火狐中使用event对象

<script>
/*firefox*/
function __firefox(){
    HTMLElement.prototype.__defineGetter__("runtimeStyle", __element_style);
    window.constructor.prototype.__defineGetter__("event", __window_event);
    Event.prototype.__defineGetter__("srcElement", __event_srcElement);
}
function __element_style(){
    return this.style;
}
function __window_event(){
    return __window_event_constructor();
}
function __event_srcElement(){
    return this.target;
}
function __window_event_constructor(){
    if(document.all){
        return window.event;
    }
    var _caller = __window_event_constructor.caller;
    while(_caller!=null){
        var _argument = _caller.arguments[0];
        if(_argument){
            var _temp = _argument.constructor;
            if(_temp.toString().indexOf("Event")!=-1){
                return _argument;
            }
        }
        _caller = _caller.caller;
    }
    return null;
}
if(window.addEventListener){
    __firefox();
}
/*end firefox*/
</script>