Wow
I've started using it and I'm really impressed with how fast and responsive it is. Tab switching and startup is instant. On my PC, Chrome lags when scrolling on YouTube or on some sites occasionally, but on Quantum, everything feels buttery smooth. Design is quite nice and not in our face. RAM usage is way lower than Chrome, too.
It'll be released on November 14, but a beta and dev edition is available if you want to test and see for yourself.
https://www.mozilla.org/en-US/firefox/quantum/