Incidentally, using the Classic Theme Restorer, I managed to bludgeon back all the junk and my FF is actually usable again. With a bit of work, the important "top left" is back to old school style complete with menubar. But the funny thing is "if I get nostalgic" I have both the "Firefox button" and the new "Hamburger button", both of which have *different* subsets of the complete features laid out in the old school menus!
Sounds like a play question for you logic types, if you take 7 menus with 11+8+6+5+8+8+9=55 visible features/menus and try either of two attempts to smush it into 18 or 12, then stuff you used to know where to find gets harder! But I guess peoples "usability studies" decides that all those menus were "too hard" or something. Correct me if I'm wrong, but I think in modern UI a "menu" (by any other name) can't be avoided. It's just whether it says "File", or "Firefox" or ("Hamburger Icon") or ("Sprocket").