MP4/H.264 video & MP3 audio support
Does Mozilla plan to add support for MP4/H.264 and MP3 formats in Firefox?
There is a complex licensing issue with MPEG-LA. If any codecs capable of streaming such media were distributed with the software and were not licensed, there could be a huge risk of being sued. Should Mozilla purchase a license, it would not fit with the free & open principles the project has had since the beginning.
Ok, so when?
It's not yet known. There could be any number of developments that take place. All that is known right now is that patents expire, in this case we'd have to wait until 2017. This is clearly unrealistic but where there is a will, there is a way!
For further details, see Robert O'Callahan's discussion his blog on MozillaZine: