I use the Certificate Patrol and Perspectives Firefox extensions. I've also disabled most of the CAs in Firefox, though Firefox's handling of invalid certificates is pretty bad, so I don't recommend doing this unless you're paranoid.
(If this is OffTopic, let me know.
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The only problem with Perspectives is they only authenticate the first connection, other stuff on the website, pics, forms are still vulnerable. Have you thought about using Convergence instead?
http://convergence.io/