[FireFox] Experimental H.264, AAC and MP3 support in Nightly Chris Pearce Experimental H.264, AAC, and MP3 support in Firefox Nightly builds on Windows 7 and later
December 19, 2012 via Planet Mozilla
As the Internet has already discovered, recently I landed patches to add a Windows Media Foundation playback backend for Firefox. This is preff'd off by default.
This allows playback of H.264 video and AAC audio in MP4 and M4A files, and MP3 audio files in HTML5 and elements in Firefox on Windows 7 and later.
To test MP4/MP3 playback, download the latest Firefox Nightly Build, and toggle the pref "media.windows-media-foundation.enabled" to "true" in about:config.
There are a few bugs I'm aware, which is why this landed preff'd off by default, but if you spot any bugs, please file a bug in Firefox's "Core :: Video/Audio" component.