Mozilla claims that Firefox Quantum will be twice as fast as Firefox 52 based on the Speedometer Benchmark. Firefox Quantum will have a new sexy look and feature many changes under the hood.
Mozilla also claims that Firefox Quantum will be faster than Google Chrome and 30% more memory efficient than Chrome. They have released a comparison video where they are comparing loading times of webpages with Firefox Quantum and Google Chrome. Firefox Quantum seems to have the advantage on most webpages.
Currently the new browser is in open beta and you can expect bugs and complications. The official release is targetted at 14 November 2017. For Desktop, Android and iOS.
Sources:
https://blog.mozilla.org/blog/2017/09/26/firefox-quantum-beta-developer-edition/
https://www.mozilla.org/en-US/firefox/quantum/