how to delete default search options in search window

Firefox is my default browser and DuckDuckGo is my default search engine. Recently something got added (not by me, or at least not on purpose) and I'd like to get rid of it. When I click on the address bar to initiate a search, seven choices appear in a drop down menu, none of which I want. These choices are: * Search with Amazon, * Search with YouTube, * Google (google.com), * Facebook (facebook.com), * Reddit (reddit.com), * Wikipedia (wikipedia.org), and *Twitter (twitter.com). How can I prevent these choices from appearing? Note: they disappear as soon as I start typing in the address bar, but I'm bothered by this unwanted clutter on my screen even if only temporary. Also, these are not in my bookmarks or my search history, nor are they on the list of checked search engines in my preference settings. Thank you.