sec_error_revoked_certificate証明書が失効したことを意味します。
Your certificate may be issued by a CA trusted by your browser and valid in time, but the CA may have revoked it, and your client is checking for revocation (which is recommended).
Certificate revocation is a mechanism that makes it possible to invalidate a certificate before its normal expiry time. Checking for revocation can be done via CRL or OCSP by the clients.
Typically, certificates are revoked upon request from the entity corresponding to that cert (i.e. the user or the server admin) if the private key has been compromised, if the CA decides the validating data wasn't sufficient after all, or perhaps automatically if the CA issues another certificate to the same entity.
A possible cause for the problem could be that you might have re-keyed your certificate, thereby making your CA revoke the old one. If you're still using the old one inadvertently (perhaps it's still available to your server in its keystore or equivalent) this error could happen.
Qualys SSL Labs's SSL checker is generally a more complete tool for checking your SSL/TLS configuration. It seems to indicate that your certificate has indeed been revoked.