I think the biggest issue is the high variance in performance between browsers overall, coupled with the declarative nature of UI rendering using the DOM. I ha

I think the biggest issue is the high variance in performance between browsers overall, coupled with the declarative nature of UI rendering using the DOM. I have a UI that runs very smoothly in Chrome and Safari (desktop, not mobile). As of Firefox 44, it's unrunnable in Firefox. Why? Don't know. Profiling says we're losing a bunch of time in "layout" but why we're losing a bunch of time in layout, I can't tell. Chrome and Safari just... Don't. And there's so much decoupling between the rendering agents on all three browsers and the language we're using to declare what should be rendered that my best tool after profiling is guess-and-check.