Does the error page have an "Advanced" button you can click to view more technical information about the reason that Firefox distrusts the certificate? I'll take a guess: a common issue is Firefox not being set up to work with your security software that intercepts and filters secure connections. Products with this feature include Avast, BitDefender, Bullguard, ESET / nod32, and Kaspersky; AVG LinkScanner / SurfShield can cause this error on search sites. ''If you have any of these products:'' This support article will walk you through checking for this problem: [[How to troubleshoot the error code "SEC_ERROR_UNKNOWN_ISSUER" on secure websites]]. If that's not the error code you get, please let us know more details.