A possible cause is a problem with the file places.sqlite that stores the bookmarks and the history. *http://kb.mozillazine.org/Bookmarks_history_and_toolbar_buttons_not_working_-_Firefox *https://support.mozilla.org/kb/Bookmarks+not+saved#w_fix-the-bookmarks-file You can also try to repair the places database with this extension: *https://addons.mozilla.org/firefox/addon/places-maintenance/ ---- It is also possible that there is a problem with the files sessionstore.js and sessionstore.bak in the Firefox Profile Folder. 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). See also: *http://kb.mozillazine.org/Session_Restore *http://kb.mozillazine.org/sessionstore.js *http://kb.mozillazine.org/Multiple_profile_files_created ---- If that didn't help then try a new profile. *https://support.mozilla.org/kb/reset-firefox-easily-fix-most-problems