My favorite Firefox add-ons

• Perspectives – Designed by a CMU research team, Perspectives asks and answers important information about self-signed security certificates. Self-signed security certificates are really only an issue if they are part of a man in the middle attack or put up by a malicious user. Thousands of legitimate websites use self signed certificates. Perspectives asks if 1) the same certificate can be seen by notaries in different parts of the internet? Aka: Is this a man-in-the-middle attack? 2) How long have the notaries been seeing this certificate? Aka: Is this a malicious website that was just setup?
• Ghostery – Tracks and notifies you about companies who are tracking you across the internet. It also gives you the choice to turn off their tracking cookies on a per company basis.
• Web Developer – A must have for anyone doing web design.
• Adblock Plus – Ok, I don’t always like seeing ads on the internet and this is a great way to block them. Also gives me the ability to turn ads on for websites I really want to support.

Updates:

• Firebug – An excellent plug-in for debugging web pages. Makes it easy to drill down on particular elements and make live changes to its style.