[crtasm]

I achieved this by turning off a handful of config options for the address bar's suggestions; setting the search input to be separate from the address bar, and hiding it via Customize Toolbar.

I think these were the most important:

  keyword.enabled
  browser.fixup.alternate.enabled
  browser.urlbar.suggest.searches

[mrob]

For many versions now, removing the separate search bar via Customize Toolbar reverts to combined URL bar and search bar. It also leaves the search option in the right-click menu.

[JohnFen]

Oooh! That explains why I haven't been able to disable that stuff from the omnibar. I hate the omnibar -- I just want text entered there to be interpreted as a URL and nothing else -- but at some point, I wasn't able to configure it to be that anymore.

If this is why, you've just made Firefox better for me! Thank you!

[crtasm]

That may be the case, but typing into my address bar does not trigger or suggest searches. Good point about the right click.