I'm going to be switching to the extended support release[1] (based on Firefox 52 but with security patches through June 18th 2018).
I don't mind WebExtensions, and cross-browser compatibility is a nice goal, but a half-baked system that breaks the most important distinguishing feature of Firefox (extensions that can modify any part of the browser) is ridiculous.
[1] https://www.mozilla.org/en-US/firefox/organizations/all/