используйте объект flash.system.Capabilities, чтобы узнать, работаете ли вы под управлением AIR / Flash Player.
var isAir : Boolean = (Capabilities.playerType == "Desktop");
var isFlashPlayer : Boolean = (Capabilities.playerType == "StandAlone");
var isBrowser : Boolean = (Capabilities.playerType == "ActiveX" || Capabilities.playerType == "PlugIn");
var isOther : Boolean = (Capabilities.playerType == "External");