This isn't quite as simple. Firefox on Android will only install a subset of extensions from addons.mozilla.org, based on an allow-list maintained by Mozilla.
But other extensions on AMO (and therefore already complying with Mozilla's policies) work satisfactorily when installed in Iceraven (a fork of Firefox on Android).
So this shows that the limited list of extensions available for Firefox on Android is not limited by technical reasons (“where possible”), but by Mozilla's choice.
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But I agree with the broad point: yes, Mozilla is pretty sketchy, but Google is orders of magnitude sketchier.