Builds for windows, os x, and linux are at
http://ftp.mozilla.org/pub/mozilla.org/firefox/try-builds/hurley@mozilla.com-31cbcfa26b62
If you wish to test with draft-08 and compression-04 instead (same code as -07, different *PN identifiers), you can download builds at http://ftp.mozilla.org/pub/mozilla.org/firefox/try-builds/hurley@mozilla.com-79063d5e5c67
Firefox will only be implementing HTTP/2 over TLS - and right now that means for https:// schemed URLs. It does enforce the protocol's >= TLS 1.1 requirement - if a server negotiates HTTP/2 with a lower TLS version it is treated as a protocol error. (there is a preference for changing that for testing purposes if you need it.)