Come up with their own privacy-focused computer and mobile OS, and mobile devices, really. I don’t think that browsers can survive as standalone software anymore. We’ve come to a point where default browsers are so tightly integrated with smartphone or computer OSes that a browser by itself offers too little value without integration. It’s going to be expensive, but they can compete with Linux distros that try to do the same but which all cannot gain any traction, polish, and long-term support.