After extensions have been installed, they can be managed in a number of ways. Right-clicking any installed extension launches a context menu that allows you to set preferences for the extension as well as visit the home page and learn more about the extension author and version number. There are also three context menu items that allow you to move the extension to the top of the list in Extension Manager or up or down. This lets you sort your extensions alphabetically if you wish.
Some extensions actually add a label to the File menu and can be accessed from the File | Tools menu selection. For example, both Mozilla Calendar and ChatZilla can be accessed from File | Tools after they have been installed.