You probably already know that Firefox lets users search from the address bar with a “Search with Google” at pinned at the top. Even if you remove Google as a search option within Preferences, this pinned option will still show up, annoying fellow DuckDuckGo users. This is where you will have to dig a bit deeper.
Note: This was tested on Linux and OpenBSD. It may be slightly different for MAC or Windows users.
Within the o in the address bar type in about:config and press Enter or Return on the keyboard.
You will get the standard warning, just select I’ll be careful, I promise!.
Within the search bar, type in browser.newtabpage.pinned and edit this field by clicking on the pencil icon.
Switch the google.com URL to DuckDuckGo.com, ecosia.org, or whatever you preferred search engine happens to be. You should also switch the @google part of the string to something else.
Once you restart the browser, you should no longer encounter the annoying “Search with Google” pin.