See if this helps: https://www.bing.com/search?q=MOZILLA_PKIX_ERROR_SELF_SIGNED_CERT

Hi FredMcD Thank you for responding. From reading the steps in the link you sent, this will allow me to get into my printer's web interface but I will always have to ignore the warning and proceed. Am I understanding that correctly? Thank you. Barbara

I don't know. If you want, I can ask another to answer that.

I contacted Epson and they don't have a clue. They blamed it on Firefox. It's not just Firefox. It's Firefox, Microsoft Edge, and even on my phone which has DuckDuckGo and my tablet which has Chrome... I get the same certificate error. Do I need to buy a certificate? I don't even know how to do that. Thank you. Barbara

Is there an 'Advanced' button on the error page ?

Can you post the base64 certificate data if available or a screenshot that shows the certificate if you click "View Certificate" ?

Hi cor-el Yes, there is an Advanced button and I can "accept the risk and continue" so I will do that. It's not like I use that web interface very often. I just needed it to set up the printer and may occasionally go in there to change a setting or something. I just wish I knew how to get a "valid certificate" so I don't have to deal with the warning. Barbara

Press the Advanced button and tell us what it says.

Just fyi, it happens with Microsoft Edge as well and also on my smartphone and my tablet. It's not a Firefox problem. It's something with the printer itself. It says:

Warning: Potential Security Risk Ahead

Firefox detected a potential security threat and did not continue to 192.168.254.71. If you visit this site, attackers could try to steal information like your passwords, emails, or credit card details.

Learn more…

192.168.254.71 uses an invalid security certificate.

The certificate is not trusted because it is self-signed.

Error code: MOZILLA_PKIX_ERROR_SELF_SIGNED_CERT

View Certificate

Web search: https://www.bing.com/search?q=MOZILLA_PKIX_ERROR_SELF_SIGNED_CERT