How to add a self-signed certificate to Firefox besides adding it as a CA?

Question

Since it's not a wise thing to add a self-signed HTTPS cert as a CA to Firefox, my question is: How can I add a self-signed certificate to Mozilla Firefox? (not as a CA). So that I will not be warned when I visit that given HTTPS site, but I will be still protected from MITM attacks, since the HTTPS cert is stored in my browser.

UPDATE: Thanks for the answers, but I cannot make the exception adding permanent. Why is this?

I'm using Firefox 30 on an Ubuntu 12.04/32bit

Solution

Use the "Add an exception" button.

Comments

[user1686]

Firefox exceptions record the certificate, so MITM attacks are impossible after the exception has been added once.

[PTW-105]

@grawity - So every time the cert changes for a site that has an exception in place, the user will receive the cert error? Interesting. Huh, you learn something new every day! Thanks for that clarification.