Anecdotally my own experience is consistent with this with the same platform+browser combination.
It appears that there are now significant numbers of sites - or at least noticeable parts or features of sites - that rely on Google-specific APIs and haven't been tested on other browsers.
However visiting those sites from Apple devices is often similarly frustrating. I'm not sure this is an anti-Firefox thing. It seems more of a not realising there are other browsers apart from Chromium-based ones thing.
I kinda wondered myself if this was some kind of coordinated effort to make Firefox not work. It wouldn't surprise me if it was later discovered that Google paid some Linux subsystem maintainer to slip in some nefarious code somewhere that altered the way Linux implements rendering specifications ever so slightly such that Firefox appeared broken. Just the conspiracy theorist in me.