Here is a list of useful Firefox extensions for web developers and programmers.

1. Greasemonkey

Greasemonkey allows users to install scripts that make on-the-fly changes to specific web pages. Greasemonkey can be used for adding new functionality to web pages, fixing rendering bugs, combining data from multiple webpages, and numerous other purposes.

2. Firebug

With Firebug you can edit, debug, and monitor CSS, HTML, and JavaScript live in any web page. Works with: Firefox: 1.5 Ã¢â‚¬â€œ 2.0.0.*

3. Web Developer

Web Developer extension adds a menu and a toolbar with various web developer tools. Works with: Firefox: 1.5 Ã¢â‚¬â€œ 2.0.0.*



4. Html Validator

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 in the status bar when browsing. Works with: Firefox: 1.5 Ã¢â‚¬â€œ 2.0.0.*

5. JavaScript Debugger

JavaScript Debugger provides a powerful JavaScript debugging environment for Mozilla based browsers. Works with Firefox: 0.9 Ã¢â‚¬â€œ 3.0a1

6. MeasureIt

With Measureit you can measure the height and width properties of page elements by drawing a ruler. Works with Firefox: 1.0 Ã¢â‚¬â€œ 2.0.0.*

7. Poster

A developer tool for interacting with web services and other web resources that lets you make HTTP requests, set the entity body, and content type. This allows you to interact with web services and inspect the results. Works with Firefox: 1.5 Ã¢â‚¬â€œ 2.0.0.*

8. CSSViewer

With this extension you can view CSS properties of page elements. Works with Firefox: 1.5 Ã¢â‚¬â€œ 2.0.0.*

9. Load Time Analyzer

The Load Time Analyzer allows developers to measure and graph how long web pages take to load in Firefox. Load Time Analyzer produces graphs that show the occurrence of events such as requests for the page, images, stylesheets and scripts, along with events like the execution of an onload script. Works with Firefox: 1.5 Ã¢â‚¬â€œ 2.0.0.*

10. FireFTP

FireFTP is a free, secure, cross-platform FTP client for Mozilla Firefox. It also includes more advanced features such as directory comparison, syncing directories while navigating, SSL encryption, search/filtering, integrity checks, remote editing, drag & drop, file hashing etc.. Works with: Firefox: 1.5 Ã¢â‚¬â€œ 2.0.0.*

11. FirePHP

Visualize and control your PHP backend from Firefox. FirePHP allows you to take a deeper look at all the work your PHP code does to generate that page you are currently looking at in your Firefox browser.

Update:

12. ColorZilla

With ColorZilla you can get a color reading from any point in your browser, quickly adjust this color and paste it into another program. You can Zoom the page you are viewing and measure distances between any two points on the page. The built-in palette browser allows choosing colors from pre-defined color sets and saving the most used colors in custom palettes.

13. X-Ray

Once installed the X-Ray command is available by right-clicking as well as in the Tools menu. When applied to a page it can help you see how the document was constructed without having to go back and forth between the sourcecode and the page in your browser. Is that list made of li, dd or p elements? Is that an h3 tag or just some bolded text? X-Ray shows you what’s beneath the surface of the page. Works with Firefox: 1.5 Ã¢â‚¬â€œ 2.0.0.* [Thanks Andy]

14. Aardvark

Aardvark allows you to clean up unwanted banners and surrounding “fluff,” especially prior to printing a page. See how the page is created, block by block. View the source code of one or more elements [Thanks Manu]

If your favorite extension is missing from the list, drop me a line i will add it to the list.

Related: Firefox Extension: PicLens, Full Screen Slideshows