the firefox browser is telling our customers who use our website that it is an unsecured site when it isn't

This Connection is Untrusted You have asked Firefox to connect securely to vault3.server-security.com.au, but we can't confirm that your connection is secure. Normally, when you try to connect securely, sites will present trusted identification to prove that you are going to the right place. However, this site's identity can't be verified. What Should I Do? If you usually connect to this site without problems, this error could mean that someone is trying to impersonate the site, and you shouldn't continue. Technical Details vault3.server-security.com.au uses an invalid security certificate. The certificate is not trusted because the issuer certificate is unknown. (Error code: sec_error_unknown_issuer) I Understand the Risks