Like.fm for Firefox allows you keept track of and show your friends what songs you are listening to from YouTube, Pandora.com, Grooveshark.com, Meemix.com, and more, in real time. Like.fm summarizes your music automatically. Your Facebook friends will be able to check up instantly to see what you are listening to. If you use Twitter you can also automatically tweet new discoveries based on what you rate the song. If you use Last.fm you can even scrobble everything tracked by Like.fm.
Additionally follow friends or random people whose music you like and see what recent great songs they discover, as they discover it!
Listen to music from iTunes or Winamp?
Like.fm's got you covered there too. Head over to http://like.fm/download to see our other music clients.
IN THE PRESS
"Like.fm is how social music should work" - http://news.cnet.com/8301-13526_3-20015614-27.html
How good is the YouTube support?
After installing, a new tab should open with further instructions. It will either ask you to login, signup, or tell you that you're all set to go.