What are your favorite Firefox add-ons for penetration testing?

I am doing a project similar to OWASP MANTRA, but with more flexibility, and better focus on tools, rather than implementing a large number of useless extensions. I have already planned for the project, but I’m seeking the security community opinion for it. Please share all the extensions you use in your daily-tests.
Mazin Ahmed

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My favorite Firefox add-ons for penetration testing:
Firebug is a nice add-on that integrates a web development tool inside the browser. With this tool, you can edit and debug HTML, CSS and JavaScript live in any webpage to see the effect of changes. It helps in analyzing JS files to find XSS vulnerabilities. It’s an really helpful add-on in finding DOM based XSS for security testing professionals.

Web Developer
Web Developer is another nice add-on that adds various web development tools in the browser. It helps in web application penetration testing