FireFox Problem. . .

I am not sure if it is a plug-in or extension whatnot.. But whenever I visit sites that are supposed to play music (Xanga/MySpace) they don't play... And I was wondering if I needed to Download an extension to allow that because when I use another browser I hear the songs...

get the right video codecs
and make sure you have quicktime and realtime alternative installed
get them here
look at the stickies.
when installing the Q & R alternatives make sure you also mark - install for Mozilla(firefox)