Open window in the center of the screen

function openWin(url){
 var title = 'Popup Window';
 var w = '550';
 var h = '700';
 
 // Fixes dual-screen position                         Most browsers      Firefox
 var dualScreenLeft = window.screenLeft != undefined ? window.screenLeft : screen.left;
 var dualScreenTop = window.screenTop != undefined ? window.screenTop : screen.top;

 var width = window.innerWidth ? window.innerWidth : document.documentElement.clientWidth ? document.documentElement.clientWidth : screen.width;
 var height = window.innerHeight ? window.innerHeight : document.documentElement.clientHeight ? document.documentElement.clientHeight : screen.height;

 var left = ((width / 2) - (w / 2)) + dualScreenLeft;
 var top = ((height / 2) - (h / 2)) + dualScreenTop;
 var newWindow = window.open(url, title, 'scrollbars=yes, width=' + w + ', height=' + h + ', top=' + top + ', left=' + left);

 // Puts focus on the newWindow
 if (window.focus) {
  newWindow.focus();
 }
}