This all mozilla's bragging about speed is premature. They should've published this article after firefox 57 reaches stable.
The current stable release 56 just can't compare to chrome.
Apparently they have decided 57 is stable already but plan to make it official tomorrow.
From my unscientific testing, 57 is only as fast as chrome, while the nightly (59) seems to be faster than chrome. They should have waited until 59 was stable.
I would be using the nightly as my main browser if I didn't have experience with crashes and bugs with nightly versions before.