<mouse>
    ....
    <context name="Frame">
     .......

<!-- prevent that the browsers do zoom in/out when navigating with ctrl + scroll up/down -->
      <mousebind button="C-Up" action="Click" >
            <action name="Focus"/>
      </mousebind>
      <mousebind button="C-Down" action="Click" >
            <action name="Focus"/>
      </mousebind>