If I press the forward/backward thumb buttons on my Logitech MX1000 mouse, thunar should navigate forwards and backards, just as firefox does. Please note that "MiscHorizontalWheelNavigates=TRUE" in thunarrc (see also Bug #1319) does not fix this for me. If I add it, thunar navigates forwards/backwards if I press the wheel horizontally (as the option suggests), not if I press the thumb buttons. xev outputs the forward thumb button as 9, the backward thumb button as 8, while pressing the wheel horizontally gives 6 and 7 (for left and right, respectively).
Fixed in revision 28993.