Every domain you visit is sent to a DNS provider of some sort. By default, that would be whatever your ISP has defined. But it is completely configurable if you

Every domain you visit is sent to a DNS provider of some sort. By default, that would be whatever your ISP has defined. But it is completely configurable if you care. So the choice isn't between Firefox sending your data somewhere and Chrome not, it is a case of both sending data to somewhere that ordinary consumers have little control over. If you are going to send DNS requests, it makes sense that they be encrypted. If such encryption becomes standard, then I would agree that there would be no case for Firefox to default to CloudFlare. As it stands, there's not many options for encrypted DNS, and general users don't want to be prompted, they just want the best security.