If you use Kubuntu/Ubuntu and Firefox 2.0 you may have noticed problems with Flash enabled web pages causing Firefox to crash. Interim solutions are here and a forum thread about the problem is here.
The interim solution is:
In the /etc/firefox/firefoxrc file, insert this line:
export XLIB_SKIP_ARGB_VISUALS=1
1. Comment out the composite section in x.org
2. Change your color depth to 24 bit, if you haven't already
YMMV. Insert disclaimer here.