Visited sites being saved, then listed if "+" alone is typed into address bar.

When a "+" sign is entered, alone, into address bar, a list of some visited sites instantly appears. How do I delete these sites and prevent sites from being saved in the future? I've searched everywhere I can find for an answer to this question, or for a place to submit it, and failed. In Privacy & Security > History I've un-checked all except "Clear history when Firefox closes" which is checked. In > "Address Bar--Firefox Suggest", I've disabled all options. I clear "Recent History, Everything" (Cookies and Site Settings are left unchecked) frequently. Thank you for your help!