRunnableMethod("CompositorBridgeChild::PrepareFinalDestroy", selfRef,
                         &CompositorBridgeChild::PrepareFinalDestroy));
 }
@@ -470,8 +468,8 @@ mozilla::ipc::IPCResult CompositorBridgeChild::RecvUpdatePluginConfigurations(
 
 #if defined(XP_WIN)
 static void ScheduleSendAllPluginsCaptured(CompositorBridgeChild* aThis,
-                                           MessageLoop* aLoop) {
-  aLoop->PostTask(NewNonOwningRunnableMethod(
+                                           nsISerialEventTarget* aThread) {
+  aThread->Dispatch(NewNonOwningRunnableMethod(
       "CompositorBridgeChild::SendAllPluginsCaptured", aThis,
       &CompositorBridgeChild::SendAllPluginsCaptured));
 }
@@ -483,12 +481,11 @@ mozilla::ipc::IPCResult CompositorBridgeChild::RecvCaptureAllPlugins(
   MOZ_ASSERT(NS_IsMainThread());
   nsIWidget::CaptureRegisteredPlugins(aParentWidget);
 
-  // Bounce the call to SendAllPluginsCaptured off the ImageBridgeChild loop,
+  // Bounce the call to SendAllPluginsCaptured off the ImageBridgeChild thread,
   // to make sure that the image updates on that thread have been processed.
-  ImageBridgeChild::GetSingleton()->GetMessageLoop()->PostTask(
-      NewRunnableFunction("ScheduleSendAllPluginsCapturedRunnable",
-                          &ScheduleSendAllPluginsCaptured, this,
-                          MessageLoop::current()));
+  ImageBridgeChild::GetSingleton()->GetThread()->Dispatch(NewRunnableFunction(
+      "ScheduleSendAllPluginsCapturedRunnable", &ScheduleSendAllPluginsCaptured,
+      this, NS_GetCurrentThread()));
   return IPC_OK();
 #else
   MOZ_ASSERT_UNREACHABLE(
diff --git a/gfx/layers/ipc/CompositorBridgeChild.h b/gfx/layers/ipc/CompositorBridgeChild.h
index c215fe70f9de..71c9d6ec706d 100644
--- a/gfx/layers/ipc/CompositorBridgeChild.h
+++ b/gfx/layers/ipc/CompositorBridgeChild.h
@@ -200,7 +200,7 @@ class CompositorBridgeChild final : public PCompositorBridgeChild,
 
   void HandleMemoryPressure();
 
-  MessageLoop* GetMessageLoop() const override { return mMessageLoop; }
+  nsISerialEventTarget* GetThread() const override { return mThread; }
 
   base::ProcessId GetParentPid() const override { return OtherPid(); }
 
@@ -373,7 +373,7 @@ class CompositorBridgeChild final : public PCompositorBridgeChild,
   std::unordered_map<uint64_t, RefPtr<TextureClient>>
       mTexturesWaitingNotifyNotUsed;
 
-  MessageLoop* mMessageLoop;
+  nsCOMPtr<nsISerialEventTarget> mThread;
 
   AutoTArray<RefPtr<TextureClientPool>, 2> mTexturePools;
 
diff --git a/gfx/layers/ipc/CompositorBridgeParent.cpp b/gfx/layers/ipc/CompositorBridgeParent.cpp
index f959a25c8ea0..6e5478358c5a 100644
--- a/gfx/layers/ipc/CompositorBridgeParent.cpp
+++ b/gfx/layers/ipc/CompositorBridgeParent.cpp
@@ -14,10 +14,7 @@
 #include "apz/src/APZCTreeManager.h"  // for APZCTreeManager
 #include "LayerTransactionParent.h"   // for LayerTransactionParent
 #include "RenderTrace.h"              // for RenderTraceLayers
-#include "base/message_loop.h"        // for MessageLoop
 #include "base/process.h"             // for ProcessId
-#include "base/task.h"                // for CancelableTask, etc
-#include "base/thread.h"              // for Thread
 #include "gfxContext.h"               // for gfxContext
 #include "gfxPlatform.h"              // for gfxPlatform
 #include "TreeTraversal.h"            // for ForEachNode
@@ -80,7 +77,6 @@
 #include "nsIWidget.h"        // for nsIWidget
 #include "nsTArray.h"         // for nsTArray
 #include "nsThreadUtils.h"    // for NS_IsMainThread
-#include "nsXULAppAPI.h"      // for XRE_GetIOMessageLoop
 #ifdef XP_WIN
 #  include "mozilla/layers/CompositorD3D11.h"
 #  include "mozilla/widget/WinCompositorWidget.h"
@@ -174,10 +170,6 @@ bool CompositorBridgeParentBase::DeallocShmem(ipc::Shmem& aShmem) {
   return PCompositorBridgeParent::DeallocShmem(aShmem);
 }
 
-static inline MessageLoop* CompositorLoop() {
-  return CompositorThreadHolder::Loop();
-}
-
 base::ProcessId CompositorBridgeParentBase::RemotePid() { return OtherPid(); }
 
 bool CompositorBridgeParentBase::StartSharingMetrics(
@@ -185,8 +177,8 @@ bool CompositorBridgeParentBase::StartSharingMetrics(
     CrossProcessMutexHandle aMutexHandle, LayersId aLayersId,
     uint32_t aApzcId) {
   if (!CompositorThreadHolder::IsInCompositorThread()) {
-    MOZ_ASSERT(CompositorLoop());
-    CompositorLoop()->PostTask(
+    MOZ_ASSERT(CompositorThread());
+    CompositorThread()->Dispatch(
         NewRunnableMethod<ipc::SharedMemoryBasic::Handle,
                           CrossProcessMutexHandle, LayersId, uint32_t>(
             "layers::CompositorBridgeParent::StartSharingMetrics", this,
@@ -206,8 +198,8 @@ bool CompositorBridgeParentBase::StartSharingMetrics(
 bool CompositorBridgeParentBase::StopSharingMetrics(
     ScrollableLayerGuid::ViewID aScrollId, uint32_t aApzcId) {
   if (!CompositorThreadHolder::IsInCompositorThread()) {
-    MOZ_ASSERT(CompositorLoop());
-    CompositorLoop()->PostTask(
+    MOZ_ASSERT(CompositorThread());
+    CompositorThread()->Dispatch(
         NewRunnableMethod<ScrollableLayerGuid::ViewID, uint32_t>(
             "layers::CompositorBridgeParent::StopSharingMetrics", this,
             &CompositorBridgeParentBase::StopSharingMetrics, aScrollId,
@@ -404,8 +396,8 @@ void CompositorBridgeParent::Initialize() {
   // FIXME: This holds on the the fact that right now the only thing that
   // can destroy this instance is initialized on the compositor thread after
   // this task has been processed.
-  MOZ_ASSERT(CompositorLoop());
-  CompositorLoop()->PostTask(NewRunnableFunction(
+  MOZ_ASSERT(CompositorThread());
+  CompositorThread()->Dispatch(NewRunnableFunction(
       "AddCompositorRunnable", &AddCompositor, this, &mCompositorBridgeID));
 
   {  // scope lock
@@ -680,22 +672,22 @@ void CompositorBridgeParent::ActorDestroy(ActorDestroyReason why) {
   // on this thread. We must keep the compositor parent alive untill the code
   // handling message reception is finished on this thread.
   mSelfRef = this;
-  MessageLoop::current()->PostTask(
+  NS_GetCurrentThread()->Dispatch(
       NewRunnableMethod("layers::CompositorBridgeParent::DeferredDestroy", this,
                         &CompositorBridgeParent::DeferredDestroy));
 }
 
 void CompositorBridgeParent::ScheduleRenderOnCompositorThread(
     const wr::RenderRootSet& aRenderRoots) {
-  MOZ_ASSERT(CompositorLoop());
-  CompositorLoop()->PostTask(NewRunnableMethod<wr::RenderRootSet>(
+  MOZ_ASSERT(CompositorThread());
+  CompositorThread()->Dispatch(NewRunnableMethod<wr::RenderRootSet>(
       "layers::CompositorBridgeParent::ScheduleComposition", this,
       &CompositorBridgeParent::ScheduleComposition, aRenderRoots));
 }
 
 void CompositorBridgeParent::InvalidateOnCompositorThread() {
-  MOZ_ASSERT(CompositorLoop());
-  CompositorLoop()->PostTask(
+  MOZ_ASSERT(CompositorThread());
+  CompositorThread()->Dispatch(
       NewRunnableMethod("layers::CompositorBridgeParent::Invalidate", this,
                         &CompositorBridgeParent::Invalidate));
 }
@@ -793,8 +785,8 @@ void CompositorBridgeParent::ResumeCompositionAndResize(int x, int y, int width,
 void CompositorBridgeParent::SchedulePauseOnCompositorThread() {
   MonitorAutoLock lock(mPauseCompositionMonitor);
 
-  MOZ_ASSERT(CompositorLoop());
-  CompositorLoop()->PostTask(
+  MOZ_ASSERT(CompositorThread());
+  CompositorThread()->Dispatch(
       NewRunnableMethod("layers::CompositorBridgeParent::PauseComposition",
                         this, &CompositorBridgeParent::PauseComposition));
 
@@ -805,8 +797,8 @@ void CompositorBridgeParent::SchedulePauseOnCompositorThread() {
 bool CompositorBridgeParent::ScheduleResumeOnCompositorThread() {
   MonitorAutoLock lock(mResumeCompositionMonitor);
 
-  MOZ_ASSERT(CompositorLoop());
-  CompositorLoop()->PostTask(
+  MOZ_ASSERT(CompositorThread());
+  CompositorThread()->Dispatch(
       NewRunnableMethod("layers::CompositorBridgeParent::ResumeComposition",
                         this, &CompositorBridgeParent::ResumeComposition));
 
@@ -821,8 +813,8 @@ bool CompositorBridgeParent::ScheduleResumeOnCompositorThread(int x, int y,
                                                               int height) {
   MonitorAutoLock lock(mResumeCompositionMonitor);
 
-  MOZ_ASSERT(CompositorLoop());
-  CompositorLoop()->PostTask(NewRunnableMethod<int, int, int, int>(
+  MOZ_ASSERT(CompositorThread());
+  CompositorThread()->Dispatch(NewRunnableMethod<int, int, int, int>(
       "layers::CompositorBridgeParent::ResumeCompositionAndResize", this,
       &CompositorBridgeParent::ResumeCompositionAndResize, x, y, width,
       height));
@@ -1226,9 +1218,9 @@ void CompositorBridgeParent::ScheduleRotationOnCompositorThread(
         &CompositorBridgeParent::ForceComposition);
     mForceCompositionTask = task;
     if (StaticPrefs::layers_orientation_sync_timeout() == 0) {
-      CompositorThreadHolder::Loop()->PostTask(task.forget());
+      CompositorThread()->Dispatch(task.forget());
     } else {
-      CompositorThreadHolder::Loop()->PostDelayedTask(
+      CompositorThread()->DelayedDispatch(
           task.forget(), StaticPrefs::layers_orientation_sync_timeout());
     }
   }
@@ -1987,13 +1979,13 @@ void CompositorBridgeParent::InitializeStatics() {
 /*static*/
 void CompositorBridgeParent::UpdateQualitySettings() {
   if (!CompositorThreadHolder::IsInCompositorThread()) {
-    if (CompositorLoop()) {
-      CompositorLoop()->PostTask(
+    if (CompositorThread()) {
+      CompositorThread()->Dispatch(
           NewRunnableFunction("CompositorBridgeParent::UpdateQualitySettings",
                               &CompositorBridgeParent::UpdateQualitySettings));
     }
 
-    // If there is no compositor loop, e.g. due to shutdown, then we can
+    // If there is no compositor thread, e.g. due to shutdown, then we can
     // safefully just ignore this request.
     return;
   }
@@ -2007,13 +1999,13 @@ void CompositorBridgeParent::UpdateQualitySettings() {
 /*static*/
 void CompositorBridgeParent::UpdateDebugFlags() {
   if (!CompositorThreadHolder::IsInCompositorThread()) {
-    if (CompositorLoop()) {
-      CompositorLoop()->PostTask(
+    if (CompositorThread()) {
+      CompositorThread()->Dispatch(
           NewRunnableFunction("CompositorBridgeParent::UpdateDebugFlags",
                               &CompositorBridgeParent::UpdateDebugFlags));
     }
 
-    // If there is no compositor loop, e.g. due to shutdown, then we can
+    // If there is no compositor thread, e.g. due to shutdown, then we can
     // safefully just ignore this request.
     return;
   }
@@ -2027,8 +2019,8 @@ void CompositorBridgeParent::UpdateDebugFlags() {
 /*static*/
 void CompositorBridgeParent::UpdateWebRenderMultithreading() {
   if (!CompositorThreadHolder::IsInCompositorThread()) {
-    if (CompositorLoop()) {
-      CompositorLoop()->PostTask(NewRunnableFunction(
+    if (CompositorThread()) {
+      CompositorThread()->Dispatch(NewRunnableFunction(
           "CompositorBridgeParent::UpdateWebRenderMultithreading",
           &CompositorBridgeParent::UpdateWebRenderMultithreading));
     }
@@ -2045,8 +2037,8 @@ void CompositorBridgeParent::UpdateWebRenderMultithreading() {
 /*static*/
 void CompositorBridgeParent::UpdateWebRenderBatchingParameters() {
   if (!CompositorThreadHolder::IsInCompositorThread()) {
-    if (CompositorLoop()) {
-      CompositorLoop()->PostTask(NewRunnableFunction(
+    if (CompositorThread()) {
+      CompositorThread()->Dispatch(NewRunnableFunction(
           "CompositorBridgeParent::UpdateWebRenderBatchingParameters",
           &CompositorBridgeParent::UpdateWebRenderBatchingParameters));
     }
@@ -2095,11 +2087,11 @@ void CompositorBridgeParent::DeallocateLayerTreeId(LayersId aId) {
   // Here main thread notifies compositor to remove an element from
   // sIndirectLayerTrees. This removed element might be queried soon.
   // Checking the elements of sIndirectLayerTrees exist or not before using.
-  if (!CompositorLoop()) {
-    gfxCriticalError() << "Attempting to post to a invalid Compositor Loop";
+  if (!CompositorThread()) {
+    gfxCriticalError() << "Attempting to post to an invalid Compositor Thread";
     return;
   }
-  CompositorLoop()->PostTask(
+  CompositorThread()->Dispatch(
       NewRunnableFunction("EraseLayerStateRunnable", &EraseLayerState, aId));
 }
 
@@ -2131,7 +2123,7 @@ void CompositorBridgeParent::SetControllerForLayerTree(
     LayersId aLayersId, GeckoContentController* aController) {
   // This ref is adopted by UpdateControllerForLayersId().
   aController->AddRef();
-  CompositorLoop()->PostTask(NewRunnableFunction(
+  CompositorThread()->Dispatch(NewRunnableFunction(
       "UpdateControllerForLayersIdRunnable", &UpdateControllerForLayersId,
       aLayersId, aController));
 }
@@ -2168,7 +2160,7 @@ void CompositorBridgeParent::PostInsertVsyncProfilerMarker(
 #if defined(MOZ_GECKO_PROFILER)
   // Called in the vsync thread
   if (profiler_is_active() && CompositorThreadHolder::IsActive()) {
-    CompositorLoop()->PostTask(
+    CompositorThread()->Dispatch(
         NewRunnableFunction("InsertVsyncProfilerMarkerRunnable",
                             InsertVsyncProfilerMarker, aVsyncTimestamp));
   }
@@ -2391,7 +2383,7 @@ void CompositorBridgeParent::NotifyDidComposite(TransactionId aTransactionId,
 }
 
 void CompositorBridgeParent::InvalidateRemoteLayers() {
-  MOZ_ASSERT(CompositorLoop() == MessageLoop::current());
+  MOZ_ASSERT(CompositorThread()->IsOnCurrentThread());
 
   Unused << PCompositorBridgeParent::SendInvalidateLayers(LayersId{0});
 
@@ -2513,13 +2505,12 @@ bool CompositorBridgeParent::IsSameProcess() const {
 }
 
 void CompositorBridgeParent::NotifyWebRenderContextPurge() {
-  MOZ_ASSERT(CompositorLoop() == MessageLoop::current());
+  MOZ_ASSERT(CompositorThread()->IsOnCurrentThread());
   RefPtr<wr::WebRenderAPI> api = mWrBridge->GetWebRenderAPI();
-  api->ClearAllCaches();
 }
 
 void CompositorBridgeParent::NotifyWebRenderDisableNativeCompositor() {
-  MOZ_ASSERT(CompositorLoop() == MessageLoop::current());
+  MOZ_ASSERT(CompositorThread()->IsOnCurrentThread());
   if (mWrBridge) {
     mWrBridge->DisableNativeCompositor();
   }
@@ -2651,8 +2642,8 @@ bool CompositorBridgeParent::UpdatePluginWindowState(LayersId aId) {
 }
 
 void CompositorBridgeParent::ScheduleShowAllPluginWindows() {
-  MOZ_ASSERT(CompositorLoop());
-  CompositorLoop()->PostTask(
+  MOZ_ASSERT(CompositorThread());
+  CompositorThread()->Dispatch(
       NewRunnableMethod("layers::CompositorBridgeParent::ShowAllPluginWindows",
                         this, &CompositorBridgeParent::ShowAllPluginWindows));
 }
@@ -2664,8 +2655,8 @@ void CompositorBridgeParent::ShowAllPluginWindows() {
 }
 
 void CompositorBridgeParent::ScheduleHideAllPluginWindows() {
-  MOZ_ASSERT(CompositorLoop());
-  CompositorLoop()->PostTask(
+  MOZ_ASSERT(CompositorThread());
+  CompositorThread()->Dispatch(
       NewRunnableMethod("layers::CompositorBridgeParent::HideAllPluginWindows",
                         this, &CompositorBridgeParent::HideAllPluginWindows));
 }
@@ -2892,7 +2883,7 @@ mozilla::ipc::IPCResult CompositorBridgeParent::RecvEndRecordingToDisk(
     aResolve(true);
   } else if (mWrBridge) {
     mWrBridge->WriteCollectedFrames()->Then(
-        MessageLoop::current()->SerialEventTarget(), __func__,
+        NS_GetCurrentThread(), __func__,
         [resolve{aResolve}](const bool success) { resolve(success); },
         [resolve{aResolve}]() { resolve(false); });
   } else {
@@ -2921,7 +2912,7 @@ mozilla::ipc::IPCResult CompositorBridgeParent::RecvEndRecordingToMemory(
   } else if (mWrBridge) {
     RefPtr<CompositorBridgeParent> self = this;
     mWrBridge->GetCollectedFrames()->Then(
-        MessageLoop::current()->SerialEventTarget(), __func__,
+        NS_GetCurrentThread(), __func__,
         [self, resolve{aResolve}](CollectedFrames&& frames) {
           resolve(self->WrapCollectedFrames(std::move(frames)));
         },
diff --git a/gfx/layers/ipc/CompositorBridgeParent.h b/gfx/layers/ipc/CompositorBridgeParent.h
index adf3c25bb70f..3722da384fb8 100644
--- a/gfx/layers/ipc/CompositorBridgeParent.h
+++ b/gfx/layers/ipc/CompositorBridgeParent.h
@@ -47,7 +47,6 @@
 #include "mozilla/layers/UiCompositorControllerParent.h"
 #include "mozilla/VsyncDispatcher.h"
 
-class MessageLoop;
 class nsIWidget;
 
 namespace mozilla {
diff --git a/gfx/layers/ipc/CompositorManagerChild.cpp b/gfx/layers/ipc/CompositorManagerChild.cpp
index cadfb1088cdf..c01b2fa5db60 100644
--- a/gfx/layers/ipc/CompositorManagerChild.cpp
+++ b/gfx/layers/ipc/CompositorManagerChild.cpp
@@ -173,9 +173,8 @@ CompositorManagerChild::CompositorManagerChild(CompositorManagerParent* aParent,
   MOZ_ASSERT(aParent);
 
   SetOtherProcessId(base::GetCurrentProcId());
-  MessageLoop* loop = CompositorThreadHolder::Loop();
   ipc::MessageChannel* channel = aParent->GetIPCChannel();
-  if (NS_WARN_IF(!Open(channel, loop, ipc::ChildSide))) {
+  if (NS_WARN_IF(!Open(channel, CompositorThread(), ipc::ChildSide))) {
     return;
   }
 
diff --git a/gfx/layers/ipc/CompositorManagerParent.cpp b/gfx/layers/ipc/CompositorManagerParent.cpp
index 3c997c9f4364..6ffaebc445f1 100644
--- a/gfx/layers/ipc/CompositorManagerParent.cpp
+++ b/gfx/layers/ipc/CompositorManagerParent.cpp
@@ -68,7 +68,7 @@ bool CompositorManagerParent::Create(
       NewRunnableMethod<Endpoint<PCompositorManagerParent>&&, bool>(
           "CompositorManagerParent::Bind", bridge,
           &CompositorManagerParent::Bind, std::move(aEndpoint), aIsRoot);
-  CompositorThreadHolder::Loop()->PostTask(runnable.forget());
+  CompositorThread()->Dispatch(runnable.forget());
   return true;
 }
 
@@ -201,7 +201,7 @@ void CompositorManagerParent::Shutdown() {
   MOZ_ASSERT(NS_IsMainThread());
 
 #ifdef COMPOSITOR_MANAGER_PARENT_EXPLICIT_SHUTDOWN
-  CompositorThreadHolder::Loop()->PostTask(NS_NewRunnableFunction(
+  CompositorThread()->Dispatch(NS_NewRunnableFunction(
       "layers::CompositorManagerParent::Shutdown",
       []() -> void { CompositorManagerParent::ShutdownInternal(); }));
 #endif
@@ -307,7 +307,7 @@ mozilla::ipc::IPCResult CompositorManagerParent::RecvReportMemory(
   // thread, so we can't just pass it over to the renderer thread. We use
   // an intermediate MozPromise instead.
   wr::RenderThread::AccumulateMemoryReport(aggregate)->Then(
-      CompositorThreadHolder::Loop()->SerialEventTarget(), __func__,
+      CompositorThread(), __func__,
       [resolver = std::move(aResolver)](MemoryReport aReport) {
         resolver(aReport);
       },
diff --git a/gfx/layers/ipc/CompositorThread.cpp b/gfx/layers/ipc/CompositorThread.cpp
index 9fc9eaa1438d..b1ccf8f2409c 100644
--- a/gfx/layers/ipc/CompositorThread.cpp
+++ b/gfx/layers/ipc/CompositorThread.cpp
@@ -19,17 +19,12 @@ namespace layers {
 static StaticRefPtr<CompositorThreadHolder> sCompositorThreadHolder;
 static bool sFinishedCompositorShutDown = false;
 
-base::Thread* CompositorThread() {
+nsISerialEventTarget* CompositorThread() {
   return sCompositorThreadHolder
              ? sCompositorThreadHolder->GetCompositorThread()
              : nullptr;
 }
 
-/* static */
-MessageLoop* CompositorThreadHolder::Loop() {
-  return CompositorThread() ? CompositorThread()->message_loop() : nullptr;
-}
-
 CompositorThreadHolder* CompositorThreadHolder::GetSingleton() {
   return sCompositorThreadHolder;
 }
@@ -41,57 +36,40 @@ CompositorThreadHolder::CompositorThreadHolder()
 
 CompositorThreadHolder::~CompositorThreadHolder() {
   MOZ_ASSERT(NS_IsMainThread());
-  if (mCompositorThread) {
-    DestroyCompositorThread(mCompositorThread);
-  }
-}
-
-/* static */
-void CompositorThreadHolder::DestroyCompositorThread(
-    base::Thread* aCompositorThread) {
-  MOZ_ASSERT(NS_IsMainThread());
-
-  MOZ_ASSERT(!sCompositorThreadHolder,
-             "We shouldn't be destroying the compositor thread yet.");
-
-  delete aCompositorThread;
   sFinishedCompositorShutDown = true;
 }
 
-/* static */ base::Thread* CompositorThreadHolder::CreateCompositorThread() {
+/* static */ already_AddRefed<nsIThread>
+CompositorThreadHolder::CreateCompositorThread() {
   MOZ_ASSERT(NS_IsMainThread());
 
   MOZ_ASSERT(!sCompositorThreadHolder,
              "The compositor thread has already been started!");
 
-  base::Thread* compositorThread = new base::Thread("Compositor");
+  nsCOMPtr<nsIThread> compositorThread;
+  nsresult rv =
+      NS_NewNamedThread("Compositor", getter_AddRefs(compositorThread));
 
-  base::Thread::Options options;
-  /* Timeout values are powers-of-two to enable us get better data.
-     128ms is chosen for transient hangs because 8Hz should be the minimally
-     acceptable goal for Compositor responsiveness (normal goal is 60Hz). */
-  options.transient_hang_timeout = 128;  // milliseconds
-  /* 2048ms is chosen for permanent hangs because it's longer than most
-   * Compositor hangs seen in the wild, but is short enough to not miss getting
-   * native hang stacks. */
-  options.permanent_hang_timeout = 2048;  // milliseconds
-#if defined(_WIN32)
-  /* With d3d9 the compositor thread creates native ui, see DeviceManagerD3D9.
-   * As such the thread is a gui thread, and must process a windows message
-   * queue or
-   * risk deadlocks. Chromium message loop TYPE_UI does exactly what we need. */
-  options.message_loop_type = MessageLoop::TYPE_UI;
-#endif
+  // TODO re-enable hangout monitor. Will be done in a follow-up thread
+  //  base::Thread::Options options;
+  //  /* Timeout values are powers-of-two to enable us get better data.
+  //     128ms is chosen for transient hangs because 8Hz should be the minimally
+  //     acceptable goal for Compositor responsiveness (normal goal is 60Hz). */
+  //  options.transient_hang_timeout = 128;  // milliseconds
+  //  /* 2048ms is chosen for permanent hangs because it's longer than most
+  //   * Compositor hangs seen in the wild, but is short enough to not miss
+  //   getting
+  //   * native hang stacks. */
+  //  options.permanent_hang_timeout = 2048;  // milliseconds
 
-  if (!compositorThread->StartWithOptions(options)) {
-    delete compositorThread;
+  if (NS_FAILED(rv)) {
     return nullptr;
   }
 
   CompositorBridgeParent::Setup();
   ImageBridgeParent::Setup();
 
-  return compositorThread;
+  return compositorThread.forget();
 }
 
 void CompositorThreadHolder::Start() {
@@ -136,8 +114,12 @@ void CompositorThreadHolder::Shutdown() {
 
 /* static */
 bool CompositorThreadHolder::IsInCompositorThread() {
-  return CompositorThread() &&
-         CompositorThread()->thread_id() == PlatformThread::CurrentId();
+  if (!CompositorThread()) {
+    return false;
+  }
+  bool in = false;
+  MOZ_ALWAYS_SUCCEEDS(CompositorThread()->IsOnCurrentThread(&in));
+  return in;
 }
 
 }  // namespace layers
diff --git a/gfx/layers/ipc/CompositorThread.h b/gfx/layers/ipc/CompositorThread.h
index 831d42ad47b0..f45e31c90baf 100644
--- a/gfx/layers/ipc/CompositorThread.h
+++ b/gfx/layers/ipc/CompositorThread.h
@@ -6,13 +6,12 @@
 #ifndef mozilla_layers_CompositorThread_h
 #define mozilla_layers_CompositorThread_h
 
-#include "base/basictypes.h"       // for DISALLOW_EVIL_CONSTRUCTORS
-#include "base/platform_thread.h"  // for PlatformThreadId
-#include "base/thread.h"           // for Thread
-#include "base/message_loop.h"
 #include "nsISupportsImpl.h"
 #include "ThreadSafeRefcountingWithMainThreadDestruction.h"
 
+class nsISerialEventTarget;
+class nsIThread;
+
 namespace mozilla {
 namespace layers {
 
@@ -23,7 +22,9 @@ class CompositorThreadHolder final {
  public:
   CompositorThreadHolder();
 
-  base::Thread* GetCompositorThread() const { return mCompositorThread; }
+  nsISerialEventTarget* GetCompositorThread() const {
+    return mCompositorThread;
+  }
 
   static CompositorThreadHolder* GetSingleton();
 
@@ -40,23 +41,20 @@ class CompositorThreadHolder final {
    */
   static void Shutdown();
 
-  static MessageLoop* Loop();
-
   // Returns true if the calling thread is the compositor thread.
   static bool IsInCompositorThread();
 
  private:
   ~CompositorThreadHolder();
 
-  base::Thread* const mCompositorThread;
+  nsCOMPtr<nsIThread> mCompositorThread;
 
-  static base::Thread* CreateCompositorThread();
-  static void DestroyCompositorThread(base::Thread* aCompositorThread);
+  static already_AddRefed<nsIThread> CreateCompositorThread();
 
   friend class CompositorBridgeParent;
 };
 
-base::Thread* CompositorThread();
+nsISerialEventTarget* CompositorThread();
 
 }  // namespace layers
 }  // namespace mozilla
diff --git a/gfx/layers/ipc/CompositorVsyncScheduler.cpp b/gfx/layers/ipc/CompositorVsyncScheduler.cpp
index 911ac3c182d4..d00a7fae73ea 100644
--- a/gfx/layers/ipc/CompositorVsyncScheduler.cpp
+++ b/gfx/layers/ipc/CompositorVsyncScheduler.cpp
@@ -110,24 +110,24 @@ void CompositorVsyncScheduler::Destroy() {
 void CompositorVsyncScheduler::PostCompositeTask(
     VsyncId aId, TimeStamp aCompositeTimestamp) {
   MonitorAutoLock lock(mCurrentCompositeTaskMonitor);
-  if (mCurrentCompositeTask == nullptr && CompositorThreadHolder::Loop()) {
+  if (mCurrentCompositeTask == nullptr && CompositorThread()) {
     RefPtr<CancelableRunnable> task =
         NewCancelableRunnableMethod<VsyncId, TimeStamp>(
             "layers::CompositorVsyncScheduler::Composite", this,
             &CompositorVsyncScheduler::Composite, aId, aCompositeTimestamp);
     mCurrentCompositeTask = task;
-    ScheduleTask(task.forget());
+    CompositorThread()->Dispatch(task.forget());
   }
 }
 
 void CompositorVsyncScheduler::PostVRTask(TimeStamp aTimestamp) {
   MonitorAutoLock lockVR(mCurrentVRTaskMonitor);
-  if (mCurrentVRTask == nullptr && CompositorThreadHolder::Loop()) {
+  if (mCurrentVRTask == nullptr && CompositorThread()) {
     RefPtr<CancelableRunnable> task = NewCancelableRunnableMethod<TimeStamp>(
         "layers::CompositorVsyncScheduler::DispatchVREvents", this,
         &CompositorVsyncScheduler::DispatchVREvents, aTimestamp);
     mCurrentVRTask = task;
-    CompositorThreadHolder::Loop()->PostDelayedTask(task.forget(), 0);
+    CompositorThread()->Dispatch(task.forget());
   }
 }
 
@@ -329,12 +329,6 @@ void CompositorVsyncScheduler::DispatchVREvents(TimeStamp aVsyncTimestamp) {
   vm->NotifyVsync(aVsyncTimestamp);
 }
 
-void CompositorVsyncScheduler::ScheduleTask(
-    already_AddRefed<CancelableRunnable> aTask) {
-  MOZ_ASSERT(CompositorThreadHolder::Loop());
-  CompositorThreadHolder::Loop()->PostDelayedTask(std::move(aTask), 0);
-}
-
 const TimeStamp& CompositorVsyncScheduler::GetLastComposeTime() const {
   MOZ_ASSERT(CompositorThreadHolder::IsInCompositorThread());
   return mLastCompose;
diff --git a/gfx/layers/ipc/CompositorVsyncScheduler.h b/gfx/layers/ipc/CompositorVsyncScheduler.h
index c4393324ee4c..bb033404aefb 100644
--- a/gfx/layers/ipc/CompositorVsyncScheduler.h
+++ b/gfx/layers/ipc/CompositorVsyncScheduler.h
@@ -109,9 +109,6 @@ class CompositorVsyncScheduler {
  private:
   virtual ~CompositorVsyncScheduler();
 
-  // Schedule a task to run on the compositor thread.
-  void ScheduleTask(already_AddRefed<CancelableRunnable>);
-
   // Post a task to run Composite() on the compositor thread, if there isn't
   // such a task already queued. Can be called from any thread.
   void PostCompositeTask(VsyncId aId, TimeStamp aCompositeTimestamp);
diff --git a/gfx/layers/ipc/ImageBridgeChild.cpp b/gfx/layers/ipc/ImageBridgeChild.cpp
index 9a09dbd88135..271ec4913dd3 100644
--- a/gfx/layers/ipc/ImageBridgeChild.cpp
+++ b/gfx/layers/ipc/ImageBridgeChild.cpp
@@ -10,7 +10,6 @@
 #include "ImageContainer.h"              // for ImageContainer
 #include "Layers.h"                      // for Layer, etc
 #include "ShadowLayers.h"                // for ShadowLayerForwarder
-#include "base/message_loop.h"           // for MessageLoop
 #include "base/platform_thread.h"        // for PlatformThread
 #include "base/process.h"                // for ProcessId
 #include "base/task.h"                   // for NewRunnableFunction, etc
@@ -38,8 +37,8 @@
 #include "nsISupportsImpl.h"         // for ImageContainer::AddRef, etc
 #include "nsTArray.h"                // for AutoTArray, nsTArray, etc
 #include "nsTArrayForwardDeclare.h"  // for AutoTArray
+#include "nsThread.h"
 #include "nsThreadUtils.h"           // for NS_IsMainThread
-#include "nsXULAppAPI.h"             // for XRE_GetIOMessageLoop
 #include "mozilla/StaticMutex.h"
 #include "mozilla/StaticPtr.h"  // for StaticRefPtr
 #include "mozilla/layers/TextureClient.h"
@@ -172,7 +171,10 @@ void ImageBridgeChild::CancelWaitForNotifyNotUsed(uint64_t aTextureId) {
 // Singleton
 static StaticMutex sImageBridgeSingletonLock;
 static StaticRefPtr<ImageBridgeChild> sImageBridgeChildSingleton;
-static Thread* sImageBridgeChildThread = nullptr;
+// sImageBridgeChildThread cannot be converted to use a generic
+// nsISerialEventTarget (which may be backed by a threadpool) until bug 1634846
+// is addressed. Therefore we keep it as an nsIThread here.
+static StaticRefPtr<nsIThread> sImageBridgeChildThread;
 
 // dispatched function
 void ImageBridgeChild::ShutdownStep1(SynchronousTask* aTask) {
@@ -293,8 +295,6 @@ void ImageBridgeChild::ForgetImageContainer(const CompositableHandle& aHandle) {
   mImageContainerListeners.erase(aHandle.Value());
 }
 
-Thread* ImageBridgeChild::GetThread() const { return sImageBridgeChildThread; }
-
 /* static */
 RefPtr<ImageBridgeChild> ImageBridgeChild::GetSingleton() {
   StaticMutexAutoLock lock(sImageBridgeSingletonLock);
@@ -310,7 +310,7 @@ void ImageBridgeChild::UpdateImageClient(RefPtr<ImageContainer> aContainer) {
     RefPtr<Runnable> runnable =
         WrapRunnable(RefPtr<ImageBridgeChild>(this),
                      &ImageBridgeChild::UpdateImageClient, aContainer);
-    GetMessageLoop()->PostTask(runnable.forget());
+    GetThread()->Dispatch(runnable.forget());
     return;
   }
 
@@ -355,7 +355,7 @@ void ImageBridgeChild::UpdateAsyncCanvasRenderer(
   RefPtr<Runnable> runnable = WrapRunnable(
       RefPtr<ImageBridgeChild>(this),
       &ImageBridgeChild::UpdateAsyncCanvasRendererSync, &task, aWrapper);
-  GetMessageLoop()->PostTask(runnable.forget());
+  GetThread()->Dispatch(runnable.forget());
 
   task.Wait();
 }
@@ -409,7 +409,7 @@ void ImageBridgeChild::FlushAllImages(ImageClient* aClient,
   RefPtr<Runnable> runnable = WrapRunnable(
       RefPtr<ImageBridgeChild>(this), &ImageBridgeChild::FlushAllImagesSync,
       &task, aClient, aContainer);
-  GetMessageLoop()->PostTask(runnable.forget());
+  GetThread()->Dispatch(runnable.forget());
 
   task.Wait();
 }
@@ -454,9 +454,11 @@ bool ImageBridgeChild::InitForContent(Endpoint<PImageBridgeChild>&& aEndpoint,
   gfxPlatform::GetPlatform();
 
   if (!sImageBridgeChildThread) {
-    sImageBridgeChildThread = new Thread("ImageBridgeChild");
-    bool success = sImageBridgeChildThread->Start();
-    MOZ_RELEASE_ASSERT(success, "Failed to start ImageBridgeChild thread!");
+    nsCOMPtr<nsIThread> thread;
+    nsresult rv = NS_NewNamedThread("ImageBridgeChld", getter_AddRefs(thread));
+    MOZ_RELEASE_ASSERT(NS_SUCCEEDED(rv),
+                       "Failed to start ImageBridgeChild thread!");
+    sImageBridgeChildThread = thread.forget();
   }
 
   RefPtr<ImageBridgeChild> child = new ImageBridgeChild(aNamespace);
@@ -464,7 +466,7 @@ bool ImageBridgeChild::InitForContent(Endpoint<PImageBridgeChild>&& aEndpoint,
   RefPtr<Runnable> runnable = NewRunnableMethod<Endpoint<PImageBridgeChild>&&>(
       "layers::ImageBridgeChild::Bind", child, &ImageBridgeChild::Bind,
       std::move(aEndpoint));
-  child->GetMessageLoop()->PostTask(runnable.forget());
+  child->GetThread()->Dispatch(runnable.forget());
 
   // Assign this after so other threads can't post messages before we connect to
   // IPDL.
@@ -501,9 +503,8 @@ void ImageBridgeChild::Bind(Endpoint<PImageBridgeChild>&& aEndpoint) {
 }
 
 void ImageBridgeChild::BindSameProcess(RefPtr<ImageBridgeParent> aParent) {
-  MessageLoop* parentMsgLoop = aParent->GetMessageLoop();
   ipc::MessageChannel* parentChannel = aParent->GetIPCChannel();
-  Open(parentChannel, parentMsgLoop, mozilla::ipc::ChildSide);
+  Open(parentChannel, aParent->GetThread(), mozilla::ipc::ChildSide);
 
   // This reference is dropped in DeallocPImageBridgeChild.
   this->AddRef();
@@ -517,7 +518,6 @@ void ImageBridgeChild::ShutDown() {
 
   ShutdownSingleton();
 
-  delete sImageBridgeChildThread;
   sImageBridgeChildThread = nullptr;
 }
 
@@ -540,7 +540,7 @@ void ImageBridgeChild::WillShutdown() {
     RefPtr<Runnable> runnable =
         WrapRunnable(RefPtr<ImageBridgeChild>(this),
                      &ImageBridgeChild::ShutdownStep1, &task);
-    GetMessageLoop()->PostTask(runnable.forget());
+    GetThread()->Dispatch(runnable.forget());
 
     task.Wait();
   }
@@ -551,7 +551,7 @@ void ImageBridgeChild::WillShutdown() {
     RefPtr<Runnable> runnable =
         WrapRunnable(RefPtr<ImageBridgeChild>(this),
                      &ImageBridgeChild::ShutdownStep2, &task);
-    GetMessageLoop()->PostTask(runnable.forget());
+    GetThread()->Dispatch(runnable.forget());
 
     task.Wait();
   }
@@ -563,17 +563,18 @@ void ImageBridgeChild::InitSameProcess(uint32_t aNamespace) {
   MOZ_ASSERT(!sImageBridgeChildSingleton);
   MOZ_ASSERT(!sImageBridgeChildThread);
 
-  sImageBridgeChildThread = new Thread("ImageBridgeChild");
-  if (!sImageBridgeChildThread->IsRunning()) {
-    sImageBridgeChildThread->Start();
-  }
+  nsCOMPtr<nsIThread> thread;
+  nsresult rv = NS_NewNamedThread("ImageBridgeChld", getter_AddRefs(thread));
+  MOZ_RELEASE_ASSERT(NS_SUCCEEDED(rv),
+                     "Failed to start ImageBridgeChild thread!");
+  sImageBridgeChildThread = thread.forget();
 
   RefPtr<ImageBridgeChild> child = new ImageBridgeChild(aNamespace);
   RefPtr<ImageBridgeParent> parent = ImageBridgeParent::CreateSameProcess();
 
   RefPtr<Runnable> runnable =
       WrapRunnable(child, &ImageBridgeChild::BindSameProcess, parent);
-  child->GetMessageLoop()->PostTask(runnable.forget());
+  child->GetThread()->Dispatch(runnable.forget());
 
   // Assign this after so other threads can't post messages before we connect to
   // IPDL.
@@ -590,15 +591,15 @@ void ImageBridgeChild::InitWithGPUProcess(
   MOZ_ASSERT(!sImageBridgeChildSingleton);
   MOZ_ASSERT(!sImageBridgeChildThread);
 
-  sImageBridgeChildThread = new Thread("ImageBridgeChild");
-  if (!sImageBridgeChildThread->IsRunning()) {
-    sImageBridgeChildThread->Start();
-  }
+  nsCOMPtr<nsIThread> thread;
+  nsresult rv = NS_NewNamedThread("ImageBridgeChld", getter_AddRefs(thread));
+  MOZ_RELEASE_ASSERT(NS_SUCCEEDED(rv),
+                     "Failed to start ImageBridgeChild thread!");
+  sImageBridgeChildThread = thread.forget();
 
   RefPtr<ImageBridgeChild> child = new ImageBridgeChild(aNamespace);
 
-  MessageLoop* loop = child->GetMessageLoop();
-  loop->PostTask(NewRunnableMethod<Endpoint<PImageBridgeChild>&&>(
+  child->GetThread()->Dispatch(NewRunnableMethod<Endpoint<PImageBridgeChild>&&>(
       "layers::ImageBridgeChild::Bind", child, &ImageBridgeChild::Bind,
       std::move(aEndpoint)));
 
@@ -612,12 +613,11 @@ void ImageBridgeChild::InitWithGPUProcess(
 
 bool InImageBridgeChildThread() {
   return sImageBridgeChildThread &&
-         sImageBridgeChildThread->thread_id() == PlatformThread::CurrentId();
+         sImageBridgeChildThread->IsOnCurrentThread();
 }
 
-MessageLoop* ImageBridgeChild::GetMessageLoop() const {
-  return sImageBridgeChildThread ? sImageBridgeChildThread->message_loop()
-                                 : nullptr;
+nsISerialEventTarget* ImageBridgeChild::GetThread() const {
+  return sImageBridgeChildThread;
 }
 
 /* static */
@@ -697,7 +697,7 @@ RefPtr<ImageClient> ImageBridgeChild::CreateImageClient(
   RefPtr<Runnable> runnable = WrapRunnable(
       RefPtr<ImageBridgeChild>(this), &ImageBridgeChild::CreateImageClientSync,
       &task, &result, aType, aImageContainer);
-  GetMessageLoop()->PostTask(runnable.forget());
+  GetThread()->Dispatch(runnable.forget());
 
   task.Wait();
 
@@ -733,7 +733,7 @@ already_AddRefed<CanvasClient> ImageBridgeChild::CreateCanvasClient(
   RefPtr<Runnable> runnable = WrapRunnable(
       RefPtr<ImageBridgeChild>(this), &ImageBridgeChild::CreateCanvasClientSync,
       &task, aType, aFlag, &result);
-  GetMessageLoop()->PostTask(runnable.forget());
+  GetThread()->Dispatch(runnable.forget());
 
   task.Wait();
 
@@ -807,7 +807,7 @@ bool ImageBridgeChild::DispatchAllocShmemInternal(
   RefPtr<Runnable> runnable = WrapRunnable(
       RefPtr<ImageBridgeChild>(this), &ImageBridgeChild::ProxyAllocShmemNow,
       &task, aSize, aType, aShmem, aUnsafe, &success);
-  GetMessageLoop()->PostTask(runnable.forget());
+  GetThread()->Dispatch(runnable.forget());
 
   task.Wait();
 
@@ -844,7 +844,7 @@ bool ImageBridgeChild::DeallocShmem(ipc::Shmem& aShmem) {
   RefPtr<Runnable> runnable = WrapRunnable(
       RefPtr<ImageBridgeChild>(this), &ImageBridgeChild::ProxyDeallocShmemNow,
       &task, &aShmem, &result);
-  GetMessageLoop()->PostTask(runnable.forget());
+  GetThread()->Dispatch(runnable.forget());
 
   task.Wait();
   return result;
@@ -999,7 +999,7 @@ void ImageBridgeChild::ReleaseCompositable(const CompositableHandle& aHandle) {
     RefPtr<Runnable> runnable =
         WrapRunnable(RefPtr<ImageBridgeChild>(this),
                      &ImageBridgeChild::ReleaseCompositable, aHandle);
-    GetMessageLoop()->PostTask(runnable.forget());
+    GetThread()->Dispatch(runnable.forget());
     return;
   }
 
diff --git a/gfx/layers/ipc/ImageBridgeChild.h b/gfx/layers/ipc/ImageBridgeChild.h
index 646a2a3eccc1..be0fa22a2d9d 100644
--- a/gfx/layers/ipc/ImageBridgeChild.h
+++ b/gfx/layers/ipc/ImageBridgeChild.h
@@ -25,12 +25,6 @@
 #include "mozilla/gfx/Rect.h"
 #include "mozilla/ReentrantMonitor.h"  // for ReentrantMonitor, etc
 
-class MessageLoop;
-
-namespace base {
-class Thread;
-}  // namespace base
-
 namespace mozilla {
 namespace ipc {
 class Shmem;
@@ -166,14 +160,7 @@ class ImageBridgeChild final : public PImageBridgeChild,
    *
    * Can be called from any thread.
    */
-  base::Thread* GetThread() const;
-
-  /**
-   * Returns the ImageBridgeChild's message loop.
-   *
-   * Can be called from any thread.
-   */
-  MessageLoop* GetMessageLoop() const override;
+  nsISerialEventTarget* GetThread() const override;
 
   base::ProcessId GetParentPid() const override { return OtherPid(); }
 
diff --git a/gfx/layers/ipc/ImageBridgeParent.cpp b/gfx/layers/ipc/ImageBridgeParent.cpp
index 2686da89f3d5..b9fd0c8d0df7 100644
--- a/gfx/layers/ipc/ImageBridgeParent.cpp
+++ b/gfx/layers/ipc/ImageBridgeParent.cpp
@@ -7,7 +7,6 @@
 #include "ImageBridgeParent.h"
 #include <stdint.h>             // for uint64_t, uint32_t
 #include "CompositableHost.h"   // for CompositableParent, Create
-#include "base/message_loop.h"  // for MessageLoop
 #include "base/process.h"       // for ProcessId
 #include "base/task.h"          // for CancelableTask, DeleteTask, etc
 #include "mozilla/ClearOnShutdown.h"
@@ -62,9 +61,9 @@ void ImageBridgeParent::Setup() {
   }
 }
 
-ImageBridgeParent::ImageBridgeParent(MessageLoop* aLoop,
+ImageBridgeParent::ImageBridgeParent(nsISerialEventTarget* aThread,
                                      ProcessId aChildProcessId)
-    : mMessageLoop(aLoop),
+    : mThread(aThread),
       mClosed(false),
       mCompositorThreadHolder(CompositorThreadHolder::GetSingleton()) {
   MOZ_ASSERT(NS_IsMainThread());
@@ -77,7 +76,7 @@ ImageBridgeParent::~ImageBridgeParent() = default;
 ImageBridgeParent* ImageBridgeParent::CreateSameProcess() {
   base::ProcessId pid = base::GetCurrentProcId();
   RefPtr<ImageBridgeParent> parent =
-      new ImageBridgeParent(CompositorThreadHolder::Loop(), pid);
+      new ImageBridgeParent(CompositorThread(), pid);
   parent->mSelfRef = parent;
 
   {
@@ -95,15 +94,15 @@ bool ImageBridgeParent::CreateForGPUProcess(
     Endpoint<PImageBridgeParent>&& aEndpoint) {
   MOZ_ASSERT(XRE_GetProcessType() == GeckoProcessType_GPU);
 
-  MessageLoop* loop = CompositorThreadHolder::Loop();
-  if (!loop) {
+  nsCOMPtr<nsISerialEventTarget> compositorThread = CompositorThread();
+  if (!compositorThread) {
     return false;
   }
 
   RefPtr<ImageBridgeParent> parent =
-      new ImageBridgeParent(loop, aEndpoint.OtherPid());
+      new ImageBridgeParent(compositorThread, aEndpoint.OtherPid());
 
-  loop->PostTask(NewRunnableMethod<Endpoint<PImageBridgeParent>&&>(
+  compositorThread->Dispatch(NewRunnableMethod<Endpoint<PImageBridgeParent>&&>(
       "layers::ImageBridgeParent::Bind", parent, &ImageBridgeParent::Bind,
       std::move(aEndpoint)));
 
@@ -133,7 +132,7 @@ void ImageBridgeParent::ShutdownInternal() {
 
 /* static */
 void ImageBridgeParent::Shutdown() {
-  CompositorThreadHolder::Loop()->PostTask(NS_NewRunnableFunction(
+  CompositorThread()->Dispatch(NS_NewRunnableFunction(
       "ImageBridgeParent::Shutdown",
       []() -> void { ImageBridgeParent::ShutdownInternal(); }));
 }
@@ -146,7 +145,7 @@ void ImageBridgeParent::ActorDestroy(ActorDestroyReason aWhy) {
     MonitorAutoLock lock(*sImageBridgesLock);
     sImageBridges.erase(OtherPid());
   }
-  MessageLoop::current()->PostTask(
+  GetThread()->Dispatch(
       NewRunnableMethod("layers::ImageBridgeParent::DeferredDestroy", this,
                         &ImageBridgeParent::DeferredDestroy));
 
@@ -219,14 +218,14 @@ mozilla::ipc::IPCResult ImageBridgeParent::RecvUpdate(
 /* static */
 bool ImageBridgeParent::CreateForContent(
     Endpoint<PImageBridgeParent>&& aEndpoint) {
-  MessageLoop* loop = CompositorThreadHolder::Loop();
-  if (!loop) {
+  nsCOMPtr<nsISerialEventTarget> compositorThread = CompositorThread();
+  if (!compositorThread) {
     return false;
   }
 
   RefPtr<ImageBridgeParent> bridge =
-      new ImageBridgeParent(loop, aEndpoint.OtherPid());
-  loop->PostTask(NewRunnableMethod<Endpoint<PImageBridgeParent>&&>(
+      new ImageBridgeParent(compositorThread, aEndpoint.OtherPid());
+  compositorThread->Dispatch(NewRunnableMethod<Endpoint<PImageBridgeParent>&&>(
       "layers::ImageBridgeParent::Bind", bridge, &ImageBridgeParent::Bind,
       std::move(aEndpoint)));
 
diff --git a/gfx/layers/ipc/ImageBridgeParent.h b/gfx/layers/ipc/ImageBridgeParent.h
index 1c5a30512819..7c5e5cd2d424 100644
--- a/gfx/layers/ipc/ImageBridgeParent.h
+++ b/gfx/layers/ipc/ImageBridgeParent.h
@@ -19,12 +19,6 @@
 #include "nsISupportsImpl.h"
 #include "nsTArrayForwardDeclare.h"  // for nsTArray
 
-class MessageLoop;
-
-namespace base {
-class Thread;
-}  // namespace base
-
 namespace mozilla {
 namespace ipc {
 class Shmem;
@@ -45,7 +39,7 @@ class ImageBridgeParent final : public PImageBridgeParent,
   typedef nsTArray<OpDestroy> OpDestroyArray;
 
  protected:
-  ImageBridgeParent(MessageLoop* aLoop, ProcessId aChildProcessId);
+  ImageBridgeParent(nsISerialEventTarget* aThread, ProcessId aChildProcessId);
 
  public:
   virtual ~ImageBridgeParent();
@@ -98,7 +92,7 @@ class ImageBridgeParent final : public PImageBridgeParent,
   // Shutdown step 1
   mozilla::ipc::IPCResult RecvWillClose();
 
-  MessageLoop* GetMessageLoop() const { return mMessageLoop; }
+  nsISerialEventTarget* GetThread() const { return mThread; }
 
   // IShmemAllocator
 
@@ -142,7 +136,7 @@ class ImageBridgeParent final : public PImageBridgeParent,
   static void ShutdownInternal();
 
   void DeferredDestroy();
-  MessageLoop* mMessageLoop;
+  nsCOMPtr<nsISerialEventTarget> mThread;
   // This keeps us alive until ActorDestroy(), at which point we do a
   // deferred destruction of ourselves.
   RefPtr<ImageBridgeParent> mSelfRef;
diff --git a/gfx/layers/ipc/ShadowLayers.cpp b/gfx/layers/ipc/ShadowLayers.cpp
index 6dde300d59d9..da0e8831e372 100644
--- a/gfx/layers/ipc/ShadowLayers.cpp
+++ b/gfx/layers/ipc/ShadowLayers.cpp
@@ -189,7 +189,7 @@ RefPtr<KnowsCompositor> ShadowLayerForwarder::GetForMedia() {
 ShadowLayerForwarder::ShadowLayerForwarder(
     ClientLayerManager* aClientLayerManager)
     : mClientLayerManager(aClientLayerManager),
-      mMessageLoop(MessageLoop::current()),
+      mThread(NS_GetCurrentThread()),
       mDiagnosticTypes(DiagnosticTypes::NO_DIAGNOSTIC),
       mIsFirstPaint(false),
       mNextLayerHandle(1) {
@@ -500,9 +500,7 @@ void ShadowLayerForwarder::RemoveTextureFromCompositable(
 }
 
 bool ShadowLayerForwarder::InWorkerThread() {
-  return MessageLoop::current() &&
-         (GetTextureForwarder()->GetMessageLoop()->id() ==
-          MessageLoop::current()->id());
+  return GetTextureForwarder()->GetThread()->IsOnCurrentThread();
 }
 
 void ShadowLayerForwarder::StorePluginWidgetConfigurations(
diff --git a/gfx/layers/ipc/ShadowLayers.h b/gfx/layers/ipc/ShadowLayers.h
index f1e811dac4aa..fa7e3da201d1 100644
--- a/gfx/layers/ipc/ShadowLayers.h
+++ b/gfx/layers/ipc/ShadowLayers.h
@@ -418,7 +418,7 @@ class ShadowLayerForwarder final : public LayersIPCActor,
  private:
   ClientLayerManager* mClientLayerManager;
   Transaction* mTxn;
-  MessageLoop* mMessageLoop;
+  nsCOMPtr<nsISerialEventTarget> mThread;
   DiagnosticTypes mDiagnosticTypes;
   bool mIsFirstPaint;
   FocusTarget mFocusTarget;
diff --git a/gfx/layers/ipc/TextureForwarder.h b/gfx/layers/ipc/TextureForwarder.h
index 49fd4a5ed013..09ad0a12add5 100644
--- a/gfx/layers/ipc/TextureForwarder.h
+++ b/gfx/layers/ipc/TextureForwarder.h
@@ -13,6 +13,7 @@
 #include "mozilla/layers/LayersTypes.h"     // for LayersBackend
 #include "mozilla/layers/TextureClient.h"   // for TextureClient
 #include "mozilla/layers/KnowsCompositor.h"
+#include "nsISerialEventTarget.h"
 
 namespace mozilla {
 namespace ipc {
@@ -47,7 +48,7 @@ class LayersIPCChannel : public LayersIPCActor,
 
   virtual base::ProcessId GetParentPid() const = 0;
 
-  virtual MessageLoop* GetMessageLoop() const = 0;
+  virtual nsISerialEventTarget* GetThread() const = 0;
 
   virtual FixedSizeSmallShmemSectionAllocator* GetTileLockAllocator() {
     return nullptr;
diff --git a/gfx/layers/ipc/UiCompositorControllerChild.cpp b/gfx/layers/ipc/UiCompositorControllerChild.cpp
index be67b4940b48..0225cb8b9db6 100644
--- a/gfx/layers/ipc/UiCompositorControllerChild.cpp
+++ b/gfx/layers/ipc/UiCompositorControllerChild.cpp
@@ -27,9 +27,7 @@ static RefPtr<nsThread> GetUiThread() {
 }
 #endif  // defined(MOZ_WIDGET_ANDROID)
 
-static bool IsOnUiThread() {
-  return GetUiThread()->SerialEventTarget()->IsOnCurrentThread();
-}
+static bool IsOnUiThread() { return GetUiThread()->IsOnCurrentThread(); }
 
 namespace mozilla {
 namespace layers {
@@ -262,8 +260,7 @@ UiCompositorControllerChild::~UiCompositorControllerChild() = default;
 void UiCompositorControllerChild::OpenForSameProcess() {
   MOZ_ASSERT(IsOnUiThread());
 
-  mIsOpen = Open(mParent->GetIPCChannel(),
-                 mozilla::layers::CompositorThreadHolder::Loop(),
+  mIsOpen = Open(mParent->GetIPCChannel(), mozilla::layers::CompositorThread(),
                  mozilla::ipc::ChildSide);
 
   if (!mIsOpen) {
diff --git a/gfx/layers/ipc/UiCompositorControllerParent.cpp b/gfx/layers/ipc/UiCompositorControllerParent.cpp
index 954e2ee725b4..8150e3682b84 100644
--- a/gfx/layers/ipc/UiCompositorControllerParent.cpp
+++ b/gfx/layers/ipc/UiCompositorControllerParent.cpp
@@ -50,7 +50,7 @@ RefPtr<UiCompositorControllerParent> UiCompositorControllerParent::Start(
       NewRunnableMethod<Endpoint<PUiCompositorControllerParent>&&>(
           "layers::UiCompositorControllerParent::Open", parent,
           &UiCompositorControllerParent::Open, std::move(aEndpoint));
-  CompositorThreadHolder::Loop()->PostTask(task.forget());
+  CompositorThread()->Dispatch(task.forget());
 
   return parent;
 }
@@ -181,7 +181,7 @@ void UiCompositorControllerParent::ToolbarAnimatorMessageFromCompositor(
     int32_t aMessage) {
   // This function can be call from ether compositor or controller thread.
   if (!CompositorThreadHolder::IsInCompositorThread()) {
-    CompositorThreadHolder::Loop()->PostTask(NewRunnableMethod<int32_t>(
+    CompositorThread()->Dispatch(NewRunnableMethod<int32_t>(
         "layers::UiCompositorControllerParent::"
         "ToolbarAnimatorMessageFromCompositor",
         this,
@@ -218,11 +218,10 @@ void UiCompositorControllerParent::NotifyUpdateScreenMetrics(
       aMetrics.GetZoom().ToScaleFactor(),
       PixelCastJustification::ScreenIsParentLayerForRoot);
   ScreenPoint scrollOffset = aMetrics.GetScrollOffset() * scale;
-  CompositorThreadHolder::Loop()->PostTask(
-      NewRunnableMethod<ScreenPoint, CSSToScreenScale>(
-          "UiCompositorControllerParent::SendRootFrameMetrics", this,
-          &UiCompositorControllerParent::SendRootFrameMetrics, scrollOffset,
-          scale));
+  CompositorThread()->Dispatch(NewRunnableMethod<ScreenPoint, CSSToScreenScale>(
+      "UiCompositorControllerParent::SendRootFrameMetrics", this,
+      &UiCompositorControllerParent::SendRootFrameMetrics, scrollOffset,
+      scale));
 #endif
 }
 
@@ -249,7 +248,7 @@ void UiCompositorControllerParent::InitializeForSameProcess() {
     SynchronousTask task(
         "UiCompositorControllerParent::InitializeForSameProcess");
 
-    CompositorThreadHolder::Loop()->PostTask(NS_NewRunnableFunction(
+    CompositorThread()->Dispatch(NS_NewRunnableFunction(
         "UiCompositorControllerParent::InitializeForSameProcess", [&]() {
           AutoCompleteTask complete(&task);
           InitializeForSameProcess();
diff --git a/gfx/layers/ipc/VideoBridgeChild.cpp b/gfx/layers/ipc/VideoBridgeChild.cpp
index a60c37de02b8..7529c29318a0 100644
--- a/gfx/layers/ipc/VideoBridgeChild.cpp
+++ b/gfx/layers/ipc/VideoBridgeChild.cpp
@@ -48,9 +48,7 @@ void VideoBridgeChild::Shutdown() {
 }
 
 VideoBridgeChild::VideoBridgeChild()
-    : mIPDLSelfRef(this),
-      mMessageLoop(MessageLoop::current()),
-      mCanSend(true) {}
+    : mIPDLSelfRef(this), mThread(NS_GetCurrentThread()), mCanSend(true) {}
 
 VideoBridgeChild::~VideoBridgeChild() = default;
 
@@ -59,7 +57,7 @@ VideoBridgeChild* VideoBridgeChild::GetSingleton() { return sVideoBridge; }
 bool VideoBridgeChild::AllocUnsafeShmem(
     size_t aSize, ipc::SharedMemory::SharedMemoryType aType,
     ipc::Shmem* aShmem) {
-  if (MessageLoop::current() != mMessageLoop) {
+  if (!mThread->IsOnCurrentThread()) {
     return DispatchAllocShmemInternal(aSize, aType, aShmem,
                                       true);  // true: unsafe
   }
@@ -106,7 +104,7 @@ bool VideoBridgeChild::DispatchAllocShmemInternal(
   RefPtr<Runnable> runnable = WrapRunnable(
       RefPtr<VideoBridgeChild>(this), &VideoBridgeChild::ProxyAllocShmemNow,
       &task, aSize, aType, aShmem, aUnsafe, &success);
-  GetMessageLoop()->PostTask(runnable.forget());
+  GetThread()->Dispatch(runnable.forget());
 
   task.Wait();
 
@@ -124,7 +122,7 @@ void VideoBridgeChild::ProxyDeallocShmemNow(SynchronousTask* aTask,
 }
 
 bool VideoBridgeChild::DeallocShmem(ipc::Shmem& aShmem) {
-  if (MessageLoop::current() == mMessageLoop) {
+  if (GetThread()->IsOnCurrentThread()) {
     if (!CanSend()) {
       return false;
     }
@@ -137,7 +135,7 @@ bool VideoBridgeChild::DeallocShmem(ipc::Shmem& aShmem) {
   RefPtr<Runnable> runnable = WrapRunnable(
       RefPtr<VideoBridgeChild>(this), &VideoBridgeChild::ProxyDeallocShmemNow,
       &task, &aShmem, &result);
-  GetMessageLoop()->PostTask(runnable.forget());
+  GetThread()->Dispatch(runnable.forget());
 
   task.Wait();
   return result;
diff --git a/gfx/layers/ipc/VideoBridgeChild.h b/gfx/layers/ipc/VideoBridgeChild.h
index 1e5b3920ed2a..69f1642d1223 100644
--- a/gfx/layers/ipc/VideoBridgeChild.h
+++ b/gfx/layers/ipc/VideoBridgeChild.h
@@ -57,7 +57,7 @@ class VideoBridgeChild final : public PVideoBridgeChild,
 
   // ClientIPCAllocator
   base::ProcessId GetParentPid() const override { return OtherPid(); }
-  MessageLoop* GetMessageLoop() const override { return mMessageLoop; }
+  nsISerialEventTarget* GetThread() const override { return mThread; }
   void CancelWaitForNotifyNotUsed(uint64_t aTextureId) override {
     MOZ_ASSERT(false, "NO RECYCLING HERE");
   }
@@ -86,7 +86,7 @@ class VideoBridgeChild final : public PVideoBridgeChild,
   virtual ~VideoBridgeChild();
 
   RefPtr<VideoBridgeChild> mIPDLSelfRef;
-  MessageLoop* mMessageLoop;
+  nsCOMPtr<nsISerialEventTarget> mThread;
   bool mCanSend;
 };
 
diff --git a/gfx/layers/ipc/VideoBridgeParent.cpp b/gfx/layers/ipc/VideoBridgeParent.cpp
index f18585041fd0..d8791ed9fbc0 100644
--- a/gfx/layers/ipc/VideoBridgeParent.cpp
+++ b/gfx/layers/ipc/VideoBridgeParent.cpp
@@ -48,7 +48,7 @@ void VideoBridgeParent::Open(Endpoint<PVideoBridgeParent>&& aEndpoint,
                              VideoBridgeSource aSource) {
   RefPtr<VideoBridgeParent> parent = new VideoBridgeParent(aSource);
 
-  CompositorThreadHolder::Loop()->PostTask(
+  CompositorThread()->Dispatch(
       NewRunnableMethod<Endpoint<PVideoBridgeParent>&&>(
           "gfx::layers::VideoBridgeParent::Bind", parent,
           &VideoBridgeParent::Bind, std::move(aEndpoint)));
diff --git a/gfx/layers/wr/AsyncImagePipelineManager.cpp b/gfx/layers/wr/AsyncImagePipelineManager.cpp
index abc24a7150bb..cdc1fb1c379d 100644
--- a/gfx/layers/wr/AsyncImagePipelineManager.cpp
+++ b/gfx/layers/wr/AsyncImagePipelineManager.cpp
@@ -551,7 +551,7 @@ void AsyncImagePipelineManager::NotifyPipelinesUpdated(
 
   // Queue a runnable on the compositor thread to process the updates.
   // This will also call CheckForTextureHostsNotUsedByGPU.
-  layers::CompositorThreadHolder::Loop()->PostTask(
+  layers::CompositorThread()->Dispatch(
       NewRunnableMethod("ProcessPipelineUpdates", this,
                         &AsyncImagePipelineManager::ProcessPipelineUpdates));
 }
diff --git a/gfx/layers/wr/WebRenderBridgeParent.cpp b/gfx/layers/wr/WebRenderBridgeParent.cpp
index 984237e5641f..e7643948d399 100644
--- a/gfx/layers/wr/WebRenderBridgeParent.cpp
+++ b/gfx/layers/wr/WebRenderBridgeParent.cpp
@@ -193,7 +193,7 @@ class ScheduleObserveLayersUpdate : public wr::NotificationHandler {
         mIsActive(aIsActive) {}
 
   void Notify(wr::Checkpoint) override {
-    CompositorThreadHolder::Loop()->PostTask(
+    CompositorThread()->Dispatch(
         NewRunnableMethod<LayersId, LayersObserverEpoch, int>(
             "ObserveLayersUpdate", mBridge,
             &CompositorBridgeParentBase::ObserveLayersUpdate, mLayersId,
@@ -217,7 +217,7 @@ class SceneBuiltNotification : public wr::NotificationHandler {
     auto startTime = this->mTxnStartTime;
     RefPtr<WebRenderBridgeParent> parent = mParent;
     wr::Epoch epoch = mEpoch;
-    CompositorThreadHolder::Loop()->PostTask(NS_NewRunnableFunction(
+    CompositorThread()->Dispatch(NS_NewRunnableFunction(
         "SceneBuiltNotificationRunnable", [parent, epoch, startTime]() {
           auto endTime = TimeStamp::Now();
 #ifdef MOZ_GECKO_PROFILER
@@ -287,7 +287,7 @@ class WebRenderBridgeParent::ScheduleSharedSurfaceRelease final
   }
 
   void Notify(wr::Checkpoint) override {
-    CompositorThreadHolder::Loop()->PostTask(
+    CompositorThread()->Dispatch(
         NewRunnableMethod<nsTArray<wr::ExternalImageKeyPair>>(
             "ObserveSharedSurfaceRelease", mWrBridge,
             &WebRenderBridgeParent::ObserveSharedSurfaceRelease,
diff --git a/gfx/thebes/DeviceManagerDx.cpp b/gfx/thebes/DeviceManagerDx.cpp
index 04be5837311e..07da4f2bcc48 100644
--- a/gfx/thebes/DeviceManagerDx.cpp
+++ b/gfx/thebes/DeviceManagerDx.cpp
@@ -1384,8 +1384,7 @@ void DeviceManagerDx::GetCompositorDevices(
 
 /* static */
 void DeviceManagerDx::PreloadAttachmentsOnCompositorThread() {
-  MessageLoop* loop = layers::CompositorThreadHolder::Loop();
-  if (!loop) {
+  if (!CompositorThread()) {
     return;
   }
 
@@ -1404,7 +1403,7 @@ void DeviceManagerDx::PreloadAttachmentsOnCompositorThread() {
           }
         }
       });
-  loop->PostTask(task.forget());
+  CompositorThread()->Dispatch(task.forget());
 }
 
 }  // namespace gfx
diff --git a/gfx/vr/VRManager.cpp b/gfx/vr/VRManager.cpp
index 7f4eff393831..85416ffed497 100644
--- a/gfx/vr/VRManager.cpp
+++ b/gfx/vr/VRManager.cpp
@@ -309,7 +309,7 @@ void VRManager::StartTasks() {
   if (!mTaskTimer) {
     mTaskInterval = GetOptimalTaskInterval();
     mTaskTimer = NS_NewTimer();
-    mTaskTimer->SetTarget(CompositorThreadHolder::Loop()->SerialEventTarget());
+    mTaskTimer->SetTarget(CompositorThread());
     mTaskTimer->InitWithNamedFuncCallback(
         TaskTimerCallback, this, mTaskInterval,
         nsITimer::TYPE_REPEATING_PRECISE_CAN_SKIP,
@@ -1380,7 +1380,7 @@ void VRManager::SubmitFrame(VRLayerParent* aLayer,
     mSubmitThread->Start();
     mSubmitThread->PostTask(task.forget());
 #else
-    CompositorThreadHolder::Loop()->PostTask(task.forget());
+    CompositorThread()->Dispatch(task.forget());
 #endif  // defined(MOZ_WIDGET_ANDROID)
   }
 }
@@ -1514,10 +1514,8 @@ void VRManager::SubmitFrameInternal(const layers::SurfaceDescriptor& aTexture,
    * frames to continue at a lower refresh rate until frame submission
    * succeeds again.
    */
-  MessageLoop* loop = CompositorThreadHolder::Loop();
-
-  loop->PostTask(NewRunnableMethod("gfx::VRManager::StartFrame", this,
-                                   &VRManager::StartFrame));
+  CompositorThread()->Dispatch(NewRunnableMethod("gfx::VRManager::StartFrame",
+                                                 this, &VRManager::StartFrame));
 #elif defined(MOZ_WIDGET_ANDROID)
   // We are already in the CompositorThreadHolder event loop on Android.
   StartFrame();
diff --git a/gfx/vr/VRThread.cpp b/gfx/vr/VRThread.cpp
index ee972226a6b5..37748544441a 100644
--- a/gfx/vr/VRThread.cpp
+++ b/gfx/vr/VRThread.cpp
@@ -7,6 +7,7 @@
 #include "VRThread.h"
 #include "nsDebug.h"
 #include "nsThreadManager.h"
+#include "nsThread.h"
 #include "nsThreadUtils.h"
 #include "VRManager.h"
 
diff --git a/gfx/vr/ipc/VRGPUChild.cpp b/gfx/vr/ipc/VRGPUChild.cpp
index 4deadbe47a1f..715c3e3c8abb 100644
--- a/gfx/vr/ipc/VRGPUChild.cpp
+++ b/gfx/vr/ipc/VRGPUChild.cpp
@@ -56,7 +56,7 @@ void VRGPUChild::Shutdown() {
 
 void VRGPUChild::ActorDestroy(ActorDestroyReason aWhy) {
   VRManager* vm = VRManager::Get();
-  mozilla::layers::CompositorThreadHolder::Loop()->PostTask(
+  mozilla::layers::CompositorThread()->Dispatch(
       NewRunnableMethod("VRGPUChild::ActorDestroy", vm, &VRManager::Shutdown));
 
   mClosed = true;
diff --git a/gfx/vr/ipc/VRManagerChild.cpp b/gfx/vr/ipc/VRManagerChild.cpp
index fc2f62197cd7..1dcdf6012543 100644
--- a/gfx/vr/ipc/VRManagerChild.cpp
+++ b/gfx/vr/ipc/VRManagerChild.cpp
@@ -40,7 +40,6 @@ void ReleaseVRManagerParentSingleton() { sVRManagerParentSingleton = nullptr; }
 
 VRManagerChild::VRManagerChild()
     : mRuntimeCapabilities(VRDisplayCapabilityFlags::Cap_None),
-      mMessageLoop(MessageLoop::current()),
       mFrameRequestCallbackCounter(0),
       mWaitingForEnumeration(false),
       mBackend(layers::LayersBackend::LAYERS_NONE) {
@@ -112,8 +111,7 @@ void VRManagerChild::InitSameProcess() {
   sVRManagerChildSingleton = new VRManagerChild();
   sVRManagerParentSingleton = VRManagerParent::CreateSameProcess();
   sVRManagerChildSingleton->Open(sVRManagerParentSingleton->GetIPCChannel(),
-                                 CompositorThreadHolder::Loop(),
-                                 mozilla::ipc::ChildSide);
+                                 CompositorThread(), mozilla::ipc::ChildSide);
 }
 
 /* static */
diff --git a/gfx/vr/ipc/VRManagerChild.h b/gfx/vr/ipc/VRManagerChild.h
index 5ccc432b6705..06dcae94b3ab 100644
--- a/gfx/vr/ipc/VRManagerChild.h
+++ b/gfx/vr/ipc/VRManagerChild.h
@@ -158,8 +158,6 @@ class VRManagerChild : public PVRManagerChild {
   bool mDisplaysInitialized;
   nsTArray<uint64_t> mNavigatorCallbacks;
 
-  MessageLoop* mMessageLoop;
-
   struct XRFrameRequest {
     XRFrameRequest(mozilla::dom::FrameRequestCallback& aCallback,
                    int32_t aHandle)
diff --git a/gfx/vr/ipc/VRManagerParent.cpp b/gfx/vr/ipc/VRManagerParent.cpp
index 9da0fa6f1f5a..609e489ec305 100644
--- a/gfx/vr/ipc/VRManagerParent.cpp
+++ b/gfx/vr/ipc/VRManagerParent.cpp
@@ -72,13 +72,12 @@ void VRManagerParent::UnregisterFromManager() {
 
 /* static */
 bool VRManagerParent::CreateForContent(Endpoint<PVRManagerParent>&& aEndpoint) {
-  MessageLoop* loop = CompositorThreadHolder::Loop();
-  if (!loop) {
+  if (!CompositorThread()) {
     return false;
   }
 
   RefPtr<VRManagerParent> vmp = new VRManagerParent(aEndpoint.OtherPid(), true);
-  loop->PostTask(NewRunnableMethod<Endpoint<PVRManagerParent>&&>(
+  CompositorThread()->Dispatch(NewRunnableMethod<Endpoint<PVRManagerParent>&&>(
       "gfx::VRManagerParent::Bind", vmp, &VRManagerParent::Bind,
       std::move(aEndpoint)));
 
@@ -102,12 +101,11 @@ void VRManagerParent::RegisterVRManagerInCompositorThread(
 
 /*static*/
 VRManagerParent* VRManagerParent::CreateSameProcess() {
-  MessageLoop* loop = CompositorThreadHolder::Loop();
   RefPtr<VRManagerParent> vmp =
       new VRManagerParent(base::GetCurrentProcId(), false);
   vmp->mCompositorThreadHolder = CompositorThreadHolder::GetSingleton();
   vmp->mSelfRef = vmp;
-  loop->PostTask(
+  CompositorThread()->Dispatch(
       NewRunnableFunction("RegisterVRManagerIncompositorThreadRunnable",
                           RegisterVRManagerInCompositorThread, vmp.get()));
   return vmp.get();
@@ -115,13 +113,11 @@ VRManagerParent* VRManagerParent::CreateSameProcess() {
 
 bool VRManagerParent::CreateForGPUProcess(
     Endpoint<PVRManagerParent>&& aEndpoint) {
-  MessageLoop* loop = CompositorThreadHolder::Loop();
-
   RefPtr<VRManagerParent> vmp =
       new VRManagerParent(aEndpoint.OtherPid(), false);
   vmp->mCompositorThreadHolder = CompositorThreadHolder::GetSingleton();
   vmp->mSelfRef = vmp;
-  loop->PostTask(NewRunnableMethod<Endpoint<PVRManagerParent>&&>(
+  CompositorThread()->Dispatch(NewRunnableMethod<Endpoint<PVRManagerParent>&&>(
       "gfx::VRManagerParent::Bind", vmp, &VRManagerParent::Bind,
       std::move(aEndpoint)));
   return true;
@@ -130,7 +126,7 @@ bool VRManagerParent::CreateForGPUProcess(
 /*static*/
 void VRManagerParent::Shutdown() {
   ReleaseVRManagerParentSingleton();
-  CompositorThreadHolder::Loop()->PostTask(NS_NewRunnableFunction(
+  CompositorThread()->Dispatch(NS_NewRunnableFunction(
       "VRManagerParent::Shutdown",
       []() -> void { VRManagerParent::ShutdownInternal(); }));
 }
diff --git a/gfx/webrender_bindings/RenderThread.cpp b/gfx/webrender_bindings/RenderThread.cpp
index 91431c0f542d..b5803bdeec8c 100644
--- a/gfx/webrender_bindings/RenderThread.cpp
+++ b/gfx/webrender_bindings/RenderThread.cpp
@@ -469,7 +469,7 @@ void RenderThread::UpdateAndRender(
 
   auto& renderer = it->second;
 
-  layers::CompositorThreadHolder::Loop()->PostTask(
+  layers::CompositorThread()->Dispatch(
       NewRunnableFunction("NotifyDidStartRenderRunnable", &NotifyDidStartRender,
                           renderer->GetCompositorBridge()));
 
@@ -487,7 +487,7 @@ void RenderThread::UpdateAndRender(
   TimeStamp end = TimeStamp::Now();
   RefPtr<const WebRenderPipelineInfo> info = renderer->FlushPipelineInfo();
 
-  layers::CompositorThreadHolder::Loop()->PostTask(
+  layers::CompositorThread()->Dispatch(
       NewRunnableFunction("NotifyDidRenderRunnable", &NotifyDidRender,
                           renderer->GetCompositorBridge(), info, aStartId,
                           aStartTime, start, end, aRender, stats));
@@ -821,7 +821,7 @@ void RenderThread::HandleWebRenderError(WebRenderError aError) {
     return;
   }
 
-  layers::CompositorThreadHolder::Loop()->PostTask(NewRunnableFunction(
+  layers::CompositorThread()->Dispatch(NewRunnableFunction(
       "DoNotifyWebRenderErrorRunnable", &DoNotifyWebRenderError, aError));
   {
     MutexAutoLock lock(mRenderTextureMapLock);
@@ -1114,7 +1114,7 @@ void wr_finished_scene_build(mozilla::wr::WrWindowId aWindowId,
     for (size_t i = 0; i < aDocumentIdsCount; ++i) {
       renderRoots[i] = wr::RenderRootFromId(aDocumentIds[i]);
     }
-    layers::CompositorThreadHolder::Loop()->PostTask(
+    layers::CompositorThread()->Dispatch(
         NewRunnableFunction("NotifyDidSceneBuild", &NotifyDidSceneBuild, cbp,
                             std::move(renderRoots), info));
   }
diff --git a/gfx/webrender_bindings/RendererOGL.cpp b/gfx/webrender_bindings/RendererOGL.cpp
index d6cc5f843634..fd03d91cb1b6 100644
--- a/gfx/webrender_bindings/RendererOGL.cpp
+++ b/gfx/webrender_bindings/RendererOGL.cpp
@@ -200,7 +200,7 @@ bool RendererOGL::EnsureAsyncScreenshot() {
     return true;
   }
   if (!mDisableNativeCompositor) {
-    layers::CompositorThreadHolder::Loop()->PostTask(
+    layers::CompositorThread()->Dispatch(
         NewRunnableFunction("DoWebRenderDisableNativeCompositorRunnable",
                             &DoWebRenderDisableNativeCompositor, mBridge));
 
@@ -219,7 +219,7 @@ void RendererOGL::CheckGraphicsResetStatus() {
   if (gl->IsSupported(gl::GLFeature::robustness)) {
     GLenum resetStatus = gl->fGetGraphicsResetStatus();
     if (resetStatus == LOCAL_GL_PURGED_CONTEXT_RESET_NV) {
-      layers::CompositorThreadHolder::Loop()->PostTask(
+      layers::CompositorThread()->Dispatch(
           NewRunnableFunction("DoNotifyWebRenderContextPurgeRunnable",
                               &DoNotifyWebRenderContextPurge, mBridge));
     }
diff --git a/media/webrtc/signaling/src/media-conduit/VideoConduit.h b/media/webrtc/signaling/src/media-conduit/VideoConduit.h
index f372ecad5da1..7ab648f3e8a3 100644
--- a/media/webrtc/signaling/src/media-conduit/VideoConduit.h
+++ b/media/webrtc/signaling/src/media-conduit/VideoConduit.h
@@ -54,7 +54,6 @@ T MinIgnoreZero(const T& a, const T& b);
 
 class VideoStreamFactory;
 class WebrtcAudioConduit;
-class nsThread;
 
 // Interface of external video encoder for WebRTC.
 class WebrtcVideoEncoder : public VideoEncoder, public webrtc::VideoEncoder {};
diff --git a/widget/windows/CompositorWidgetParent.cpp b/widget/windows/CompositorWidgetParent.cpp
index 1bc839f2b729..d59dce6905e2 100644
--- a/widget/windows/CompositorWidgetParent.cpp
+++ b/widget/windows/CompositorWidgetParent.cpp
@@ -216,7 +216,7 @@ void CompositorWidgetParent::UpdateCompositorWnd(const HWND aCompositorWnd,
   SendUpdateCompositorWnd(reinterpret_cast<WindowsHandle>(aCompositorWnd),
                           reinterpret_cast<WindowsHandle>(aParentWnd))
       ->Then(
-          layers::CompositorThreadHolder::Loop()->SerialEventTarget(), __func__,
+          layers::CompositorThread(), __func__,
           [self](const bool& aSuccess) {
             if (aSuccess && self->mRootLayerTreeID.isSome()) {
               self->mSetParentCompleted = true;