--- a/dom/media/mediasource/TrackBuffersManager.cpp
+++ b/dom/media/mediasource/TrackBuffersManager.cpp
@@ -167,16 +167,29 @@ TrackBuffersManager::QueueTask(SourceBuf
   MOZ_ASSERT(OnTaskQueue());
   mQueue.Push(aTask);
   ProcessTasks();
 }
 
 void
 TrackBuffersManager::ProcessTasks()
 {
+  // A second Detach task was queued, prior the first one running, ignore it.
+  if (!GetTaskQueue()) {
+    RefPtr<SourceBufferTask> task = mQueue.Pop();
+    if (!task) {
+      return;
+    }
+    MOZ_RELEASE_ASSERT(task->GetType() == SourceBufferTask::Type::Detach,
+                       "only detach task could happen here!");
+    MSE_DEBUG("Could not process the task '%s' after detached",
+              task->GetTypeName());
+    return;
+  }
+
   MOZ_ASSERT(OnTaskQueue());
   typedef SourceBufferTask::Type Type;
 
   if (mCurrentTask) {
     // Already have a task pending. ProcessTask will be scheduled once the
     // current task complete.
     return;
   }