How to detect whether default browser has been launched completely using adobe air

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HTML

desktop

AS3

hi all,
how can i detect that default browser has been launched completely, here is my plan.
task is to open a web link when user opens the application and when that web link has been loaded completely in browser i want to close my application
has successfully opened the web link, currently application is closing after certain amount of time which is not that logical.

What I have tried:

import flash.net.URLRequest;
import flash.events.MouseEvent;
import flash.display.NativeWindow;

function evnt_window_initPosition(event:Event) {//starting position
stage.nativeWindow.x=(Capabilities.screenResolutionX - this.width)/2;
stage.nativeWindow.y=(Capabilities.screenResolutionY - this.height)/2;
}
stage.addEventListener(Event.ACTIVATE, evnt_window_initPosition);

var _counter:int=0;
var _myurl:URLRequest=new URLRequest("http://e.dunya.com.pk/index.php?e_name=isl");
 navigateToURL(_myurl, "_blank");
stage.addEventListener(Event.ENTER_FRAME,onenterframe);
function onenterframe(e:Event):void
{
_counter++;
if(_counter==150)
{
NativeApplication.nativeApplication.exit();
}
} 

update:added in code block