Whois and geo-location
ShowIP : Show the IP address of the current page in the status bar. It also allows querying custom services by IP (right mouse button) and Hostname (left mouse button), like whois, netcraft.
Shazou : The product called Shazou (pronounced Shazoo it is Japanese for mapping) enables the user with one-click to map and geo-locate any website they are currently viewing.
HostIP.info Geolocation : Displays Geolocation information for a website using hostip.info data. Works with all versions of Firefox.
Active Whois : Starting Active Whois to get details about any Web site owner and its host server.
Bibirmer Toolbar : An all-in-one extension. But auditors need to play with the toolbox. It includes ( WhoIs, DNS Report, Geolocation , Traceroute , Ping ). Very useful for information gathering phase
Enumeration / fingerprinting
Header Spy: Shows HTTP headers on statusbar
Header Monitor : This is Firefox extension for display on statusbar panel any HTTP response header of top level document returned by a web server. Example: Server (by default), Content-Encoding, Content-Type, X-Powered-By and others.
People Search and Public Record: This Firefox extension is a handy menu tool for investigators, reporters, legal professionals, real estate agents, online researchers and anyone interested in doing their own basic people searches and public record lookups as well as background research.
Googling and spidering
Advanced dork : Gives quick access to Google’s Advanced Operators directly from the context menu. This could be used to scan for hidden files or narrow in a target anonymously (via the scroogle.org option) [Updated Definition. Thanks to CP author of Advanced Dork]
SpiderZilla : Spiderzilla is an easy-to-use website mirror utility, based on Httrack from www.httrack.com.
View Dependencies : View Dependencies adds a tab to the "page info" window, in which it lists all the files which were loaded to show the current page. (useful for a spidering technique)