I listen to music on my computer approximately 100% of the time, so few things annoy me more than web pages with background music (worse still are those banner ads that talk, wow are those annoying). Usually the "sound off" button is hard to find and seems to appear only well after the music starts. I think it's time for web browsers to treat sound the same way they treat pop-ups. By default background sound should be muted (just as pop-ups are blocked), but users are notified that sound is muted and have the option to un-mute once or always for that site. This seems totally feasible, though it may be difficult given that most background music is played from within a Flash based website. I'm sure there's some ambitious young plug-in developer who's up to the challenge, and if not perhaps Firefox developers will create such a feature one day. I've already added this idea to Firefox Feature Brainstorming wiki, so my fingers are crossed.