Today 10 years ago I went to Poland to buy a Phone with pre installed #Firefox OS on. The Phone was a Alcatel One, so very shitty. Two years later I installed Firefox OS on my Nexus 5 instead.
It was a very good concept, but sadly rolled out on too shitty hardware so it never caught on.
It's incredibly impractical. The website requires me to go through 2 different 2fas on top of the username/password. If I used it 1/2 times a month, fine. But I use it far too often for it to be usable without the app honestly. Plus, my VPN is pretty much always on on my desktop. And my bank really, really doesn't enjoy that and I regularly get locked out and have to make a phone call to get unlocked. On the phone with the app, it's not an issue.
So until that's solved (proably won't be, it's not their fault), that's a no for me.