How can I disable the search engine drop-down box that appears when I type in the search bar?

Even though I have unchecked the one-click search engine checkbox in Options/Search, I've suddenly found that Firefox has started showing the choose-your-search-engine-and-change-search-settings dropdown menu whenever I start typing something in to the search box. I haven't been able to find any immediate solutions on the web and I am a bit lost for ideas. Using Firefox 43.0