Synergy Forward/Backward Mouse Buttons
Synergy is an awesome application that allows you to use a single keyboard/mouse for multiple computers. However, out of the box it does not set up backward/forward mouse buttons.
Save your synergy configuration file and add these two lines (button numbers may vary) to
mousebutton(6) = keystroke(WWWBack) mousebutton(7) = keystroke(WWWForward)
This has been tested and works with a Logitech G400 (aka MX518) and G500s.