I accept your point of view, but the GP was suggesting this is another in a long list of bugs introduced into Catalina. Since, anecdotally, I have first hand experience of this affecting me on other platforms as well as previous macOS versions, logic and reason suggest that the problem was not in fact introduced in Catalina, but lies squarely at the foot of Mozilla. Not everything is fair and balanced. I believe, in this case, that Mozilla are solely at fault, not any of the OS vendors/distributors.

Apologies if this comes across as tetchy; I've been dealing with pettiness and unreasonableness all day. My intention was not to defend Apple (or anyone else) or to besmirch Mozilla. I was merely trying to be helpful by pointing out that this problem affects the same software in the same way on different platform.

No OS should ever fall over because of a misbehaving application. That's one of their fundamental jobs, and failing at it is a defect. The fact that all the major OSes do doesn't vindicate them; nor is it particularly surprising that Catalina doesn't pull away from the pack. It is, however, disappointing.

That is one way of looking at it. I'd argue that it's not a particularly usefully of looking at it. Ideologies aside, your last sentence says a lot. The fact remains that buggy software from a cross platform vendor is causing this issue across the platforms they provide the software for. Be under no illusion, the issue is Mozilla's a no-one else.