Your browser trusts many certification authorities and sub-authorities quietly, every time you enter an HTTPS website. This add-on for advanced users reveals when certificates are updated, so you can ensure it was a legitimate change.
KeyManager Tool: Firefox Add-on for Key Generation, Certificate Enrollment, CRL Signing, and Identity and Authority Delegation
Securely bypasses Firefox HTTPS security errors by verifying certificates using a collection of Network Notaries. See http://www.cs.cmu.edu/~perspectives/