Firefox has indeed come a huge way in the last two years.
- It's multi-process architecture redesign _really_ improved performance (it's like using a whole new browser, honestly. If you haven't at least tried it, it's worth a shot).
- Mozilla's commitment to privacy (I know in the eyes of some, their current commitment isn't enough) is the best option you have outside of Safari / macOS.
- In version 71, battery drain on macOS is indeed largely improved
- The multi-account containers, anti-tracking and anti-fingerprinting are a breath of fresh air (yes, I know they are not perfect). I am satisfied that each time I sign on to YouTube, my recommended videos are just a bunch of random things.
- Firefox looks like it will remain one of the only browsers that fully supports current ad-blocking technology. (Yes, I know about Brave, but that's besides the point).
- The devtools section has seen a lot of attention that easily brings the experience on par with Chrome (in my experience).
- Firefox on Android with AdBlock drastically speeds up browsing the internet on mobile devices.
But, despite all of these good points, the browser still feels... clunky.
Sure, the UI performance drastically improved since Quantum, but really, open a fresh Firefox window, browse to your favorite site and click around a little. Then, try the same thing with Chrome / Chromium / Edge. I don't know exactly what it is, but these other browsers just feel that little bit "smoother" or more "modern".
Say what you will about Google and Chrome. But morals aside, in my opinion, there's no denying they built a world-leading software product that has vastly increased the perceived quality expectations of browser users.
Note: I still remain a primary Firefox user. The eye-candy is nice, but for me it's not worth sacrificing all of the other pros of Firefox.
EDIT: grammar