I tried to do this, and I had to switch back. My setup is that I have loads of tabs open, with a vertical tab manager on the side. And FF has a pretty nice extension for that, plus you can take back some screen space by removing the top tabs using some css.
Anyway, when I have the same tabs and extensions in FF as in Chrome, the FF CPU usage is huge. I tried several things from the web, but nothing helped. Now I'm back on Chrome, which is less nice looking and less convenient, but the CPU usage is barely anything.
I use an MBP 15" 2017 with 16g ram, 300+ tabs open as I type, with tree style tabs on firefox. No issues. I would complain about ram usage, but there is certainly no high cpu usage from vertical tabs.
Anyway, when I have the same tabs and extensions in FF as in Chrome, the FF CPU usage is huge. I tried several things from the web, but nothing helped. Now I'm back on Chrome, which is less nice looking and less convenient, but the CPU usage is barely anything.