I've been working on getting the Mediabar to be tab-friendly over the last few days. Currently Mediabar re-discovers all the media on a page every time a user goes to a new url (by clicking or entering something new in the location bar) and when the user switches tabs. That's the behavior that I'm working on fixing.
In order to fix it, I'm doing a minor redesign of how Mediabar works internally. I've been hanging out on
irc.mozilla.org and picking up interesting tidbits of information.
After I fix this issue, there are a bunch of minor issues to fix and then I think it'll be golden. I think it's going to take another few days at least--probably more on the order of another week.