The nsIDOMGeoPositionCallback interface is called when updated position information is available.  You need to implement this interface to accept callbacks after using nsIDOMGeolocation.watchPosition().

dom/interfaces/geolocation/NsIDOMGeoPositionCallback.idlScriptable
Please add a summary to this article.
  Last changed in Gecko 1.9.1 (Firefox 3.5 / Thunderbird 3.0 / SeaMonkey 2.0)

Method overview

void handleEvent(in nsIDOMGeoPosition position);

Methods

handleEvent()

Called when new position information is available.

void handleEvent(
  in nsIDOMGeoPosition position
);
Parameters
position
An nsIDOMGeoPosition object indicating the updated location information.