Tuesday the 14th of November 2017 was the day that Mozilla released their newest (and fastest) release of Firefox until now: Firefox 57, Quantum. Reading the "marketing" text about more speed, less memory usage and a more beautiful browser, I was skeptical. After a quick download off their archive servers, I was very pleasantly surprised.
Firefox Quantum is quite a bit faster than the previous versions, even I notice it. I have not really checked the memory usage, but it seems to be a bit more efficient (my virtual machine with Firefox in it has more free RAM available than before whilst browsing online). The GUI got a slight overhaul and made me think of the Atom editor. This seems to be deemed "beautiful" nowadays, fine, I do not mind (or care much for that). The search function in the preferences menu is nice though.
I'd really suggest you try it out yourself, it's worth it.