As I am one of the many Firefox users I use many of its add-ons which make my work so much easier. And I would like to share with you list of 30 best handpicked Firefox add-ons, very useful for web designers and developers.
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.
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.