H.264 support for Firefox Linux has landed, the same way it did on Windows. Instead of including the codec directly in Firefox, the browser relies on Operating System level tools to play H.264 video. To enable OS-native codec support for H.264 in Linux, Firefox relies directly on the ubiquitous open source GStreamer libraries.
You can grab the latest version of Firefox Nightly from the Nightly downloads page. Once installed head to about:config and turn on the preference media.gstreamer.enabled
If you compile Firefox on Linux, you need to install gstreamer: `libgstreamer0.10-dev` and `libgstreamer-plugins-base0.10-dev`
H.264 is best known as being one of the codec standards for Blu-ray Discs. It is also widely used by streaming internet sources, such as videos from Vimeo, YouTube, and the iTunes Store, web software such as the Adobe Flash Player and Microsoft Silverlight.
Firefox for Android, Windows (7 and Vista) and Firefox OS already support H.264 and MP3.