FEBE (Firefox Environment Backup Extension) allows you to quickly and easily backup your Firefox extensions. In fact, it goes beyond just backing up -- It will actually rebuild your extensions individually into installable .xpi files.
Bypass compulsory web registration with the context menu via www.bugmenot.com.
Lets you load pages in IE with a single right-click, or mark certain sites to *always* load in IE.
Get international weather forecasts from AccuWeather.com and display them in any toolbar or statusbar with this highly customizable and unobtrusive extension.
Automatically find user scripts on Userscripts.org (requires Greasemonkey or Scriptish)
Add useful extra features to Gmail, like hierarchical labels, an unread message icon on your browser tab, file attachment icons, and more.
Select text and it's automatically copied to the clipboard. Also pastes on middle click.
(Formerly Local Install) The primary goal of this extension is to provide the tools needed to install and manage extensions and themes locally and tons of other features.
Note: With Toolkit 6.0 Auto Archiving is fully working in Firefox 2.0 and temp...
Implements a useful error page when a website cannot be reached. Will add Try Again, Google Cache, Coralize, Wayback, Ping, Trace, and Whois buttons, along with...
Detects Duplicate Bookmarks when bookmarks are added and specify where is the previous URL. You can also search and delete duplicates URL already in your Bookmarks.
Firefox 13 support is available from http://bookmarkdd.mozdev.org in version 1.1.1.
Note from Mozilla: This add-on has been discontinued. Try Google Minimalist instead.
CustomizeGoogle enhances Google by adding information and removing unwanted information.