@nchapman - I'm trying to find the Persona issue, but cannot. There are browser inconsistencies when setting and reading a cookie in JS. The behavior is as expected in most browsers, but in a few, even with cookies disabled, you are able to use JS to read the cookie you just set. The only 100% sure method of determining if cookies are enabled is to see if the server receives it.

We could have the initial call to the page set a session cookie (which I believe it already does) and then see if the cookie exists in the call to `/config`, which would simplify this check.