This looks like a good idea: Introducing State Partitioning.
Sometimes I have a problem where I connect to my server without using a certificate, and then later need to connect using a certificate. But if I’ve already selected not to use a certificate then Firefox doesn’t prompt again so I have been having to restart my browser when that happens, which was a real pain, until now!
To clear your SSL session state in Firefox choose History -> Clear Recent History… and then select “Active Logins” and click “Clear Now”. Then the next time you connect to your SSL server Firefox will prompt for which certificate to use.