When an SSL certificate expires FF considers it invalid. It thus shows the "Untrusted connection" page and offers the "Add exception..." dialog. In this dialog "Confirm Security Exception" is greyed out. What the *$&, either allow me to override or don't offer me a choice. Like this it's misleading and angry-making. Also, where the bleep is the mozilla bugtracker upstream? It's not discoverable through the website.
Got any link you care to share so we can debug?
As I tested with your link and it worked fine I am closing worksforme. I am also closing due to fact you have stated on irc that your problem was resolved when resetting the profile.