diff -r 000000000000 -r 6474c204b198 gfx/src/nsRect.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gfx/src/nsRect.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,43 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "nsRect.h"
+#include "mozilla/gfx/Types.h"          // for NS_SIDE_BOTTOM, etc
+#include "nsDeviceContext.h"            // for nsDeviceContext
+#include "nsString.h"               // for nsAutoString, etc
+#include "nsMargin.h"                   // for nsMargin
+
+static_assert((int(NS_SIDE_TOP) == 0) &&
+              (int(NS_SIDE_RIGHT) == 1) &&
+              (int(NS_SIDE_BOTTOM) == 2) &&
+              (int(NS_SIDE_LEFT) == 3),
+              "The mozilla::css::Side sequence must match the nsMargin nscoord sequence");
+
+#ifdef DEBUG
+// Diagnostics
+
+FILE* operator<<(FILE* out, const nsRect& rect)
+{
+  nsAutoString tmp;
+
+  // Output the coordinates in fractional pixels so they're easier to read
+  tmp.AppendLiteral("{");
+  tmp.AppendFloat(NSAppUnitsToFloatPixels(rect.x,
+                       nsDeviceContext::AppUnitsPerCSSPixel()));
+  tmp.AppendLiteral(", ");
+  tmp.AppendFloat(NSAppUnitsToFloatPixels(rect.y,
+                       nsDeviceContext::AppUnitsPerCSSPixel()));
+  tmp.AppendLiteral(", ");
+  tmp.AppendFloat(NSAppUnitsToFloatPixels(rect.width,
+                       nsDeviceContext::AppUnitsPerCSSPixel()));
+  tmp.AppendLiteral(", ");
+  tmp.AppendFloat(NSAppUnitsToFloatPixels(rect.height,
+                       nsDeviceContext::AppUnitsPerCSSPixel()));
+  tmp.AppendLiteral("}");
+  fputs(NS_LossyConvertUTF16toASCII(tmp).get(), out);
+  return out;
+}
+
+#endif // DEBUG