Privacy Engineer @ Firefox here ... Extensions operate on requests before the platform-level channel classifier. In theory, the platform-level classifier shou

Privacy Engineer @ Firefox here ... Extensions operate on requests before the platform-level channel classifier. In theory, the platform-level classifier should be faster than the webRequest API, but we've not measured it specifically. Running both uBO and and Tracking Protection can give some extra coverage; I've noticed sometimes the Tracking Protection shield pops up even though uBO (and Privacy Badger) are running.