--- a/layout/base/nsFrameTraversal.cpp
+++ b/layout/base/nsFrameTraversal.cpp
@@ -28,23 +28,21 @@ public:
   virtual void Prev();
 
   nsFrameIterator(nsPresContext* aPresContext, nsIFrame *aStart,
                   nsIteratorType aType, bool aLockScroll, bool aFollowOOFs);
 
 protected:
   void      setCurrent(nsIFrame *aFrame){mCurrent = aFrame;}
   nsIFrame *getCurrent(){return mCurrent;}
-  void      setStart(nsIFrame *aFrame){mStart = aFrame;}
   nsIFrame *getStart(){return mStart;}
   nsIFrame *getLast(){return mLast;}
   void      setLast(nsIFrame *aFrame){mLast = aFrame;}
   int8_t    getOffEdge(){return mOffEdge;}
   void      setOffEdge(int8_t aOffEdge){mOffEdge = aOffEdge;}
-  void      SetLockInScrollView(bool aLockScroll){mLockScroll = aLockScroll;}
 
   /*
    Our own versions of the standard frame tree navigation
    methods, which, if the iterator is following out-of-flows,
    apply the following rules for placeholder frames:
    
    - If a frame HAS a placeholder frame, getting its parent
    gets the placeholder's parent.
@@ -80,25 +78,25 @@ protected:
   virtual nsIFrame* GetLastChildInner(nsIFrame* aFrame);  
 
   virtual nsIFrame* GetNextSiblingInner(nsIFrame* aFrame);
   virtual nsIFrame* GetPrevSiblingInner(nsIFrame* aFrame);
 
   nsIFrame* GetPlaceholderFrame(nsIFrame* aFrame);
   bool      IsPopupFrame(nsIFrame* aFrame);
 
-  nsPresContext* mPresContext;
-  bool mLockScroll;
-  bool mFollowOOFs;
-  nsIteratorType mType;
+  nsPresContext* const mPresContext;
+  const bool mLockScroll;
+  const bool mFollowOOFs;
+  const nsIteratorType mType;
 
 private:
-  nsIFrame *mStart;
-  nsIFrame *mCurrent;
-  nsIFrame *mLast; //the last one that was in current;
+  nsIFrame* const mStart;
+  nsIFrame* mCurrent;
+  nsIFrame* mLast; //the last one that was in current;
   int8_t    mOffEdge; //0= no -1 to far prev, 1 to far next;
 };
 
 
 
 // Bidi visual iterator
 class nsVisualIterator: public nsFrameIterator
 {
@@ -136,16 +134,21 @@ NS_NewFrameTraversal(nsIFrameEnumerator 
                      nsIFrame *aStart,
                      nsIteratorType aType,
                      bool aVisual,
                      bool aLockInScrollView,
                      bool aFollowOOFs)
 {
   if (!aEnumerator || !aStart)
     return NS_ERROR_NULL_POINTER;
+
+  if (aFollowOOFs) {
+    aStart = nsPlaceholderFrame::GetRealFrameFor(aStart);
+  }
+
   nsCOMPtr<nsIFrameEnumerator> trav;
   if (aVisual) {
     trav = new nsVisualIterator(aPresContext, aStart, aType,
                                 aLockInScrollView, aFollowOOFs);
   } else {
     trav = new nsFrameIterator(aPresContext, aStart, aType,
                                aLockInScrollView, aFollowOOFs);
   }
@@ -180,27 +183,27 @@ NS_IMETHODIMP
 
 // nsFrameIterator implementation
 
 NS_IMPL_ISUPPORTS1(nsFrameIterator, nsIFrameEnumerator)
 
 nsFrameIterator::nsFrameIterator(nsPresContext* aPresContext, nsIFrame *aStart,
                                  nsIteratorType aType, bool aLockInScrollView,
                                  bool aFollowOOFs)
+: mPresContext(aPresContext),
+  mLockScroll(aLockInScrollView),
+  mFollowOOFs(aFollowOOFs),
+  mType(aType),
+  mStart(aStart),
+  mCurrent(aStart),
+  mLast(aStart),
+  mOffEdge(0)
 {
-  mOffEdge = 0;
-  mPresContext = aPresContext;
-  if (aFollowOOFs && aStart)
-    aStart = nsPlaceholderFrame::GetRealFrameFor(aStart);
-  setStart(aStart);
-  setCurrent(aStart);
-  setLast(aStart);
-  mType = aType;
-  SetLockInScrollView(aLockInScrollView);
-  mFollowOOFs = aFollowOOFs;
+  MOZ_ASSERT(!aFollowOOFs || aStart->GetType() != nsGkAtoms::placeholderFrame,
+             "Caller should have resolved placeholder frame");
 }
 
 
 
 nsIFrame*
 nsFrameIterator::CurrentItem()
 {
   if (mOffEdge)