The default, in friendly big blue colors, is to "Allow suggestions" with the alternative called "Customize in settings". It is also not clear if disabling "suggestions", switches off all its machinery or merely prevents them from being shown.

As others have said up this thread, the problem is not as much the feature itself, but the fact that Mozilla deemed it perfectly fine to roll out something like this in the first place.

It becomes increasingly obvious that Mozilla no longer understands (or cares!) what it was that made Firefox special, made people stick with it and what the motivation and priorities of these people are.