FireFox has always been a good browser, but as of the latest release has become THE browser that I use daily. FireFox extensions make it wickedly powerful. As a web developer I find many of the extensions invaluable. Here’s the best of the best…

Web developer`s toolbar

Web Developer`s tool bar probably will become one of the best plugins You`ve ever seen. It comes with his own tool bar that gives many useful tools for analyzing, validating and optimizing web-pages. The great thing about this plugin is that it’s on a few different browsers, so if you switch between them you will be able to use the same plugin on all.

Web Developer Toolbar

Firebug

Firebug is pretty similar as web developer, but it comes across with few different powerful options. You have an ability to edit, debug, and monitor CSS, HTML, and JavaScript right in any web page.

ColorZilla

ColorZilla offers You an advanced eyedropper, colorPicker, page Zoomer and other colorful goodies.

HTML Validator

This plugin displays the number of found errors of the site you are viewing. It adds HTML validation inside Firefox and Mozilla.

YSlow

YSlow, a Yahoo product, analyzes web pages and tells you why they’re slow based on the rules for high performance web sites. YSlow is a Firefox add-on integrated with the popular Firebug web development tool.

This plugin completes FireBug functionality to make Firefox an unbeatable web development tool.

Live HTTP Headers

It allows you to view and analyze HTTP headers (requests and responses) in web-browser with several useful features built-in. It’s great tool for watching a series of HTTP requests and their result codes.

CSSViewer

With this extension you can view CSS properties of related page elements. Very handy, when You got large CSS file with styles overlapping each other, to analyze why something is not displayed in the way You wanted.

FireShot

FireShot is a Firefox extension that creates screenshots of web pages. Unlike other extensions, this plugin provides a set of editing and annotation tools, which let users quickly modify captures and insert text and graphical annotations.

Window Resizer

The Browser Window Resizer is useful for testing different screen sizes.

Supports the 640×480, 800×600, 1024×768, 1280×800, 1280×1024, 1600×1200 resolutions.