Behind the Bikeshed

This mockup shows that the status bar by default is invisible if the add-ons are not active.  If the user hovers over the status bar, it appears semi-transparently and add-on icons can activated via a click.  Once the API for rich interactive panels is added, this could be a resultant action.  The user can “pin” the bar by clicking on a pin icon.  If a particular add-on is acting on a page, the status bar shows by default with the active add-on’s icon opaque and slightly glowing.