I may have solved the problem -- inadvertently, I admit.
I searched for a popup blocker that would work with all browsers, and found Google AdBlocker.
http://googleadblocker.com/
I downloaded it -- it's a zipped file -- unzipped it, opened the installer file, double-clicked on the installer, and haven't seen the Zinc Ad popup since.
I don't know if it's working in conjunction with AdBlock, or in place of it, but it's working, and that's what I wanted.
I am using K-Meleon 75.1.
The version of AdBlock I installed came from K-Meleon's forums: 1.3.9
I would prefer not to post the site the problem was occurring on for reason relating to personal privacy. No offense intended; I just want to maintain my anonymity
there.