diff --git a/layout/generic/nsHTMLFrame.cpp b/layout/generic/nsHTMLFrame.cpp
index 0ba2a37cf3b..067f3dedd58 100644
--- a/layout/generic/nsHTMLFrame.cpp
+++ b/layout/generic/nsHTMLFrame.cpp
@@ -60,6 +60,8 @@ public:
     return NS_OK;
   }
 
+  NS_IMETHOD ListTag(FILE* out) const;
+
 protected:
   virtual PRIntn GetSkipSides() const;
 };
@@ -233,3 +235,15 @@ RootFrame::HandleEvent(nsIPresContext& aPresContext,
   return NS_OK;
 }
 
+// Output the frame's tag
+NS_IMETHODIMP
+RootFrame::ListTag(FILE* out) const
+{
+  if (nsnull == mContent) {
+    fprintf(out, "*Root(-1)@%p", this);
+  } else {
+    return nsFrame::ListTag(out);
+  }
+}
+
+
diff --git a/layout/html/base/src/nsHTMLFrame.cpp b/layout/html/base/src/nsHTMLFrame.cpp
index 0ba2a37cf3b..067f3dedd58 100644
--- a/layout/html/base/src/nsHTMLFrame.cpp
+++ b/layout/html/base/src/nsHTMLFrame.cpp
@@ -60,6 +60,8 @@ public:
     return NS_OK;
   }
 
+  NS_IMETHOD ListTag(FILE* out) const;
+
 protected:
   virtual PRIntn GetSkipSides() const;
 };
@@ -233,3 +235,15 @@ RootFrame::HandleEvent(nsIPresContext& aPresContext,
   return NS_OK;
 }
 
+// Output the frame's tag
+NS_IMETHODIMP
+RootFrame::ListTag(FILE* out) const
+{
+  if (nsnull == mContent) {
+    fprintf(out, "*Root(-1)@%p", this);
+  } else {
+    return nsFrame::ListTag(out);
+  }
+}
+
+