Start FF in Safe Mode and try to find the problem. Or you can create a new Profile and see if problem still persists. To start the Profile Manager: Close Firefox completely, Start-> Run-> type firefox -p Firefox Help: How To Manage Profiles Standard diagnostic (Firefox) - MozillaZine Knowledge Base http://kb.mozillazine.org/Standard_diagnostic_%28Firefox%29 I always leave the Default Profile as is and create two more. Depends on what I'm doing, to which Profile I use. You can create a Profile just to test add-ons and themes.