Firefox Developer Edition, works for me (C&P'd that link into my browser). Could be a session-based issue, have you tried flushing your cache / deleting cookies?
FWIW it seems to be fixed now (i didn't do the cache/cookie deletion thing because i didn't want to lose existing sessions in other sites).
Very likely session-based. I do wish Firefox let us delete stuff for individual domains, Chrome's control over that kinda stuff is much better :(
