Thing is, sound support (WebAudio or HTML5 <audio> alone) is not a priority for most browsers, Firefox included. I like that Google is so aggressive - maybe some of the other browser vendors will begin to care.
I ranted about the <audio> element quite a while ago[1] and many points are still valid. Also, <audio> can't be used for "dynamic" sound at all. Chrome's/Safari's WebAudio is the way to and Mozilla agrees, but hasn't done anything implementation wise.
[1] http://www.phoboslab.org/log/2011/03/the-state-of-html5-audi...