User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.12) Gecko/20101205 Gentoo Firefox/3.6.12 Build Identifier: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.12) Gecko/20101205 Gentoo Firefox/3.6.12 Firefox should highlight if an SSL certificate changes for a site. Possibly with options to only highlight if it changes a long time before it expires or if the authority changes. Reproducible: Always Steps to Reproduce: 1. Go to a site. 2. Man in the middle the site with another "valid" certificate. 3. Revisit the site. Actual Results: The site is loaded silently with the MITM able to see the traffic. Expected Results: Firefox should highlight that a certificate changed. This functionality is implemented (albeit not very reliably) in the CertPatrol extension but it should be in the core.