Awesome! Thanks, Arlo! Is there also a ticket open to work around Arthur's discover that Firefox Private Mode (and therefore TBB all the time) buries the surfacing of Alt-Used headers? 

 > https://twitter.com/arthuredelstein/status/1042194259368013825

I've worked out a way to work around this somewhat with a custom webserver, but overall it's a pain in the arse.

Thanks!

    -a