--- a/dom/media/MediaDecoder.cpp
+++ b/dom/media/MediaDecoder.cpp
@@ -1031,16 +1031,17 @@ MediaDecoder::ShouldThrottleDownload()
   return stats.mDownloadRate > factor * stats.mPlaybackRate;
 }
 
 void
 MediaDecoder::DownloadProgressed()
 {
   MOZ_ASSERT(NS_IsMainThread());
   MOZ_DIAGNOSTIC_ASSERT(!IsShutdown());
+  AbstractThread::AutoEnter context(AbstractMainThread());
   UpdatePlaybackRate();
   GetOwner()->DownloadProgressed();
   GetResource()->ThrottleReadahead(ShouldThrottleDownload());
 }
 
 void
 MediaDecoder::NotifyDownloadEnded(nsresult aStatus)
 {