--- a/dom/media/MediaDecoder.cpp
+++ b/dom/media/MediaDecoder.cpp
@@ -1172,16 +1172,23 @@ void
 MediaDecoder::SeekingStarted()
 {
   MOZ_ASSERT(NS_IsMainThread());
   MOZ_DIAGNOSTIC_ASSERT(!IsShutdown());
   mOwner->SeekStarted();
 }
 
 void
+MediaDecoder::DispatchPendingTasks()
+{
+  mDecoderStateMachine->DispatchPendingTasks();
+}
+}
+
+void
 MediaDecoder::ChangeState(PlayState aState)
 {
   MOZ_ASSERT(NS_IsMainThread());
   MOZ_ASSERT(!IsShutdown(), "SHUTDOWN is the final state.");
 
   if (mNextState == aState) {
     mNextState = PLAY_STATE_PAUSED;
   }

--- a/dom/media/MediaDecoder.h
+++ b/dom/media/MediaDecoder.h
@@ -364,16 +364,19 @@ private:
   // Returns true if the decoder can't participate in video decode suspending.
   bool HasSuspendTaint() const;
 
   /******
    * The following methods must only be called on the main
    * thread.
    ******/
 
+  // Dispatch any pending tasks in the main thread tail dispatcher in order.
+  void DispatchPendingTasks();
+
   // Change to a new play state. This updates the mState variable and
   // notifies any thread blocking on this object's monitor of the
   // change. Call on the main thread only.
   virtual void ChangeState(PlayState aState);
 
   // Called from MetadataLoaded(). Creates audio tracks and adds them to its
   // owner's audio track list, and implies to video tracks respectively.
   // Call on the main thread only.

--- a/dom/media/MediaDecoderStateMachine.h
+++ b/dom/media/MediaDecoderStateMachine.h
@@ -221,16 +221,26 @@ public:
       if (self->mAudioOffloading != aAudioOffloading) {
         self->mAudioOffloading = aAudioOffloading;
         self->ScheduleStateMachine();
       }
     });
     OwnerThread()->Dispatch(r.forget());
   }
 
+  void DispatchPendingTasks()
+  {
+    MOZ_ASSERT(NS_IsMainThread());
+    AbstractThread* mainThread = AbstractThread::MainThread();
+    // Direct tasks need to be drained...
+    mainThread->TailDispatcher().DrainDirectTasks();
+    // ...before state and normal tasks.
+    mainThread->TailDispatchTasksFor(OwnerThread());
+  }
+
   // Drop reference to mResource. Only called during shutdown dance.
   void BreakCycles() {
     MOZ_ASSERT(NS_IsMainThread());
     mResource = nullptr;
   }
 
   TimedMetadataEventSource& TimedMetadataEvent() {
     return mMetadataManager.TimedMetadataEvent();