No, absolutely with you on this! I didn't mean that I don't understand because you can simply change the string (because agreed, most people don't know and can't be expected to know about this).

What I meant is: in 20 years of FF usage, I have come across ~5-10 broken sites (legitimate or UA, doesn't matter).

So I can't understand when people say they can't use FF because it breaks so many sites.