33 Add-ons in this Collection
Firebug by Joe Hewitt, Jan Odvarko, others
Greasemonkey by Anthony Lieuallen, Aaron Boodman, others
The best security you can get in a web browser!
Allow active content to run only from sites you trust, and protect yourself against XSS and Clickjacking attacks.
Automate Firefox. Record and replay repetitive tasks. If you're tired of manually visiting the same sites, filling out forms, downloading files and extracting data, then iMacros is for you! Save time, effort and money with iMacros browser automation!
Fight the text ads! Element Hiding Helper is a companion extension for Adblock Plus meant to make creating element hiding rules easier.
Use tamperdata to view and modify HTTP/HTTPS headers and post parameters...
As of Firefox 33, Venkman *no longer works*, as the APIs which it needs have been removed.
Advanced Eyedropper, Color Picker, Gradient Generator and other colorful goodies...
View HTTP headers of a page and while browsing.
Draw a ruler across any webpage to check the width, height, or alignment of page elements in pixels.
RightToClick by IKRG
Control what gets sent as the HTTP Referer on a per-site basis.