Maybe compare manifest v2 friendly Firefox with uBlock Origin vs eventual Chrome without it :)
In seriousness, though, this is an issue. Elsewhere, I observe arguments about eg userbenchmark rankings, and the comparative relevance of single-core vs multicore performance. Are you playing a game, or rendering video 24/7 -- or running some entirely synthetic workload that allows for a peak performance the real world would never achieve? Same kinda problem.
Situation seems to happen some time after visiting ad-heavy sites (yeah I know I should install an ad-blocker). Have others noticed this? Seems to be Chrome. I also use Firefox and occasionally Safari but have not noticed that with those browsers.