Cannot now access my trusted website

[willythecat]

Bit of a long shot here.
Used to be able to login to my trusted banking website using older versions of Firefox.
Not sure which versions though, sorry.
Have now upgraded to the latest version of FF (Quantum 61.0.1) and now, when l try to access their site, it comes up
saying "An error occurred while you were trying to login".
All my login details to their site have never been changed, and even they have confirmed this.
Do you need any more info or have you any ideas on what the problem could be?
Regards

[DanRaisch]

Clear the browser cache https://kb.iu.edu/d/ahic#firefox

Delete any cookies relating to the site(s) involved (Tools->Options->Privacy & Security->Manage Data->select and remove anything relating to the bank's site.