Thanks for your efforts. I cannot image, where to put a delay with my problem. Once the browser is loaded, javascript refreshes the page every 20s on its own. However, after a few hours, Wifi connection is dropped (and obviously lost permanently) and the webpage "freezes".
Concerning autostart on boot with udev. My approach was the following, but it fails

"/etc/udev/rules.d/99-mmcblk0p3-autostart.rules ":
Code:
KERNEL=="mmcblk0p3", ACTION=="add", RUN+="/etc/init.d/startbrowser.sh start"
Is there really no other way? What does the crontab-return: "applet not found" mean by the way? Any way to use cron?