Also, now I can make that announcement: tonight, TenFourFox played its first MP3 audio file properly with its own internal decoder in-browser (using a modified version of minimp3, a heavily distilled-down version of ffmpeg's MP3 decoder component). Although Firefox can play MP3s using OS X AudioToolbox, the AudioToolbox in 10.4 does not support MP3, so we had to roll our own implementation. Although the codec is still under patent, it's old and we're non-profit and the code has been part of Linux distros for a long time, so we might be able to sneak by without anyone caring. (I hope I won't regret this.)
This code is not ready for primetime: it can't seek within a stream yet, it asserts all over the place with some MP3 files -- I suspect another lurking endian problem in Mozilla's built-in MP3 frame parser since I've already had to fix one of them to even get this far -- and it crashes if you try to queue up two files, though this is a memory allocator issue with its decoder tables and I have an idea how to fix it. It's also kind of slow, though this is partially because I'm on a debug build, partially because the code is not very optimized, and partially because Mozilla disables bigger buffering with audio-only streams, all of which are solveable.
However, the payoff is now music streaming sites like Amazon Cloud Player will "just work." (Amazon Music complains it needs Flash, but it really doesn't. Disable Flash on an Intel Mac running Firefox and you'll see.) And actually that's what I wrote it for, because now OmniWeb crashes trying to run Amazon Music, which is what I used to use on the G5 in the background. I write code to scratch my itches and the priorities for TenFourFox are decided accordingly. If there is a particular feature you want, I strongly urge you to sit down and write it and submit it. Ahem.
Please note that this doesn't really improve MP4 support; the codec glue is quite different and will have to be hacked in separately. I don't have a timeframe for MPEG-4 support and it is not currently a priority for me because the QTE meets my use cases currently. You, of course, can contribute. Ahem, I say.
The target is 31.4.0, though it will ship disabled in that version, so you'll have to turn it on. If it works well, we'll loosen it for 31.5. However, I still need to get 34 working first, and I still want to complete our IonMonkey implementation. I'm determined to get to 38 before concluding parity.