Screensavers no longer work
After updating to firefox 4.0 my screensavers no longer play. I get an error message that the video card needs to be updated.
Opaite Mbohovái (2)
Try running Firefox in Diagnose Firefox issues using Troubleshoot Mode. If it functions properly in that configuration, then one of your add-ons is the culprit.
You can also check the Graphics section at the bottom of the Help > Troubleshooting Information page if there are problems with the graphics display card.