diff --git a/mozilla/gfx/public/nsIRenderingContext.h b/mozilla/gfx/public/nsIRenderingContext.h
index f0edbef7042..cf4d7107823 100644
--- a/mozilla/gfx/public/nsIRenderingContext.h
+++ b/mozilla/gfx/public/nsIRenderingContext.h
@@ -890,15 +890,20 @@ struct nsBoundingMetrics {
   }
 
   /* Append another bounding metrics */
-  /* Notice that leftBearing is not set. The user must set leftBearing on 
-     initialization and (repeatedly) use this operator to append 
-     other bounding metrics on the right.
-   */
   void 
   operator += (const nsBoundingMetrics& bm) {
-    if (ascent < bm.ascent) ascent = bm.ascent;
-    if (descent < bm.descent) descent = bm.descent;   
-    rightBearing = PR_MAX(rightBearing, width + bm.rightBearing);
+    if (ascent + descent == 0 && rightBearing - leftBearing == 0) {
+      ascent = bm.ascent;
+      descent = bm.descent;
+      leftBearing = width + bm.leftBearing;
+      rightBearing = width + bm.rightBearing;
+    }
+    else {
+      if (ascent < bm.ascent) ascent = bm.ascent;
+      if (descent < bm.descent) descent = bm.descent;   
+      leftBearing = PR_MIN(leftBearing, width + bm.leftBearing);
+      rightBearing = PR_MAX(rightBearing, width + bm.rightBearing);
+    }
     width += bm.width;
   }
 };
diff --git a/mozilla/layout/mathml/base/src/nsMathMLTokenFrame.cpp b/mozilla/layout/mathml/base/src/nsMathMLTokenFrame.cpp
index 5935eb3c5b4..8bc3f470005 100644
--- a/mozilla/layout/mathml/base/src/nsMathMLTokenFrame.cpp
+++ b/mozilla/layout/mathml/base/src/nsMathMLTokenFrame.cpp
@@ -129,7 +129,6 @@ nsMathMLTokenFrame::Reflow(nsPresContext*          aPresContext,
   aDesiredSize.mBoundingMetrics.Clear();
 
   nsSize availSize(aReflowState.ComputedWidth(), aReflowState.ComputedHeight());
-  PRInt32 count = 0;
   nsIFrame* childFrame = GetFirstChild(nsnull);
   while (childFrame) {
     // ask our children to compute their bounding metrics
@@ -146,16 +145,12 @@ nsMathMLTokenFrame::Reflow(nsPresContext*          aPresContext,
       return rv;
     }
 
-    // origins are used as placeholders to store the child's ascent and descent.
+    // origins are used as placeholders to store the child's ascent.
     childFrame->SetRect(nsRect(0, childDesiredSize.ascent,
                                childDesiredSize.width, childDesiredSize.height));
     // compute and cache the bounding metrics
-    if (0 == count)
-      aDesiredSize.mBoundingMetrics  = childDesiredSize.mBoundingMetrics;
-    else
-      aDesiredSize.mBoundingMetrics += childDesiredSize.mBoundingMetrics;
+    aDesiredSize.mBoundingMetrics += childDesiredSize.mBoundingMetrics;
 
-    count++;
     childFrame = childFrame->GetNextSibling();
   }
 
diff --git a/mozilla/layout/mathml/base/src/nsMathMLmfencedFrame.cpp b/mozilla/layout/mathml/base/src/nsMathMLmfencedFrame.cpp
index 17b42239b57..91009c63a13 100644
--- a/mozilla/layout/mathml/base/src/nsMathMLmfencedFrame.cpp
+++ b/mozilla/layout/mathml/base/src/nsMathMLmfencedFrame.cpp
@@ -287,7 +287,6 @@ nsMathMLmfencedFrame::doReflow(nsPresContext*          aPresContext,
   // XXX The above decision was revisited in bug 121748 and this code can be
   // refactored to use nsMathMLContainerFrame::Reflow() at some stage.
 
-  PRInt32 count = 0;
   nsReflowStatus childStatus;
   nsSize availSize(aReflowState.ComputedWidth(), aReflowState.ComputedHeight());
   nsIFrame* firstChild = aForFrame->GetFirstChild(nsnull);
@@ -325,10 +324,7 @@ nsMathMLmfencedFrame::doReflow(nsPresContext*          aPresContext,
       descent = childDescent;
     if (ascent < childDesiredSize.ascent)
       ascent = childDesiredSize.ascent;
-    if (0 == count++)
-      aDesiredSize.mBoundingMetrics  = childDesiredSize.mBoundingMetrics;
-    else
-      aDesiredSize.mBoundingMetrics += childDesiredSize.mBoundingMetrics;
+    aDesiredSize.mBoundingMetrics += childDesiredSize.mBoundingMetrics;
 
     childFrame = childFrame->GetNextSibling();
   }