Bookmark on the side is a sidebar feature. As to your FF having issues running without someone there to see what is going on that makes this harder to know what happened to the FF or what installed and caused the problems. Couple link to read over and see if they can isolate the issues. https://support.mozilla.org/en-US/kb/troubleshoot-and-diagnose-firefox-problems https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode And worse comes to worst is to completely uninstall of Firefox and deleting the Firefox/Mozilla browser folder to remove any offending problems. But before going this route make sure to backup your profile, data, bookmark, logins so you can by using Firefox FAQ to backup and then restore them back. As since there is no history of your computer or OS or what version of Firefox no one can know what is the causes or if Addon/Extension is causing the problem. But if you use Firefox trouble shooting mode and it runs fine then that would mean Addon/extension issue and then to disable all of them and turn on/off one at a time to find the offending software and remove it while running Firefox browser each time to insure it working. Otherwise if the problems remains in TroubleShooting mode that would mean a corrupted Firefox browser/folder and only fix is to completely uninstall Firefox and reinstall it again and hope the issue is gone.