[Porygon]

I think this is the check box in question: https://pomf2.lain.la/f/8v4aq9sg.png

It is located at "Settings" -> "Privacy & Security" -> "Website Advertising Preferences" and is checked by default.

[instagib]

I followed the top level comment and added

Boolean dom.private-attribution.submission.enabled False

It disabled the checkbox after updating Firefox. I set it to true to test and it enabled the checkbox also.