Mozilla has enabled support for WebRTC and H.264 & MP3 (on Windows 7) by default for Firefox 21 nightly build and for early adopters Firefox for Windows 8 is available for testing.
WebRTC enabled by default
Till now you need to manually enable WebRTC in Firefox aurora/night builds by setting about:config preference media.peerconnection.enabled value to true, now that’s no longer needed because Mozilla has turned on support for WebRTC by default in Firefox 21 nightly.
H.264 & MP3 support also enabled by default on Windows 7
Since some time for now Firefox OS and Firefox for Android already support H.264 and MP3, but for desktop Firefox till now you can turn on support by changing preference media.windows-media-foundation.enabled value to true which is also no longer needed on Windows for nightly build because Mozilla had turned this pref. on by default.
If you’ve installed Firefox nightly on Windows 8 then set it as default browser to see the metro UI of browser.