diff -r 000000000000 -r 6474c204b198 layout/mathml/nsMathMLmphantomFrame.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/layout/mathml/nsMathMLmphantomFrame.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,35 @@
+/* -*- 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 "nsMathMLmphantomFrame.h"
+#include "mozilla/gfx/2D.h"
+
+//
+// <mphantom> -- make content invisible but preserve its size
+//
+
+nsIFrame*
+NS_NewMathMLmphantomFrame(nsIPresShell* aPresShell, nsStyleContext* aContext)
+{
+  return new (aPresShell) nsMathMLmphantomFrame(aContext);
+}
+
+NS_IMPL_FRAMEARENA_HELPERS(nsMathMLmphantomFrame)
+
+nsMathMLmphantomFrame::~nsMathMLmphantomFrame()
+{
+}
+
+NS_IMETHODIMP
+nsMathMLmphantomFrame::InheritAutomaticData(nsIFrame* aParent)
+{
+  // let the base class get the default from our parent
+  nsMathMLContainerFrame::InheritAutomaticData(aParent);
+
+  mPresentationData.flags |= NS_MATHML_STRETCH_ALL_CHILDREN_VERTICALLY;
+
+  return NS_OK;
+}