Try to rename the cert8.db file (cert8.db.old) and delete the cert_override.txt file in the Firefox profile folder to remove intermediate certificates and exceptions that Firefox has stored. If that has helped to solve the problem then you can remove the renamed cert8.db.old file. Firefox will automatically store intermediate certificates that servers send in the Certificate Manager for future use. You can use this button to go to the current Firefox profile folder: *Help -> Troubleshooting Information -> Profile Directory:<br>Windows: Show Folder; Linux: Open Directory; Mac: Show in Finder *http://kb.mozillazine.org/Profile_folder_-_Firefox