GWT Window.ClosingEvent setMessage在FF浏览器中不起作用

Question

我可以在IE中覆盖默认消息（ setMessage ），但它在FireFox中不起作用

         Window.addWindowClosingHandler(new Window.ClosingHandler() {
        @Override
        public void onWindowClosing(final Window.ClosingEvent closingEvent) {

          //Working in IE, but not in FF
     closingEvent.setMessage(mailingAddressExtractionMessages.mailingAddressExtraction_unsavedDataAlertMessage());

        }
    });