This increasingly happens to me. It won’t make me switch to Chrome but it’s an extremely worrying sign. I remember the New Yorker subscription page was totally broken in Firefox, and have had issues with login for my credit card

Having been using FF since it went out, I have recently - maybe starting in 2018- been finding some broken sites here and there, mostly new flashy sites, but I found some government, university related manually developed sites with issues in FF.

I've reported a few, and yes, they tell me, the devs do not test their code for Firefox and yes, since then I started to ask about the devs testing here and there, and more and more dev teams are not testing code for FF compatibility.

I know you can not take my word for this, please consider it an opinion, I think FF has started to be phased out in web development, and its compatibility relays mainly now in highly used - fully compatible with FF - frameworks like Wordpress and similar.