google.maps.event.addDomListener mousedown on Firefox

got some problem with this code. The map did not become "undraggable" on Firefox immediately after mousedown on div, but on Chrome is ok.

  google.maps.event.addDomListener(div,'mousedown',function(e) {

    console.log("draggable START ", map.get('draggable') );
    map.set('draggable', false);
    console.log("draggable END", map.get('draggable') );
    google.maps.event.trigger(map, 'resize');   

});

Here is a fiddle https://jsfiddle.net/benderlio/njyeLujs/

FF version is 54.0.1 windows 10 On chrome the map is not draggable after mouse down on white box, but on FF you can move the map and the white box on mousedown

Thanks.