It's the perfect setup really, you can turn it off, but if you want it you can type "? <search term>" into the address bar and it'll go to default search - or use one of your engine short codes as the first word "@google hackernews"

about:config -> keyword.enabled -> false (to stop sending possible search terms automatically to your default search engine, this includes when you type a URL firefox mistakes for a search term)

about:config -> browser.fixup.alternate.enabled -> false (to stop firefox trying a DNS lookup/connection with the term you typed with www. before, .com after)

This is something... but it isn't perfect. The address bar is still not purely an address bar. It still defaults to sending a query to a search engine (I like to use this to search for partial URL matches, for example, navigating git repos that I use frequently). That's what the search bar is for. Bah humbug. Even with all these options set, FF still encourages confusion between URLs and searching.

I'm not sure I understand.. there's an internal search (tabs, history, bookmarks) which sounds like what you're doing - there's no search engine used for this. Or do you mean the Search suggestions (Settings -> Search -> uncheck "Provide search suggestions" to disable, some of these suggestions are FF generated)