Firefox does not play Youtube videos

I´m using Firefox Developer Edition on Windows. With one of the updates within version 37 youtube videos would not play anymore. I am not sure whether this is due to youtube´s permanent switch to HTML video or to one of the updates. In case someone stumbles over similar issues you can check at what video codecs can be played by your browser. In case you are missing „MSE & WebM VP9“ (see picture) as I did you can tell Firefox to enable that one.


screenshot-www youtube com 2015-02-08 14-38-04



  • Enter „about:config“ and confirm you will be careful
  • Enter media.mediasource.webm.enabled
  • Set the value to true

After reloading the youtube HTML-video page all codecs should be available. In case you are missing other codecs search for media.mediasource and try to set these values to true as well.

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