Support for playing H.264/AAC in MP4 and support for playing MP3 audio files in HTML5 <video> and <audio> elements has now been switched on by default for Windows 7 and later in the Firefox Nightly channel. You no longer need to set the pref to enable it. Please test MP4/MP3 support in Firefox Nightly builds, and file bugs in the "Core:: Video/Audio" component in Bugzilla.
Assuming no catastrophic bugs are found, H.264/AAC/MP3 support in Firefox on Windows 7 and later should ship in Firefox22 21, which is scheduled to be released around June 25 May 14.
Edit 25 Feb 2013: Corrected target release, it's Firefox 21, not Firefox 22.
Assuming no catastrophic bugs are found, H.264/AAC/MP3 support in Firefox on Windows 7 and later should ship in Firefox
Edit 25 Feb 2013: Corrected target release, it's Firefox 21, not Firefox 22.
