Unknown Certificate Issuer

The certificate authority that issued the server's TLS certificate is not trusted by Firefox's certificate store, often seen with self-signed certificates or an incomplete chain.

References

searchfox.org/nss/source/lib/util/secerr.h
support.mozilla.org/en-US/kb/what-do-network-error-messages-mean

In this namespace

← previous SEC_ERROR_EXPIRED_CERTIFICATE Certificate Expired next → SSL_ERROR_BAD_CERT_DOMAIN Certificate Domain Mismatch

NS_ERROR_REDIRECT_LOOP NS_ERROR_UNKNOWN_HOST NS_ERROR_UNKNOWN_PROTOCOL NS_ERROR_UNKNOWN_PROXY_HOST SEC_ERROR_EXPIRED_CERTIFICATE SEC_ERROR_UNKNOWN_ISSUER SSL_ERROR_BAD_CERT_DOMAIN