- Open about:config
Type keyword in the filter box
Change the "keyword.URL" string to http://127.0.0.1
Leave "keyword.enabled" as TRUE.
Now if you make a typo, as long as there isn't an identical URL out there, you will be presented with the "Server not found" message, showing you the URL you typed, instead of being redirected to your default search engine. This is exactly how the address bar should behave in my opinion, as searching is what the search bar is for!
The search bar still works as it should. Changing default search provider works fine but leaves this setting alone.
This should also prevent the occasional search-engine redirects when you've actually typed the correct address, as happened to me (again) earlier, probably caused by a temporary connection issue with the site in question.
NOTE: You might want to copy the original URL in case you wish to restore it later, in my case https://duckduckgo.com/?t=lm&q=