Are you using the Default Theme? ''If not, switch to the Default Theme.'' If it isn't a problem with a 3rd party Theme, try the Firefox SafeMode. <br /> ''A troubleshooting mode, which disables most other Add-ons.'' # 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 (without the Shft key) to open it again.'' If it is good in the Firefox SafeMode, your problem is probably caused by an extension, and you need to figure out which one. <br /> http://support.mozilla.com/en-US/kb/troubleshooting+extensions+and+themes