This is much more interesting than it may appear at first. Mozilla has previously been not just opposed, but vehemently opposed to using the H.264 codec. They view it as patent encumbered.
If you ask Google, one of the reasons they started work on the rival VP8 (the video portion of WebM, which may still also be patent encumbered, by the way) was because of this. They wanted a HTML5 video codec that would span the entire web.
It caused a bit of a shitstorm when Google announced they’d drop H.264 support in Chrome — even though they were keeping Flash built in. It sounded like a nightmare scenario that wouldn’t work.
And it didn’t. In fact, over a year later, Chrome has yet to drop H.264 support.
Now Mozilla is talking about supporting H.264 because basically they have no choice. Their Boot2Gecko mobile OS project will be a complete non-starter without it. And if they do it there, they’re thinking about doing it elsewhere, it seems.
The most interesting quote from Mozilla director of research, Andreas Gal:
Google pledged many things they didn’t follow through with and our users and our project are paying the price. H.264 wont go away. Holding out just a little longer buys us exactly nothing.
Stop me if you’ve heard this before: Google over-promised and under-delivered. Badly.