There seems to be an issue with Firefox 18.104.22.168 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.
The playlist for this week - and an acknowledgment of the passing of two greats in Bo Diddley and Utah Phillips. NonDescript, Tuesdays, 9am-10am PDT (12pm-1pm EDT) Webcast @ KCSB-FM 91.9 in Santa Barbara Show Playlist @ Website Podcast: