It isn't about the browser. It is about search and ads which are not free or open source. There are alternatives but Google's market share is ~92% which is similar level to ie when Microsoft faced it's anti trust case. They pay off mozzila & apple to be default search. Bing has 7% market share and they are the only "real" competition.

The browser is just one more way google maintains it's core search business. E.g. their recently released topics api