Just ran the service worker. The first on the list that appeared was click-now-on.me. I unregistered for that and about 4 others that I don't think I need. (I left things like Google Drive and YouTube, or should I remove those, too?)
I'll reply here again if I get more popups. Am I right that the click-now-on.me is slowing down my computer? I'll watch that, too, to see if it improves.
Thanks for your help!
df