Firefox up until now supported only the Webm format in regards to HTML5 video and not the widely used h.264 format as well. This made the browser look inferior to Google Chrome on sites such as YouTube as it could not be used to play all videos on the video hosting site if the HTML5 beta was joined.
Mozilla found a compromise to remedy the situation at least for some users. Windows Vista and newer versions of Windows ship with the h.264 codec included, and that is what the new version of Firefox makes use of to bring support for the format to Firefox.
It is disabled by default, let me show you how to enable it.
- Open the about:config dialog again, it is explained above how you do that.
- Type media.windows-media-foundation.enabled in the search form and double-click the entry afterwards to set it to true. This enables the h.264 format in the browser.