I stopped using firefox years ago when chrome got good, and was happy. I wasn't happy with chrome recently (especially memory and CPU usage), and tried switching back to firefox shortly after the quantum release. I've been happily using it since, and have found comparable or lower resource usage. It actually does fine for me, even with tons of tabs (or as fine as any web browser does).

Sure. I hear that, but there have been some specific MacOS issues that have lead to it performing worse on MacOS than on other platforms, and they seem to be getting addressed in the Nightly builds.

In general, I've found it to be much better than Chrome, but as always YMMV.

I've had the same feeling many times with both Firefox and Chrome in the past.

I think in the end that's something that you have to test out for yourself periodically, as it seems to be great differences of which is the best performer across OSs and devices. As a rule of thumb I try to do a short evaluation of each of them every ~5 releases.