As some of you are having problems with the original xfire client, especially performance related here is the chatclient i use:
Pidgin (http://www.pidgin.im/)
and a Plugin called gfire (http://gfireproject.org/)
I had to turn off the game detection for UT2004, otherwise pidgin crashs from time to time. But this may be related to my PC. Game detection for other games are working.
This should also work on Linux!
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