in reply to
Logged in status does not persist (http://perlmonks.org/ + no "third party" cookie)
After a tcpdump, I saw that after perlmonks.org has been resolved to an IP address, that (IP address) gets resolved to perlmonks.pair.com host name. Hence the cookie problem with using "Accept cookies only from the site I visit" option but not with "Accept cookies".
Now, if log in on perlmonks.pair.com AND choose "Accept cookies only from the site I visit" option, I have no more ephemerally logged in problem.