How could you tabbox fill all the space?

Question

Does anyone know how I can make a TabBox to fill all the space? I tried this:

<tabbox id="MyTabBox" flex="1">
  <tabs>  
    <tab label="Income" />
    <tab label="Taxes" />
  </tabs>   
  <tabpanels flex="1">
    <tabpanel>
      <button label="Calculate" flex="0"/>
    </tabpanel>  
    <tabpanel> 
    </tabpanel>  
  </tabpanels>
</tabbox>

The TabBox looks great, but it causes the Button to fill the entire height of the first TabPanel, despite its flex attribute. If I limit the height of the button, this also makes the TabBox type short, and not what I need.

Thank.

Update: now the window code looks like this:

<?xml version="1.0"?>
<?xml-stylesheet type="text/css" href="chrome://global/skin/" ?>
<?xml-stylesheet type="text/css" href="chrome://MyExtension/skin/MyExtension.css" ?>

<!DOCTYPE window SYSTEM "chrome://MyExtension/locale/translations.dtd">

<window id="MyExtension-MainWindow"
  title="My Extension"
  xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
  xmlns:html="http://www.w3.org/1999/xhtml">

<html:link rel="icon" href="chrome://MyExtension/skin/MyExtensionFavIcon.png"/>

<tabbox id="MyTabBox" flex="1">
  <tabs>  
    <tab label="Income" />
    <tab label="Taxes" />
  </tabs>   
  <tabpanels flex="1">
    <tabpanel align="start">
      <button label="Calculate" flex="0"/>
    </tabpanel>  
    <tabpanel> 
    </tabpanel>  
  </tabpanels>
</tabbox>

</window>

FavIcon OK, OK button, TabBox shortened, which sucks: - (

Answer 1

align="center" button ( align , ). . - IIRC stretch.