FireCAT (Firefox Catalog of Auditing exTension) is a mindmap of the most efficient security auditing extensions for Firefox.
This mindmap is constantly updated to reflect changes in existing add-ons and add new extensions to the list that prove useful for security professionals but also interested users.
Update: The service has last been updated in 2010 which means that it is too old to be of much use. While you may still be able to find some tools that are used today, it is easier to browse the official Mozilla Add-ons store manually instead.
FireCAT 1.4 is currently available for download as a browsable html file or pdf document. The pdf document displays the mindmap of security extensions while the html file displays the extensions in a linked list. I was a bit astonished that the pdf document did not contain links to the homepage of listed extensions as it reduces the usefulness of it quite a bit.
If you are interested in an add-on, you would have to search for it manually if you are using the pdf file.
The mindmap offers an interesting and in depth overview. Second tier categories include Security Audition, IT Security Related, Network Utilities and Information Gathering among others. Each category may contain subcategories or extensions that are listed underneath it.
The best way to work with FireCAT is in my opinion to download both the pdf document and html file.
The pdf document has the advantage that it provides an better overview while the html file contains the links that are needed to download and install the listed extensions.
Update 2: newer versions of the mindmap are only provided as Freemind sources. You need to download and load the source into the application to display the information it contains.
Freemind is an open source mind-mapping application that is written in Java. You can download it from the project website over at Sourceforge.