Need help creating an update for a XUL Application

Hello,
I hope this is the right place to ask  this, I originally wanted to post it in the mozilla.dev.tech.xpinstall Google Group, but that Forum seems to be solely populated by Spambots.
I'm currently working on a standalone  Xul Application in which I want to use the Mozilla update mechanism, and I'm having some trouble to get it all running properly. I've got the update server all  setup and the auto updater working so that it checks for updates on the server, but I can't figure out how to create an actual update. I've found this page in the Wiki:
https://wiki.mozilla.org/UpdateGeneration
But it only describes how to use the tools to generate a mar file from a set of files, not what these files look like and how they need to be structured. Can anyone here help me out with this?

Kind regards,
Florian