And this is also the release where they drop the support for disabling "Proton" UI and therefore Firefox will no longer respect my system color scheme, and I will lose even more vertical space. Thanks...
Noooooooooooooo. I just updated and ran into this as well. It is still possible to enable the compact mode from about:config but it looks like the new tab style can't be easily changed anymore.
Oh well, see if it still hurts in a few days.