<i>Firefox won't use system codecs because they might be insecure, they might be buggy</i><p>This does not address the original objection. Calls to the Mac and Windows are <i>not</i> known to be any less buggy or insecure than calls to the h264 APIs. So why accept one and not the other? The only sane answer of course is that you can't build an app at all without calling the OS basic APIs of your host machine, but you can try to have an ugly work around h264.