If you receive a warning Your Connection is not secure, SEC_ERROR_UNKNOWN_ISSUER when you visit a site using Firefox, you can resolve this issue by following this post.

If you receive error message, MOZILLA PKIX ERROR MITM DETECTED or ERROR SELF SIGNED CERT or SEC ERROR UNKNOWN ISSUER, then it means that Firefox is not able to trust certificates issued on secured ...

Mozilla has halted the automatic updates to Firefox 65 as users are unable to browse web sites due to certificate errors. These errors are being caused by conflicts between various antivirus ...