This should be possible in Firefox without changing some fucking about:config setting, but here we are. Go into about:config and create the following boolean setting, and set it to true:
browser.urlbar.update2.engineAliasRefresh
Now you can add a new Entry to the list of search engines, set the url to a string containing %s, which is your search query. Then you can also set it as your default search, meaning it will be used when searching through the address bar.