* Go to `about:config`
* Change `browser.urlbar.update2.engineAliasRefresh` to true
* Now you can go to `about:preferences#search`
* ...and click the "Add" button below Search Shortcuts
* Add `https://www.google.com/search?q=%s&udm=14` as your URL.
* Set the name to "Google Web" or whatever you prefer and choose a keyword. You can also change your default search engine or other preferences.