Privacy-focused browser Brave explained in a blog post why it will ban Google's Federated Learning of Cohorts proposal, calling it a step in the wrong direction. It said, "the privacy-affecting aspects of FLoC have never been enabled in Brave releases; the additional implementation details of FLoC will be removed from all Brave releases with this week's stable release." Brave believes the technology is harmful to users and will inform sites about their browsing history, making it easier for them to track users online. Not only this, but Brave also believes FLoc will be detrimental to publishers.
UPDATE: 140421 - The Register reports on how other browsers are similarly concerned about Google's latest advertising initiative, with most claiming that they will not be implementing the technology. Mozilla, claims that they believe advertising and privacy can co-exist.