diff -r 352ba4e9d85c toolkit/spatial-navigation/SpatialNavigation.js
--- a/toolkit/spatial-navigation/SpatialNavigation.js	Sat Sep 20 23:01:34 2008 +0300
+++ b/toolkit/spatial-navigation/SpatialNavigation.js	Mon Sep 22 23:23:44 2008 -0400
@@ -91,7 +91,13 @@ function _onInputKeyPress (event, callba
   // ensure that we let the arrow keys work properly.
 
   var target = event.target;
-  
+
+  var doc = target.ownerDocument;
+
+  // Disable snav for XUL content (e.g. about:config)
+  if (doc instanceof Ci.nsIDOMXULDocument)
+    return ;
+
   if (target instanceof Ci.nsIDOMHTMLHtmlElement) {
       _focusNextUsingCmdDispatcher(event, callback);
       return;
@@ -162,8 +168,6 @@ function _onInputKeyPress (event, callba
   var focusedRect = _inflateRect(target.getBoundingClientRect(),
                                  - gRectFudge);
 
-  var doc = target.ownerDocument;
-
   var treeWalker = doc.createTreeWalker(doc, Ci.nsIDOMNodeFilter.SHOW_ELEMENT, snavfilter, false);
   var nextNode;