Greetings, @Flood and Flood's wife
Thank you for your reply.
TL;DR: I have solved the problem by disabling "Safe Browsing." Perhaps the fact that Kaspersky Free does not support Opera is the real problem? I don't know.
Also, regarding the two sets of instructions you provided, respectively:
These instructions -- which are well over 3.5 years old -- direct me to a "Threats and exclusions" section that does not exist in Kaspersky Free, and as a bonus contain a link that leads to a 404 error.
These instructions, which are well over 2.5 years old, do not apply to Kaspersky Free.
Both of these articles need to be updated. Please pass my concerns to whoever is responsible for documentation.
Thanks again for your time.
-Mal