Firefox 57.0 Released
Hopefully most of the missing extensions will be developed sooner rather than later. I have 15 extensions installed, 14 of which are "Legacy".The most critical one, Tree Style Tabs, has been converted. That was the key blocker that prevented me from seriously using Chrome. But many more remain; Cookie Controller, RefControl, some kind of Classic Theme Restorer equivalent (to get a menu bar back for Bookmarks, at a minimum), etc.