I was on the phone with a tech support supervisor about a different issue, when I mentioned that I use Firefox.
The supervisor said that they test the website only with EDGE, Chrome, and Safari, but not Firefox. In fact, I have been using Firefox successfully for many years now with Citibank. (The one-step update is a separate issue.) I said something about being very unhappy with this policy. That comment was ignored, but then the supervisor thanked me for being a Citibank customer for 35 years. Oh, the cognitive dissonance. 🤔