I've heard from a number of folks that it'd be very useful for Firefox to let you mute a particular tab in the browser, since more and more sites are incorporating music or other audio content, and users are leaving more tabs open in the background, and they don't necessarily want to hear those tabs while listening to tunes or working.
So I looked around for a way to do this (ideally something I could integrate with site-specific preferences, so you could specify which sites are allowed to quack), and the closest I could find is FlashMute, a small Windows app written by Einar Otto Stangvik that mutes all Flash (and other browser-based sound).
It's like a global mute for browsers, and although it isn't open source, its author says it will be once he gets around to pushing it to Google Code.
But it doesn't let you mute individual tabs, much less specific sites, so it's not quite the feature folks have been clamoring for. So I asked around a bit, and smart folks seem to think it would be very hard to well nigh impossible to implement this on Windows, except possibly on Vista with major changes to our plugin architecture.
Anyone know different or know what the situation is on other platforms?