These web apps are quite usable on Chrome and useless lag fests on Firefox.

Do I prefer the modern "let's ship a JS renderer with every webpage" approach? No, definitely not. Unfortunately, quite a few web applications and websites u visit disagree with me.

There's also a perceptable difference in terms of browser responsiveness outside the page itself. Firefox seems to take longer to process UI input in my experience, for reasons I don't entirely get. There's a slight but visible delay before the page starts rendering that Chrome doesn't have, and that small delay adds up when you're working in web UIs fir a significant part of the day.