Looks interesting (like the expiration=never). Uses Mozilla Persona, which I hadn't heard of before. Apparently 'Persona' is no longer being developed by Mozilla since early/2014(1). Also... warnings that 'Persona' isn't secure for high-value data(2).
(1) http://techcrunch.com/2014/03/08/mozilla-stops-developing-it...
(2) http://benjamin.smedbergs.us/blog/2014-02-11/dont-use-mozill...