This video (stream, ogg container, theora, vorbis, served by icecast 2) does play in Fx3.1a2 - the autoplay attribute and controls is enabled:
no Fallback content
The stream will frequently stutter and stop. It can be resumed by hitting the play button (a lot). Also audio will desync.
It won't resume after an chained ogg change. See bug 455165
From time to time you'll see a more or less garbled preview.
Also Firefox keeps pulling the stream.