gecko-dev/suite/common/sidebar/sidebarBindings.xml

<?xml version="1.0"?>

<bindings id="globalBindings"
  xmlns="http://www.mozilla.org/xbl"
  xmlns:html="http://www.w3.org/1999/xhtml"
  xmlns:xul="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul">
  
  <binding id="texttab">
    <content>
      <xul:image class="box-texttab-left"/>
      <xul:vbox class="box-texttab-text-container" inherits="value" flex="1">
        <xul:spring flex="1"/>
        <xul:text class="box-texttab-text" inherits="value=label" crop="right"/>
        <xul:spring flex="1"/>
      </xul:vbox>
      <xul:image class="box-texttab-right"/>
      <xul:spring class="box-texttab-right-space"/>
    </content>
  </binding>

  <binding id="sidebar-header-box" extends="xul:box">
    <content align="center">
      <xul:text class="sidebar-header-text" inherits="value=label,crop" crop="right" flex="1"/>
      <xul:box>
        <children/>
      </xul:box>
    </content>
  </binding>
  
</bindings>