Three browsers, two devices, three environments and four roles is seventy-two combinations. Nobody chose that. It arrived one reasonable decision at a time.
The senior job here is to make the multiplication visible and then spend it deliberately.
Start from what failures you are actually buying protection against.
Cross-browser bugs are real but rare, and they cluster. Layout and CSS, date and number formatting, media playback, and very new web platform features. Business logic is the same JavaScript everywhere, so it does not differ by engine.