--- a/dom/media/mediasource/SourceBuffer.cpp
+++ b/dom/media/mediasource/SourceBuffer.cpp
@@ -574,21 +574,17 @@ SourceBuffer::HighestEndTime()
   return mTrackBuffersManager
          ? mTrackBuffersManager->HighestEndTime().ToSeconds()
          : 0.0;
 }
 
 NS_IMPL_CYCLE_COLLECTION_CLASS(SourceBuffer)
 
 NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(SourceBuffer)
-  // Tell the TrackBuffer to end its current SourceBufferResource.
-  TrackBuffersManager* manager = tmp->mTrackBuffersManager;
-  if (manager) {
-    manager->Detach();
-  }
+  tmp->Detach();
   NS_IMPL_CYCLE_COLLECTION_UNLINK(mMediaSource)
   NS_IMPL_CYCLE_COLLECTION_UNLINK(mBuffered)
 NS_IMPL_CYCLE_COLLECTION_UNLINK_END_INHERITED(DOMEventTargetHelper)
 
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(SourceBuffer,
                                                   DOMEventTargetHelper)
   NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mMediaSource)
   NS_IMPL_CYCLE_COLLECTION_TRAVERSE(mBuffered)