This has a lot to do with the ever increasing incompetence of web devs than it has to do with Firefox imho. I do performance testing for a living and Firefox creams Chrome on sites where the devs know what they are doing. I don't think of Chrome as faster, but better designed to hide developer mistakes.
Chrome basically keeps the mediocre developer who can't rtfm in business just the same way Microsoft did back in the day. Same pointlessness on Android.
I call it the Trump definition of success - pander to the lowest common denominator and pretend there isn't a price to be paid.
speaking as a web dev who's obsessed with payload size, TTFB and web app performance, i find your statement to be patently false.
i have well-written code that runs very fast in FF, and it always runs even faster in Chrome. not just JS, but also repaint and layout. FF does handle some absurd cases better: giant dom trees & scrolling, RAM usage, lazy tabs.
as a long-time Firefox bug hunter and nightly user, i hope Firefox/Quantum & Servo can reverse this pattern, for sure.
