More really decent Firefox Addons...

• ColorZilla
  ...provides an eyedropper, like photoshop

• ThrashMail.net
  ...dummy email address generator

• FFmyIp
  ...displays your machine's ip address

• LoremIpsum Content Generator
  ...generates lorem ipsum text for your web designs

• FireFtp
  ...ftp file manager addon for firefox

• FireBug
  ...the best web debugger in history

• Web Developer Toolbar
  ...very competent web design addon

• Delicious Toolbar
  ...add your del.ici.ous links to firefox

• YSlow
  ...addon to FireBug, ranks your sites performance and offers solutuions to speed it up

• FireCookie
  ...addon to FireBug, gives you total control of cookies

• Tails
  ...Microformats statusbar extension, lights up when it sees microformat code in a webpage

• PicLens
  ...instantly transforms your browser into a full-screen 3D experience for viewing images across the web

All tested to work with the latest Firefox 2.0.0.11 build.

Unit Testing

• Selenium IDE - Firefox Plugin