PrivacyTests.org - https://privacytests.org/
is an interesting website where many privacy aspects of several modern web browsers are compared in a table format. There's no specific test for Firefox with the 'arkenfox' user.js, but If you're a Firefox user who incorporated their configuration, i would guess that the data for Librewolf would compare closely to Firefox with the 'arkenfox' user.js since they're using it in their project.