Web Developer Tool Bar

A must needed tool bar for developers,The Web Developer extension adds a menu and a toolbar to the browser with various web developer tools. It is designed for Firefox, Flock and Seamonkey, and will run on any platform that these browsers support including Windows, Mac OS X and Linux.

Features

The Web Developer extension adds a menu and a toolbar to the browser with various web developer tools like:-
View Anchor Information
View Color Information
View Document Outline
View Document Size
View Generated Source
View Meta Tag Information
The 'Clear Session Cookies'
The 'Display Element Information'
The 'Display Image File Sizes'
The 'Display Ruler'
The 'Display Topographic Information'
The 'Edit CSS' feature
The 'Show Comments'
Disable Proxy
Disable Strict JavaScript Warnings
Display Abbreviations
Display Page Magnifier
Display Page Validation
Outline Images With Oversized Dimensions
Outline Links With Ping Attributes
Outline Table Captions
Validate Local Accessibility
Clear All Private Data
Convert Select Elements To Text Inputs
Delete Path Cookies
Disable External Site Images
Disable Meta Redirects
Disable Minimum Font Size
Disable Print Styles
Display Alt Attributes
Display Div Order
Display Element Information
Display Line Guides
Display Object Information
Display Stack Levels
Display Table Depth
Display Table Information
Display Title Attributes
Edit HTML
Enable Form Fields
Make Frames Resizable
Make Images Full Size
Outline All Images
Outline Background Images
Outline External Links
Outline Headings
Outline Positioned Elements
Show Hidden Elements
Show Window Chrome
Small Screen Rendering
And many more..

Get it here
https://addons.mozilla.org/en-US/firefox/addon/60
http://chrispederick.com/work/web-developer/

Some other Web Development firefox Add-ons
https://addons.mozilla.org/en-US/firefox/browse/type:1/cat:4
https://addons.mozilla.org/en-US/firefox/addon/1843