Earlier quoted context omitted.
Performance of Firefox has steadily gotten worse lately. My bank's website has massive lag when scrolling (1 second to redraw? Great!), but it works perfectly fine in Chrome. Firefox also gets into a state where screen updates in Streeview are laggy after anywhere from a few hours to a couple of days, but I can't figure out a way to predictably reproduce it on demand. Meanwhile, Chrome is snappy all the time. I also…
This is probably much more your bank's fault than it is FF. I think Mozilla has badly neglected FF to the point they probably deserve to die so a new org can take their place, but the blame for that most likely falls at the feet of the bank for not testing on FF.
Or they do some batshit insane "polyfill" nonsense that turns the into 56 layers of nested divs behind the hood.
HTML hasn't caught up either, there's no that invokes the native toggle switch that every OS already has, devs are forced to mimic the toggle with 85 layers of nested divs.