The one, and only benchmark, I care about is battery longevity. Not how long battery lasts before needing charge, but how many years it lasts before dropping to say 80% of original capacity that it needs to be replaced or the phone needs to be updated. Most, if not all, modern phones are performant enough that I won’t need to update for a long time, if not for the battery issues. At least for my use case.
1) Firefox on mobile, with addons. Battery consumption is reduced a lot with less javascript, less ads downloaded, less domains contacted etc. From my quick tests, Firefox was perhaps efficient as a default installation compared to Chrome, or on a wifi with a pihole/nextdns type setup. But out and about in the world
2) Downloaded videos, podcasts, music or books. If I store my stuff on the device by downloading at home on wifi, it uses way less power than streaming over mobile data. My battery lasts for really long time playing videos from storage compared to for example Youtube.
I often wonder how much the battery life of a phone is a function of battery size and phone cpu & screen technology, vs web technologies and website design/performance. I can sort-of control for the latter.