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.
Allows you to quickly switch to a different language (User Interface, Spell Checker Dictionary and Website content) in your Mozilla application.
As of Firefox 33, Venkman *no longer works*, as the APIs which it needs have been removed.
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.
A suite of tools for developers.
Collections are groups of related add-ons that anyone can create and share.Explore Collections