I have just installed Debian Squeeze on my laptop. unluckily this machine has a Radeon HD3400 video card; while the AMD proprietary drivers can make its 3D capabilities to work with pretty good performances they’ve always been a source of trouble. This time I had no problem of incompatibilities with Xorg and the drivers were already pre-packaged in the distribution.
The problem that arose after their installation was a bad rendering of Firefox: some regions of the Firefox (Iceweasel) window were just grayed out. I suspect, but I’m not sure, that this bad behaviour happened while I had some Flash applets opened; also, I don’t know if my architecture, amd64, plays has a role into this.
The solution, that I’ve found on a German forum, involves setting a particular option of the graphic driver via the following command:
# aticonfig --set-pcs-str=DDX,ForceXAA,TRUE
After setting that option and restarting X the issue was resolved.