Security and privacy isn't only prevalent on browser frontend features. There are battles happening within every standardized Web specification. Without more than one major player, one company would be allowed to dictate the level of security and private within every API. There are also initiatives that push the Web forward in security like with Let's Encrypt or Do Not Track. Mozilla also advances into new areas of technology to try to ensure they remain open.

It's totally fine to prefer one browser or the other. It's great to have an actual choice. But the ideals and values aren't just for show.