Firefox's problem is the company behind it, not the rendering engine. Firefox is actually a pretty fine browser if you pair it with uBlock Origin and neuter its wide range of user-hostile "features" and keep maintaining that as updates often introduce new "features" you'll need to disable.
Sure. This has happened before and they do eventually fix it. Then a different problem might happen on another page a few months later, and this'll last a few weeks.
Probably best solved by changing banks... firefox works just fine with the ~4 banks I currently use. Though the situation is probably worse on the usa-side of the pond.
Conversely, one of my banks returns a server error if you visit from Chrome. Their "solution" was to put a banner at the top advising an alternate browser.
Not only Mozilla's privacy claims are smoke and mirrors (you need uBlock Origin to get any reasonable privacy on the web today - why is it not included by default despite being permissively licensed?), they have opt-out telemetry (in breach of the GDPR), the browser will load a page with Google Analytics on first run and will nag you with bullshit on nearly every update (and it updates often) not to mention change the UI all the time for no good reason.
Firefox is the most user-hostile free & open-source software that I know of, and more hostile than a lot of paid, proprietary software.
