Some basic Troubleshooting steps you can try: Try to start Firefox in <u>Safe Mode</u> to see whether that works. *Windows: hold down the Shift key while starting Firefox *Mac: hold down the Options key while starting Firefox You can create a new profile to test if your current profile is causing the problem. See "Creating a profile": *https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles *http://kb.mozillazine.org/Standard_diagnostic_-_Firefox#Profile_issues If the new profile works then you can transfer files from a previously used profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over problems. *http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox Boot the computer in Windows Safe Mode with network support (press F8 on the boot screen or hold down the Shift key) to see whether that has effect. *http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/ *http://www.7tutorials.com/4-ways-boot-safe-mode-windows-10