Do you have ESET security software?

You can retrieve the certificate and check details like who issued certificates and expiration dates of certificates.

• click "Advanced" to expand the error message
• click "Add Exception" to open "Add Security Exception"

If this isn't possible then open "Add Security Exception" by pasting this URL in the location/address bar and paste the URL of the website (https://xxx.xxx) in it's location field.

• chrome://pippki/content/exceptionDialog.xul

Let Firefox retrieve the certificate -> "Get Certificate"

• click the "View" button and inspect the certificate
  check who is the issuer of the certificate

You can see details like intermediate certificates that are used in the Delete tab.

Who is the issuer of the certificate?

Cor-el

Thanks for your advise. the problem was Eset! as in SSL/TLS filtered application I removed the Firefox and now is working fine. But is it make my computer vulnerable to any threat or not?

Pejijan said

the problem was Eset! as in SSL/TLS filtered application I removed the Firefox and now is working fine. But is it make my computer vulnerable to any threat or not?

ESET normally intercepts all your browsing requests and filters server responses for security threats. With SSL/TLS filtering turned off, ESET will only filter regular HTTP connections, and not HTTPS connections. That's a significant number of sites that won't be filtered, including Facebook, Google, and other biggies. But I don't know how often this filter actually blocks anything. ??

If you want to make this feature work in Firefox, I think the steps are in past threads (I'd need to search them up...).

See also "The Risks of SSL Inspection":

• https://insights.sei.cmu.edu/cert/2015/03/the-risks-of-ssl-inspection.html