how to remove event listener from fabricjs canvas

I am using fabricjs to build an interactive map in html5.

When the DOM loads, I add my mouseover listener to my fabricjs canvas instance by calling: *my_event_setter( true )*.

Then for the sake of testing, I want to remove the listener once I do my first mouseover by calling: *my_event_setter( false )*. That should thus remove the mouseover listener, but it does not.

my_event_setter = function( toggle )
  { var lvo =  { 'object:over' : function(e){ mouseover_handler( e ) } } ;
    toggle ? my_fabric_canvas.on( lvo ) : my_fabric_canvas.off( lvo ) ;
  } 
mouseover_handler = function( e )
  { my_event_setter( false ) ;
  }