Do you have that problem when running in the Firefox SafeMode?<br/> ''A troubleshooting mode.''<br /> You can open the Firefox 4.0 SafeMode by holding the '''Shft''' key when you use the Firefox desktop or Start menu shortcut. Or use the Help menu item, click on '''Restart with Add-ons Disabled...''' while Firefox is running. <br /> ''To exit the Firefox Safe Mode, just close Firefox and wait a few seconds before using the Firefox shortcut to open it again.'' If not, see this: <br /> http://support.mozilla.com/en-US/kb/troubleshooting+extensions+and+themes

The hardware acceleration was the trick. Thanks