For a while Firefox was slower, and Chrome was quicker. That really was important plus Android/Chrome was a combination as well with the proliferation of the cheap smartphone. A sizeable portions of devs came unto the market with that background, and chrome dev tools had a bit of an edge with a few functionalities.

Firefox never had a monopoly, unless you still count Netscape Navigator in that. IE was big until 2006-08, started dropping off quickly after that, Firefox won a big share in that time, but at some point Chrome just chipped away marketshare for reasons stated above.

I think bundling was a big deal by Google, something Microsoft got punished for, but Google never.