When implementing bug 463155 we discovered that the audio element can be not shown and set to autoplay. For email messages this could be quite annoying. Additionally even if the controls are set to be shown, we still can't hook the context menu Play/Pause functions to control the audio element. For the time being, we are therefore disabling autoplay and this bug should investigate possible UIs for allowing re-enabling of autoplay (if desired) and controlling audio elements properly.
The XBL scoping seems to have fixed the lack of controls in FF https://bugzilla.mozilla.org/show_bug.cgi?id=449358#c38 Not so in TB however. I can get the audio and video controls to appear and play in native video/audio mode by using an iframe rather than the video/audio tag. Example code: *iframe src="http://upload.wikimedia.org/wikipedia/en/0/04/Rayman_2_music_sample.ogg" autoplay="true"></iframe> Produces the controls and they work fine. This is just an FYI, as I realize this is a low priority bug. I'm also not sure the iframe behavior is a direct result of the XBL scoping, but I suspect so.
It could be that we're blocking something too much in our content policy that somehow prevents the controls. Without debugging nsMsgContentPolicy to find out what is/isn't being blocked when a message with video/audio loads, it is hard to say though.
In 17 version i see no controls and not able to play audio from message. With iframe TB offers me to download file. With audio tag it shows nothing at all.