There is a separate, more experimental, build available that supports HTTP/2 for http:// URIs using Alternate-Services and the "h2t" profile. This allows HTTP/2 over TLS for http:// URIs in some cases without verification of the SSL certificate. That code is at
https://tbpl.mozilla.org/?tree=Try&rev=077151e1c38e c1545e78e17e and downloads https://ftp.mozilla.org/pub/mozilla.org/firefox/try-builds/mcmanus@ducksong.com-077151e1c38ec1545e78e17e/]