diff --git a/content/media/mediasource/MediaSourceDecoder.cpp b/content/media/mediasource/MediaSourceDecoder.cpp
index 293b78605eb7..378c72e46a12 100644
--- a/content/media/mediasource/MediaSourceDecoder.cpp
+++ b/content/media/mediasource/MediaSourceDecoder.cpp
@@ -29,6 +29,45 @@ namespace mozilla {
 
 class SubBufferDecoder;
 
+class MediaSourceStateMachine : public MediaDecoderStateMachine
+{
+public:
+  MediaSourceStateMachine(MediaDecoder* aDecoder,
+                          MediaDecoderReader* aReader,
+                          bool aRealTime = false)
+    : MediaDecoderStateMachine(aDecoder, aReader, aRealTime)
+  {
+  }
+
+  already_AddRefed<SubBufferDecoder> CreateSubDecoder(const nsACString& aType,
+                                                      MediaSourceDecoder* aParentDecoder) {
+    if (!mReader) {
+      return nullptr;
+    }
+    MediaSourceReader* reader = static_cast<MediaSourceReader*>(mReader.get());
+    return reader->CreateSubDecoder(aType, aParentDecoder, mDecodeTaskQueue);
+  }
+
+  nsresult EnqueueDecoderInitialization() {
+    AssertCurrentThreadInMonitor();
+    if (!mReader) {
+      return NS_ERROR_FAILURE;
+    }
+    RefPtr<nsIRunnable> task =
+      NS_NewRunnableMethod(this, &MediaSourceStateMachine::InitializePendingDecoders);
+    return mDecodeTaskQueue->Dispatch(task);
+  }
+
+private:
+  void InitializePendingDecoders() {
+    if (!mReader) {
+      return;
+    }
+    MediaSourceReader* reader = static_cast<MediaSourceReader*>(mReader.get());
+    reader->InitializePendingDecoders();
+  }
+};
+
 MediaSourceDecoder::MediaSourceDecoder(dom::HTMLMediaElement* aElement)
   : mMediaSource(nullptr)
 {
@@ -45,8 +84,7 @@ MediaSourceDecoder::Clone()
 MediaDecoderStateMachine*
 MediaSourceDecoder::CreateStateMachine()
 {
-  mReader = new MediaSourceReader(this, mMediaSource);
-  return new MediaDecoderStateMachine(this, mReader);
+  return new MediaSourceStateMachine(this, new MediaSourceReader(this, mMediaSource));
 }
 
 nsresult
@@ -110,7 +148,21 @@ MediaSourceDecoder::DetachMediaSource()
 already_AddRefed<SubBufferDecoder>
 MediaSourceDecoder::CreateSubDecoder(const nsACString& aType)
 {
-  return mReader->CreateSubDecoder(aType, this);
+  if (!mDecoderStateMachine) {
+    return nullptr;
+  }
+  MediaSourceStateMachine* sm = static_cast<MediaSourceStateMachine*>(mDecoderStateMachine.get());
+  return sm->CreateSubDecoder(aType, this);
+}
+
+nsresult
+MediaSourceDecoder::EnqueueDecoderInitialization()
+{
+  if (!mDecoderStateMachine) {
+    return NS_ERROR_FAILURE;
+  }
+  MediaSourceStateMachine* sm = static_cast<MediaSourceStateMachine*>(mDecoderStateMachine.get());
+  return sm->EnqueueDecoderInitialization();
 }
 
 } // namespace mozilla
diff --git a/content/media/mediasource/MediaSourceDecoder.h b/content/media/mediasource/MediaSourceDecoder.h
index 082d26e50f72..40ac01471f6c 100644
--- a/content/media/mediasource/MediaSourceDecoder.h
+++ b/content/media/mediasource/MediaSourceDecoder.h
@@ -18,7 +18,6 @@ namespace mozilla {
 
 class MediaResource;
 class MediaDecoderStateMachine;
-class MediaSourceReader;
 class SubBufferDecoder;
 
 namespace dom {
@@ -45,12 +44,13 @@ public:
 
   already_AddRefed<SubBufferDecoder> CreateSubDecoder(const nsACString& aType);
 
+  nsresult EnqueueDecoderInitialization();
+
 private:
   // The owning MediaSource holds a strong reference to this decoder, and
   // calls Attach/DetachMediaSource on this decoder to set and clear
   // mMediaSource.
   dom::MediaSource* mMediaSource;
-  nsRefPtr<MediaSourceReader> mReader;
 };
 
 } // namespace mozilla
diff --git a/content/media/mediasource/MediaSourceReader.cpp b/content/media/mediasource/MediaSourceReader.cpp
index 8ae822833206..2db7bd43984a 100644
--- a/content/media/mediasource/MediaSourceReader.cpp
+++ b/content/media/mediasource/MediaSourceReader.cpp
@@ -11,7 +11,6 @@
 #include "MediaDecoderOwner.h"
 #include "MediaSource.h"
 #include "MediaSourceDecoder.h"
-#include "SharedThreadPool.h"
 #include "SubBufferDecoder.h"
 
 #ifdef MOZ_FMP4
@@ -42,7 +41,6 @@ MediaSourceReader::MediaSourceReader(MediaSourceDecoder* aDecoder, dom::MediaSou
   , mActiveAudioDecoder(-1)
   , mMediaSource(aSource)
 {
-  mTaskQueue = new MediaTaskQueue(GetMediaDecodeThreadPool());
 }
 
 bool
@@ -137,7 +135,6 @@ MediaSourceReader::Shutdown()
   for (uint32_t i = 0; i < mDecoders.Length(); ++i) {
     mDecoders[i]->GetReader()->Shutdown();
   }
-  mTaskQueue->Shutdown();
 }
 
 void
@@ -302,7 +299,8 @@ CreateReaderForType(const nsACString& aType, AbstractMediaDecoder* aDecoder)
 
 already_AddRefed<SubBufferDecoder>
 MediaSourceReader::CreateSubDecoder(const nsACString& aType,
-                                    MediaSourceDecoder* aParentDecoder)
+                                    MediaSourceDecoder* aParentDecoder,
+                                    MediaTaskQueue* aTaskQueue)
 {
   // XXX: Why/when is mDecoder null here, since it should be equal to aParentDecoder?!
   nsRefPtr<SubBufferDecoder> decoder =
@@ -315,18 +313,16 @@ MediaSourceReader::CreateSubDecoder(const nsACString& aType,
   // This reader will then forward them onto the state machine via this
   // reader's callback.
   RefPtr<MediaDataDecodedListener<MediaSourceReader>> callback =
-    new MediaDataDecodedListener<MediaSourceReader>(this, mTaskQueue);
+    new MediaDataDecodedListener<MediaSourceReader>(this, aTaskQueue);
   reader->SetCallback(callback);
-  reader->SetTaskQueue(mTaskQueue);
+  reader->SetTaskQueue(aTaskQueue);
   reader->Init(nullptr);
   ReentrantMonitorAutoEnter mon(aParentDecoder->GetReentrantMonitor());
   MSE_DEBUG("MediaSourceReader(%p)::CreateSubDecoder subdecoder %p subreader %p",
             this, decoder.get(), reader.get());
   decoder->SetReader(reader);
   mPendingDecoders.AppendElement(decoder);
-  RefPtr<nsIRunnable> task =
-    NS_NewRunnableMethod(this, &MediaSourceReader::InitializePendingDecoders);
-  if (NS_FAILED(mTaskQueue->Dispatch(task))) {
+  if (NS_FAILED(static_cast<MediaSourceDecoder*>(mDecoder)->EnqueueDecoderInitialization())) {
     MSE_DEBUG("MediaSourceReader(%p): Failed to enqueue decoder initialization task", this);
     return nullptr;
   }
diff --git a/content/media/mediasource/MediaSourceReader.h b/content/media/mediasource/MediaSourceReader.h
index 78ec809ce9a8..95bde7f75b29 100644
--- a/content/media/mediasource/MediaSourceReader.h
+++ b/content/media/mediasource/MediaSourceReader.h
@@ -71,7 +71,8 @@ public:
   nsresult Seek(int64_t aTime, int64_t aStartTime, int64_t aEndTime,
                 int64_t aCurrentTime) MOZ_OVERRIDE;
   already_AddRefed<SubBufferDecoder> CreateSubDecoder(const nsACString& aType,
-                                                      MediaSourceDecoder* aParentDecoder);
+                                                      MediaSourceDecoder* aParentDecoder,
+                                                      MediaTaskQueue* aTaskQueue);
 
   void Shutdown();
 
@@ -108,8 +109,6 @@ private:
   nsTArray<nsRefPtr<SubBufferDecoder>> mPendingDecoders;
   nsTArray<nsRefPtr<SubBufferDecoder>> mDecoders;
 
-  nsRefPtr<MediaTaskQueue> mTaskQueue;
-
   int32_t mActiveVideoDecoder;
   int32_t mActiveAudioDecoder;
   dom::MediaSource* mMediaSource;