Add debugging code for random assertion bug 563980.

content/base/src/nsGenericElement.cpp

@@ -2075,6 +2075,12 @@ nsGenericElement::~nsGenericElement()
 {
   NS_PRECONDITION(!IsInDoc(),
                   "Please remove this from the document properly");
+#ifdef DEBUG
+  if (IsInDoc()) {
+    printf("The element still in the document is:\n");
+    List(stdout, 2, nsCString());
+  }
+#endif
 }
 
 NS_IMETHODIMP