Some more info? Version and platform at least? First guess would be permissions of user directory incorrect. [[Profiles - Where Firefox stores your bookmarks, passwords and other user data|Profile Info]] [[Use the Profile Manager to create and remove Firefox profiles|Profile Manager Help]] [[Profiles - Where Firefox stores your bookmarks, passwords and other user data|Directories]]

Check if you have a profiles.ini file in the "%AppData%\Mozilla\Firefox\" folder (Linux: ~/.mozilla/firefox; Mac:~/Library/Application Support/Firefox/). This usually happens when the profile that is marked in the profiles.ini file as Default=1 is missing. *http://kb.mozillazine.org/profiles.ini_file If there is still a profiles.ini file, but the profile folder is no longer present then delete the profiles.ini file to force Firefox to create a new default profile.<br /> Otherwise you can create a new profile and use "Choose Folder" to recover an existing profile. Create a new profile as a test to check if your current profile is causing the problems. See "Creating a profile": *https://support.mozilla.org/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 some files from an existing profile to the new profile, but be careful not to copy corrupted files. *http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox