In Kiosk mode, a prestart script can be used to define whether a web session should be triggered when the kiosk application starts. It can obviously also setup a few things before the application startup.
The prestart script is /etc/xdg/webkiosk/prestart. It will be used if it exists and is executable.
If the script returns 0, a web session will be triggered at startup. Any other return code will start the kiosk in display mode.