Add TortoiseSVN commands to link context menus to allow easily browsing Subversion repositories. Must have TortoiseSVN already installed.
FireXPath is a Firebug extension that adds a development tool to edit, inspect and generate XPath expressions.
Track Changes in Firebug
Firecookie is an extension for Firebug that makes possible to view and manage cookies in your browser
Detects what javascript libraries are being used on the current page and displays the result as icons with detailed tooltips in the statusbar.
IDE for FireFox plug-in developers and business analysts who create User Interface mock-ups. A WYSIWYG XUL editor