The top part of 1st post is the new stuff, the stuff quoted with small font was old information. I marked it now with red letters


Now that you installed that old xulrunner, we first need to get rid of it.
Open terminal with enter:

devel-su (enter --> rootme)
apt-get remove xulrunner*

Then download the new installer: link to 2nd development version (from 1st post). After you installed this deb file, you will get an update notification which you should follow. Otherwise go to settings and update application to search for updates manually. The update will install the new version. After that you can start it from the homescreen icon.