Wow finally! I have to admit while I love Firefox using it on macOS just feels crappy as it is so out of place. I am a huge user of the macOS "Look Up" content menu feature and it being missing in Firefox always frustrates me.
As silly as it sounds this might just be enough to get me to use Firefox as my main browser on macOS. I have played around with Nightly recently and love the new UI design. Can't wait for this to hit release.