You can enable/disable webrender in about:config if you want to try it out (gfx.webrender.all). I've switched to it on my laptop (HD Graphics 620, Gentoo Linux). So far so good.
It's a shame it hasn't made it over to Mac yet - graphics card options are a lot more limited there so you'd figure it would be easier to support. But I suppose it's a much smaller market share.
There is a known severe performance issue on MacBooks with retina screens and integrated Intel graphics which this is suppose to be the solution to. Unfortunately this doesn't seem to have driven macOS to be a priority for the rollout.
macOS never seems to be a priority at Mozilla, which kind of sucks. Another power management issue is video decoding. Even when I force YouTube to play .mp4 instead of VP9, my battery use is still 2-3x higher on Firefox than Safari, despite H264 acceleration being easily available via VideoToolBox, and VideoToolBox has been available since 2011 (Lion) or 2012 (Mountain Lion).
I also love the new Firefox Preview on Android, which I believe is the first time that it uses the "Quantum" improvements. I can't really decide if I like the speed or the new design more, though. I like that the private mode can be permanently enabled/disabled with a tap and how tabs are now presented in it. Still looking forward for extensions to be supported.
It may be worth noting that WebRender was already deployed to Win10/Nvidia users in Firefox 67.