All those extensions are used for development of chrome and content code.
As of Firefox 33, Venkman *no longer works*, as the APIs which it needs have been removed.
Help make Firefox better. The Add-on Compatibility Reporter enables you to report if the Firefox add-ons that you're using are working properly.
Useful tools for the nightly tester.
A suite of tools for developers.
Inspect the DOM of HTML, XUL, and XML pages, including the mail...
Collections are groups of related add-ons that anyone can create and share.Explore Collections