On Firefox I have Adblock Plus, Privacy Possum and Privacy Badger extensions while on Safari I have no extensions. I know they exist but I've never quite been able to figure out how to get them. But this DOES explain why on at least one site I need to use absolutely will NOT let me in with Firefox but with Safari I can get in no problem.
I will definitely be letting them know that if I have to accept exposure to danger to use the site, I won't be using them anymore!
Anyway... based on what I've seen in the documentation it seems to me that LibreWolf may well be worth a try...
I just need to get passed "tweaking" my recent High Sierra upgrade and then I think I'll give it a try!