Since my precedent review, I had issues with Chromium on some sites, so Waterfox came back to be my main browser, even if Chromium is faster.
But moving forward, some XUL extensions started to have issues: MAFF stopped working, FEBE too, now Cookiebro seems to go the same path...
XUL support was the main reason why I switched from Firefox Quantum to Waterfox and, though I've achieved a viable Firefox UI through a combination of userChrome.css and theme, plus various tricks to restore my workflow, I still have issues (in particular, the version of 1Password for FFQ won't work with all my other browsers, while an old version works everywhere except for FFQ! :-/ )
The next version of Waterfox is cooking (based on FF68 ESR) and it's very likely that it will break a lot of things. At that point, the gap between Waterfox and Firefox might only be about privacy — which you can achieve with a bunch of addons and tweaks in Firefox, so...
Wait and see. ;-)