--- a/dom/media/MediaCache.h
+++ b/dom/media/MediaCache.h
@@ -220,17 +220,17 @@ public:
   // This must be called (and return) before the ChannelMediaResource
   // used to create this MediaCacheStream is deleted.
   void Close();
   // This returns true when the stream has been closed
   bool IsClosed() const { return mClosed; }
   // Returns true when this stream is can be shared by a new resource load
   bool IsAvailableForSharing() const
   {
-    return !mClosed &&
+    return !mClosed && !mIsPrivateBrowsing &&
       (!mDidNotifyDataEnded || NS_SUCCEEDED(mNotifyDataEndedStatus));
   }
   // Get the principal for this stream. Anything accessing the contents of
   // this stream must have a principal that subsumes this principal.
   nsIPrincipal* GetCurrentPrincipal() { return mPrincipal; }
   // Ensure a global media cache update has run with this stream present.
   // This ensures the cache has had a chance to suspend or unsuspend this stream.
   // Called only on main thread. This can change the state of streams, fire