Start Firefox in <u>[[Safe Mode]]</u> to check if one of the extensions is causing the problem (switch to the DEFAULT theme: Firefox (Tools) > Add-ons > Appearance/Themes). *Don't make any changes on the Safe mode start window. *https://support.mozilla.com/kb/Safe+Mode ---- Clear the cache and the cookies from sites that cause problems. "Clear the Cache": * Tools > Options > Advanced > Network > Offline Storage (Cache): "Clear Now" "Remove Cookies" from sites causing problems: * Tools > Options > Privacy > Cookies: "Show Cookies" ---- You can also try to delete the files sessionstore.js [2] and sessionstore.bak in the Firefox Profile Folder. * Help > Troubleshooting Information > Profile Directory: Open Containing Folder * http://kb.mozillazine.org/Profile_folder_-_Firefox If you see files sessionstore-##.js with a number in the left part of the name like sessionstore-1.js then delete those as well. 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). See also: * [1] http://kb.mozillazine.org/Session_Restore * [2] http://kb.mozillazine.org/sessionstore.js ---- Do a malware check with some malware scanning programs.<br /> You need to scan with all programs because each program detects different malware.<br /> Make sure that you update each program to get the latest version of their databases before doing a scan.<br /> * http://www.malwarebytes.org/mbam.php - Malwarebytes' Anti-Malware * http://www.superantispyware.com/ - SuperAntispyware * http://www.microsoft.com/windows/products/winfamily/defender/default.mspx - Windows Defender: Home Page * http://www.safer-networking.org/en/index.html - Spybot Search & Destroy * http://www.lavasoft.com/products/ad_aware_free.php - Ad-Aware Free See also: * "Spyware on Windows": http://kb.mozillazine.org/Popups_not_blocked