When I visit a website that requires PKI client certificates Firefox will allow the user to select which certificate to present.
How do you present a different PKI client certificate to a server once you have already presented one, in Firefox?
This blogpost describes what you are looking for:
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.
来源：https://stackoverflow.com/questions/24040662/how-do-you-present-a-different-pki-client-certificate-to-a-server-once-you-have