The Web Developer extension adds various web developer tools to the browser.
Draw a ruler across any webpage to check the width, height, or alignment of page elements in pixels.
YSlow analyzes web pages and suggests ways to improve their performance based on a set of rules for high performance web pages.
http://yslow.org is the official open source website.
HTML Validator is a Mozilla extension that adds HTML validation inside Firefox and Mozilla. The number of errors of a HTML page is seen on the form of an icon
For Firefox 23+, you need 0.958 (under review)
CodeBurner is a Firefox add-on that integrates with Firebug, to extend it with reference material for HTML and CSS.
Open With Photoshop is a new companion for web and graphic designers to open up any web image with Adobe Photoshop via a single and quick mouse click.
Pixel Perfect is a Firefox/Firebug extension that allows web developers and designers to easily overlay a web composition over top of the developed HTML.
Have you noticed that everybody looks the titles of your open tabs? It has a name: Paranoia! And a solution too: TabRenamizer!
Display horizontal and vertical floating guides, exactly the way you use it in photoshop. Helps improving layout, placing elements in proper grids, laying out elements symmetrically and structure a design.
The cure for tabitis
If you keep tons of tabs open because you want to continue reading them later, Taboo is for you. Taboo lets you save a page for later (taking a screenshot, and using the Session Saver code to remember scroll location and form f...
Collections are groups of related add-ons that anyone can create and share.Explore Collections