Thanks. I figured it out. It was the last extension I installed about a week ago:
Cookie Notice Blocker
1.7.0
Remove most of those annoying “We value your privacy” banners & cookie notices from websites.
ID: odhmfmnoejhihkmfebnolljiibpnednn
Inspect viewsbackground page
Will try to write to the author about this. Curious that it only happens on one particular site and not others. I’m guessing that only sites trying to display cookies notices will have this behavior.