The writing's on the wall, though, so you can just use something like MediaElement.js' Flash fallback until Mozilla ships OS H.264 support for other platforms. That's a much better situation than having to double your media transcoding & storage costs.
Firefox doesn't support H264, but it can offload the decoding to the OS. So if your OS doesn't have it, it won't work. This affects Windows XP, which still has substantial users.
