Out of curiosity, were these high CPU usages on pages with any sort of video playing (culprits for me were Twitch or any live stream)? I was also having these issues, and I want to use Firefox, but the performance in the past was just too difficult.
Google Maps, unfortunately, still made my CPU temp spike 30C+ as soon as I opened it. I use Maps a lot, so this is still a deal breaker for me.
Interesting thing I've noticed: If you don't use chat much and just want the video, try using Twitch's "pop-out" player that opens in its own window- for me this uses far less CPU (even in Chrome)
Chrome's "switch to fullscreen" transition on twitch for me is super laggy though, and I haven't been able to solve that one (Firefox switches to fullscreen smoothly).