It didn't connect to FF site yet. I would say check your security software.

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 error text (SEC_ERROR_UNKNOWN_ISSUER) to show the certificate chain *click "Copy text to clipboard" and paste the base64 certificate chain text in a reply If clicking the blue error text doesn't provide the certificate chain then try these steps to inspect the certificate. *open the Servers tab in the Certificate Manager **Options/Preferences -> Privacy & Security<br>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. You can check this article to see if your security software is covered. *https://support.mozilla.org/en-US/kb/troubleshoot-SEC_ERROR_UNKNOWN_ISSUER