How did you clear that data? Via Firefox built-in means or via external software? You should always do this via Firefox and that shouldn't cause problems. If you use external software then there is always a risk. Try to start Firefox with the about:blank page by creating a copy of the current Firefox desktop shortcut. Add a space and <b>-url "about:blank"</b> to the target field in the Properties. ---- Create a new profile as a test to check if your current profile is causing the problem. 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 files from a previously used profile to the new profile, but be cautious not to copy corrupted files to avoid carrying over problems. *http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox