Strange error attempting to log in to HN

I've been unable to login to HN from Firefox for more than a month now. It is a very strange behaviour. It rejects the cookie named "user" because it is already expired. When I check the "set-cookie" header, I can see that the expiration date is in the future, in 2038 in fact. I have no idea why the cookie expiry date is being rejected.

Anyone here has gone through a similar problem? How did you solve that?