gecko/toolkit/content/widgets/resizer.xml

<?xml version="1.0"?>

<bindings id="resizerBindings"
   xmlns="http://www.mozilla.org/xbl">

  <binding id="resizer">
    <resources>
      <stylesheet src="chrome://global/skin/resizer.css"/>
    </resources>
    <implementation>
      <constructor>
      <![CDATA[
        // don't do this for viewport resizers; causes a crash related to
        // bugs 563665 and 581536 otherwise
        if (this.parentNode == this.ownerDocument.documentElement)
          return;

        // if the direction is rtl, set the rtl attribute so that the
        // stylesheet can use this to make the cursor appear properly
        var direction = window.getComputedStyle(this, "").direction;
        if (direction == "rtl") {
          this.setAttribute("rtl", "true");
        }
      ]]>
      </constructor>
    </implementation>
  </binding>

</bindings>