Pcmanfm and openbox mouse back

sudo apt-get install xdotool

in openbox configuration, section <context name="Client"> insert:

  <mousebind button="Button8" action="Press">
    <action name="If">
      <query target="default">
        <name>*pcmanfm*</name>
      </query>
      <then>
        <action name="Execute">
            <command>
                xdotool key BackSpace
            </command>
        </action>
      </then>
    </action>
  </mousebind>