diff --git a/mozilla/layout/base/nsIPresShell.h b/mozilla/layout/base/nsIPresShell.h
index c17e8f84a41..b4ff3815070 100644
--- a/mozilla/layout/base/nsIPresShell.h
+++ b/mozilla/layout/base/nsIPresShell.h
@@ -345,8 +345,8 @@ public:
    * Tell the pres shell that a frame needs to be marked dirty and needs
    * Reflow.  It's OK if this is an ancestor of the frame needing reflow as
    * long as the ancestor chain between them doesn't cross a reflow root.  The
-   * bits to add should be some combination of NS_FRAME_IS_DIRTY and
-   * NS_FRAME_HAS_DIRTY_CHILDREN.
+   * bit to add should be eithr NS_FRAME_IS_DIRTY or
+   * NS_FRAME_HAS_DIRTY_CHILDREN (but not both!).
    */
   enum IntrinsicDirty {
     // XXXldb eResize should be renamed
@@ -356,7 +356,7 @@ public:
   };
   NS_IMETHOD FrameNeedsReflow(nsIFrame *aFrame,
                               IntrinsicDirty aIntrinsicDirty,
-                              nsFrameState aBitsToAdd) = 0;
+                              nsFrameState aBitToAdd) = 0;
 
   NS_IMETHOD CancelAllPendingReflows() = 0;
 
diff --git a/mozilla/layout/base/nsPresShell.cpp b/mozilla/layout/base/nsPresShell.cpp
index 884fa57eb5f..34d20bc6f78 100644
--- a/mozilla/layout/base/nsPresShell.cpp
+++ b/mozilla/layout/base/nsPresShell.cpp
@@ -813,7 +813,7 @@ public:
   NS_IMETHOD GetPlaceholderFrameFor(nsIFrame*  aFrame,
                                     nsIFrame** aPlaceholderFrame) const;
   NS_IMETHOD FrameNeedsReflow(nsIFrame *aFrame, IntrinsicDirty aIntrinsicDirty,
-                              nsFrameState aBitsToAdd);
+                              nsFrameState aBitToAdd);
   NS_IMETHOD CancelAllPendingReflows();
   NS_IMETHOD IsSafeToFlush(PRBool& aIsSafeToFlush);
   NS_IMETHOD FlushPendingNotifications(mozFlushType aType);
@@ -3114,10 +3114,10 @@ PresShell::VerifyHasDirtyRootAncestor(nsIFrame* aFrame)
 
 NS_IMETHODIMP
 PresShell::FrameNeedsReflow(nsIFrame *aFrame, IntrinsicDirty aIntrinsicDirty,
-                            nsFrameState aBitsToAdd)
+                            nsFrameState aBitToAdd)
 {
-  NS_PRECONDITION(aBitsToAdd == NS_FRAME_IS_DIRTY ||
-                  aBitsToAdd == NS_FRAME_HAS_DIRTY_CHILDREN,
+  NS_PRECONDITION(aBitToAdd == NS_FRAME_IS_DIRTY ||
+                  aBitToAdd == NS_FRAME_HAS_DIRTY_CHILDREN,
                   "Unexpected bits being added");
 
   // XXX Add this assertion at some point!?  nsSliderFrame triggers it a lot.
@@ -3152,7 +3152,7 @@ PresShell::FrameNeedsReflow(nsIFrame *aFrame, IntrinsicDirty aIntrinsicDirty,
   // Grab |wasDirty| now so we can go ahead and update the bits on
   // aFrame and then get |targetFrameDirty|.
   PRBool wasDirty = NS_SUBTREE_DIRTY(aFrame);
-  aFrame->AddStateBits(aBitsToAdd);
+  aFrame->AddStateBits(aBitToAdd);
   PRBool targetFrameDirty = ((aFrame->GetStateBits() & NS_FRAME_IS_DIRTY) != 0);
 #define FRAME_IS_REFLOW_ROOT(_f)                   \
   ((_f->GetStateBits() & NS_FRAME_REFLOW_ROOT) &&  \
diff --git a/mozilla/layout/mathml/base/src/nsMathMLmtableFrame.cpp b/mozilla/layout/mathml/base/src/nsMathMLmtableFrame.cpp
index bbeb0761f8f..68c9b500779 100644
--- a/mozilla/layout/mathml/base/src/nsMathMLmtableFrame.cpp
+++ b/mozilla/layout/mathml/base/src/nsMathMLmtableFrame.cpp
@@ -458,8 +458,8 @@ nsMathMLmtableOuterFrame::AttributeChanged(PRInt32  aNameSpaceID,
   if (aAttribute == nsGkAtoms::displaystyle_) {
     nsMathMLContainerFrame::RebuildAutomaticDataForChildren(mParent);
     nsMathMLContainerFrame::PropagateScriptStyleFor(tableFrame, mPresentationData.scriptLevel);
-    // XXXbz I have no idea why this is reflowing the _parent_ instead of
-    // us...
+    // Need to reflow the parent, not us, because this can actually
+    // affect siblings.
     PresContext()->PresShell()->
       FrameNeedsReflow(mParent, nsIPresShell::eStyleChange, NS_FRAME_IS_DIRTY);
     return NS_OK;