Can't say anything about the browser speed - Konq 3.3 runs fine for me.
But XMMS.... I've also noticed occasionally it stops playing for no apparent reason. I think I've tracked it down to the system trying to play a system sound effect (a beep or something similar to notify an error), and that seems to try to take over the sound system. XMMS then stops playing at the end of the current song, and tells me there's a problem with the sound config. A few attempts to restart, and it starts working again, but it is annoying.
I don't play music so often that it's a major problem, but if I did, it would be driving me mad.
I don't know if that's the same problem you're experiencing, but if it is, then I hope I've been of some help.
All the best.