Flex :: Osx - Cannot Retrieve The Browser URL For Mac OS Users

I'm developing a very simple flex application on Windows 7 64 Bits.It retrieves the user url and then show it:

public var bm:IBrowserManager;
protected function button1_clickHandler(event:MouseEvent):void{
bm= BrowserManager.getInstance();
bm.init();
Alert.show("Your URL is : " + bm.url);
}

On my Windows 64 Bits machine (Chrome, FF), it works fine and returns the URL.But, when I run my project on a Mac OS X machine (Safari, Chrome, FF) : it shows:

Alert.show(Your URL is : Null);

I think that it cannot retrieve the browser instance or cannot init the browser manager.