I think this is in Nightly and now Firefox Developer Edition (54) behing a pref: https://twitter.com/mozhacks/status/821005161602646016 https://twitter.com/mozh

I think this is in Nightly and now Firefox Developer Edition (54) behing a pref: https://twitter.com/mozhacks/status/821005161602646016 https://twitter.com/mozhacks/status/821005161602646016