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.
Note: This problem seemed to resolve with iTunes 7.6.1.
Hear it here: www.chairpage.com Its a very fresh record. Granted, its been twelve years or so since Frogstomp, but its amazing to hear how far they have come. Its probably not for everybody, but its worth a listen or two.