Try to delete the profiles.ini file to force Firefox to create a new default profile. *http://kb.mozillazine.org/profiles.ini_file *http://kb.mozillazine.org/Profile_folder_-_Firefox Can't you launch the Profile Manager by adding a space and the -P switch to the command line? 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 *http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox