Type about:config in the url bar. Click yes or whatever to get through the warning. paste "app.update.silent" into the search bar. change false to true. This sets the silent feature to true so that is enabled. Enjoy.
Alternatively install the classic theme restorer to get most of the old look back Classic Theme Restorer (Customize Australis) :: Add-ons for Firefox . And yes I agree with you that the new ui is complete shit.