Web Developer

The Web Developer extension adds a menu and a toolbar with various web developer tools. Probably the most important browser a developer should have.
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Site Information Tool

Provides information about a webpage (or website) including rankings, domain registration data (whois), IP information, server response and page data, thumbnail and more.
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FireFTP

FireFTP is a free, secure, cross-platform FTP client for Mozilla Firefox which provides easy and intuitive access to FTP servers.
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PHP Developer Toolbar

With this addon you can search functions quickly for the official function description directly into your browser without a new tab.Plus,many tools to help PHP developers.
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Firebug

Firebug integrates with Firefox to put a wealth of development tools at your fingertips while you browse. You can edit, debug, and monitor CSS, HTML, and JavaScript live in any web page.
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YSlow

YSlow analyzes web pages and tells you why they’re slow based on Yahoo!’s rules for high performance web sites.
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Total Validator

Perform multiple validations and take screen shots in one go. This 5-in-1 validator works with external, internal, or local web pages using the Total Validator service or local copy of the desktop tool.
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SEOQuake SEO extension

Seoquake is a Mozilla Firefox SEO extension aimed primarily at helping web masters who deal with search engine optimization(SEO) and internet promotion of web sites. Seoquake allows to obtain and investigate many important SEO parameters of the internet.
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PageDiff

Pagediff is a simple page compare application. It helps web developers and designers to see HTML-code(text) differences between web pages.
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JavaScript Debugger

Aims to provide a powerful JavaScript debugging environment for Mozilla based browsers.
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iMacros

iMacros was designed to automate the most repetitious tasks on the web. If there’s an activity you have to do repeatedly, just record it in iMacros. The next time you need to do it, the entire macro will run at the click of a button.
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Greasemonkey

Allows you to customize the way a webpage displays using small bits of JavaScript.
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Codetch

Get the feel of Dreamweaver in a Firefox extension. Edit your documents right next to your web pages as you surf.
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Addon Developer Helper

This addon helps extension developers by providing easy way to restart Firefox. It also clears XPCOM cache during restart so that developer doesnt need to do it manually. It also helps loading unpacked addon source mainly used during development.
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Aardvark

Cool utility for cleaning up a page (for printing or better viewing) as well as for web development.
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