There's some irony that the push to the open html5 standard with force Firefox to have to somehow integrate the propriety codec h.264 into its browser.
h.264 is to video what mp3 was to music: a proprietary format that has become the widespread standard that you can't ignore anymore. Firefox is trying to push the open video format Theora, but like ogg chances are it won't ever get widespread support unless popular mindset changes. And nearly all video sites are using h.264, so what's the chance they're all going to convert their video to an unaccepted open format in the short term? So Firefox really can't ignore h.264 if html5 takes off and youtube starts pushing it as an "upgrade".
There a good discussion on this on slashdot:
http://news.slashdot.org/story/10/01/22/021257/Vimeo-Also-Introduces-HTML5-Video-Player?art_pos=8
So it's not a cut-and-dry thing to support h.264 in Firefox, because the GPL license that Firefox is built on forbids it from including a proprietary code in its code base. To integrate h.264, they either can (a) release an "international" version of the browser that can ignore American patent law, or (b) include support through an external module that would be downloaded separately from the browser.
They have a patch being developed that will do (b), but it's not very workable and runs at way too slow a fps right now. Plus if they do (b) then they'd have to pay licensing fees I think, which is estimated to be $6,000,000, or around 6% of Mozilla's income per year. That's quite a bit.
I like (a) but it'd require you to go through hoops to download it, but it could be the start of a campaign to make people realize the benefits of open video formats.