I just now tried to reinstall version 67.0 while online. It made no difference. I could not recover any settings from version 66.0.5 or find any way of doing so. I must be missing something significant to make it do what it did for you.
Well, I'm now in almost the same boat as you; I, too, have lost my settings, and regardless of which earlier version I install I get the v 67.0 setup screen. I even tried cloning back my AM clone, but with no joy. Something changed when I updated, but I haven't got a clue what it might be.
The "almost" is my saver, because I almost never use Firefox, so I had almost no settings to lose.
I've got no idea what I may have done differently on my first try, but that's now academic.
I wonder if this is all bug-related, and the next version will correct it?
For the moment, the best I can suggest is your contacting Mozilla.
