Thanks for the feedback.
I get the authentication message on another install I did directly from a new .iso cd image I downloaded right off the site again this weekend - so it’s probably not malware.
I’m guessing it has to do with their branding on the Firefox browser, or something related to the custom look in mint.
Much appreciated, thanks.
Oh wait, that’s Freespire with the branded browser.
(duh) Was working with both this weekend, got them mixed up.
But anyway. Probably not an issue I guess.