By default Kiosk Browser disables access to all system menus and dialog's, so when you press and hold the power button you will never see the power off dialog. You can disable this feature under Settings >Advanced > Hide System Dialogs. This will allow the device to be powered down without exiting Kiosk Browser. BEWARE some shutdown dialogs display options such as flight mode, the end user will be able to toggle this and we cannot disable it.
Customer support service by UserEcho