[CentOS] Can't print from Firefox

Hi,

I've just installed CentOS 5.0 on my father's laptop, in replacement of 
Windows XP. Everything runs fine, except I can't seem to print from 
Firefox.

So far, I can print a test page from the CUPS interface (as root). As 
user, printing works fine from applications such as GEdit or 
OpenOffice.org Writer. But I can't print anything from Firefox.

Any suggestions?

Niki Kovacs