isToggleOn = 0
function OnEvent(event, arg)
    --OutputLogMessage("event = %s, arg = %s\n", event, arg);

        if( event == "MOUSE_BUTTON_PRESSED"  and arg == 4 ) then
            if (isToggleOn == 0) then
                PressKey("lshift")
                Sleep(10)
                PressKey("f")
                isToggleOn = 1

            elseif (isToggleOn == 1) then
                ReleaseKey("lshift")
                Sleep(10)
                ReleaseKey("f")
                isToggleOn = 0
            end
        end
end