If anyone reading this was wondering, like me, "how can I automate diff'ing about:preferences to scan for new checkboxes that were inserted and opted-in without my knowledge?"—you can track the zip archive browser/omni.ja in the Firefox install root, and diff this specific file inside that archive (en-US for example),

    localization/en-US/browser/preferences/preferences.ftl

Which is a plain-text localization file whose version diff will, in this example, contain:

    1274,1282d1217
    < website-advertising-header = Website Advertising Preferences
    < 
    < website-advertising-private-attribution =
    <     .label = Allow websites to perform privacy-preserving ad measurement
    <     .accesskey = a
    < 
    < website-advertising-private-attribution-description = This helps sites understand how their ads perform without collecting data about you.
    <

It might be pragmatic to run this as an OS hook of some kind! Pop a short warning dialog every time Firefox adds a checkbox. Probably much shorter than the complete patch notes.