In Windows 7 at least, Firefox breaks out each tab into its own subpanel in the Volume Mixer and each instance of Flash (for example) that might be producing sound. It's pretty easy from there to determine which tab is making a racket.
Really? My understanding was the IE was the only major browser that would use multiple Flash instances. You may have just noticed a difference between HTML5 audio/HTML5 video/web audio and sound from plug-ins. (I can check later when near a Windows box.)
Also, I'm generally curious about how IE is able to get away with this since I think the Chrome team said creating multiple Flash instances wasn't reliable because Flash wasn't designed for it in some way (in addition to eating a lot of memory.)
Apologies, I was wrong - that's what I get for posting without checking what I'd seen before. You are right, only one Flash instance shows up for multiple sources playing audio/video.
