Okay, I have found a m3u.shtml file which seems to be a script that redirectsto an actual m3u link... and that was then actually opened in XMMS (the application i have configured Firefox to open m3u files in).
And will xmms play it directly by starting it from the Firefox window? Thats the point where my problems are beginning. On my system xmms crashes here. But when I save the m3u.shtml file on the disk an load it manually into xmms outside of Firefox everything works. But this is circuitous.
Flori