Firefox and its derivatives are the only browsers that challenge Google's monopoly on browser engines and prevent them from making unilateral changes to all web browsers based on them, including Vivaldi. DuckDuckGo is a good search engine though.
Welllll I mean technically webkit is totally separate from chromes blink fork for the last several years. I.e. browers like safari and gnome's epiphany. That said, safari is mac/iOS only and epiphany sucks ass so...
Fair enough. GNOME Web is the only cross platform non Blink or Gecko browser, and like you say it has flaws compared to those two, such as lack of extension support.