Have checked in control panel, uninstall program to see if you have a program installed recently that you don't recognize? Have you checked the FF add-ons to see if there is one that you don't recognize? Sometimes when updating a program, if you don't pay attention, they install programs you don't want. You have to pay attention for check boxes that you need to uncheck before you install the update. If all these steps are checked and you have run malware and spybot checking apps, have you tried uninstalling and reinstalling FF? Uninstalling and reinstalling still saves all your add-on and bookmarks.