Unfortunately, it doesn't work anymore. This feature has been removed by GTK developers because of "this may surprise user" : https://bugzilla.gnome.org/show_bug.cgi?id=630226. It doesn't seem that they are going to reimplement it.
** Bug watch added: GNOME Bug Tracker #630226 https://bugzilla.gnome.org/show_bug.cgi?id=630226 -- You received this bug notification because you are a member of Desktop Packages, which is subscribed to gtk+3.0 in Ubuntu. https://bugs.launchpad.net/bugs/872055 Title: GtkNotbook scrolling tabs throug mouse doesn't work anymore Status in “gtk+3.0” package in Ubuntu: Confirmed Bug description: I don't know why, but scrolling through tabs using the mouse wheel (also on touchpads) doesn't work anymore. Thats pretty annoying, is this feature of gnome one of the most used by me. Where can I, or can it be enabled? Ubuntu 11.10 x64 gnome To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/gtk+3.0/+bug/872055/+subscriptions -- Mailing list: https://launchpad.net/~desktop-packages Post to : desktop-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~desktop-packages More help : https://help.launchpad.net/ListHelp