This is normal, because some environments have servers with names like intranet. When your DNS returns a plain 404, Firefox then sends the word to your preferred search engine. But if the DNS service sends back its own results page, that preempts the normal behavior. Perhaps there is an add-on to work around this? I do not recall seeing one, but you can search here: https://addons.mozilla.org/en-US/firefox/ For many years the address bar search was called the keyword service, so in addition to other queries, you might search for add-ons related to keywords.