This pack includes some Extension/Addons which are useful for developers.
The greatest user script engine on the Internet (a fork of Greasemonkey).
DOM Inspector is a tool that can be used to inspect and edit the live DOM of any web document or XUL application. The DOM can be navigated using a two-paned window displaying a variety of different views on the document and all nodes within.
Automatically find user scripts on Userscripts.org (requires Greasemonkey or Scriptish)
An add-on that helps you test add-ons you create with the Add-on Builder.