Enable 5-button mouse

1. If you have a 5-button mouse, you can enable the forward and back buttons as follows:

   sudo cp /etc/X11/xorg.conf /etc/X11/xorg.conf.backup.mouse
   sudo gedit /etc/X11/xorg.conf
   

   Change:

   Section "InputDevice"
    ...
    Driver "mouse"
    ...
    Option "Emulate3Buttons" ...
    Option "ZAxisMapping"    ...
    ...
   EndSection
   

   to:

   Section "InputDevice"
    ...
    Driver "mouse"
    ...
    Option "Emulate3Buttons" "false"
    Option "Buttons"         "7"
    Option "ButtonMapping"   "1 2 3 8 9 10 11"
    Option "ZAxisMapping"    "4 5"
    ...
   EndSection
   

2. (optional) Restart Gnome Desktop Manager for these settings to take effect.