Fix for bug 106656. tabs' use of child nodes is inconsistent

r/sr=jag, bzbarsky, a=asa

xpfe/global/resources/content/bindings/tabbox.xml

@@ -215,7 +215,7 @@
         <![CDATA[
           const tabs = this.childNodes;
           for (var i = 0; i < tabs.length; i++) {
-            if (tabs.selected)
+            if (tabs[i].selected)
               return i;
           }
           // throw an exception when no tab is selected (we shouldn't get here)
@@ -486,14 +486,7 @@
     <handlers>
       <handler event="click" button="0">
       <![CDATA[
-        var tabs = this.parentNode;
-        do {
-          if (tabs.localName == "tabs")
-            break;
-          tabs = tabs.parentNode;
-        } while(tabs.localName != "tabbox");
-        tabs.selectedItem = this;
-        if (!this.selected) this.selected = true;
+        this.parentNode.selectedItem = this;
       ]]>
       </handler>