fullScreen_btn.onRelease = fullScreen_btn.onReleaseOutside = toggleFullScreen;
fullScreen_btn.onRollOver = onRollOverHandler;
fullScreen_btn.onRollOut = onRollOutHandler;

function onRollOverHandler()
{
}

function onRollOutHandler():Void
{
		
}

function toggleFullScreen():Void
{
	if( Stage["displayState"] == "normal"){
		goFullScreen();
	} else {
		exitFullScreen();
	}
}
function goFullScreen():Void
{
	   Stage["displayState"] = "fullScreen";
}

function exitFullScreen():Void
{
   Stage["displayState"] = "normal";
}

AS2: FullScreen

ActionScript