Thank you davehawley and leocg. http://thenextweb.com/insider/2012/07/25/netotiate-encourages-online-haggling-with-new-website-plug-in/ describes the new "marketing service" I found offered at www.netotiate.com. I searched the registry and could not find a key with "netotiate" in the name. I then blocked cookies and local storage for netotiate.com, www.netotiate.com, and plugin.netotiate.com, all of which I found listed in Opera/Settings/Privacy and Security/All cookies and site data. Blocking all three seems to have worked. Thank you so much.