diff --git a/layout/mathml/mathml.css b/layout/mathml/mathml.css
index 4e0f937d491e..d3cfa5e408cc 100644
--- a/layout/mathml/mathml.css
+++ b/layout/mathml/mathml.css
@@ -467,3 +467,17 @@ msub > :not(:first-child),
 msup > :not(:first-child),
 msubsup > :not(:first-child),
 mmultiscripts > :not(:first-child) { -moz-script-level:+1; }
+
+/*****************************************/
+/* Controlling directionality            */
+/*****************************************/
+
+math[dir="rtl"], mstyle[dir="rtl"], mrow[dir="rtl"],
+mi[dir="rtl"], mn[dir="rtl"], mo[dir="rtl"], mtext[dir="rtl"], ms[dir="rtl"] {
+    direction: rtl;
+}
+
+math[dir="ltr"], mstyle[dir="ltr"], mrow[dir="ltr"],
+mi[dir="ltr"], mn[dir="ltr"], mo[dir="ltr"], mtext[dir="ltr"], ms[dir="ltr"] {
+    direction: ltr;
+}
diff --git a/layout/mathml/nsMathMLContainerFrame.cpp b/layout/mathml/nsMathMLContainerFrame.cpp
index 4d6fa6d76e27..939880390cb7 100644
--- a/layout/mathml/nsMathMLContainerFrame.cpp
+++ b/layout/mathml/nsMathMLContainerFrame.cpp
@@ -1193,20 +1193,21 @@ class nsMathMLContainerFrame::RowChildFrameIterator {
 public:
   explicit RowChildFrameIterator(nsMathMLContainerFrame* aParentFrame) :
     mParentFrame(aParentFrame),
-    mChildFrame(aParentFrame->mFrames.FirstChild()),
     mX(0),
     mCarrySpace(0),
-    mFromFrameType(eMathMLFrameType_UNKNOWN)
+    mFromFrameType(eMathMLFrameType_UNKNOWN),
+    mRTL(NS_MATHML_IS_RTL(aParentFrame->mPresentationData.flags))
   {
+    if (!mRTL) {
+      mChildFrame = aParentFrame->mFrames.FirstChild();
+    } else {
+      mChildFrame = aParentFrame->mFrames.LastChild();
+    }
+
     if (!mChildFrame)
       return;
 
     InitMetricsForChild();
-    // Remove left correction in <msqrt> because the sqrt glyph itself is
-    // there first.
-    if (mParentFrame->GetContent()->Tag() == nsGkAtoms::msqrt_) {
-      mX = 0;
-    }
   }
 
   RowChildFrameIterator& operator++()
@@ -1214,7 +1215,12 @@ public:
     // add child size + italic correction
     mX += mSize.mBoundingMetrics.width + mItalicCorrection;
 
-    mChildFrame = mChildFrame->GetNextSibling();
+    if (!mRTL) {
+      mChildFrame = mChildFrame->GetNextSibling();
+    } else {
+      mChildFrame = mChildFrame->GetPrevSibling();
+    }
+
     if (!mChildFrame)
       return *this;
 
@@ -1251,16 +1257,29 @@ private:
   PRInt32 mCarrySpace;
   eMathMLFrameType mFromFrameType;
 
+  bool mRTL;
+
   void InitMetricsForChild()
   {
     GetReflowAndBoundingMetricsFor(mChildFrame, mSize, mSize.mBoundingMetrics,
                                    &mChildFrameType);
-    nscoord leftCorrection;
-    GetItalicCorrection(mSize.mBoundingMetrics, leftCorrection,
-                        mItalicCorrection);
+    nscoord leftCorrection, rightCorrection;
+    GetItalicCorrection(mSize.mBoundingMetrics,
+                        leftCorrection, rightCorrection);
+    if (!mChildFrame->GetPrevSibling() &&
+        mParentFrame->GetContent()->Tag() == nsGkAtoms::msqrt_) {
+      // Remove leading correction in <msqrt> because the sqrt glyph itself is
+      // there first.
+      if (!mRTL) {
+        leftCorrection = 0;
+      } else {
+        rightCorrection = 0;
+      }
+    }
     // add left correction -- this fixes the problem of the italic 'f'
     // e.g., <mo>q</mo> <mi>f</mi> <mo>I</mo> 
     mX += leftCorrection;
+    mItalicCorrection = rightCorrection;
   }
 };
 
diff --git a/layout/mathml/nsMathMLContainerFrame.h b/layout/mathml/nsMathMLContainerFrame.h
index 272424fff176..343f8ed28f9e 100644
--- a/layout/mathml/nsMathMLContainerFrame.h
+++ b/layout/mathml/nsMathMLContainerFrame.h
@@ -193,6 +193,14 @@ public:
                    nsIAtom*        aAttribute,
                    PRInt32         aModType);
 
+  // helper function to apply mirroring to a horizontal coordinate, if needed.
+  nscoord
+  MirrorIfRTL(nscoord aParentWidth, nscoord aChildWidth, nscoord aChildLeading)
+  {
+    return (NS_MATHML_IS_RTL(mPresentationData.flags) ?
+            aParentWidth - aChildWidth - aChildLeading : aChildLeading);
+  }
+
   // --------------------------------------------------------------------------
   // Additional methods 
 
diff --git a/layout/mathml/nsMathMLmencloseFrame.cpp b/layout/mathml/nsMathMLmencloseFrame.cpp
index 8d6f8c1d60d9..81ef101de8aa 100644
--- a/layout/mathml/nsMathMLmencloseFrame.cpp
+++ b/layout/mathml/nsMathMLmencloseFrame.cpp
@@ -241,7 +241,8 @@ nsMathMLmencloseFrame::BuildDisplayList(nsDisplayListBuilder*   aBuilder,
 
     nsRect rect;
     mMathMLChar[mRadicalCharIndex].GetRect(rect);
-    rect.MoveBy(rect.width, 0);
+    rect.MoveBy(NS_MATHML_IS_RTL(mPresentationData.flags) ?
+                -mContentWidth : rect.width, 0);
     rect.SizeTo(mContentWidth, mRuleThickness);
     rv = DisplayBar(aBuilder, this, rect, aLists);
     NS_ENSURE_SUCCESS(rv, rv);
@@ -518,12 +519,15 @@ nsMathMLmencloseFrame::PlaceInternal(nsRenderingContext& aRenderingContext,
   ///////////////
   // radical notation:
   if (IsToDraw(NOTATION_RADICAL)) {
+    nscoord *dx_leading =
+      NS_MATHML_IS_RTL(mPresentationData.flags) ? &dx_right : &dx_left;
+    
     if (aWidthOnly) {
       nscoord radical_width = mMathMLChar[mRadicalCharIndex].
         GetMaxWidth(PresContext(), aRenderingContext);
       
       // Update horizontal parameters
-      dx_left = NS_MAX(dx_left, radical_width);
+      *dx_leading = NS_MAX(*dx_leading, radical_width);
     } else {
       // Stretch the radical symbol to the appropriate height if it is not
       // big enough.
@@ -539,7 +543,7 @@ nsMathMLmencloseFrame::PlaceInternal(nsRenderingContext& aRenderingContext,
       mMathMLChar[mRadicalCharIndex].GetBoundingMetrics(bmRadicalChar);
 
       // Update horizontal parameters
-      dx_left = NS_MAX(dx_left, bmRadicalChar.width);
+      *dx_leading = NS_MAX(*dx_leading, bmRadicalChar.width);
 
       // Update vertical parameters
       radicalAscent = bmBase.ascent + psi + mRuleThickness;
@@ -653,14 +657,17 @@ nsMathMLmencloseFrame::PlaceInternal(nsRenderingContext& aRenderingContext,
                                                     bmLongdivChar.ascent +
                                                     bmLongdivChar.descent));
 
-    if (IsToDraw(NOTATION_RADICAL))
-      mMathMLChar[mRadicalCharIndex].SetRect(nsRect(dx_left -
-                                                    bmRadicalChar.width,
+    if (IsToDraw(NOTATION_RADICAL)) {
+      nscoord dx = NS_MATHML_IS_RTL(mPresentationData.flags) ?
+        dx_left + bmBase.width : dx_left - bmRadicalChar.width;
+
+      mMathMLChar[mRadicalCharIndex].SetRect(nsRect(dx,
                                                     aDesiredSize.ascent -
                                                     radicalAscent,
                                                     bmRadicalChar.width,
                                                     bmRadicalChar.ascent +
                                                     bmRadicalChar.descent));
+    }
 
     mContentWidth = bmBase.width;
 
diff --git a/layout/mathml/nsMathMLmfencedFrame.cpp b/layout/mathml/nsMathMLmfencedFrame.cpp
index fcadba532e6b..02aeeee64b2d 100644
--- a/layout/mathml/nsMathMLmfencedFrame.cpp
+++ b/layout/mathml/nsMathMLmfencedFrame.cpp
@@ -383,13 +383,27 @@ nsMathMLmfencedFrame::Reflow(nsPresContext*          aPresContext,
   nscoord dx = 0;
   nsBoundingMetrics bm;
   bool firstTime = true;
-  if (mOpenChar) {
-    PlaceChar(mOpenChar, ascent, bm, dx);
+  nsMathMLChar *leftChar, *rightChar;
+  bool isRTL = NS_MATHML_IS_RTL(mPresentationData.flags);
+  if (isRTL) {
+    leftChar = mCloseChar;
+    rightChar = mOpenChar;
+  } else {
+    leftChar = mOpenChar;
+    rightChar = mCloseChar;
+  }
+
+  if (leftChar) {
+    PlaceChar(leftChar, ascent, bm, dx);
     aDesiredSize.mBoundingMetrics = bm;
     firstTime = false;
   }
 
-  childFrame = firstChild;
+  if (isRTL) {
+    childFrame = this->GetLastChild(nsIFrame::kPrincipalList);
+  } else {
+    childFrame = firstChild;
+  }
   while (childFrame) {
     nsHTMLReflowMetrics childSize;
     GetReflowAndBoundingMetricsFor(childFrame, childSize, bm);
@@ -405,16 +419,21 @@ nsMathMLmfencedFrame::Reflow(nsPresContext*          aPresContext,
     dx += childSize.width;
 
     if (i < mSeparatorsCount) {
-      PlaceChar(&mSeparatorsChar[i], ascent, bm, dx);
+      PlaceChar(&mSeparatorsChar[isRTL ? mSeparatorsCount - 1 - i : i],
+                ascent, bm, dx);
       aDesiredSize.mBoundingMetrics += bm;
     }
     i++;
 
-    childFrame = childFrame->GetNextSibling();
+    if (isRTL) {
+      childFrame = childFrame->GetPrevSibling();
+    } else {
+      childFrame = childFrame->GetNextSibling();
+    }
   }
 
-  if (mCloseChar) {
-    PlaceChar(mCloseChar, ascent, bm, dx);
+  if (rightChar) {
+    PlaceChar(rightChar, ascent, bm, dx);
     if (firstTime)
       aDesiredSize.mBoundingMetrics  = bm;
     else  
diff --git a/layout/mathml/nsMathMLmfracFrame.cpp b/layout/mathml/nsMathMLmfracFrame.cpp
index ca544d952e95..da170f5548df 100644
--- a/layout/mathml/nsMathMLmfracFrame.cpp
+++ b/layout/mathml/nsMathMLmfracFrame.cpp
@@ -501,18 +501,26 @@ nsMathMLmfracFrame::PlaceInternal(nsRenderingContext& aRenderingContext,
     mReference.y = aDesiredSize.ascent;
     
     if (aPlaceOrigin) {
-      FinishReflowChild(frameNum, presContext, nsnull, sizeNum,
-                        leftSpace,
-                        aDesiredSize.ascent - numShift - sizeNum.ascent, 0);
+      nscoord dx, dy;
 
-      mLineRect.SetRect(leftSpace + bmNum.width,
-                        aDesiredSize.ascent - mBoundingMetrics.ascent,
-                        mLineRect.width,
-                        aDesiredSize.height - 2 * padding);
+      // place numerator
+      dx = MirrorIfRTL(aDesiredSize.width, sizeNum.width,
+                       leftSpace);
+      dy = aDesiredSize.ascent - numShift - sizeNum.ascent;
+      FinishReflowChild(frameNum, presContext, nsnull, sizeNum, dx, dy, 0);
 
-      FinishReflowChild(frameDen, presContext, nsnull, sizeDen,
-                        leftSpace + bmNum.width + mLineRect.width,
-                        aDesiredSize.ascent + denShift - sizeDen.ascent, 0);
+      // place the fraction bar
+      dx = MirrorIfRTL(aDesiredSize.width, mLineRect.width,
+                       leftSpace + bmNum.width);
+      dy = aDesiredSize.ascent - mBoundingMetrics.ascent;
+      mLineRect.SetRect(dx, dy,
+                        mLineRect.width, aDesiredSize.height - 2 * padding);
+
+      // place denominator
+      dx = MirrorIfRTL(aDesiredSize.width, sizeDen.width,
+                       leftSpace + bmNum.width + mLineRect.width);
+      dy = aDesiredSize.ascent + denShift - sizeDen.ascent;
+      FinishReflowChild(frameDen, presContext, nsnull, sizeDen, dx, dy, 0);
     }
 
   }
@@ -549,8 +557,9 @@ class nsDisplayMathMLSlash : public nsDisplayItem {
 public:
   nsDisplayMathMLSlash(nsDisplayListBuilder* aBuilder,
                        nsIFrame* aFrame, const nsRect& aRect,
-                       nscoord aThickness)
-    : nsDisplayItem(aBuilder, aFrame), mRect(aRect), mThickness(aThickness) {
+                       nscoord aThickness, bool aRTL)
+    : nsDisplayItem(aBuilder, aFrame), mRect(aRect), mThickness(aThickness),
+      mRTL(aRTL) {
     MOZ_COUNT_CTOR(nsDisplayMathMLSlash);
   }
 #ifdef NS_BUILD_REFCNT_LOGGING
@@ -565,6 +574,7 @@ public:
 private:
   nsRect    mRect;
   nscoord   mThickness;
+  bool      mRTL;
 };
 
 void nsDisplayMathMLSlash::Paint(nsDisplayListBuilder* aBuilder,
@@ -581,10 +591,19 @@ void nsDisplayMathMLSlash::Paint(nsDisplayListBuilder* aBuilder,
   gfxContext *gfxCtx = aCtx->ThebesContext();
   gfxPoint delta = gfxPoint(presContext->AppUnitsToGfxUnits(mThickness), 0);
   gfxCtx->NewPath();
-  gfxCtx->MoveTo(rect.BottomLeft());
-  gfxCtx->LineTo(rect.BottomLeft() + delta);
-  gfxCtx->LineTo(rect.TopRight());
-  gfxCtx->LineTo(rect.TopRight() - delta);
+
+  if (mRTL) {
+    gfxCtx->MoveTo(rect.TopLeft());
+    gfxCtx->LineTo(rect.TopLeft() + delta);
+    gfxCtx->LineTo(rect.BottomRight());
+    gfxCtx->LineTo(rect.BottomRight() - delta);
+  } else {
+    gfxCtx->MoveTo(rect.BottomLeft());
+    gfxCtx->LineTo(rect.BottomLeft() + delta);
+    gfxCtx->LineTo(rect.TopRight());
+    gfxCtx->LineTo(rect.TopRight() - delta);
+  }
+
   gfxCtx->ClosePath();
   gfxCtx->Fill();
 }
@@ -596,7 +615,8 @@ nsMathMLmfracFrame::DisplaySlash(nsDisplayListBuilder* aBuilder,
                                  const nsDisplayListSet& aLists) {
   if (!aFrame->GetStyleVisibility()->IsVisible() || aRect.IsEmpty())
     return NS_OK;
-  
+
   return aLists.Content()->AppendNewToTop(new (aBuilder)
-      nsDisplayMathMLSlash(aBuilder, aFrame, aRect, aThickness));
+      nsDisplayMathMLSlash(aBuilder, aFrame, aRect, aThickness,
+                           NS_MATHML_IS_RTL(mPresentationData.flags)));
 }
diff --git a/layout/mathml/nsMathMLmmultiscriptsFrame.cpp b/layout/mathml/nsMathMLmmultiscriptsFrame.cpp
index 0dc08ac01eb5..8991866fccba 100644
--- a/layout/mathml/nsMathMLmmultiscriptsFrame.cpp
+++ b/layout/mathml/nsMathMLmmultiscriptsFrame.cpp
@@ -417,7 +417,11 @@ nsMathMLmmultiscriptsFrame::Place(nsRenderingContext& aRenderingContext,
         // place the base ...
         childFrame = baseFrame;
         dy = aDesiredSize.ascent - baseSize.ascent;
-        FinishReflowChild (baseFrame, PresContext(), nsnull, baseSize, dx, dy, 0);
+        FinishReflowChild (baseFrame, PresContext(), nsnull, baseSize,
+                           MirrorIfRTL(aDesiredSize.width,
+                                       baseSize.width,
+                                       dx),
+                           dy, 0);
         dx += bmBase.width + italicCorrection;
       }
       else if (mprescriptsFrame != childFrame) {
@@ -440,13 +444,21 @@ nsMathMLmmultiscriptsFrame::Place(nsRenderingContext& aRenderingContext,
 
           dy = aDesiredSize.ascent - subScriptSize.ascent +
             maxSubScriptShift;
-          FinishReflowChild (subScriptFrame, PresContext(), nsnull, subScriptSize,
-                             dx + (width-subScriptSize.width)/2, dy, 0);
+          FinishReflowChild (subScriptFrame, PresContext(), nsnull,
+                             subScriptSize,
+                             MirrorIfRTL(aDesiredSize.width,
+                                         subScriptSize.width,
+                                         dx + (width-subScriptSize.width)/2),
+                             dy, 0);
 
           dy = aDesiredSize.ascent - supScriptSize.ascent -
             maxSupScriptShift;
-          FinishReflowChild (supScriptFrame, PresContext(), nsnull, supScriptSize,
-                             dx + (width-supScriptSize.width)/2, dy, 0);
+          FinishReflowChild (supScriptFrame, PresContext(), nsnull,
+                             supScriptSize,
+                             MirrorIfRTL(aDesiredSize.width,
+                                         supScriptSize.width,
+                                         dx + (width-supScriptSize.width)/2),
+                             dy, 0);
 
           dx += width + scriptSpace;
         }
diff --git a/layout/mathml/nsMathMLmpaddedFrame.cpp b/layout/mathml/nsMathMLmpaddedFrame.cpp
index cd730dbd4aad..ad7a0df09fa4 100644
--- a/layout/mathml/nsMathMLmpaddedFrame.cpp
+++ b/layout/mathml/nsMathMLmpaddedFrame.cpp
@@ -133,10 +133,11 @@ nsMathMLmpaddedFrame::ProcessAttributes()
   }
 
   // lspace
-  mLeftSpaceSign = NS_MATHML_SIGN_INVALID;
+  mLeadingSpaceSign = NS_MATHML_SIGN_INVALID;
   GetAttribute(mContent, nsnull, nsGkAtoms::lspace_, value);
   if (!value.IsEmpty()) {
-    ParseAttribute(value, mLeftSpaceSign, mLeftSpace, mLeftSpacePseudoUnit);
+    ParseAttribute(value, mLeadingSpaceSign, mLeadingSpace,
+                   mLeadingSpacePseudoUnit);
   }
 
   // voffset
@@ -380,23 +381,28 @@ nsMathMLmpaddedFrame::Place(nsRenderingContext& aRenderingContext,
 
   nscoord height = mBoundingMetrics.ascent;
   nscoord depth  = mBoundingMetrics.descent;
-  // In MathML2 (http://www.w3.org/TR/MathML2/chapter3.html#presm.mpadded),
-  // lspace is "the amount of space between the left edge of a bounding box
-  // and the start of the rendering of its contents' bounding box" and the
-  // default is zero.
+  // The REC says:
   //
-  // In MathML3 draft
-  // http://www.w3.org/TR/2007/WD-MathML3-20070427/chapter3.html#id.3.3.6.2,
-  // lspace is "the amount of space between the left edge of the bounding box
-  // and the positioning poin [sic] of the mpadded element" and the default is
-  // "same as content".
+  // "The lspace attribute ('leading' space) specifies the horizontal location
+  // of the positioning point of the child content with respect to the
+  // positioning point of the mpadded element. By default they coincide, and
+  // therefore absolute values for lspace have the same effect as relative
+  // values."
   //
-  // In both cases, "MathML renderers should ensure that, except for the
-  // effects of the attributes, relative spacing between the contents of
-  // mpadded and surrounding MathML elements is not modified by replacing an
-  // mpadded element with an mrow element with the same content."
+  // "MathML renderers should ensure that, except for the effects of the
+  // attributes, the relative spacing between the contents of the mpadded
+  // element and surrounding MathML elements would not be modified by replacing
+  // an mpadded element with an mrow element with the same content, even if
+  // linebreaking occurs within the mpadded element."
+  //
+  // (http://www.w3.org/TR/MathML/chapter3.html#presm.mpadded)
+  // 
+  // "In those discussions, the terms leading and trailing are used to specify
+  // a side of an object when which side to use depends on the directionality;
+  // ie. leading means left in LTR but right in RTL."
+  // (http://www.w3.org/TR/MathML/chapter3.html#presm.bidi.math)
   nscoord lspace = 0;
-  // In MATHML3, "width" will be the bounding box width and "advancewidth" will
+  // In MathML3, "width" will be the bounding box width and "advancewidth" will
   // refer "to the horizontal distance between the positioning point of the
   // mpadded and the positioning point for the following content".  MathML2
   // doesn't make the distinction.
@@ -404,6 +410,7 @@ nsMathMLmpaddedFrame::Place(nsRenderingContext& aRenderingContext,
   nscoord voffset = 0;
 
   PRInt32 pseudoUnit;
+  nscoord initialWidth = width;
 
   // update width
   pseudoUnit = (mWidthPseudoUnit == NS_MATHML_PSEUDO_UNIT_ITSELF)
@@ -427,9 +434,9 @@ nsMathMLmpaddedFrame::Place(nsRenderingContext& aRenderingContext,
   depth = NS_MAX(0, depth);
 
   // update lspace
-  if (mLeftSpacePseudoUnit != NS_MATHML_PSEUDO_UNIT_ITSELF) {
-    pseudoUnit = mLeftSpacePseudoUnit;
-    UpdateValue(mLeftSpaceSign, pseudoUnit, mLeftSpace,
+  if (mLeadingSpacePseudoUnit != NS_MATHML_PSEUDO_UNIT_ITSELF) {
+    pseudoUnit = mLeadingSpacePseudoUnit;
+    UpdateValue(mLeadingSpaceSign, pseudoUnit, mLeadingSpace,
                 mBoundingMetrics, lspace);
   }
 
@@ -445,20 +452,25 @@ nsMathMLmpaddedFrame::Place(nsRenderingContext& aRenderingContext,
   // attributes, tweak our metrics and move children to achieve the desired visual
   // effects.
 
-  if (mLeftSpaceSign != NS_MATHML_SIGN_INVALID) { // there was padding on the left
-    // dismiss the left italic correction now (so that our parent won't correct us)
+  if ((NS_MATHML_IS_RTL(mPresentationData.flags) ?
+       mWidthSign : mLeadingSpaceSign) != NS_MATHML_SIGN_INVALID) {
+    // there was padding on the left. dismiss the left italic correction now
+    // (so that our parent won't correct us)
     mBoundingMetrics.leftBearing = 0;
   }
 
-  if (mWidthSign != NS_MATHML_SIGN_INVALID) { // there was padding on the right
-    // dismiss the right italic correction now (so that our parent won't correct us)
+  if ((NS_MATHML_IS_RTL(mPresentationData.flags) ?
+       mLeadingSpaceSign : mWidthSign) != NS_MATHML_SIGN_INVALID) {
+    // there was padding on the right. dismiss the right italic correction now
+    // (so that our parent won't correct us)
     mBoundingMetrics.width = width;
     mBoundingMetrics.rightBearing = mBoundingMetrics.width;
   }
 
   nscoord dy = height - mBoundingMetrics.ascent;
-  nscoord dx = lspace;
-
+  nscoord dx = NS_MATHML_IS_RTL(mPresentationData.flags) ?
+    width - initialWidth - lspace : lspace;
+    
   aDesiredSize.ascent += dy;
   aDesiredSize.width = mBoundingMetrics.width;
   aDesiredSize.height += dy + depth - mBoundingMetrics.descent;
diff --git a/layout/mathml/nsMathMLmpaddedFrame.h b/layout/mathml/nsMathMLmpaddedFrame.h
index 168cb92d0a4a..00235f014d1a 100644
--- a/layout/mathml/nsMathMLmpaddedFrame.h
+++ b/layout/mathml/nsMathMLmpaddedFrame.h
@@ -83,19 +83,19 @@ private:
   nsCSSValue mWidth;
   nsCSSValue mHeight;
   nsCSSValue mDepth;
-  nsCSSValue mLeftSpace;
+  nsCSSValue mLeadingSpace;
   nsCSSValue mVerticalOffset;
 
   PRInt32    mWidthSign;
   PRInt32    mHeightSign;
   PRInt32    mDepthSign;
-  PRInt32    mLeftSpaceSign;
+  PRInt32    mLeadingSpaceSign;
   PRInt32    mVerticalOffsetSign;
 
   PRInt32    mWidthPseudoUnit;
   PRInt32    mHeightPseudoUnit;
   PRInt32    mDepthPseudoUnit;
-  PRInt32    mLeftSpacePseudoUnit;
+  PRInt32    mLeadingSpacePseudoUnit;
   PRInt32    mVerticalOffsetPseudoUnit;
 
   // helpers to process the attributes
diff --git a/layout/mathml/nsMathMLmrootFrame.cpp b/layout/mathml/nsMathMLmrootFrame.cpp
index b9513fea9c02..e12f4fb98b3e 100644
--- a/layout/mathml/nsMathMLmrootFrame.cpp
+++ b/layout/mathml/nsMathMLmrootFrame.cpp
@@ -356,35 +356,41 @@ nsMathMLmrootFrame::Reflow(nsPresContext*          aPresContext,
   nscoord dxIndex, dxSqr;
   GetRadicalXOffsets(bmIndex.width, bmSqr.width, fm, &dxIndex, &dxSqr);
 
-  // place the index
-  nscoord dx = dxIndex;
-  nscoord dy = aDesiredSize.ascent - (indexRaisedAscent + indexSize.ascent - bmIndex.ascent);
-  FinishReflowChild(indexFrame, aPresContext, nsnull, indexSize, dx, dy, 0);
-
-  // place the radical symbol and the radical bar
-  dx = dxSqr;
-  dy = indexClearance + leading; // leave a leading at the top
-  mSqrChar.SetRect(nsRect(dx, dy, bmSqr.width, bmSqr.ascent + bmSqr.descent));
-  dx += bmSqr.width;
-  mBarRect.SetRect(dx, dy, bmBase.width, ruleThickness);
-
-  // place the base
-  dy = aDesiredSize.ascent - baseSize.ascent;
-  FinishReflowChild(baseFrame, aPresContext, nsnull, baseSize, dx, dy, 0);
-
-  mReference.x = 0;
-  mReference.y = aDesiredSize.ascent;
-
-  mBoundingMetrics.width = dx + bmBase.width;
+  mBoundingMetrics.width = dxSqr + bmSqr.width + bmBase.width;
   mBoundingMetrics.leftBearing = 
     NS_MIN(dxIndex + bmIndex.leftBearing, dxSqr + bmSqr.leftBearing);
-  mBoundingMetrics.rightBearing = dx +
+  mBoundingMetrics.rightBearing = dxSqr + bmSqr.width +
     NS_MAX(bmBase.width, bmBase.rightBearing);
 
   aDesiredSize.width = mBoundingMetrics.width;
   aDesiredSize.mBoundingMetrics = mBoundingMetrics;
   GatherAndStoreOverflow(&aDesiredSize);
 
+  // place the index
+  nscoord dx = dxIndex;
+  nscoord dy = aDesiredSize.ascent - (indexRaisedAscent + indexSize.ascent - bmIndex.ascent);
+  FinishReflowChild(indexFrame, aPresContext, nsnull, indexSize,
+                    MirrorIfRTL(aDesiredSize.width, indexSize.width, dx),
+                    dy, 0);
+
+  // place the radical symbol and the radical bar
+  dx = dxSqr;
+  dy = indexClearance + leading; // leave a leading at the top
+  mSqrChar.SetRect(nsRect(MirrorIfRTL(aDesiredSize.width, bmSqr.width, dx),
+                          dy, bmSqr.width, bmSqr.ascent + bmSqr.descent));
+  dx += bmSqr.width;
+  mBarRect.SetRect(MirrorIfRTL(aDesiredSize.width, bmBase.width, dx),
+                   dy, bmBase.width, ruleThickness);
+
+  // place the base
+  dy = aDesiredSize.ascent - baseSize.ascent;
+  FinishReflowChild(baseFrame, aPresContext, nsnull, baseSize,
+                    MirrorIfRTL(aDesiredSize.width, baseSize.width, dx),
+                    dy, 0);
+
+  mReference.x = 0;
+  mReference.y = aDesiredSize.ascent;
+
   aStatus = NS_FRAME_COMPLETE;
   NS_FRAME_SET_TRUNCATION(aStatus, aReflowState, aDesiredSize);
   return NS_OK;
diff --git a/layout/mathml/nsMathMLmsubFrame.cpp b/layout/mathml/nsMathMLmsubFrame.cpp
index 5916380269af..d1608f3a0a3a 100644
--- a/layout/mathml/nsMathMLmsubFrame.cpp
+++ b/layout/mathml/nsMathMLmsubFrame.cpp
@@ -203,10 +203,12 @@ nsMathMLmsubFrame::PlaceSubScript (nsPresContext*      aPresContext,
   if (aPlaceOrigin) {
     nscoord dx, dy;
     // now place the base ...
-    dx = 0; dy = aDesiredSize.ascent - baseSize.ascent;
+    dx = aFrame->MirrorIfRTL(aDesiredSize.width, baseSize.width, 0);
+    dy = aDesiredSize.ascent - baseSize.ascent;
     FinishReflowChild (baseFrame, aPresContext, nsnull, baseSize, dx, dy, 0);
     // ... and subscript
-    dx = bmBase.width; 
+    dx = aFrame->MirrorIfRTL(aDesiredSize.width, subScriptSize.width,
+                             bmBase.width);
     dy = aDesiredSize.ascent - (subScriptSize.ascent - actualSubScriptShift);
     FinishReflowChild (subScriptFrame, aPresContext, nsnull, subScriptSize, dx, dy, 0);
   }
diff --git a/layout/mathml/nsMathMLmsubsupFrame.cpp b/layout/mathml/nsMathMLmsubsupFrame.cpp
index 44a1ba5b8e46..d312dce5b2cb 100644
--- a/layout/mathml/nsMathMLmsubsupFrame.cpp
+++ b/layout/mathml/nsMathMLmsubsupFrame.cpp
@@ -336,16 +336,19 @@ nsMathMLmsubsupFrame::PlaceSubSupScript(nsPresContext*      aPresContext,
   if (aPlaceOrigin) {
     nscoord dx, dy;
     // now place the base ...
-    dx = 0; dy = aDesiredSize.ascent - baseSize.ascent;
+    dx = aFrame->MirrorIfRTL(aDesiredSize.width, baseSize.width, 0);
+    dy = aDesiredSize.ascent - baseSize.ascent;
     FinishReflowChild(baseFrame, aPresContext, nsnull,
                       baseSize, dx, dy, 0);
     // ... and subscript
-    dx = bmBase.width;
+    dx = aFrame->MirrorIfRTL(aDesiredSize.width, subScriptSize.width,
+                             bmBase.width);
     dy = aDesiredSize.ascent - (subScriptSize.ascent - subScriptShift);
     FinishReflowChild(subScriptFrame, aPresContext, nsnull,
                       subScriptSize, dx, dy, 0);
     // ... and the superscript
-    dx = bmBase.width + italicCorrection;
+    dx = aFrame->MirrorIfRTL(aDesiredSize.width, supScriptSize.width,
+                             bmBase.width + italicCorrection);
     dy = aDesiredSize.ascent - (supScriptSize.ascent + supScriptShift);
     FinishReflowChild(supScriptFrame, aPresContext, nsnull,
                       supScriptSize, dx, dy, 0);
diff --git a/layout/mathml/nsMathMLmsupFrame.cpp b/layout/mathml/nsMathMLmsupFrame.cpp
index e361569981a5..f9e5bb769acd 100644
--- a/layout/mathml/nsMathMLmsupFrame.cpp
+++ b/layout/mathml/nsMathMLmsupFrame.cpp
@@ -241,10 +241,12 @@ nsMathMLmsupFrame::PlaceSuperScript(nsPresContext*      aPresContext,
   if (aPlaceOrigin) {
     nscoord dx, dy;
     // now place the base ...
-    dx = 0; dy = aDesiredSize.ascent - baseSize.ascent;
+    dx = aFrame->MirrorIfRTL(aDesiredSize.width, baseSize.width, 0);
+    dy = aDesiredSize.ascent - baseSize.ascent;
     FinishReflowChild (baseFrame, aPresContext, nsnull, baseSize, dx, dy, 0);
     // ... and supscript
-    dx = bmBase.width + italicCorrection;
+    dx = aFrame->MirrorIfRTL(aDesiredSize.width, supScriptSize.width,
+                             bmBase.width + italicCorrection);
     dy = aDesiredSize.ascent - (supScriptSize.ascent + actualSupScriptShift);
     FinishReflowChild (supScriptFrame, aPresContext, nsnull, supScriptSize, dx, dy, 0);
   }