You know what else uses power? Ads! Particularly the flashy animated ones that fingerprint the browser and hoover up data to prove you're a real human ad impression. I'd wager it doesn't take too many of those slipping through the net to completely undo your "power saving" of a slightly more efficient way of blocking resources.

Has anyone actually done some quantitative research here? I've been using Firefox with uBO for years on Android and of all the apps on my phone, Firefox is not the one that's chewing through battery.