When I used Firefox to open a website which is our own website so I surely know we do pay $$ to purchase an external certificate for it. But I got the message "Your connection is not secure" and
"this website uses an invalid security certificate". It also said:
"The certificate is not trusted because it hasn't been verified as issued by a trusted authority using a secure signature." While I clicked "view" for details, it includes a message
"Couldn't verify this certificate because the issuer is unknown". Further investigation shows the certificate was issued by
COMODO RSA CA.
I cannot see why this issuer "COMODO CA" is unknown and not trusted. Can you help me understand this please ? (I understand I can add this site to exception list but I want to know why.) Thanks.