using userChrome.css is now essential to hide/alter interface elements you want to change. there are lots of useful code snippets on r/firefox and r/firefoxcss

as for add-ons tree style tab is the real lifesafer in these early days. easily the most powerful alternative to the default tab bar, albeit still buggy and cpu heavy. it provides me some modicum of tab group-like management until a better way appears

anyway, even just with early add-ons this is pretty useable now, so at least for me FF57 won't be a jarring transition