Mozilla Firefox is no doubt the best known Internet Surfing Tool till now. Here are some of my favorites add-ons for web development. I hope you will enjoy them all :
2) ColorZilla : This add-on is used to find the color code of the pixel.
3) Tamper Data : Use tamperdata to view and modify HTTP/HTTPS headers and post parameters. Its used to trace and time http response/requests.
5) User Agent Switcher : Adds a menu and a toolbar button to switch the user agent of the browser.
6) Greasefire : It automatically find Greasemonkey scripts on Userscripts.org (requires Greasemonkey).
7) Web Developer : This add-on adds a menu and a toolbar with various web developer tools.
8) Stylish : Customize the look of the application and of websites with Stylish, a user styles manager.
9) Flagfox : Displays a country flag depicting the location of the current website's server and provides quick access to detailed location and webserver information.
10) Image Zoom : As the name indicates, it adds zoom functionality for images.
11) Screengrab : It helps to saves entire webpages as images.
12) Subtile : Subtile is a highly customizable extension to allow people without mozilla development knowledge to create their own (sub)extension, limited to a menu attached to a toolbar button.
13) HTML Validator : It 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 in the status bar when browsing.
14) Extended Statusbar : It adds a statusbar to Mozilla Firefox with speed, percentage, time and loaded size (similar to Opera's one).
16) MeasureIt : Its used to draw out a ruler to get the pixel width and height of any elements on a webpage.
18) Inline Code Finder : Inline Code Finder is an add-on to Firebug, to be able to find HTML elements with any of the below issues:
20) Docked JS-Console : It Docks the JS-Console to the Bottom of the Browser, feel free to have a look at the source (see below) and suggest enhancements.
21) FirePHP : It enables you to log to your Firebug Console using a simple PHP method call.
22) Linkification : It allows you to convert text links into genuine and clickable links.
23) SQLite Manager : This add-on is used to manage any SQLite database on your computer.
24) DOM Inspector : Inspect the DOM of HTML, XUL, and XML pages, including the mail chrome.
25) LoremIpsum Content Generator : It writes loremipsum content for demo pages.
26) ViewSourceWith : The main goal of this add-on is to view page source.
27) View Source Chart : Draws A Color-Coded Chart of a Web Page's Source Code.
28) X-Ray : See the tags on a page without viewing the sourcecode.
29) UrlParams : Shows you the GET and POST parameters of the current website in the sidebar.
31) XPather : This add-on is used to see the Xpath information.
33) TestGen4Web : This records the user action on the page, form fills, etc, and can save the recording to a file, replay it back for you on demand.
34) Adsense Preview : The name speaks it all. Its used to preview the Google ads that may show on any web page.
35) CSSViewer : A simple CSS property viewer.