Unknow audio?

Wow, my Firefox doesn't greet me. Could that be from a page open somewhere in Firefox? If you don't see a speaker icon on any of your open tabs, try immediately clicking the List All Tabs drop-down (there's a button similar to a wide v at the right end of the tab bar). That list should show a speaker icon next to any page playing audio, but this is only there for a short time after it stops.