Comparto con Uds. los addons que más utilizo en Firefox. Las descripciones las tienen dentro de cada link, así como la opción de descarga.
Addons de Seguridad iT y Pentest
Passive REcon
https://addons.mozilla.org/mn/firefox/addon/passiverecon/
FoxyProxy
http://support.microsoft.com/kb/2505743
Https Everywhere
https://www.eff.org/https-everywhere
SQL Inject Me
https://addons.mozilla.org/en-us/firefox/addon/sql-inject-me/
Access Me
https://addons.mozilla.org/mn/firefox/addon/access-me/
Xss Me
https://addons.mozilla.org/en-us/firefox/addon/xss-me/
Add N Edit Cookies
https://addons.mozilla.org/en-us/firefox/addon/add-n-edit-cookies-13793/
Add & Edit Cookies +
https://addons.mozilla.org/en-us/firefox/addon/add-n-edit-cookies-92079/
Live Http Headers
https://addons.mozilla.org/en-us/firefox/addon/live-http-headers/
Network toosl (Router Status)
http://www.brothersoft.com/router-status-216375.html
Wot
https://addons.mozilla.org/es-ES/firefox/addon/wot-safe-browsing-tool/
Active Whois
https://addons.mozilla.org/es-ES/firefox/addon/active-whois-plugin-for-firefo/
WebDeveloper
https://addons.mozilla.org/es-ES/firefox/addon/web-developer/
User Agent Switcher
https://addons.mozilla.org/mn/firefox/addon/user-agent-switcher/
HackBar
https://addons.mozilla.org/mn/firefox/addon/hackbar/
FireCookie
https://addons.mozilla.org/mn/firefox/addon/firecookie
Tamper Data
https://addons.mozilla.org/mn/firefox/addon/tamper-data/
TorButton
https://addons.mozilla.org/mn/firefox/addon/torbutton
NoScript
https://addons.mozilla.org/en-us/firefox/addon/noscript/
Utilitarios Varios - (No de seguridad)
Adblock Plus
https://addons.mozilla.org/es-ES/firefox/addon/adblock-plus/
CoolPreviews
https://addons.mozilla.org/es-ES/firefox/addon/coolpreviews/
TooManyTabs
https://addons.mozilla.org/en-us/firefox/addon/toomanytabs-saves-your-memory/
Picnik
https://addons.mozilla.org/es-ES/firefox/addon/picnik/
Pixlr Grabber
https://addons.mozilla.org/es-ES/firefox/addon/pixlr-grabber/
Image Zoom
https://addons.mozilla.org/es-ES/firefox/addon/image-zoom/
Flash Got
https://addons.mozilla.org/es-ES/firefox/addon/flashgot/
DownThemAll
https://addons.mozilla.org/es-ES/firefox/addon/downthemall/
Download Status Bar
https://addons.mozilla.org/es-ES/firefox/addon/download-statusbar/
ColorZilla
https://addons.mozilla.org/es-ES/firefox/addon/colorzilla/
Febe (Backup Firefox extensions)
https://addons.mozilla.org/mn/firefox/addon/febe/
Reminder Fox
https://addons.mozilla.org/mn/firefox/addon/reminderfox
Capture Fox
https://addons.mozilla.org/mn/firefox/addon/capture-fox/