Why has Firefox stopped searching from the search bar?

I’m on Firefox 78.0.2 (64-bit) running on Win10. In Firefox, I’ve got DuckDuckGo as my default search engine.

I used to hit <Ctrl>-T to open a new tab, type a search phrase in the address bar, hit <Enter> and it would return search results. For the last several weeks, when I’ve hit <Enter>, I get the DuckDuckGo home page and the thrill of retyping my search terms.

I’m reasonably certain that I adjusted a setting or two several weeks ago, but I didn’t realize that it had impacted the "search from address bar of a new tab" functionality, so I didn’t realize I’d broken anything important with my changes. About the only thing I remember changing was setting the "Use the address bar for search and navigation" to "Add search bar in toolbar". I’ve since changed it back, but that doesn’t seem to have resolved the issue.

I think I may have changed the "Search Suggestions" section (clearing all check marks), but I set it back to what I believe the default was and that hasn’t resolved the issue either.

Here are my current search page settings:

I did note this 5 year old question about Firefox search was noted in the "similar questions", but it doesn’t address this issue at all. There is also this 1-year-old question which is the exact same issue but in FF v68 & v69, and says that it was resolved in v71. Maybe this is a regression of that bug.

Does anyone know what setting I may have changed that broke this behavior? Is this something actually broken in Firefox?