Even with the pref "Show search suggestions in address bar results" disabled, suggestions for Google and other search engines are still shown when using the one-off search buttons.

Steps to reproduce: see video in attachment.

This was an explicit choice, entering Search Mode is a user choice (you must confirm it with Enter) and then it's a full search with suggestions, that pretty much replaces the old search bar in functionality.
If you don't want suggestions at all, you must disable the global Search Suggestions pref, that is grouping all the ones below.
The "Show Search Suggestions in address bar" pref only controls normal searches (typing a string) out of Search Mode.

We are planning a user preferences refresh for the next versions to make them clearer, since after so many changes they can be confusing.

(In reply to Marco Bonardo [:mak] from comment #1)

This was an explicit choice, entering Search Mode is a user choice (you must confirm it with Enter) and then it's a full search with suggestions, that pretty much replaces the old search bar in functionality.
If you don't want suggestions at all, you must disable the global Search Suggestions pref, that is grouping all the ones below.
The "Show Search Suggestions in address bar" pref only controls normal searches (typing a string) out of Search Mode.

We are planning a user preferences refresh for the next versions to make them clearer, since after so many changes they can be confusing.

Thanks, that explains a lot. So basically, this pref only controls whether suggestions are shown for the default search engine?
Maybe the checkbox can be moved to the Default Search Engine section of about:preference#search to make this clear?

Search mode is a way to let users have best of both worlds between the urlbar and the search bar, you can use the urlbar without sending your keystrokes to a remote search engine by disabling search suggestions in it, while you still can restrict your search to a search engine at will, and then get remote suggestions.
I don't know how prefs will be reorganized, that's more a question for our user experience dept.

(In reply to Marco Bonardo [:mak] from comment #3)

Search mode is a way to let users have best of both worlds between the urlbar and the search bar, you can use the urlbar without sending your keystrokes to a remote search engine by disabling search suggestions in it, while you still can restrict your search to a search engine at will, and then get remote suggestions.

I really like this solution. It combines the privacy of the search bar (no URL keystrokes sent) with the "one stop shop" experience of the urlbar. And we can get different suggestions for each search engine. Great job!