Top 20 Firefox Extensions You Don't Want To Miss

1. Tab Effect - adds a 3D cube transitional effect while switching tabs. It uses Direct X and is only compatible with Windows.
2. Tab Scope - displays a real time thumbnail preview of a web page you hover over its tab. You can zoom into the thumbnail, navigate to links from inside the thumbnail itself.
3. Fission - puts the progress bar inside the address bar Safari style. Changing the progress bar’s colour is also possible.
4. ChromaTabs - colours tabs on Firefox based on a website’s hostname. A similar extension is colorful tabs.
   
5. AgingTabs - highlights the selected tab and makes unused tabs fade with time.
6. Tab Mix Plus - is a must have Firefox addon that can let you manage tabs easily. Tens of features are available and you gotta grab this one.
7. Speed Dial - can help you quickly access your most visited browsers in Opera style.
8. Showcase - shows the thumbnails of all open tabs in a single place - be it on a tab, a window or a sidebar for easy management open tabs.
9. Faviconize Tab - reduces a tab’s with to accomodate only the favicon
10. LocationBar - parses the URL of a web page, adds the ability to navigate around a domain’s directories - go up a level and down.
11. HighlightAll - highlights all occurences of the selected text in a web page. Stylish - allows you tweak the style of webpages easily, and this site has a large base of user created styles for you to use.
12. FoxyTunes - lets you control your media player inside Firefox.
13. Smart Link - makes plain text URLs clickable.
14. DocuFarm - can preview any PDF, PPT, DOC files, etc. preserving their original format.
15. Mouse Gestures - control Firefox by cursor movements.
    
16. PageAddict - displays a summary of how much time you spent on each website along with a graph.
17. SmileyXtra - can easily insert smileys into blog posts, forums etc.
18. Coolris Previews - previews a web page’s content when you hover over a link, and lets you instantly share them with others.
19. FullerScreen - removes tabs and toolbars from the F11 Full screen preview.
20. Firebug - filled with web development tools for you to use.