Might have been better to set up a configuration in the xorg.conf.d directory.
I also use Xfce, I put a file in "/etc/X11/xorg.conf.d/" named "10-synaptics.conf"
Code:
Section "InputClass"
Identifier "touchpad catchall"
Driver "synaptics"
MatchIsTouchpad "on"
MatchDevicePath "/dev/input/event*"
Option "TapButton1" "1"
Option "TapButton2" "2"
Option "TapButton3" "3"
Option "VertTwoFingerScroll" "on"
Option "HorizTwoFingerScroll" "on"
EndSection
No need for gnome