In Fedora 18 the Adwaita GTK+ theme has dropdowns messed up in some programs. The text on the drop downs is light grey on white and it's hard to read.
To fix this install the Gnome Tweak tool and a different GTK+ theme:
yum install greybird-gtk2-theme greybird-gtk3-theme gnome-tweak-tool
Then open Tweak Tool. Under "Gtk+ Theme" select "Greybird".