Open HTML select dropdown programmatically

I am trying to open programmatically a select box (html dropdown/select box, notfile picker) in javascript using this code

http://ift.tt/1HoAWtC

function openSelect() {

     var element = document.getElementById("s")
       var worked = false;
     if (document.createEvent) { // all browsers
         var e = document.createEvent("MouseEvents");
         e.initMouseEvent("mousedown", true, true, window, 0, 0, 0, 0, 0, false, false, false, false, 0, null);


         worked = element.dispatchEvent(e);

     } else if (element.fireEvent) { // ie
         worked = element.fireEvent("onmousedown");
     }

 }

but only seems to work in chrome. Not in ie 11 not in firefox.

Anyone any ideas?

Thanks