Bug 1021023 - Fix 'document is null' error in CssLogic_findCssSelector when inspecting <window> in XUL document. r=pbrosset

toolkit/devtools/styleinspector/css-logic.js

@@ -917,10 +917,13 @@ CssLogic.findCssSelector = function CssLogic_findCssSelector(ele) {
     }
   }
 
-  // So we can be unique w.r.t. our parent, and use recursion
-  index = positionInNodeList(ele, ele.parentNode.children) + 1;
-  selector = CssLogic_findCssSelector(ele.parentNode) + ' > ' +
-          tagName + ':nth-child(' + index + ')';
+  // Not unique enough yet.  As long as it's not a child of the document,
+  // continue recursing up until it is unique enough.
+  if (ele.parentNode !== document) {
+    index = positionInNodeList(ele, ele.parentNode.children) + 1;
+    selector = CssLogic_findCssSelector(ele.parentNode) + ' > ' +
+            tagName + ':nth-child(' + index + ')';
+  }
 
   return selector;
 };