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.