I discovered a certificate using a "public private key", in this case a key that is part of OpenSSL's test suite. This would not necessarily be a particularly interesting event. It happens every now and then that people use private keys they find on the Internet, likely due to a lack of understanding of public key cryptography. I usually report them for revocation, and move on. However, this one is a bit more unusual. It has been issued by the CA Digicert - for a domain owned by Digicert. https://groups.google.com/a/mozilla.org/g/dev-security-policy/c/d21mtDJ7YXQ