FoxyProxy is an advanced proxy management tool that completely replaces Firefox's limited proxying capabilities. For a simpler tool and less advanced configuration options, please use FoxyProxy Basic.
Xmarks is the #1 bookmarking and open tab add-on. Keep your bookmarks, and open tabs backed up and synchronized across computers and browsers. Mobile phones with Premium access. Utilize LastPass to sync passwords!
InFormEnter adds a small, clickable icon next to every input field in a web form, from where you can select the item to be inserted - no typing required.
Useful tools for the nightly tester.
Select text and it's automatically copied to the clipboard. Also pastes on middle click.
Note from Mozilla: This add-on has been discontinued. Try DragIt instead.
Allows you to open links in new tabs, and do more with drag and drop gestures easier.