Firefox and Opera support Ogg and WebM web video. Those two browsers are together in fighting for a patent-unencumbered web - they refuse to use h264.
What you need to read is
here and
here.
The second article is particularly interesting - Firefox are being stubborn now as Mozilla was at the turn of the millennium, when they turned off their
working ActiveX implementation forever, despite pressure from users.
For the record, currently there is a patent moratorium on h264 used as web video issued by MPEG-LA that was supposed to end in 2011 and now is ending in 2015. Why do you think they would have a patent moratorium on h264 for the web? Because that moratorium doesn't last forever - if it did I'd expect Firefox to support h264. Their decision is about protecting the principles of the web.
Just for interests sake Firefox, being distributed to what 500 million people? would have to cough up an order of hundreds of millions if MPEG-LA were charging them. (of course there's the obvious option of using OS codecs and not paying that money, but that's the type of money that's collected for h264 patent licenses)
Also for interests sake by far and away the best codecs for h264, and a lot of video formats, are developed as free software. x264 is possibly one of the most expert talented groups of free software coders around.
But Mozilla and Opera do not believe that a patent-encumbered video format has a place on the web. If you treat the web with the smallest bit of regard for it's principles, you'd be behind them.