Web development tools are often hard to find. Here is a list of add-ons for Firefox to help make your development allot easier. This selection was hand picked by stylized web. Having all your tools in one browser is a must.

1. CSSMate – online CSS editor extension, similar with EditCSS.
2. ViewSourceWith – let you view page source with external applications.
3. PicLens – transforms your browser into a full-screen 3D experience for viewing web images.
4. FireShot -creates screenshots of web pages which you can modify.
5. SeoQuake – helps with search engine optimization and internet promotion of web sites.
6. Font Finder – simply highlight a single element and right click to view all CSS style.
7. Live HTTP Headers – view HTTP headers of a page and while browsing.
8. Modify Headers – allows you to add, modify and filter http request headers.
9. CSSViewer – simple and useful extension for view any part of CSS property at current pages.
10. EditCSS – it is easy way to view or modifier any stylesheets in the Sidebar just right click.
11. Firebug – view, edit, and monitor CSS, HTML and Javascript live at any web pages.
12. View Formatted Source – Displays formatted and color-coded source for each element.
13. Professor X – let’s you see inside a pages head without viewing the source code.
14. CSS validator – one click to valid a page using the W3C CSS validator.
15. Validaty – provides you a button to validate a page using a validator like validator.w3.org.
16. Html Validator – adds HTML validation inside Firefox and Mozilla.
17. Copy as HTML Link – creates an HTML link to the current page using the selected text.
18. TableTools – sorts, filters or copies any HTML table.
19. CHM Reader – make firefox support Compiled HTML file reading.
20. PageDiff – Helps web developers and designers to see HTML code differences between web pages.
21. Clipmarks – let you save any parts of current web pages.
22. SourceEditor – view and edit source of HTML element.
23. Total Validator – provides true HTML validation using the official DTDs.
24. LinkChecker – check the validity of links on any web page.
25. Web Developer – adds a menu and a toolbar with various web developer tools.
26. Style Sheet Chooser II – allows you to choose author-provided alternate styles for a web site.
27. View Dependencies – lists all files which were loaded to show the page at a tab of info window.
28. Accessibar – enabling easy manipulation of web page display and text-to-speech output.
29. Aardvark – used for cleaning up a page prior to printing it for making the page more readable.
30. JSview – Adds ability to view the source code of external files.

Please feel free to add to this list.