There seems to be an issue with Firefox 22.214.171.124 and iTunes 7.6 on OS X with regards to M3U files. I've noticed this issue with eMusic as well. To solve this, I've included the URL of the actual streams, and if you enter that URL in Advanced --> Open Stream, that should work. There's also this script, but I haven't had a chance to try it yet.
http://www.roadrunnerrecords.com/blabbermouth.net/news.aspx?mode=Article&newsitemID=12747 I would rather listen to John Denver or Megadeth. If it ain't a joke by MeMeMetallica then the estate off John Dever should sue.