Last time I tried v57 it was the same speed as v55 and prior that already have E10s for year or two. Where as v56 and v57 have changes to API and addons despite claiming support for v57 do not work anyway.
Locked at v55 waiting for addons and FF to get their stuff together and cooperate.
FF has been fine since moving to 64bit and especially after multi threading with E10s, didn't see any speed or memory reduction with the so often mentioned v57 with some fancy name given to it I don't remember quantum or what is it. It's the same as prior versions, just reskinned and addon API changed.
Hundreds of tabs work fine in v55, quick start up and exit, low memory foot print. Chrome can't do this, it doesn't have the settings and even if it had their multi threading is multi processing = R.I.P. RAM anyway.
So why would anyone use v57 now? Runs the same as older versions but addons don't support it yet.