See Enable background updates on Firefox for Windows when Firefox is not running for requirements of the Background Updates feature.

You can also check the Windows Task Scheduler if there's an update task in the Mozilla folder (ghacks.net info).

Hey! Thanks a lot for your answer.

I reinstalled everything and deleted all appdata in this process.

After a new installation of Firefox 96.0.3 all the requirements are met. The default profile used is called "default-release" but that is what Firefox does automatically.

The scheduled task is also there. But it doesn't work. For no, known to me, reason the scheduled task just showed changed times for the next runtime. But the last runtime, the result and the log never changed.

So i forced this task to run immediately and it did! It changed the next runtime, the last runtime, result and log. But did not install the newest version of Firefox. Firefox was not running at this time!

Since then, we are back to changing the next runtime value but nothing else.

Any ideas what i can check / change?

Thanks a lot!

For more information about the Background Updates feature, see https://firefox-source-docs.mozilla.org/toolkit/mozapps/update/docs/BackgroundUpdates.html

You wrote in your original post, We want to use Firefox in our school. The school computers are running Windows 10 in a domain.

Since you are running Firefox in an organizational setting, I'll move this question to the Firefox for Enterprise forum, where you may find more help.

This might be something you would better off opening a bug for (because it sounds like a bug).

https://bugzilla.mozilla.org/enter_bug.cgi

The developers of the feature can help you directly there.