Michael Parekh outlines his favourites:
1. Google Preview: shows a tiny preview windows of web pages against the list of search results.
2. QuickNote: allows you to quickly grab pieces of text off other applications, and store it in a small, mini-notebook.
3. ForecastFox: graphical personalized weather forecast display in the lower left side of your browser window.
4. Super DragAndGo: allows you to drag and open any link in a web page, by literally dragging and dropping it onto an open area of the page.
5. Yahoo! Companion: gives you a customized Yahoo! toolbar, just as in Internet Explorer (IE).
6. Bandwidth Tester: quick bandwidth tester for your broadband connection.
7. Dictionary Search: Just select a piece of text and ask for a definition.
8. GoogleBar: your favorite Google tool bar now on Firefox from IE.
9. FireFix: fixes common misspellings in the address bar on the fly.
10. LinkPreview: drag the arrow onto a link and it shows you a quick preview window.