This new tab behavior doesn’t require changing the address bar search feature, it has its own preference. The hardest part is learning its name:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk.

More info on about:config: Configuration Editor for Firefox. The moderators would like us to remind you that changes made through this back door aren’t fully supported and aren’t guaranteed to continue working in the future. Since I use this one myself, I feel comfortable mentioning it, even if it does turn out to be temporary relief only.

(2) In the search box in the page, type or paste handoff and pause while the list is filtered

(3) Double-click the browser.newtabpage.activity-stream.improvesearch.handoffToAwesomebar preference to switch the value from true to false

Success?