The Add-on Builder Beta is a hosted, online build environment, and provides a robust code editor with built-in revisioning, module selection, testing tools and build tools. Add-ons created with the tools are restartless by default, meaning users do not have to interupt their browsing to begin using your add-on right away. Two examples of available add-ons built with these tools are CopyShortURL and Grooveshark Remote Control. You also have the ability to share your work with other developers either selectively or through addons.mozilla.org.”]
Source: https://blog.mozilla.org/addons/2011/06/21/add-on_sdk-builder-_beta/