Maybe web publishers need to let go of this idea of pixel-perfect rendering and identical JavaScript behavior across browsers, and instead just worry about publishing good content. The web is not Adobe InDesign or Photoshop. At its essence it is a system for publishing text and hyperlinks that point to other content. Get the content right and don't worry so much about whether the scrollbar is 2 pixels thick or 3.
I, too, remember how this opinion was repeated as nauseam about a decade ago. It didn’t make much sense then, and even less now.
Nobody today expects identical rendering: people are used to responsive websites, native widgets etc. The problem people are actually experiencing (far less now than in the past) were more serious, such as z-axis ordering differences resulting in backgrounds obscuring content.
For JavaScript, I struggle with how non-“identical behavior” would express itself, except as a blank page and a small red icon in devtools.
