nationalsupplynetwork
A few days ago I visited a website "nationalsupplynetwork.com" using Safari 14.0.3. I did not transact any business there, but I came close. I may have left an unordered item in my shopping cart. Now, when I open "Preferences:Websites" right after booting up, various table items show "nationalsupplynetwork.com" as a "Currently Open Website". That is, Safari thinks that nsn.com is open, but I can't see any such window/tab/site. What might I have done wrong to have such a thing, and how do I get rid of it? Malwarebytes does not show this as a problem.
MacBook Pro