Vivaldi provides arguably the most customizable UI of any browser out of the box (see: ability to move tabs to any side of the screen), plus their culture seems

Vivaldi provides arguably the most customizable UI of any browser out of the box (see: ability to move tabs to any side of the screen), plus their culture seems to me to be all about customization and providing options. I like that. Firefox ESR is pointless - it's just delaying the inevitable. I tried Midori, but it runs poorly on KDE. Palemoon is pretty bad - I tried it and it doesn't properly support existing XUL extensions that work fine in Firefox, so it's a no-go in my book. Waterfox, on the other hand, is fast, works exactly like Firefox, and is at least willing to give continued XUL support a shot. So, it's Vivaldi or Waterfox as best I can figure at this point.