Please go to: Settings(preferences) --> Search Then: Search Suggestions:

Disable: Show search suggestions in address bar results

That should be it.

Below, go to Change settings for other address bar suggestions it will navigate to: Address Bar / When using the address bar, suggest Disable or enable as you see fit. I think the Search engines under the "Address Bar" is about the custom search engines one can define (i have a custom search for youtube, for example: y <search term>).

A better guide here: https://support.mozilla.org/en-US/kb/address-bar-autocomplet...