Nice to see Firefox doing this. Supposedly version 70 (next major version) will fix the CPU usage for Firefox on Mac OS (although we'll see).
Can see Apple doing this at some point as well - but its not a free thing to do, so it'd be interesting to see how they did it.
I'm more interested in why the thing performs so poorly.
Whatever the jump to Quantum was seems to be somewhat incompatible on a broad spectrum? When I use it on my 2018 MBP, it doesn't always perform well, *especially* loading reddit with its thumbnails. (Not a slow internet speed thing, just lots of lag.) I don't experience this issue in Chrome.
Also sometimes has issues accessing web pages. I also use it on a custom built desktop PC at home, and it has the website access issue. Doesn't seem to have performance problems there.
I *want* to use it more, but I struggle to support it more.