Why do you offer it for free?
(I do think you could make value-added browser services a business, but you'd have to go to enterprises to do it.)
You could argue that to be successful at generating a passive income of any magnitude, you'd be better off selling value-added services on top of a free browser rather than just selling a browser. I'd be curious to hear that argument, because the opposite seems true: making freemium work means that you need to invest not just in making a great free product that people will use, but also invest in creating enough additional value to make the sale. Thus I think wanting a lower commitment to the company actually says you should just sell the browser.