nsSiteSecurityService has various logging messages like "no backup pin", it would be good if those would also show up in the console. It might even be useful to show when everything succeeded so you can be sure HPKP is working.

+1 ... out of interest, is there any way to see the HPKP status of a domain? i.e. did it work? about:networking only shows SPDY/SSL support. "HTTP logging" seems to be pretty busy, but no real mention of HPKP checking - just a mention of it parsing the header. https://developer.mozilla.org/en-US/docs/Mozilla/Debugging/HTTP_logging

Bug 932179 is pretty good, it shows the HPKP status.