The prefwindow binding contains the following deck: <xul:deck anonid="paneDeck" flex="1"> <children includes="prefpane"/> </xul:deck> Since the prefpanes aren't real child nodes of the deck, deck.childNodes.length is 0 and deck.selectedPanel will error out in deck.selectedPanel here <http://mxr-test.landfill.bugzilla.org/seamonkey/source/xpfe/global/resources/content/bindings/general.xml#335>: return this.childNodes[this.selectedIndex]; (prefwindow users can work around the issue by accessing the prefwindow.preferencePanes array directly.)

selectedPanel will also give incorrect results if any panel is hidden.

As a workaround I iterate through the sibling nodes. Works perfectly for our Mozmill tests.

(In reply to neil@parkwaycc.co.uk from comment #1) > selectedPanel will also give incorrect results if any panel is hidden. What's more, using it as a setter will also do the wrong thing in that case. Sigh.