Firefox does incidentally error if it sees duplicate serial numbers from the same issuer, though it wouldn't detect this case since the browser won't see precer

Firefox does incidentally error if it sees duplicate serial numbers from the same issuer, though it wouldn't detect this case since the browser won't see precertificates in a TLS handshake. https://support.mozilla.org/en-US/kb/Certificate-contains-the-same-serial-number-as-another-certificate https://support.mozilla.org/en-US/kb/Certificate-contains-th... I don't think this is intended to be a security feature, but simply an error from the depths of NSS where some code uses (issuer, serial) as a unique index.