Rename (or delete) secmod.db (secmod.db.old) and maybe also cert8.db (cert8.db.old) in the [http://kb.mozillazine.org/Profile_folder_-_Firefox Profile Folder] in case there is a problem with the files. The file ''cert8.db'' stores your user certificates, so if you have user certificates then you may want to export them now and import them after having removed cert8.db. See Tools > Options > Advanced > Encryption: Certificates: View Certificates If that works then you can delete the renamed files or undo the changes if you want to revert the process.