Congratulations, it's really an unparalleled performance of parallel performance.
I updated my developer version yesterday and it was as if Firefox - already ludicrously fast compared to before - turned on the turbo booster.
Obviously, I'm not complaining ;)
Guess it must be a specific bug that affected my hardware more than the average person then.
If you want to read the latest info, there is a good status post from a couple of days ago:
https://mozillagfx.wordpress.com/2017/11/27/webrender-newsle...
Of course it could be any incremental improvement instead of some big named feature.