Disabling audio?

I use the firefox browser at work and i was wondering if there was any way to disable the audio in it. What I'd like to do is play either a CD or some MP3s without having to hear the audio from the browser or other programs.....so I either need to isolate the audio in a media player, or disable the sound in firefox. anyone know how?

Eric

PS ive already tried disabling all the media plugins in firefox and it didnt work, everything still plays!