This feature is obsolete. Although it may still work in some browsers, its use is discouraged since it could be removed at any time. Try to avoid using it.
Provides a means for an app to check whether it is installed. This function is typically called from an origin that hosts an app.
navigator.mozApps.amInstalled( callback )
A callback function; it is called with one argument: an
Appobject if the app is installed, or