Jhaddix wrote an interesting blog posting showing some tools that can be added to firefox to perform penetration testing activities. The ones I like most are FoxyProxy (for TOR navigation), Wappalizer (to recognize content management system), Add N Edit Cookies (to evaluate and inspect cookies) and SQL Inject Me (for SQL Injection).

Please read the article at http://www.securityaegis.com/hacking-with-your-browser/

-- Manuel Humberto Santander Peláez | http://twitter.com/manuelsantander | http://manuel.santander.name | msantand at isc dot sans dot org