--- a/dom/media/mediasource/SourceBufferTask.h
+++ b/dom/media/mediasource/SourceBufferTask.h
@@ -18,17 +18,18 @@ namespace mozilla {
 class SourceBufferTask {
 public:
   NS_INLINE_DECL_THREADSAFE_REFCOUNTING(SourceBufferTask);
   enum class Type  {
     AppendBuffer,
     Abort,
     Reset,
     RangeRemoval,
-    EvictData
+    EvictData,
+    Detach
   };
 
   typedef Pair<bool, SourceBufferAttributes> AppendBufferResult;
   typedef MozPromise<AppendBufferResult, nsresult, /* IsExclusive = */ true> AppendPromise;
   typedef MozPromise<bool, nsresult, /* IsExclusive = */ true> RangeRemovalPromise;
 
   virtual Type GetType() const = 0;
 
@@ -93,11 +94,17 @@ public:
 
   static const Type sType = Type::EvictData;
   Type GetType() const override { return Type::EvictData; }
 
   media::TimeUnit mPlaybackTime;
   int64_t mSizeToEvict;
 };
 
+class DetachTask : public SourceBufferTask {
+public:
+  static const Type sType = Type::Detach;
+  Type GetType() const override { return Type::Detach; }
+};
+
 } // end mozilla namespace
 
 #endif
\ No newline at end of file

--- a/dom/media/mediasource/TrackBuffersManager.cpp
+++ b/dom/media/mediasource/TrackBuffersManager.cpp
@@ -94,17 +94,16 @@ TrackBuffersManager::TrackBuffersManager
   , mNewMediaSegmentStarted(false)
   , mActiveTrack(false)
   , mType(aType)
   , mParser(ContainerParser::CreateForMIMEType(aType))
   , mProcessedInput(0)
   , mTaskQueue(aParentDecoder->GetDemuxer()->GetTaskQueue())
   , mParentDecoder(new nsMainThreadPtrHolder<MediaSourceDecoder>(aParentDecoder, false /* strict */))
   , mEnded(false)
-  , mDetached(false)
   , mVideoEvictionThreshold(Preferences::GetUint("media.mediasource.eviction_threshold.video",
                                                  100 * 1024 * 1024))
   , mAudioEvictionThreshold(Preferences::GetUint("media.mediasource.eviction_threshold.audio",
                                                  30 * 1024 * 1024))
   , mEvictionOccurred(false)
   , mMonitor("TrackBuffersManager")
 {
   MOZ_ASSERT(NS_IsMainThread(), "Must be instanciated on the main thread");
@@ -157,20 +156,16 @@ TrackBuffersManager::QueueTask(SourceBuf
 }
 
 void
 TrackBuffersManager::ProcessTasks()
 {
   MOZ_ASSERT(OnTaskQueue());
   typedef SourceBufferTask::Type Type;
 
-  if (mDetached) {
-    return;
-  }
-
   if (mCurrentTask) {
     // Already have a task pending. ProcessTask will be scheduled once the
     // current task complete.
     return;
   }
   RefPtr<SourceBufferTask> task = mQueue.Pop();
   if (!task) {
     // nothing to do.
@@ -203,32 +198,36 @@ TrackBuffersManager::ProcessTasks()
                   task->As<EvictDataTask>()->mSizeToEvict);
       break;
     case Type::Abort:
       // not handled yet, and probably never.
       break;
     case Type::Reset:
       CompleteResetParserState();
       break;
+    case Type::Detach:
+      mTaskQueue = nullptr;
+      MOZ_DIAGNOSTIC_ASSERT(mQueue.Length() == 0,
+                            "Detach task must be the last");
+      return;
     default:
       NS_WARNING("Invalid Task");
   }
   GetTaskQueue()->Dispatch(NewRunnableMethod(this, &TrackBuffersManager::ProcessTasks));
 }
 
 // A PromiseHolder will assert upon destruction if it has a pending promise
 // that hasn't been completed. It is possible that a task didn't get processed
 // due to the owning SourceBuffer having shutdown.
 // We resolve/reject all pending promises and remove all pending tasks from the
 // queue.
 void
 TrackBuffersManager::CancelAllTasks()
 {
   typedef SourceBufferTask::Type Type;
-  MOZ_DIAGNOSTIC_ASSERT(mDetached);
 
   if (mCurrentTask) {
     mQueue.Push(mCurrentTask);
     mCurrentTask = nullptr;
   }
 
   RefPtr<SourceBufferTask> task;
   while ((task = mQueue.Pop())) {
@@ -383,17 +382,17 @@ TrackBuffersManager::Ended()
   mEnded = true;
 }
 
 void
 TrackBuffersManager::Detach()
 {
   MOZ_ASSERT(NS_IsMainThread());
   MSE_DEBUG("");
-  mDetached = true;
+  QueueTask(new DetachTask());
 }
 
 void
 TrackBuffersManager::CompleteResetParserState()
 {
   MOZ_ASSERT(OnTaskQueue());
   MSE_DEBUG("");
 
@@ -752,54 +751,43 @@ TrackBuffersManager::SegmentParserLoop()
     }
   }
 }
 
 void
 TrackBuffersManager::NeedMoreData()
 {
   MSE_DEBUG("");
-  if (mDetached) {
-    // We've been detached.
-    return;
-  }
   MOZ_DIAGNOSTIC_ASSERT(mCurrentTask && mCurrentTask->GetType() == SourceBufferTask::Type::AppendBuffer);
   MOZ_DIAGNOSTIC_ASSERT(mSourceBufferAttributes);
 
   mCurrentTask->As<AppendBufferTask>()->mPromise.Resolve(
     SourceBufferTask::AppendBufferResult(mActiveTrack,
                                          *mSourceBufferAttributes),
                                          __func__);
   mSourceBufferAttributes = nullptr;
   mCurrentTask = nullptr;
   ProcessTasks();
 }
 
 void
 TrackBuffersManager::RejectAppend(nsresult aRejectValue, const char* aName)
 {
   MSE_DEBUG("rv=%d", aRejectValue);
-  if (mDetached) {
-    // We've been detached.
-    return;
-  }
   MOZ_DIAGNOSTIC_ASSERT(mCurrentTask && mCurrentTask->GetType() == SourceBufferTask::Type::AppendBuffer);
 
   mCurrentTask->As<AppendBufferTask>()->mPromise.Reject(aRejectValue, __func__);
   mSourceBufferAttributes = nullptr;
   mCurrentTask = nullptr;
   ProcessTasks();
 }
 
 void
 TrackBuffersManager::ScheduleSegmentParserLoop()
 {
-  if (mDetached) {
-    return;
-  }
   GetTaskQueue()->Dispatch(NewRunnableMethod(this, &TrackBuffersManager::SegmentParserLoop));
 }
 
 void
 TrackBuffersManager::ShutdownDemuxers()
 {
   if (mVideoTracks.mDemuxer) {
     mVideoTracks.mDemuxer->BreakCycles();

--- a/dom/media/mediasource/TrackBuffersManager.h
+++ b/dom/media/mediasource/TrackBuffersManager.h
@@ -392,19 +392,16 @@ private:
   // mSourceBufferAttributes.mAppendWindowStart/End
   media::TimeInterval mAppendWindow;
 
   // Strong references to external objects.
   nsMainThreadPtrHandle<MediaSourceDecoder> mParentDecoder;
 
   // Set to true if mediasource state changed to ended.
   Atomic<bool> mEnded;
-  // Set to true if the parent SourceBuffer has shutdown.
-  // We will not reschedule or process new task once mDetached is set.
-  Atomic<bool> mDetached;
 
   // Global size of this source buffer content.
   Atomic<int64_t> mSizeSourceBuffer;
   const int64_t mVideoEvictionThreshold;
   const int64_t mAudioEvictionThreshold;
   Atomic<bool> mEvictionOccurred;
 
   // Monitor to protect following objects accessed across multipple threads.