Wappalyzer is a browser extension that identifies software on websites.
Skips unnecessary pages on sites like Rapidshare, 4Shared, zShare, Mediafire, and more. Try it out, or watch a demo at http://www.skipscreen.com
Why click through ad-laden pages and wait for countdowns when your computer can do it for you
Color tools for web development.
Color picker and eyedropper + saving colors and trying out colors with drag and drop.
Makes your Bookmarks Toolbar appear in multiple rows.
For Firefox 4 use: Multirow Bookmarks Toolbar Plus, available here:
Extends the function of the drag-and-drop mouse gesture so that it can be used to load URLs, do a web search of selected text on a page, or save an image on a page. The successor to Super DragAndGo.