If it helps, when the feature was first introduced (43, I believe), the pref to control it was browser.urlbar.unifiedcomplete. It was later removed.

In addition to the search with, I believe it also changed up how the awesomebar search itself worked, weighting url contents, for example, much higher than page titles, and (I want to say just based on end user experience) throwing away page visit frequency information. Strangely, it would also recommend pages I had never visited, if that page was top level and something I had visited was further down.