dep composed on 2018-05-19 16:29 (UTC-0400):

> i used only a few gnome apps, the most indespensible of which id gthumb. i 
> just opened it for the first time since the upgrade and found navigation 
> impossible: there are no scrollbars!

> might anyone here know the package that contains the scrollbars?

On Debian Stretch, I think it's something from this list:

ii  adwaita-icon-theme                   3.22.0-1+deb9u1                   all          default icon theme of GNOME
ii  gnome-icon-theme                     3.12.0-2                          all          GNOME Desktop icon theme
ii  gtk-qt-engine-trinity                4:14.0.5~pre8-0debian9.0.0+0      amd64        theme engine using Qt for GTK+ 2.x and Trinity
ii  gtk-update-icon-cache                3.22.11-1                         amd64        icon theme caching utility
ii  gtk3-tqt-engine-trinity              4:14.0.5~pre7-0debian9.0.0+0      amd64        GTK3 theme engine for TDE
ii  hicolor-icon-theme                   0.15-1                            all          default fallback theme for FreeDesktop.org icon themes
ii  libgtk-3-0:amd64                     3.22.11-1                         amd64        GTK+ graphical user interface library
ii  libgtk-3-common                      3.22.11-1                         all          common files for the GTK+ graphical user interface library
ii  libgtk2.0-0:amd64                    2.24.31-2                         amd64        GTK+ graphical user interface library
ii  libgtk2.0-common                     2.24.31-2                         all          common files for the GTK+ graphical user interface library

At least in Firefox 60 and SeaMonkey 2.49.3 I have them.
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