SEC_ERROR_UNKNOWN_ISSUER
Firefox doesn't recognise the certificate's issuer
Seen in Firefox
Firefox's equivalent of an untrusted chain: it can't connect the certificate to a trusted root.
Common causes
- A missing intermediate certificate (Firefox does not fetch missing intermediates the way some browsers do).
- A self-signed or private-CA certificate.
- Antivirus or a corporate proxy re-signing HTTPS traffic.
How to fix it
- Serve the full chain from the server.
- Use a publicly trusted certificate.
- Turn off HTTPS scanning in antivirus, or install the proxy CA properly via enterprise policy.
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Related errors
- NET::ERR_CERT_DATE_INVALID · The certificate has expired or is not yet valid
- NET::ERR_CERT_AUTHORITY_INVALID · The certificate isn't issued by a trusted authority
- NET::ERR_CERT_COMMON_NAME_INVALID · The certificate doesn't cover this name
- ERR_SSL_PROTOCOL_ERROR · The secure connection failed during the handshake
- ERR_SSL_VERSION_OR_CIPHER_MISMATCH · No TLS version or cipher in common
- You cannot visit this site right now because the website uses HSTS · HSTS blocks the bypass of a certificate error
- NET::ERR_CERT_REVOKED · The certificate has been revoked by its issuer
- NET::ERR_CERT_WEAK_SIGNATURE_ALGORITHM · The certificate is signed with an insecure algorithm
- NET::ERR_CERT_INVALID · The certificate is malformed or breaks platform rules
- NET::ERR_CERTIFICATE_TRANSPARENCY_REQUIRED · The certificate is not logged in Certificate Transparency
- ERR_SSL_UNRECOGNIZED_NAME_ALERT · The server has no site configured for this hostname
- ERR_SSL_OBSOLETE_VERSION · The site uses an outdated TLS version