Did you check to see if the certificate on both sides matches? If one doesn't match there could be some issues with site usage. If it doesn't you might ask them what other certificates your missing to properly access the page.

There is likely no need for an exception. As you can see in the screenshot, this is about mixed passive content being present on the page. This is content like images on a secure HTTPS page that comes over an open HTTP connection and Firefox warns about this by showing a padlock with an exclamation mark. You can see more detail about what content this is about in the Web Console. *"3-bar" menu button or Tools -> Web Developer *https://developer.mozilla.org/en-US/Tools/Web_Console *Loading mixed (insecure) display content “http://gbot.run/images/gbot_background.png” on a secure page ---- See also: *https://support.mozilla.org/en-US/kb/mixed-content-blocking-firefox *https://support.mozilla.org/en-US/kb/content-blocking *https://support.mozilla.org/en-US/kb/control-center-site-privacy-and-security-firefox