Firefox finds every site - even Mozilla - insecure
Firefox finds every site "insecure" saying it has been configured wrong - even for its own site (Mozilla.com).
There is security software like Avast, Kaspersky, BitDefender and ESET that intercept secure connections and send their own certificate.
- uses an invalid security certificate SSL_ERROR_BAD_CERT_DOMAIN
- configured their website improperly
How to troubleshoot the error code "SEC_ERROR_UNKNOWN_ISSUER" on secure websites https://support.mozilla.org/en-US/kb/troubleshoot-SEC_ERROR_UNKNOWN_ISSUER
You can check if there is more detail available about the issuer of the certificate.
- click the "Advanced" button show more detail
- click the blue SEC_ERROR_UNKNOWN_ISSUER message to show the certificate chain
- click "Copy text to clipboard" and paste the base64 certificate chain text in a reply
If clicking the SEC_ERROR_UNKNOWN_ISSUER text doesn't provide the certificate chain then try these steps to inspect the certificate.
- open the Server tab in the Certificate Manager
- Options/Preferences -> Privacy & Security -> Certificates: View Certificates -> Servers: "Add Exception"
- paste the URL of the website (https://xxx.xxx) in it's Location field.
Let Firefox retrieve the certificate -> "Get Certificate"
- click the "View" button and inspect the certificate
You can see detail like the issuer of the certificate and intermediate certificates in the Details tab.