Configure Touchpad of Toshiba Portege Z30 on Debian

/etc/X11/xorg.conf.d/50-synaptics.conf:

Section "InputClass"
        Identifier "touchpad catchall custom"
        Driver "synaptics"
        MatchIsTouchpad "on"
# This option is recommend on all Linux systems using evdev, but cannot be
# enabled by default. See the following link for details:
# http://who-t.blogspot.com/2010/11/how-to-ignore-configuration-errors.html
        MatchDevicePath "/dev/input/event*"

        Option "TapButton1" "1"
        Option "TapButton2" "2"
        Option "HorizTwoFingerScroll" "1"
EndSection

...and disable Gnome's mouse daemon via

dconf write /org/gnome/settings-daemon/plugins/mouse/active false

Restart xorg.