Well it may not be cpu performance that firefox struggles with on linux. There is a Touchpad Scrolling Bug for firefox on wayland, that neither GTK nor firefox want to fix (if I remember correctly).
There are some more things like that, that suggest Firefox team focuses more on Firefox for windows than Firefox for linux.
I read about "how much Crap there is in windows" and thought linux should be much smoother to run on my laptop. But it turns out to be the opposite. Firefox for windows works much better than Firefox for linux. For me windows just works. Linux even without telemetry struggles to perform as good as windows.
Well it may not be cpu performance that firefox struggles with on linux. There is a Touchpad Scrolling Bug for firefox on wayland, that neither GTK nor firefox want to fix (if I remember correctly). There are some more things like that, that suggest Firefox team focuses more on Firefox for windows than Firefox for linux.