Start Firefox in <u>[[Safe Mode|Safe Mode]]</u> to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem (switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance). *Do NOT click the Reset button on the Safe mode start window or otherwise make changes. *https://support.mozilla.org/kb/Safe+Mode *https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes ----- You can check for problems with the sessionstore.js and sessionstore.bak files in the Firefox Profile Folder that store session data. Delete the sessionstore.js file and possible sessionstore-##.js files with a number and sessionstore.bak in the Firefox Profile Folder. *Help > Troubleshooting Information > Profile Directory: Open Containing Folder *http://kb.mozillazine.org/Profile_folder_-_Firefox Deleting sessionstore.js will cause App Tabs and Tab Groups and open and closed (undo) tabs to get lost, so you will have to create them again (make a note or bookmark them). *http://kb.mozillazine.org/Multiple_profile_files_created