It's virtually impossible to search for anything without sending your search string to google. Yah right Mozilla is "privacy focused".
How are you supposed to use search autocomplete with any other search engine except your default?
I understand mozilla wants a spike of search revenue with settings reset, making address bar unusable.
Autocomplete works for me in the nightly (at least for DDG) so if it doesn't right now, it'll be fixed eventually.
It's possible though exceedingly cumbersome. You select the search engine first, then type the query. If that doesn't work with the default settings of displaying the engines right away, it certainly does if you turn off ‘Show search engines’ in settings and go via the button. Wikipedia auto-completion finally works for me.
However, I can't say that this UI is better than the old one for the default case of not caring about non-default-engine completion.