On my main PC.. 12 yrs old w/ with Win 7 and first gen Core i5 CPU & factory cooler. One intake fan and one outtake fan plus Powersupply fan.

1- idle

2- Random surfing incl youtube vids using Waterfox classic
-----------------------------------------------------------------------------all browsers loaded w/same addons
3- Random surfing incl youtube vids using Vivaldi then latest Chrome

4- idle

They're all within a reasonable range, just surprised that Waterfox runs more efficiently (and is also slightly quicker too). I cleaned and replaced the thermal paste on my CPU a couple of days ago and wondered if it made a difference since last time I did it ~4 years ago. Small difference noted.