Firefox

Ironically, all of these things except Abrowser are based on Konqueror’s original engine, KHTML, so Konqueror was actually the OG engine. KHTML was forked to WebKit, which was forked to Blink, which became the underpinnings of Qt WebEngine, which Konqueror now uses.

This is also why KHTML still appears in the user agent strings for all of these engines, but back in the day the Gecko engine used in Mozilla products was already a thing and KHTML was the alternative to that, hence “KHTML, like Gecko”.