Firefox.
No, not Firefox of today; I'm talking about Firefox 20 years ago that defeated IE6 by sheer force of nerds alone.
Of course, the landscape is vastly different now and Firefox today is about the most not-nerd thing next to Chrome. If there's a a browser here to save us anywhere, I'm not seeing it.
Firefox was significantly better than IE though: it was faster, had more features, and things like that. This is what made Firefox popular, not "sheer force of nerds".
Chrome, when released, also had some significant improvements to Firefox. In particular, it was loads faster. This changed with "Firefox Quantum" (59 IIRC), but "too little, too late" I guess.
Firefox was better because it had tabbed browsing, integrated search, pop-up blocking, and extensions, but I was responsible for monitoring our perf back then and I can say for certain that we were not faster.