Wow, really? I've gone from regarding Firefox as a complete also-ran that I would never use unless necessary, to making it my default browser. Quantum is significantly faster than Chrome on my machine - it does eat more battery, but I feel it's worth it for something this fast & smooth. It feels like I got a new computer. (I'm using a 2012 MacBook Pro with 16GB RAM, still on El Capitan.)

Agreeing with this - I've switched to Firefox on all my devices and I'm incredibly happy with it!

A big understated benefit is being able to run unlock/Adblock on my phone - which has made a big difference in mobile usability.

In my experience, it's spectacular. I've switched back from Chromium to Firefox. It feels snappier than Chrome, and the newer dev tools means I don't miss Firebug.

That's not the normal experience – try uninstalling any extensions and check about:healthreport.

I noticed this a few times when having a massive number of open tabs around (500+). In these cases one process of firefox consumed 100 % CPU and another 40-60 %; restarting Firefox removed the excessive CPU consumption and the spinners as well.

It's not a popular opinion here, but FF57 is bad enough that I have given up on it for the first time in maybe 7 or 8 years. I am now using either Waterfox or Qutebrowser for everything.