Gmail uses https and it doesn't have a problem with that. So I'm guessing it has something to do with that website's certificate. However it affects only Firefox 4.0 on Ubuntu 11.04. I don't think other browsers are missing any discrepancies because Firefox 4.0 on Windows doesn't complain when I access that site.
I'm unable to add the site to my list of exceptions as I've mentioned in the first post. When I click on the button, nothing happens.
mygre.ets.org uses an invalid security certificate.
The certificate is not trusted because no issuer chain was provided.
(Error code: sec_error_unknown_issuer)
The certificate is definitely valid because it works for Chrome and even Firefox on Windows. There's something about the default Firefox that comes with 11.04 that causes this problem.
The site has this certificate: VeriSign Class 3 Secure Server CA - G2