--- a/dom/media/MediaDecoder.cpp
+++ b/dom/media/MediaDecoder.cpp
@@ -1054,16 +1054,17 @@ MediaDecoder::NotifySuspendedStatusChang
 
 void
 MediaDecoder::NotifyBytesDownloaded()
 {
   MOZ_ASSERT(NS_IsMainThread());
   MOZ_DIAGNOSTIC_ASSERT(!IsShutdown());
   UpdatePlaybackRate();
   GetOwner()->DownloadProgressed();
+  mResource->ThrottleReadahead(CanPlayThrough());
 }
 
 void
 MediaDecoder::NotifyDownloadEnded(nsresult aStatus)
 {
   MOZ_ASSERT(NS_IsMainThread());
   MOZ_DIAGNOSTIC_ASSERT(!IsShutdown());