Tried that on a "sandbox" computer. Funny, but first notice I saw when FF 57 started for the first time, was its turtle warning: "Mozilla Firefox seems slow... to... start".
So much for super-duperfast Quantum. And I only had DuckDuckGo add-on enabled.
Not impressed, really. I get tired of endless UI changes, and that mad race (who will post more major updates - Google Chrom or Mozilla) is really dull. I remember the time when major version change in Firefox was a really major change.
Now every major version upgrade can be described as "we fixed a lot of bugs - most of which we introduced ourselves recently - and yes, we add new bells and whistles to replace old ones - aren't we great?"
And yes, not all the add-ons I expected to see have released at least Beta version of their Web Extension incarnation. And some are totally screwed while doing so (e.g., Xmarks).
Something tells me I get FF 57 on sandbox computers for some time, until I make sure it is good to use.
I also will use a separate Mozilla ID to set up sync - for those computers where I risked running FF 57.
In short: yet another "major release", again with fife and drums, but with greater disasters involved.