Dropping support for legacy extensions absolutely gutted what made Firefox different from every other browser. I'll use Firefox 56 and NoScript until the end of time before I use a browser with tabs above the address bar.
Dropping support for these extensions made it possible to create Firefox Quantum. Also, I'm using Firefox with tabs on the side with Tree Style Tab and a simple userChrome.css hack. No need to stay with an outdated version just for that.
Yeah, I resisted the upgrade to FF Quantum for a while, but ultimately made the move and it's worked out well. The biggest things I needed were a WebExtension version of Tree Style Tabs, plus the restyling options from https://github.com/Aris-t2/CustomCSSforFx .