How to Activate Media Source Extensions in Firefox for Youtube

Firefox is going to enable Media Source Extensions in version 31. But you can enable Media Source Extensions right now with a simple tweaks. I have been using Firefox 29. When I visit YouTube’s HTML5 Video Player page, I can see that my firefox  does not support Media Source Extensions, MSE & H.264  and MSE & WebM VP9. Although it supports HTMLVideoElement, H.264 and WebM VP8.

Why you need MSE?

According to, Media Source Extensions (MSE) extend the HTMLVideoElement to allow JavaScript to generate media streams for playback which in turn makes way for new features such as adaptive streaming or time shifting in live streams.

With this Media Source Extensions activated you can enjoy a better you tube experience.

If you use the HTML5 player instead of default player , some video resolutions will not be supported. For example, 1080p quality is not displayed for instance if Media Source Extensions is not supported by the web browser.

How to Activate Media Source Extensions in Firefox for Youtube

To Activate MSE in Firefox:

  1. Type about:config into the address bar and hit enter.
  2. Click on “I’ll be careful, I Promise !” if a warning message is displayed.
  3. Search for media.mediasource.enabled and double-click to enable media source extensions. It will turn into true.

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