--- a/layout/base/nsCSSFrameConstructor.cpp
+++ b/layout/base/nsCSSFrameConstructor.cpp
@@ -4567,19 +4567,19 @@ nsCSSFrameConstructor::FindMathMLData(El
     SIMPLE_MATHML_CREATE(annotation_, NS_NewMathMLTokenFrame),
     SIMPLE_MATHML_CREATE(annotation_xml_, NS_NewMathMLmrowFrame),
     SIMPLE_MATHML_CREATE(mi_, NS_NewMathMLTokenFrame),
     SIMPLE_MATHML_CREATE(mn_, NS_NewMathMLTokenFrame),
     SIMPLE_MATHML_CREATE(ms_, NS_NewMathMLTokenFrame),
     SIMPLE_MATHML_CREATE(mtext_, NS_NewMathMLTokenFrame),
     SIMPLE_MATHML_CREATE(mo_, NS_NewMathMLmoFrame),
     SIMPLE_MATHML_CREATE(mfrac_, NS_NewMathMLmfracFrame),
-    SIMPLE_MATHML_CREATE(msup_, NS_NewMathMLmsupFrame),
-    SIMPLE_MATHML_CREATE(msub_, NS_NewMathMLmsubFrame),
-    SIMPLE_MATHML_CREATE(msubsup_, NS_NewMathMLmsubsupFrame),
+    SIMPLE_MATHML_CREATE(msup_, NS_NewMathMLmmultiscriptsFrame),
+    SIMPLE_MATHML_CREATE(msub_, NS_NewMathMLmmultiscriptsFrame),
+    SIMPLE_MATHML_CREATE(msubsup_, NS_NewMathMLmmultiscriptsFrame),
     SIMPLE_MATHML_CREATE(munder_, NS_NewMathMLmunderoverFrame),
     SIMPLE_MATHML_CREATE(mover_, NS_NewMathMLmunderoverFrame),
     SIMPLE_MATHML_CREATE(munderover_, NS_NewMathMLmunderoverFrame),
     SIMPLE_MATHML_CREATE(mphantom_, NS_NewMathMLmphantomFrame),
     SIMPLE_MATHML_CREATE(mpadded_, NS_NewMathMLmpaddedFrame),
     SIMPLE_MATHML_CREATE(mspace_, NS_NewMathMLmspaceFrame),
     SIMPLE_MATHML_CREATE(none, NS_NewMathMLmspaceFrame),
     SIMPLE_MATHML_CREATE(mprescripts_, NS_NewMathMLmspaceFrame),

--- a/layout/generic/nsFrameIdList.h
+++ b/layout/generic/nsFrameIdList.h
@@ -85,19 +85,16 @@ FRAME_ID(nsMathMLmoFrame)
 FRAME_ID(nsMathMLmoverFrame)
 FRAME_ID(nsMathMLmpaddedFrame)
 FRAME_ID(nsMathMLmphantomFrame)
 FRAME_ID(nsMathMLmrootFrame)
 FRAME_ID(nsMathMLmrowFrame)
 FRAME_ID(nsMathMLmspaceFrame)
 FRAME_ID(nsMathMLmsqrtFrame)
 FRAME_ID(nsMathMLmstyleFrame)
-FRAME_ID(nsMathMLmsubFrame)
-FRAME_ID(nsMathMLmsubsupFrame)
-FRAME_ID(nsMathMLmsupFrame)
 FRAME_ID(nsMathMLmtableFrame)
 FRAME_ID(nsMathMLmtableOuterFrame)
 FRAME_ID(nsMathMLmtdFrame)
 FRAME_ID(nsMathMLmtdInnerFrame)
 FRAME_ID(nsMathMLmtrFrame)
 FRAME_ID(nsMathMLmunderFrame)
 FRAME_ID(nsMathMLmunderoverFrame)
 FRAME_ID(nsMathMLsemanticsFrame)

--- a/layout/mathml/moz.build
+++ b/layout/mathml/moz.build
@@ -21,16 +21,13 @@ CPP_SOURCES += [
     'nsMathMLmoFrame.cpp',
     'nsMathMLmpaddedFrame.cpp',
     'nsMathMLmphantomFrame.cpp',
     'nsMathMLmrootFrame.cpp',
     'nsMathMLmrowFrame.cpp',
     'nsMathMLmspaceFrame.cpp',
     'nsMathMLmsqrtFrame.cpp',
     'nsMathMLmstyleFrame.cpp',
-    'nsMathMLmsubFrame.cpp',
-    'nsMathMLmsubsupFrame.cpp',
-    'nsMathMLmsupFrame.cpp',
     'nsMathMLmtableFrame.cpp',
     'nsMathMLmunderoverFrame.cpp',
     'nsMathMLsemanticsFrame.cpp',
 ]
 

deleted file mode 100644
--- a/layout/mathml/nsMathMLmsubFrame.cpp
+++ /dev/null
@@ -1,193 +0,0 @@
-/* -*- 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 "nsCOMPtr.h"
-#include "nsFrame.h"
-#include "nsPresContext.h"
-#include "nsStyleContext.h"
-#include "nsStyleConsts.h"
-
-#include "nsMathMLmsubFrame.h"
-#include <algorithm>
-
-//
-// <msub> -- attach a subscript to a base - implementation
-//
-
-nsIFrame*
-NS_NewMathMLmsubFrame(nsIPresShell* aPresShell, nsStyleContext* aContext)
-{
-  return new (aPresShell) nsMathMLmsubFrame(aContext);
-}
-
-NS_IMPL_FRAMEARENA_HELPERS(nsMathMLmsubFrame)
-
-nsMathMLmsubFrame::~nsMathMLmsubFrame()
-{
-}
-
-NS_IMETHODIMP
-nsMathMLmsubFrame::TransmitAutomaticData()
-{
-  // if our base is an embellished operator, let its state bubble to us
-  mPresentationData.baseFrame = mFrames.FirstChild();
-  GetEmbellishDataFrom(mPresentationData.baseFrame, mEmbellishData);
-
-  // 1. The REC says:
-  // The <msub> element increments scriptlevel by 1, and sets displaystyle to
-  // "false", within subscript, but leaves both attributes unchanged within base.
-  // 2. The TeXbook (Ch 17. p.141) says the subscript is compressed
-  UpdatePresentationDataFromChildAt(1, -1,
-    ~NS_MATHML_DISPLAYSTYLE | NS_MATHML_COMPRESSED,
-     NS_MATHML_DISPLAYSTYLE | NS_MATHML_COMPRESSED);
-
-  return NS_OK;
-}
-
-/* virtual */ nsresult
-nsMathMLmsubFrame::Place (nsRenderingContext& aRenderingContext,
-                          bool                 aPlaceOrigin,
-                          nsHTMLReflowMetrics& aDesiredSize)
-{
-  // extra spacing after sup/subscript
-  nscoord scriptSpace = nsPresContext::CSSPointsToAppUnits(0.5f); // 0.5pt as in plain TeX
-
-  // subscriptshift
-  //
-  // "Specifies the minimum amount to shift the baseline of subscript down; the
-  // default is for the rendering agent to use its own positioning rules."
-  //
-  // values: length
-  // default: automatic
-  //
-  // We use 0 as the default value so unitless values can be ignored.
-  // As a minimum, negative values can be ignored.
-  //
-  nscoord subScriptShift = 0;
-  nsAutoString value;
-  GetAttribute(mContent, mPresentationData.mstyle,
-               nsGkAtoms::subscriptshift_, value);
-  if (!value.IsEmpty()) {
-    ParseNumericValue(value, &subScriptShift, 0, PresContext(), mStyleContext);
-  }
-
-  return nsMathMLmsubFrame::PlaceSubScript(PresContext(), 
-                                           aRenderingContext,
-                                           aPlaceOrigin,
-                                           aDesiredSize,
-                                           this,
-                                           subScriptShift,
-                                           scriptSpace);
-}
-
-// exported routine that both munder and msub share.
-// munder uses this when movablelimits is set.
-nsresult
-nsMathMLmsubFrame::PlaceSubScript (nsPresContext*      aPresContext,
-                                   nsRenderingContext& aRenderingContext,
-                                   bool                 aPlaceOrigin,
-                                   nsHTMLReflowMetrics& aDesiredSize,
-                                   nsMathMLContainerFrame* aFrame,
-                                   nscoord              aUserSubScriptShift,
-                                   nscoord              aScriptSpace)
-{
-  // force the scriptSpace to be atleast 1 pixel 
-  aScriptSpace = std::max(nsPresContext::CSSPixelsToAppUnits(1), aScriptSpace);
-
-  ////////////////////////////////////
-  // Get the children's desired sizes
-
-  nsBoundingMetrics bmBase, bmSubScript;
-  nsHTMLReflowMetrics baseSize;
-  nsHTMLReflowMetrics subScriptSize;
-  nsIFrame* baseFrame = aFrame->GetFirstPrincipalChild();
-  nsIFrame* subScriptFrame = nullptr;
-  if (baseFrame)
-    subScriptFrame = baseFrame->GetNextSibling();
-  if (!baseFrame || !subScriptFrame || subScriptFrame->GetNextSibling()) {
-    // report an error, encourage people to get their markups in order
-    if (aPlaceOrigin) {
-      aFrame->ReportChildCountError();
-    }
-    return aFrame->ReflowError(aRenderingContext, aDesiredSize);
-  }
-  GetReflowAndBoundingMetricsFor(baseFrame, baseSize, bmBase);
-  GetReflowAndBoundingMetricsFor(subScriptFrame, subScriptSize, bmSubScript);
-
-  // get the subdrop from the subscript font
-  nscoord subDrop;
-  GetSubDropFromChild(subScriptFrame, subDrop);
-  // parameter v, Rule 18a, App. G, TeXbook
-  nscoord minSubScriptShift = bmBase.descent + subDrop;
-
-  //////////////////
-  // Place Children
-  
-  // get min subscript shift limit from x-height
-  // = h(x) - 4/5 * sigma_5, Rule 18b, App. G, TeXbook
-  nscoord xHeight = 0;
-  nsRefPtr<nsFontMetrics> fm;
-  nsLayoutUtils::GetFontMetricsForFrame(baseFrame, getter_AddRefs(fm));
-
-  xHeight = fm->XHeight();
-  nscoord minShiftFromXHeight = (nscoord) 
-    (bmSubScript.ascent - (4.0f/5.0f) * xHeight);
-
-  // subScriptShift
-  // = minimum amount to shift the subscript down set by user or from the font
-  // = sub1 in TeX
-  // = subscriptshift attribute * x-height
-  nscoord subScriptShift, dummy;
-  // get subScriptShift default from font
-  GetSubScriptShifts (fm, subScriptShift, dummy);
-
-  subScriptShift = 
-    std::max(subScriptShift, aUserSubScriptShift);
-
-  // get actual subscriptshift to be used
-  // Rule 18b, App. G, TeXbook
-  nscoord actualSubScriptShift = 
-    std::max(minSubScriptShift,std::max(subScriptShift,minShiftFromXHeight));
-  // get bounding box for base + subscript
-  nsBoundingMetrics boundingMetrics;
-  boundingMetrics.ascent = 
-    std::max(bmBase.ascent, bmSubScript.ascent - actualSubScriptShift);
-  boundingMetrics.descent = 
-    std::max(bmBase.descent, bmSubScript.descent + actualSubScriptShift);
-
-  // add aScriptSpace to the subscript's width
-  boundingMetrics.width = bmBase.width + bmSubScript.width + aScriptSpace;
-  boundingMetrics.leftBearing = bmBase.leftBearing;
-  boundingMetrics.rightBearing = std::max(bmBase.rightBearing, bmBase.width +
-    std::max(bmSubScript.width + aScriptSpace, bmSubScript.rightBearing));
-  aFrame->SetBoundingMetrics (boundingMetrics);
-
-  // reflow metrics
-  aDesiredSize.ascent = 
-    std::max(baseSize.ascent, subScriptSize.ascent - actualSubScriptShift);
-  aDesiredSize.height = aDesiredSize.ascent +
-    std::max(baseSize.height - baseSize.ascent,
-           subScriptSize.height - subScriptSize.ascent + actualSubScriptShift);
-  aDesiredSize.width = boundingMetrics.width;
-  aDesiredSize.mBoundingMetrics = boundingMetrics;
-
-  aFrame->SetReference(nsPoint(0, aDesiredSize.ascent));
-
-  if (aPlaceOrigin) {
-    nscoord dx, dy;
-    // now place the base ...
-    dx = aFrame->MirrorIfRTL(aDesiredSize.width, baseSize.width, 0);
-    dy = aDesiredSize.ascent - baseSize.ascent;
-    FinishReflowChild (baseFrame, aPresContext, nullptr, baseSize, dx, dy, 0);
-    // ... and subscript
-    dx = aFrame->MirrorIfRTL(aDesiredSize.width, subScriptSize.width,
-                             bmBase.width);
-    dy = aDesiredSize.ascent - (subScriptSize.ascent - actualSubScriptShift);
-    FinishReflowChild (subScriptFrame, aPresContext, nullptr, subScriptSize, dx, dy, 0);
-  }
-
-  return NS_OK;
-}

deleted file mode 100644
--- a/layout/mathml/nsMathMLmsubFrame.h
+++ /dev/null
@@ -1,45 +0,0 @@
-/* -*- 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/. */
-
-#ifndef nsMathMLmsubFrame_h___
-#define nsMathMLmsubFrame_h___
-
-#include "mozilla/Attributes.h"
-#include "nsCOMPtr.h"
-#include "nsMathMLContainerFrame.h"
-
-//
-// <msub> -- attach a subscript to a base
-//
-
-class nsMathMLmsubFrame : public nsMathMLContainerFrame {
-public:
-  NS_DECL_FRAMEARENA_HELPERS
-
-  friend nsIFrame* NS_NewMathMLmsubFrame(nsIPresShell* aPresShell, nsStyleContext* aContext);
-
-  NS_IMETHOD
-  TransmitAutomaticData() MOZ_OVERRIDE;
-
-  virtual nsresult
-  Place(nsRenderingContext& aRenderingContext,
-        bool                 aPlaceOrigin,
-        nsHTMLReflowMetrics& aDesiredSize) MOZ_OVERRIDE;
-
-  static nsresult
-  PlaceSubScript (nsPresContext*      aPresContext,
-                  nsRenderingContext& aRenderingContext,
-                  bool                 aPlaceOrigin,
-                  nsHTMLReflowMetrics& aDesiredSize,
-                  nsMathMLContainerFrame* aForFrame,
-                  nscoord              aUserSubScriptShift,
-                  nscoord              aScriptSpace);
-
- protected:
-  nsMathMLmsubFrame(nsStyleContext* aContext) : nsMathMLContainerFrame(aContext) {}
-  virtual ~nsMathMLmsubFrame();
-};
-
-#endif /* nsMathMLmsubFrame_h___ */

deleted file mode 100644
--- a/layout/mathml/nsMathMLmsubsupFrame.cpp
+++ /dev/null
@@ -1,341 +0,0 @@
-/* -*- 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 "nsCOMPtr.h"
-#include "nsFrame.h"
-#include "nsPresContext.h"
-#include "nsStyleContext.h"
-#include "nsStyleConsts.h"
-#include "nsRenderingContext.h"
-
-#include "nsMathMLmsubsupFrame.h"
-#include <algorithm>
-
-//
-// <msubsup> -- attach a subscript-superscript pair to a base - implementation
-//
-
-nsIFrame*
-NS_NewMathMLmsubsupFrame(nsIPresShell* aPresShell, nsStyleContext* aContext)
-{
-  return new (aPresShell) nsMathMLmsubsupFrame(aContext);
-}
-
-NS_IMPL_FRAMEARENA_HELPERS(nsMathMLmsubsupFrame)
-
-nsMathMLmsubsupFrame::~nsMathMLmsubsupFrame()
-{
-}
-
-NS_IMETHODIMP
-nsMathMLmsubsupFrame::TransmitAutomaticData()
-{
-  // if our base is an embellished operator, let its state bubble to us
-  mPresentationData.baseFrame = mFrames.FirstChild();
-  GetEmbellishDataFrom(mPresentationData.baseFrame, mEmbellishData);
-
-  // 1. The REC says:
-  //    The <msubsup> element increments scriptlevel by 1, and sets displaystyle to
-  //    "false", within subscript and superscript, but leaves both attributes
-  //    unchanged within base.
-  // 2. The TeXbook (Ch 17. p.141) says the superscript inherits the compression
-  //    while the subscript is compressed
-  UpdatePresentationDataFromChildAt(1, -1,
-    ~NS_MATHML_DISPLAYSTYLE,
-     NS_MATHML_DISPLAYSTYLE);
-  UpdatePresentationDataFromChildAt(1,  1,
-     NS_MATHML_COMPRESSED,
-     NS_MATHML_COMPRESSED);
-
-  return NS_OK;
-}
-
-/* virtual */ nsresult
-nsMathMLmsubsupFrame::Place(nsRenderingContext& aRenderingContext,
-                            bool                 aPlaceOrigin,
-                            nsHTMLReflowMetrics& aDesiredSize)
-{
-  // extra spacing between base and sup/subscript
-  nscoord scriptSpace = 0;
-
-  // subscriptshift
-  //
-  // "Specifies the minimum amount to shift the baseline of subscript down; the
-  // default is for the rendering agent to use its own positioning rules."
-  //
-  // values: length
-  // default: automatic
-  //
-  // We use 0 as the default value so unitless values can be ignored.
-  // As a minimum, negative values can be ignored.
-  //
-  nsAutoString value;
-  nscoord subScriptShift = 0;
-  GetAttribute(mContent, mPresentationData.mstyle,
-               nsGkAtoms::subscriptshift_, value);
-  if (!value.IsEmpty()) {
-    ParseNumericValue(value, &subScriptShift, 0, PresContext(), mStyleContext);
-  }
-  // superscriptshift
-  //
-  // "Specifies the minimum amount to shift the baseline of superscript up; the
-  // default is for the rendering agent to use its own positioning rules."
-  //
-  // values: length
-  // default: automatic
-  //
-  // We use 0 as the default value so unitless values can be ignored.
-  // As a minimum, negative values can be ignored.
-  //
-  nscoord supScriptShift = 0;
-  GetAttribute(mContent, mPresentationData.mstyle,
-               nsGkAtoms::superscriptshift_, value);
-  if (!value.IsEmpty()) {
-    ParseNumericValue(value, &supScriptShift, 0, PresContext(), mStyleContext);
-  }
-
-  return nsMathMLmsubsupFrame::PlaceSubSupScript(PresContext(),
-                                                 aRenderingContext,
-                                                 aPlaceOrigin,
-                                                 aDesiredSize,
-                                                 this,
-                                                 subScriptShift,
-                                                 supScriptShift,
-                                                 scriptSpace);
-}
-
-// exported routine that both munderover and msubsup share.
-// munderover uses this when movablelimits is set.
-nsresult
-nsMathMLmsubsupFrame::PlaceSubSupScript(nsPresContext*      aPresContext,
-                                        nsRenderingContext& aRenderingContext,
-                                        bool                 aPlaceOrigin,
-                                        nsHTMLReflowMetrics& aDesiredSize,
-                                        nsMathMLContainerFrame* aFrame,
-                                        nscoord              aUserSubScriptShift,
-                                        nscoord              aUserSupScriptShift,
-                                        nscoord              aScriptSpace)
-{
-  // force the scriptSpace to be atleast 1 pixel
-  nscoord onePixel = nsPresContext::CSSPixelsToAppUnits(1);
-  aScriptSpace = std::max(onePixel, aScriptSpace);
-
-  ////////////////////////////////////
-  // Get the children's desired sizes
-
-  nsHTMLReflowMetrics baseSize;
-  nsHTMLReflowMetrics subScriptSize;
-  nsHTMLReflowMetrics supScriptSize;
-  nsBoundingMetrics bmBase, bmSubScript, bmSupScript;
-  nsIFrame* subScriptFrame = nullptr;
-  nsIFrame* supScriptFrame = nullptr;
-  nsIFrame* baseFrame = aFrame->GetFirstPrincipalChild();
-  if (baseFrame)
-    subScriptFrame = baseFrame->GetNextSibling();
-  if (subScriptFrame)
-    supScriptFrame = subScriptFrame->GetNextSibling();
-  if (!baseFrame || !subScriptFrame || !supScriptFrame ||
-      supScriptFrame->GetNextSibling()) {
-    // report an error, encourage people to get their markups in order
-    if (aPlaceOrigin) {
-      aFrame->ReportChildCountError();
-    }
-    return aFrame->ReflowError(aRenderingContext, aDesiredSize);
-  }
-  GetReflowAndBoundingMetricsFor(baseFrame, baseSize, bmBase);
-  GetReflowAndBoundingMetricsFor(subScriptFrame, subScriptSize, bmSubScript);
-  GetReflowAndBoundingMetricsFor(supScriptFrame, supScriptSize, bmSupScript);
-
-  // get the subdrop from the subscript font
-  nscoord subDrop;
-  GetSubDropFromChild(subScriptFrame, subDrop);
-  // parameter v, Rule 18a, App. G, TeXbook
-  nscoord minSubScriptShift = bmBase.descent + subDrop;
-
-  // get the supdrop from the supscript font
-  nscoord supDrop;
-  GetSupDropFromChild(supScriptFrame, supDrop);
-  // parameter u, Rule 18a, App. G, TeXbook
-  nscoord minSupScriptShift = bmBase.ascent - supDrop;
-
-  //////////////////
-  // Place Children
-  //////////////////
-
-  //////////////////////////////////////////////////
-  // Get subscript shift
-  // slightly different from nsMathMLmsubFrame.cpp
-  //////////////////////////////////////////////////
-
-  // subScriptShift{1,2}
-  // = minimum amount to shift the subscript down
-  // = sub{1,2} in TeXbook
-  // subScriptShift1 = subscriptshift attribute * x-height
-  nscoord subScriptShift1, subScriptShift2;
-
-  nsRefPtr<nsFontMetrics> fm;
-  nsLayoutUtils::GetFontMetricsForFrame(baseFrame, getter_AddRefs(fm));
-  aRenderingContext.SetFont(fm);
-
-  // get x-height (an ex)
-  nscoord xHeight = fm->XHeight();
-
-  nscoord ruleSize;
-  GetRuleThickness (aRenderingContext, fm, ruleSize);
-
-  // Get subScriptShift{1,2} default from font
-  GetSubScriptShifts (fm, subScriptShift1, subScriptShift2);
-
-  if (0 < aUserSubScriptShift) {
-    // the user has set the subscriptshift attribute
-    float scaler = ((float) subScriptShift2) / subScriptShift1;
-    subScriptShift1 = std::max(subScriptShift1, aUserSubScriptShift);
-    subScriptShift2 = NSToCoordRound(scaler * subScriptShift1);
-  }
-
-  // get a tentative value for subscriptshift
-  // Rule 18d, App. G, TeXbook
-  nscoord subScriptShift =
-    std::max(minSubScriptShift,std::max(subScriptShift1,subScriptShift2));
-
-  //////////////////////////////////////////////////
-  // Get supscript shift
-  // same code from nsMathMLmsupFrame.cpp
-  //////////////////////////////////////////////////
-
-  // get min supscript shift limit from x-height
-  // = d(x) + 1/4 * sigma_5, Rule 18c, App. G, TeXbook
-  nscoord minShiftFromXHeight = (nscoord)
-    (bmSupScript.descent + (1.0f/4.0f) * xHeight);
-
-  // supScriptShift{1,2,3}
-  // = minimum amount to shift the supscript up
-  // = sup{1,2,3} in TeX
-  // supScriptShift1 = superscriptshift attribute * x-height
-  // Note that there are THREE values for supscript shifts depending
-  // on the current style
-  nscoord supScriptShift1, supScriptShift2, supScriptShift3;
-  // Set supScriptShift{1,2,3} default from font
-  GetSupScriptShifts (fm, supScriptShift1, supScriptShift2, supScriptShift3);
-  if (0 < aUserSupScriptShift) {
-    // the user has set the superscriptshift attribute
-    float scaler2 = ((float) supScriptShift2) / supScriptShift1;
-    float scaler3 = ((float) supScriptShift3) / supScriptShift1;
-    supScriptShift1 = std::max(supScriptShift1, aUserSupScriptShift);
-    supScriptShift2 = NSToCoordRound(scaler2 * supScriptShift1);
-    supScriptShift3 = NSToCoordRound(scaler3 * supScriptShift1);
-  }
-
-  // get sup script shift depending on current script level and display style
-  // Rule 18c, App. G, TeXbook
-  nscoord supScriptShift;
-  nsPresentationData presentationData;
-  aFrame->GetPresentationData(presentationData);
-  if ( aFrame->StyleFont()->mScriptLevel == 0 &&
-       NS_MATHML_IS_DISPLAYSTYLE(presentationData.flags) &&
-      !NS_MATHML_IS_COMPRESSED(presentationData.flags)) {
-    // Style D in TeXbook
-    supScriptShift = supScriptShift1;
-  }
-  else if (NS_MATHML_IS_COMPRESSED(presentationData.flags)) {
-    // Style C' in TeXbook = D',T',S',SS'
-    supScriptShift = supScriptShift3;
-  }
-  else {
-    // everything else = T,S,SS
-    supScriptShift = supScriptShift2;
-  }
-
-  // get tentative value for superscriptshift
-  // Rule 18c, App. G, TeXbook
-  supScriptShift =
-    std::max(minSupScriptShift,std::max(supScriptShift,minShiftFromXHeight));
-
-  //////////////////////////////////////////////////
-  // Negotiate between supScriptShift and subScriptShift
-  // so that there will be enough gap between them
-  // Rule 18e, App. G, TeXbook
-  //////////////////////////////////////////////////
-
-  nscoord gap =
-    (supScriptShift - bmSupScript.descent) -
-    (bmSubScript.ascent - subScriptShift);
-  if (gap < 4.0f * ruleSize) {
-    // adjust subScriptShift to get a gap of (4.0 * ruleSize)
-    subScriptShift += NSToCoordRound ((4.0f * ruleSize) - gap);
-  }
-
-  // next we want to ensure that the bottom of the superscript
-  // will be > (4/5) * x-height above baseline
-  gap = NSToCoordRound ((4.0f/5.0f) * xHeight -
-                        (supScriptShift - bmSupScript.descent));
-  if (gap > 0) {
-    supScriptShift += gap;
-    subScriptShift -= gap;
-  }
-
-  //////////////////////////////////////////////////
-  // Do the Placing
-  //////////////////////////////////////////////////
-
-  // get bounding box for base + subscript + superscript
-  nsBoundingMetrics boundingMetrics;
-  boundingMetrics.ascent =
-    std::max(bmBase.ascent, (bmSupScript.ascent + supScriptShift));
-  boundingMetrics.descent =
-   std::max(bmBase.descent, (bmSubScript.descent + subScriptShift));
-
-  // leave aScriptSpace after both super/subscript
-  // add italicCorrection between base and superscript
-  // add "a little to spare" as well (see TeXbook Ch.11, p.64), as we
-  // estimate the italic creation ourselves and it isn't the same as TeX 
-  nscoord italicCorrection;
-  GetItalicCorrection(bmBase, italicCorrection);
-  italicCorrection += onePixel;
-  boundingMetrics.width = bmBase.width + aScriptSpace +
-    std::max((italicCorrection + bmSupScript.width), bmSubScript.width);
-  boundingMetrics.leftBearing = bmBase.leftBearing;
-  boundingMetrics.rightBearing = bmBase.width +
-    std::max((italicCorrection + bmSupScript.rightBearing), bmSubScript.rightBearing);
-  aFrame->SetBoundingMetrics(boundingMetrics);
-
-  // reflow metrics
-  aDesiredSize.ascent =
-    std::max(baseSize.ascent, 
-       std::max(subScriptSize.ascent - subScriptShift,
-              supScriptSize.ascent + supScriptShift));
-  aDesiredSize.height = aDesiredSize.ascent +
-    std::max(baseSize.height - baseSize.ascent,
-       std::max(subScriptSize.height - subScriptSize.ascent + subScriptShift, 
-              supScriptSize.height - subScriptSize.ascent - supScriptShift));
-  aDesiredSize.width = boundingMetrics.width;
-  aDesiredSize.mBoundingMetrics = boundingMetrics;
-
-  aFrame->SetReference(nsPoint(0, aDesiredSize.ascent));
-
-  if (aPlaceOrigin) {
-    nscoord dx, dy;
-    // now place the base ...
-    dx = aFrame->MirrorIfRTL(aDesiredSize.width, baseSize.width, 0);
-    dy = aDesiredSize.ascent - baseSize.ascent;
-    FinishReflowChild(baseFrame, aPresContext, nullptr,
-                      baseSize, dx, dy, 0);
-    // ... and subscript
-    dx = aFrame->MirrorIfRTL(aDesiredSize.width, subScriptSize.width,
-                             bmBase.width);
-    dy = aDesiredSize.ascent - (subScriptSize.ascent - subScriptShift);
-    FinishReflowChild(subScriptFrame, aPresContext, nullptr,
-                      subScriptSize, dx, dy, 0);
-    // ... and the superscript
-    dx = aFrame->MirrorIfRTL(aDesiredSize.width, supScriptSize.width,
-                             bmBase.width + italicCorrection);
-    dy = aDesiredSize.ascent - (supScriptSize.ascent + supScriptShift);
-    FinishReflowChild(supScriptFrame, aPresContext, nullptr,
-                      supScriptSize, dx, dy, 0);
-  }
-
-  return NS_OK;
-}

deleted file mode 100644
--- a/layout/mathml/nsMathMLmsubsupFrame.h
+++ /dev/null
@@ -1,46 +0,0 @@
-/* -*- 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/. */
-
-#ifndef nsMathMLmsubsupFrame_h___
-#define nsMathMLmsubsupFrame_h___
-
-#include "mozilla/Attributes.h"
-#include "nsCOMPtr.h"
-#include "nsMathMLContainerFrame.h"
-
-//
-// <msubsup> -- attach a subscript-superscript pair to a base
-//
-
-class nsMathMLmsubsupFrame : public nsMathMLContainerFrame {
-public:
-  NS_DECL_FRAMEARENA_HELPERS
-
-  friend nsIFrame* NS_NewMathMLmsubsupFrame(nsIPresShell* aPresShell, nsStyleContext* aContext);
-
-  NS_IMETHOD
-  TransmitAutomaticData() MOZ_OVERRIDE;
-
-  virtual nsresult
-  Place(nsRenderingContext& aRenderingContext,
-        bool                 aPlaceOrigin,
-        nsHTMLReflowMetrics& aDesiredSize) MOZ_OVERRIDE;
-
-  static nsresult
-  PlaceSubSupScript(nsPresContext*      aPresContext,
-                    nsRenderingContext& aRenderingContext,
-                    bool                 aPlaceOrigin,
-                    nsHTMLReflowMetrics& aDesiredSize,
-                    nsMathMLContainerFrame* aForFrame,
-                    nscoord              aUserSubScriptShift,
-                    nscoord              aUserSupScriptShift,
-                    nscoord              aScriptSpace);
-
-protected:
-  nsMathMLmsubsupFrame(nsStyleContext* aContext) : nsMathMLContainerFrame(aContext) {}
-  virtual ~nsMathMLmsubsupFrame();
-};
-
-#endif /* nsMathMLmsubsupFrame_h___ */

deleted file mode 100644
--- a/layout/mathml/nsMathMLmsupFrame.cpp
+++ /dev/null
@@ -1,231 +0,0 @@
-/* -*- 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 "nsCOMPtr.h"
-#include "nsFrame.h"
-#include "nsPresContext.h"
-#include "nsStyleContext.h"
-#include "nsStyleConsts.h"
-
-#include "nsMathMLmsupFrame.h"
-#include <algorithm>
-
-//
-// <msup> -- attach a superscript to a base - implementation
-//
-
-nsIFrame*
-NS_NewMathMLmsupFrame(nsIPresShell* aPresShell, nsStyleContext* aContext)
-{
-  return new (aPresShell) nsMathMLmsupFrame(aContext);
-}
-
-NS_IMPL_FRAMEARENA_HELPERS(nsMathMLmsupFrame)
-
-nsMathMLmsupFrame::~nsMathMLmsupFrame()
-{
-}
-
-NS_IMETHODIMP
-nsMathMLmsupFrame::TransmitAutomaticData()
-{
-  // if our base is an embellished operator, its flags bubble to us
-  mPresentationData.baseFrame = mFrames.FirstChild();
-  GetEmbellishDataFrom(mPresentationData.baseFrame, mEmbellishData);
-
-  // 1. The REC says:
-  // The <msup> element increments scriptlevel by 1, and sets displaystyle to
-  // "false", within superscript, but leaves both attributes unchanged within base.
-  // 2. The TeXbook (Ch 17. p.141) says the superscript *inherits* the compression,
-  // so we don't set the compression flag. Our parent will propagate its own.
-  UpdatePresentationDataFromChildAt(1, -1,
-    ~NS_MATHML_DISPLAYSTYLE,
-     NS_MATHML_DISPLAYSTYLE);
-
-  return NS_OK;
-}
-
-/* virtual */ nsresult
-nsMathMLmsupFrame::Place(nsRenderingContext& aRenderingContext,
-                         bool                 aPlaceOrigin,
-                         nsHTMLReflowMetrics& aDesiredSize)
-{
-  // extra spacing after sup/subscript
-  nscoord scriptSpace = nsPresContext::CSSPointsToAppUnits(0.5f); // 0.5pt as in plain TeX
-
-  // superscriptshift
-  //
-  // "Specifies the minimum amount to shift the baseline of superscript up; the
-  // default is for the rendering agent to use its own positioning rules."
-  //
-  // values: length
-  // default: automatic
-  //
-  // We use 0 as the default value so unitless values can be ignored.
-  // As a minimum, negative values can be ignored.
-  //
-  nsAutoString value;
-  nscoord supScriptShift = 0;
-  GetAttribute(mContent, mPresentationData.mstyle,
-               nsGkAtoms::superscriptshift_, value);
-  if (!value.IsEmpty()) {
-    ParseNumericValue(value, &supScriptShift, 0, PresContext(), mStyleContext);
-  }
-
-  return nsMathMLmsupFrame::PlaceSuperScript(PresContext(), 
-                                             aRenderingContext,
-                                             aPlaceOrigin,
-                                             aDesiredSize,
-                                             this,
-                                             supScriptShift,
-                                             scriptSpace);
-}
-
-// exported routine that both mover and msup share.
-// mover uses this when movablelimits is set.
-nsresult
-nsMathMLmsupFrame::PlaceSuperScript(nsPresContext*      aPresContext,
-                                    nsRenderingContext& aRenderingContext,
-                                    bool                 aPlaceOrigin,
-                                    nsHTMLReflowMetrics& aDesiredSize,
-                                    nsMathMLContainerFrame* aFrame,
-                                    nscoord              aUserSupScriptShift,
-                                    nscoord              aScriptSpace)
-{
-  // force the scriptSpace to be at least 1 pixel 
-  nscoord onePixel = nsPresContext::CSSPixelsToAppUnits(1);
-  aScriptSpace = std::max(onePixel, aScriptSpace);
-
-  ////////////////////////////////////
-  // Get the children's desired sizes
-
-  nsHTMLReflowMetrics baseSize;
-  nsHTMLReflowMetrics supScriptSize;
-  nsBoundingMetrics bmBase, bmSupScript;
-  nsIFrame* supScriptFrame = nullptr;
-  nsIFrame* baseFrame = aFrame->GetFirstPrincipalChild();
-  if (baseFrame)
-    supScriptFrame = baseFrame->GetNextSibling();
-  if (!baseFrame || !supScriptFrame || supScriptFrame->GetNextSibling()) {
-    // report an error, encourage people to get their markups in order
-    if (aPlaceOrigin) {
-      aFrame->ReportChildCountError();
-    }
-    return aFrame->ReflowError(aRenderingContext, aDesiredSize);
-  }
-  GetReflowAndBoundingMetricsFor(baseFrame, baseSize, bmBase);
-  GetReflowAndBoundingMetricsFor(supScriptFrame, supScriptSize, bmSupScript);
-
-  // get the supdrop from the supscript font
-  nscoord supDrop;
-  GetSupDropFromChild(supScriptFrame, supDrop);
-  // parameter u, Rule 18a, App. G, TeXbook
-  nscoord minSupScriptShift = bmBase.ascent - supDrop;
-
-  //////////////////
-  // Place Children 
-  
-  // get min supscript shift limit from x-height
-  // = d(x) + 1/4 * sigma_5, Rule 18c, App. G, TeXbook
-  nscoord xHeight = 0;
-  nsRefPtr<nsFontMetrics> fm;
-  nsLayoutUtils::GetFontMetricsForFrame(baseFrame, getter_AddRefs(fm));
-
-  xHeight = fm->XHeight();
-  nscoord minShiftFromXHeight = (nscoord) 
-    (bmSupScript.descent + (1.0f/4.0f) * xHeight);
-  nscoord italicCorrection;
-  GetItalicCorrection(bmBase, italicCorrection);
-
-  // supScriptShift{1,2,3}
-  // = minimum amount to shift the supscript up
-  // = sup{1,2,3} in TeX
-  // supScriptShift1 = superscriptshift attribute * x-height
-  // Note that there are THREE values for supscript shifts depending
-  // on the current style
-  nscoord supScriptShift1, supScriptShift2, supScriptShift3;
-  // Set supScriptShift{1,2,3} default from font
-  GetSupScriptShifts (fm, supScriptShift1, supScriptShift2, supScriptShift3);
-
-  if (0 < aUserSupScriptShift) {
-    // the user has set the superscriptshift attribute
-    float scaler2 = ((float) supScriptShift2) / supScriptShift1;
-    float scaler3 = ((float) supScriptShift3) / supScriptShift1;
-    supScriptShift1 = 
-      std::max(supScriptShift1, aUserSupScriptShift);
-    supScriptShift2 = NSToCoordRound(scaler2 * supScriptShift1);
-    supScriptShift3 = NSToCoordRound(scaler3 * supScriptShift1);
-  }
-
-  // get sup script shift depending on current script level and display style
-  // Rule 18c, App. G, TeXbook
-  nscoord supScriptShift;
-  nsPresentationData presentationData;
-  aFrame->GetPresentationData (presentationData);
-  if ( aFrame->StyleFont()->mScriptLevel == 0 && 
-       NS_MATHML_IS_DISPLAYSTYLE(presentationData.flags) &&
-      !NS_MATHML_IS_COMPRESSED(presentationData.flags)) {
-    // Style D in TeXbook
-    supScriptShift = supScriptShift1;
-  }
-  else if (NS_MATHML_IS_COMPRESSED(presentationData.flags)) {
-    // Style C' in TeXbook = D',T',S',SS'
-    supScriptShift = supScriptShift3;
-  }
-  else {
-    // everything else = T,S,SS
-    supScriptShift = supScriptShift2;
-  }
-
-  // get actual supscriptshift to be used
-  // Rule 18c, App. G, TeXbook
-  nscoord actualSupScriptShift = 
-    std::max(minSupScriptShift,std::max(supScriptShift,minShiftFromXHeight));
-
-  // bounding box
-  nsBoundingMetrics boundingMetrics;
-  boundingMetrics.ascent =
-    std::max(bmBase.ascent, (bmSupScript.ascent + actualSupScriptShift));
-  boundingMetrics.descent =
-    std::max(bmBase.descent, (bmSupScript.descent - actualSupScriptShift));
-
-  // leave aScriptSpace after superscript
-  // add italicCorrection between base and superscript
-  // add "a little to spare" as well (see TeXbook Ch.11, p.64), as we
-  // estimate the italic creation ourselves and it isn't the same as TeX 
-  italicCorrection += onePixel;
-  boundingMetrics.width = bmBase.width + italicCorrection +
-                          bmSupScript.width + aScriptSpace;
-  boundingMetrics.leftBearing = bmBase.leftBearing;
-  boundingMetrics.rightBearing = bmBase.width + italicCorrection +
-                                 bmSupScript.rightBearing;
-  aFrame->SetBoundingMetrics(boundingMetrics);
-
-  // reflow metrics
-  aDesiredSize.ascent =
-    std::max(baseSize.ascent, (supScriptSize.ascent + actualSupScriptShift));
-  aDesiredSize.height = aDesiredSize.ascent +
-    std::max(baseSize.height - baseSize.ascent,
-           (supScriptSize.height - supScriptSize.ascent - actualSupScriptShift));
-  aDesiredSize.width = boundingMetrics.width;
-  aDesiredSize.mBoundingMetrics = boundingMetrics;
-
-  aFrame->SetReference(nsPoint(0, aDesiredSize.ascent));
-
-  if (aPlaceOrigin) {
-    nscoord dx, dy;
-    // now place the base ...
-    dx = aFrame->MirrorIfRTL(aDesiredSize.width, baseSize.width, 0);
-    dy = aDesiredSize.ascent - baseSize.ascent;
-    FinishReflowChild (baseFrame, aPresContext, nullptr, baseSize, dx, dy, 0);
-    // ... and supscript
-    dx = aFrame->MirrorIfRTL(aDesiredSize.width, supScriptSize.width,
-                             bmBase.width + italicCorrection);
-    dy = aDesiredSize.ascent - (supScriptSize.ascent + actualSupScriptShift);
-    FinishReflowChild (supScriptFrame, aPresContext, nullptr, supScriptSize, dx, dy, 0);
-  }
-
-  return NS_OK;
-}

deleted file mode 100644
--- a/layout/mathml/nsMathMLmsupFrame.h
+++ /dev/null
@@ -1,45 +0,0 @@
-/* -*- 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/. */
-
-#ifndef nsMathMLmsupFrame_h___
-#define nsMathMLmsupFrame_h___
-
-#include "mozilla/Attributes.h"
-#include "nsCOMPtr.h"
-#include "nsMathMLContainerFrame.h"
-
-//
-// <msup> -- attach a superscript to a base
-//
-
-class nsMathMLmsupFrame : public nsMathMLContainerFrame {
-public:
-  NS_DECL_FRAMEARENA_HELPERS
-
-  friend nsIFrame* NS_NewMathMLmsupFrame(nsIPresShell* aPresShell, nsStyleContext* aContext);
-
-  NS_IMETHOD
-  TransmitAutomaticData() MOZ_OVERRIDE;
-
-  virtual nsresult
-  Place(nsRenderingContext& aRenderingContext,
-        bool                 aPlaceOrigin,
-        nsHTMLReflowMetrics& aDesiredSize) MOZ_OVERRIDE;
-
-  static nsresult
-  PlaceSuperScript (nsPresContext*      aPresContext,
-                    nsRenderingContext& aRenderingContext,
-                    bool                 aPlaceOrigin,
-                    nsHTMLReflowMetrics& aDesiredSize,
-                    nsMathMLContainerFrame* aForFrame,
-                    nscoord              aUserSupScriptShift,
-                    nscoord              aScriptSpace);
-
-protected:
-  nsMathMLmsupFrame(nsStyleContext* aContext) : nsMathMLContainerFrame(aContext) {}
-  virtual ~nsMathMLmsupFrame();
-};
-
-#endif /* nsMathMLmsupFrame_h___ */

--- a/layout/mathml/nsMathMLmunderoverFrame.cpp
+++ b/layout/mathml/nsMathMLmunderoverFrame.cpp
@@ -8,19 +8,17 @@
 #include "nsFrame.h"
 #include "nsPresContext.h"
 #include "nsStyleContext.h"
 #include "nsStyleConsts.h"
 #include "nsINameSpaceManager.h"
 #include "nsRenderingContext.h"
 
 #include "nsMathMLmunderoverFrame.h"
-#include "nsMathMLmsubsupFrame.h"
-#include "nsMathMLmsupFrame.h"
-#include "nsMathMLmsubFrame.h"
+#include "nsMathMLmmultiscriptsFrame.h"
 #include <algorithm>
 
 //
 // <munderover> -- attach an underscript-overscript pair to a base - implementation
 // <mover> -- attach an overscript to a base - implementation
 // <munder> -- attach an underscript to a base - implementation
 //
 
@@ -305,37 +303,37 @@ nsMathMLmunderoverFrame::Place(nsRenderi
                                nsHTMLReflowMetrics& aDesiredSize)
 {
   nsIAtom* tag = mContent->Tag();
   if ( NS_MATHML_EMBELLISH_IS_MOVABLELIMITS(mEmbellishData.flags) &&
        !NS_MATHML_IS_DISPLAYSTYLE(mPresentationData.flags)) {
     //place like sub sup or subsup
     nscoord scriptSpace = nsPresContext::CSSPointsToAppUnits(0.5f);
     if (tag == nsGkAtoms::munderover_) {
-      return nsMathMLmsubsupFrame::PlaceSubSupScript(PresContext(),
-                                                     aRenderingContext,
-                                                     aPlaceOrigin,
-                                                     aDesiredSize,
-                                                     this, 0, 0,
-                                                     scriptSpace);
+      return nsMathMLmmultiscriptsFrame::PlaceMultiScript(PresContext(),
+                                                          aRenderingContext,
+                                                          aPlaceOrigin,
+                                                          aDesiredSize,
+                                                          this, 0, 0,
+                                                          scriptSpace);
     } else if (tag == nsGkAtoms::munder_) {
-      return nsMathMLmsubFrame::PlaceSubScript(PresContext(),
-                                               aRenderingContext,
-                                               aPlaceOrigin,
-                                               aDesiredSize,
-                                               this, 0,
-                                               scriptSpace);
+      return nsMathMLmmultiscriptsFrame::PlaceMultiScript(PresContext(),
+                                                          aRenderingContext,
+                                                          aPlaceOrigin,
+                                                          aDesiredSize,
+                                                          this, 0, 0,
+                                                          scriptSpace);
     } else {
       NS_ASSERTION(tag == nsGkAtoms::mover_, "mContent->Tag() not recognized");
-      return nsMathMLmsupFrame::PlaceSuperScript(PresContext(),
-                                                 aRenderingContext,
-                                                 aPlaceOrigin,
-                                                 aDesiredSize,
-                                                 this, 0,
-                                                 scriptSpace);
+      return nsMathMLmmultiscriptsFrame::PlaceMultiScript(PresContext(),
+                                                          aRenderingContext,
+                                                          aPlaceOrigin,
+                                                          aDesiredSize,
+                                                          this, 0, 0,
+                                                          scriptSpace);
     }
     
   }
 
   ////////////////////////////////////
   // Get the children's desired sizes
 
   nsBoundingMetrics bmBase, bmUnder, bmOver;