To manage all your Firefox addons, extensions and theme, type about:addons in the URL box and hit Enter. You’ll now an elegant interface that lists all your installed Firefox addons with options to disable and configure them. On the left hand menu, you can easily switch to addon, plugin or the theme browser. Clicking on the extensions tab will list all your installed addons. You can enable or disable addons or modify their settings all from this page. The plugin tab shows you the list of other plugins like PDF viewer, Windows media player component etc. The appearance tab lists all Firefox themes installed on your computer.
There is also a handy search bar at the top that you can use to search for themes or addons and install them on the fly. Add-ons manager is a great tool to manage addons, plugins and themes for Firefox browser.