This is the relevant post from the Mozilla nightly blog: https://blog.nightly.mozilla.org/2018/06/01/improving-dns-pr... It confirms that the default is off. It also gives a much more nuanced view of the level of partnership. CF is currently the partner for a study regarding that feature. That study still requires opt-in (and currently nightly) The patch in September will bring the feature to mainline FF, but it’s still default off and hidden behind “about:config”
