Just putting in a warm word for Waterfox.
With its update to 55.2.2 (Oct '17), it now has its own separate location for profile folders.
Concerned about the impending add-on change in FF 57, I've just now moved over to WF. If you copy and paste your profiles from FF location to WF location, and then make sure that the profiles.ini in WF has the same contents as the FF profiles.ini, you'll be reproducing, in WF, all your settings, add-ons, bookmarks. It would be worth checking that all the add-ons survive the transfer: I think I had to (re-)enable one or two. All in all, though, an easy process.
So much so that I uninstalled FF stable and ESR from my computer.