Mozilla published about $500M in royalties revenue "earned through Firefox web browser search partnerships and distribution deals around the world" [1] in 2016 against ~900M active clients [2]. Which means browsers as a business model currently approximately monetize at around $0.55/user/year.
This is done by search engine partnerships, default bookmarks and distribution deals. Is this good or bad? What if you wanted to build a browser around speed, privacy, ad/tracking blocking features?
[1] https://www.mozilla.org/en-US/foundation/annualreport/2016/ [2] https://data.firefox.com/dashboard/user-activity