Earlier quoted context omitted.
Sorry but requiring web devs to ignore the last 4~5 years of progress is just unacceptable. Not that that would fix the situation, there are still rendering inconsistencies between browsers when using stuff like margins floats and tables.
Then do as I: develop in Firefox and if it works there (and isn't a PWA where maybe you get in trouble with Safari?) then it works everywhere. Less testing, less bugs. Whats not to like? Contrast to Chrome first developers who often get caught by cross browsers incompatibilities just like they did back in the days when they were IE first developers : )
There are plenty of gotchas in layout/rendering as well, where either the standard is under specified, or Firefox has some small bugs. Maybe Chrome has many-chrome only APIs, but the developer will always need to test in Chrome and iOS Safari 13 (or whatever your oldest supported iOS version is).
Chrome and iOS are where the users are, and a good website or app should be usable and beautiful for everyone.