Fix bug #9925: Down arrow behaves incorrectly.

suite/common/sidebar/customize.js

@@ -122,6 +122,7 @@ function moveDown() {
     var optionAfter    = list.childNodes.item(index+1);
     list.remove(index+1);
     list.insertBefore(optionAfter, selectedOption);
+    list.selectedIndex = index + 1;
     enableButtons();
     enableSave();
   }

xpfe/components/sidebar/resources/customize.js

@@ -122,6 +122,7 @@ function moveDown() {
     var optionAfter    = list.childNodes.item(index+1);
     list.remove(index+1);
     list.insertBefore(optionAfter, selectedOption);
+    list.selectedIndex = index + 1;
     enableButtons();
     enableSave();
   }