[jmholla]

Isn't it the opposite. It's opt-out for testing and is supposed to be opt-in when it goes live? I mean, I just disabled it and I am certain I didn't opt-in to it given that I had to go to about:config to have the setting show up.

You can opt-in to actively be a part of FLoC, but if you don't opt-out, Google may randomly choose you to be part of their testing.

Edit: I think your point may have been from the perspective of a website owner. Sorry.