Do you mean this: https://github.com/mozilla/policy-templates#appautoupdate

My interpretation of the "Compatibility" line is that it lists the earliest compatible version(s), and that unless it lists a last compatible version, the policy is still enabled in Firefox currently.

Well, it's giving me all sorts of errors on intune so I'm assuming that's not the earliest compatible version.

What kinds of errors?

Note: I am not personally familiar with Intune, so someone else will need to help you interpret what you're seeing.

The template definitely is supposed to work with Intune, and in case the README is incomplete, you can cross-check this article: Manage Firefox with Microsoft Endpoint Manager (Intune).

What specific errors?

“Remediation Failed” is the error.

Only Firefox ADMX policy works. Managed bookmarks, auto updates, etc don’t work.

So you can ingest the ADMX but adding individual policies per the instructions here:

https://support.mozilla.org/en-US/kb/managing-firefox-intune

isn't working?

Can you post one of the policy that is failing?