search engines pay for 80% of mozilla's cheques, so search engines have 80% control over mozilla's income, which is a bit iffy, especially for something meant to be community controlled and directed (non profit open source right?)
What I don’t understand is why are there no paid browsers? I’d pay $xx(x?) for a browser where I’m the customer, not the product. Every open-source browser is either awful and outdated, or is beholden to outside interests, or internal monetization strategy.