Earlier today we ran into a problem after we installed new certificates issued by Comodo High Assurance on our servers.  The problem was with Firefox, where it was displaying "The certificate is not trusted because the issuer certificate is unknown.(Error code: sec_error_unknown_issuer)".  Other browsers, including IE and Chrome did not have problems.


Searching the web, the solution was to install the intermediate/chain certificate on our web server.  What we couldn't figure out was why it didn't happen to other browsers (apparently they already had those certs pre-installed, where Firefox didn't), and more importantly, how to install them on our web servers.

After playing around with different pound options, we found that we needed to have the Comodo CA cert added to the "Cert" file.  The Comodo CA certificate also had to be at the end (after the private key and our cert). 

Granted I know very little about SSL, but wanted to put this out there, in case somebody runs into a problem with CA certificates which are not preinstalled on the browser.