FoxyProxy Standard https://addons.mozilla.org/en-US/firefox/addon/foxyproxy-standard/
Firebug https://addons.mozilla.org/en-US/firefox/addon/firebug/
Web Developer https://addons.mozilla.org/de/firefox/addon/web-developer/
User Agent Switcher https://addons.mozilla.org/en-US/firefox/addon/user-agent-switcher/
Live HTTP Headers https://addons.mozilla.org/en-US/firefox/addon/live-http-headers/
Tamper Data https://addons.mozilla.org/en-US/firefox/addon/tamper-data/
Hackbar https://addons.mozilla.org/en-US/firefox/addon/hackbar/
WebSecurity https://addons.mozilla.org/en-us/firefox/addon/websecurify/
xAdd N Edit Cookies https://addons.mozilla.org/en-US/firefox/addon/add-n-edit-cookies-13793/
XSS Me https://addons.mozilla.org/en-us/firefox/addon/xss-me/
SQL Inject Me https://addons.mozilla.org/en-us/firefox/addon/sql-inject-me/
FlagFox https://addons.mozilla.org/en-us/firefox/addon/flagfox/
CrytoFox https://addons.mozilla.org/en-US/firefox/addon/cryptofox/
xAccess Me https://addons.mozilla.org/en-US/firefox/addon/access-me/