Why don't browsers have a mute button?

Ever pull up a site with content you wanted to read, but had endure the obnoxious music it was streaming, which was playing over the music you were already playing in iTunes (or whatever your "music jukebox" of choice is, but come on, it's iTunes, isn't it?)? Surely there's a way to mute that unsolicited music even if the site doesn't have a mute button. Browsing the web is all about you being in control, right?