Well, you're wrong. A monopoly is when there are no viable alternatives. "Mono" meaning "one".

Firefox presented not only a viable alternative, but was a demonstrably better browser. According to this site [0] Firefox peaked at 47.5% (vs IE 40.2%).

That is reversing a browser monopoly. Period.

[0] https://www.visualcapitalist.com/cp/the-rise-and-fall-of-pop...