If you receive the following error in firefox when you try to visit a secure web site:
https://mywebsite.com/index.php Secure Connection Failed An error occurred during a connection to mywebsite.com. Issuer certificate is invalid. (Error code: sec_error_ca_cert_invalid)
You have to restore default SSL security certificates/authorities/servers in Firefox.
1. Click Help menu.
2. Click Troubleshooting information.
3. Click Show folder button.
4. Close Firefox.
5. Rename cert8.db to cert8.db.old
6. Open firefox