I'm doing nothing funky with cookies - default firefox installation on mac. I get the ads each time before login and have to login each time. Just fyi
Your browser is doing something with cookies as I tested this extensively prior to turning it on.
You have both confirmed it is not showing to logged in users, which is good.
You both visit NSC multiple times a day, have to log in each time and get the ad each time.
Both NSC logins and the ad are controlled by cookies. For whatever reason (intentionally or otherwise) your browser is not retaining cookies, at least for NSC and the ad network, which is why you are having to login repeatedly and get the ad repeatedly.