Certificate viewer enhancements: PEM format view, file export, trust configuration
Easily upload pictures to alternate hosting. Supports FTP, Imgur and ImageShack.
Places a "Manage Folder" item on the context menu of bookmark folders, which opens the "Places Organizer" expanded to that folder.
View Dependencies adds a tab to the Page Info window, in which it lists all the files which were loaded to show the current page.
Changes the selected search engine in the search bar by scrolling the mouse over the searchbar or search context menu. Also supports keyboard shortcuts ctrl+k and ctrl+shift+k to change the search engine with the keyboard.
A simple extension to send web pages to your Kindle instantly
Adds toolbar button and context menus for invoking the DOM Inspector (DOMi) for either chrome or content elements.
This simple add-on allows you to enter your location using longitude and latitude (available from http://www.whatismygeolocation.com/ for free) for use with geolocation enabled websites.
The about:me page provides a fun way to see personalized patterns and trends in browsing history.
Fission combines address bar and progress bar (Safari style). This makes the progress bar more visible and allows for a nice visual effect.
Cool utility for cleaning up a page (for printing or better viewing) as well as for web development. Displays a red rectangle on the element under the mouse -- hit "w" to go wider (get the containing element), then hit other keystrokes to remove, etc
Platypus is a Firefox extension which lets you modify a Web page from your browser -- "What You See Is What You Get" -- and then save those changes as a Greasemonkey script so that they'll be repeated the next time you visit the page.