nsIDOMEventListener in Firefox 3.0

 The nsIDOMEventListener interface is a callback interface for
 listening to events in the Document Object Model.

 For more information on this interface please see 
 http://www.w3.org/TR/DOM-Level-2-Events/

 @status FROZEN


 This method is called whenever an event occurs of the type for which 
 the EventListener interface was registered.

 @param   evt The Event contains contextual information about the 
              event. It also contains the stopPropagation and 
              preventDefault methods which are used in determining the 
              event's flow and default action.