Comment 4 for bug 1053302

fyi: http://askubuntu.com/questions/34214/how-do-i-disable-overlay-scrollbars

Just disabling or removing the overlay-scrollbars as described by the other answers will get you back the scroll bars, but they will be missing the stepper buttons at the end of the bars because they have been disabled in the Ambiance theme. To re-enable them, put the following in the ~/.gtkrc-2.0 file:

style "default" {
  engine "murrine" {
    stepperstyle = 0
  }
}

and the following into the file ~/.config/gtk-3.0/gtk.css:

.scrollbar {
  -GtkScrollbar-has-backward-stepper: 1;
  -GtkScrollbar-has-forward-stepper: 1;
}

Usually, restarting the applications is enough for the changes to apply.

To make the stepper buttons better-looking, add this to .scrollbar: -GtkRange-slider-width: 16; -GtkRange-stepper-size: 17; – Håkon A. Hjortland Aug 21 '12 at 7:56