Firefox often changes their security policies.  This sometimes prevents users from logging in using Firefox but logins with Chrome and IE work properly.

1. In Firefox, select Firefox > Preferences > Advanced > Certificates > View certificates.
2. Select the Server tab.  Delete the entry/entries for your Security Analytics server.
3. Restart firefox.

In Firefox version 33, select Firefox > Preferences > Advanced > Encryption > View certificates > Your certificates.

Select and delete the offending certificates for your server and restart Firefox.