Created attachment 367978 [details]
screenshot of corruption

Description of problem:
When a Firefox window is partially obscured by another window, rapid scrolling of the firefox window causes screen corruption. It looks like an xserver/x driver problem

There's an ubuntu bug report here with the same problem on binary nvidia drivers, so looks more likely to be a general x server issue.
https://bugs.launchpad.net/ubuntu/+source/firefox-3.5/+bug/398583

Version-Release number of selected component (if applicable):
xorg-x11-server-Xorg-1.7.1-7.fc12.i686
xorg-x11-drv-intel-2.9.1-1.fc12.i686

How reproducible:
Sometimes takes a few attempts, and doesn't happen on some websites, but it's consistently reproducible.

Steps to Reproduce:
1. Open firefox at longish website eg slashdot.org, and place a gnome terminal window above it (any will do)
2. scroll down rapidly using mouse wheel. Slow scrolling does not seem to trigger the corruption
  
Actual results:
screen corruption appears above the edge of the gnome terminal window

Expected results:
No screen corruption

Additional info:
see screenshot of corruption