diff --git a/mozilla/layout/base/nsCSSFrameConstructor.cpp b/mozilla/layout/base/nsCSSFrameConstructor.cpp
index 197776af853..f70eff0e97a 100644
--- a/mozilla/layout/base/nsCSSFrameConstructor.cpp
+++ b/mozilla/layout/base/nsCSSFrameConstructor.cpp
@@ -1694,8 +1694,7 @@ MoveChildrenTo(nsFrameManager*          aFrameManager,
     // anonymous block frame, but oddly they aren't -- need to
     // investigate that...)
     if (aNewParentSC)
-      aPresContext->FrameManager()->ReParentStyleContext(aFrameList,
-                                                         aNewParentSC);
+      aPresContext->FrameManager()->ReParentStyleContext(aFrameList);
 #endif
 
     aFrameList = aFrameList->GetNextSibling();
@@ -3798,8 +3797,7 @@ nsCSSFrameConstructor::ConstructTableColFrame(nsFrameConstructorState& aState,
                       aNewFrame);
   // if the parent frame was anonymous then reparent the style context
   if (aIsPseudoParent) {
-    aState.mFrameManager->
-      ReParentStyleContext(aNewFrame, parentFrame->GetStyleContext());
+    aState.mFrameManager->ReParentStyleContext(aNewFrame);
   }
 
   // construct additional col frames if the col frame has a span > 1
@@ -12089,14 +12087,12 @@ nsCSSFrameConstructor::ProcessChildren(nsFrameConstructorState& aState,
 // Support for :first-line style
 
 static void
-ReparentFrame(nsPresContext* aPresContext,
+ReparentFrame(nsFrameManager* aFrameManager,
               nsIFrame* aNewParentFrame,
-              nsStyleContext* aParentStyleContext,
               nsIFrame* aFrame)
 {
   aFrame->SetParent(aNewParentFrame);
-  aPresContext->FrameManager()->ReParentStyleContext(aFrame,
-                                                     aParentStyleContext);
+  aFrameManager->ReParentStyleContext(aFrame);
 }
 
 // Special routine to handle placing a list of frames into a block
@@ -12162,8 +12158,10 @@ nsCSSFrameConstructor::WrapFramesInFirstLineFrame(
 
     // Give the inline frames to the lineFrame <b>after</b> reparenting them
     kid = firstInlineFrame;
+    NS_ASSERTION(lineFrame->GetStyleContext() == firstLineStyle,
+                 "Bogus style context on line frame");
     while (kid) {
-      ReparentFrame(aState.mPresContext, lineFrame, firstLineStyle, kid);
+      ReparentFrame(aState.mFrameManager, lineFrame, kid);
       kid = kid->GetNextSibling();
     }
     lineFrame->SetInitialChildList(aState.mPresContext, nsnull,
@@ -12204,7 +12202,6 @@ nsCSSFrameConstructor::AppendFirstLineFrames(
     return rv;
   }
   nsIFrame* lineFrame = lastBlockKid;
-  nsStyleContext* firstLineStyle = lineFrame->GetStyleContext();
 
   // Find the first and last inline frame in aFrameItems
   nsIFrame* kid = aFrameItems.childList;
@@ -12232,7 +12229,7 @@ nsCSSFrameConstructor::AppendFirstLineFrames(
   lastInlineFrame->SetNextSibling(nsnull);
   kid = firstInlineFrame;
   while (kid) {
-    ReparentFrame(aState.mPresContext, lineFrame, firstLineStyle, kid);
+    ReparentFrame(aState.mFrameManager, lineFrame, kid);
     kid = kid->GetNextSibling();
   }
   aState.mFrameManager->AppendFrames(lineFrame, nsnull, firstInlineFrame);
@@ -12274,12 +12271,10 @@ nsCSSFrameConstructor::InsertFirstLineFrames(
     if (firstBlockKid->GetType() == nsLayoutAtoms::lineFrame) {
       // We already have a first-line frame
       nsIFrame* lineFrame = firstBlockKid;
-      nsStyleContext* firstLineStyle = lineFrame->GetStyleContext();
 
       if (isInline) {
         // Easy case: the new inline frame will go into the lineFrame.
-        ReparentFrame(aState.mPresContext, lineFrame, firstLineStyle,
-                      newFrame);
+        ReparentFrame(aState.mFrameManager, lineFrame, newFrame);
         aState.mFrameManager->InsertFrames(lineFrame, nsnull, nsnull,
                                            newFrame);
 
@@ -12317,7 +12312,9 @@ nsCSSFrameConstructor::InsertFirstLineFrames(
 
           // Give the inline frames to the lineFrame <b>after</b>
           // reparenting them
-          ReparentFrame(aPresContext, lineFrame, firstLineStyle, newFrame);
+          NS_ASSERTION(lineFrame->GetStyleContext() == firstLineStyle,
+                       "Bogus style context on line frame");
+          ReparentFrame(aPresContext, lineFrame, newFrame);
           lineFrame->SetInitialChildList(aState.mPresContext, nsnull,
                                          newFrame);
         }
@@ -12376,8 +12373,7 @@ nsCSSFrameConstructor::InsertFirstLineFrames(
         else {
           // We got lucky: aPrevSibling was the last inline frame in
           // the line-frame.
-          ReparentFrame(aState.mPresContext, aBlockFrame, firstLineStyle,
-                        newFrame);
+          ReparentFrame(aState.mFrameManager, aBlockFrame, newFrame);
           aState.mFrameManager->InsertFrames(aBlockFrame, nsnull,
                                              prevSiblingParent, newFrame);
           aFrameItems.childList = nsnull;
diff --git a/mozilla/layout/base/nsFrameManager.cpp b/mozilla/layout/base/nsFrameManager.cpp
index 086c5b26942..5ac5b94cb2f 100644
--- a/mozilla/layout/base/nsFrameManager.cpp
+++ b/mozilla/layout/base/nsFrameManager.cpp
@@ -914,82 +914,98 @@ nsFrameManager::DebugVerifyStyleTree(nsIFrame* aFrame)
 #endif // DEBUG
 
 nsresult
-nsFrameManager::ReParentStyleContext(nsIFrame* aFrame, 
-                                     nsStyleContext* aNewParentContext)
+nsFrameManager::ReParentStyleContext(nsIFrame* aFrame)
 {
-  nsresult result = NS_ERROR_NULL_POINTER;
-  if (aFrame) {
-    // DO NOT verify the style tree before reparenting.  The frame
-    // tree has already been changed, so this check would just fail.
-    nsStyleContext* oldContext = aFrame->GetStyleContext();
-    if (oldContext) {
-      nsPresContext *presContext = GetPresContext();
-      nsRefPtr<nsStyleContext> newContext;
-      result = NS_OK;
-      newContext = mStyleSet->ReParentStyleContext(presContext, oldContext,
-                                                   aNewParentContext);
-      if (newContext) {
-        if (newContext != oldContext) {
-          PRInt32 listIndex = 0;
-          nsIAtom* childList = nsnull;
-          nsIFrame* child;
+  // DO NOT verify the style tree before reparenting.  The frame
+  // tree has already been changed, so this check would just fail.
+  nsStyleContext* oldContext = aFrame->GetStyleContext();
+  // XXXbz can oldContext really ever be null?
+  if (oldContext) {
+    nsPresContext *presContext = GetPresContext();
+    nsRefPtr<nsStyleContext> newContext;
+    nsIFrame* providerFrame = nsnull;
+    PRBool providerIsChild = PR_FALSE;
+    nsIFrame* providerChild = nsnull;
+    aFrame->GetParentStyleContextFrame(presContext, &providerFrame,
+                                       &providerIsChild);
+    nsStyleContext* newParentContext = nsnull;
+    if (providerIsChild) {
+      ReParentStyleContext(providerFrame);
+      newParentContext = providerFrame->GetStyleContext();
+      providerChild = providerFrame;
+    } else if (providerFrame) {
+      newParentContext = providerFrame->GetStyleContext();
+    } else {
+      NS_NOTREACHED("Reparenting something that has no usable parent? "
+                    "Shouldn't happen!");
+    }
+
+    newContext = mStyleSet->ReParentStyleContext(presContext, oldContext,
+                                                 newParentContext);
+    if (newContext) {
+      if (newContext != oldContext) {
+        PRInt32 listIndex = 0;
+        nsIAtom* childList = nsnull;
+        nsIFrame* child;
           
-          aFrame->SetStyleContext(presContext, newContext);
+        aFrame->SetStyleContext(presContext, newContext);
 
-          do {
-            child = aFrame->GetFirstChild(childList);
-            while (child) {
-              if (NS_FRAME_OUT_OF_FLOW != (child->GetStateBits() & NS_FRAME_OUT_OF_FLOW)) {
-                // only do frames that are in flow
-                if (nsLayoutAtoms::placeholderFrame == child->GetType()) {
-                  // get out of flow frame and recurse there
-                  nsIFrame* outOfFlowFrame =
-                    nsPlaceholderFrame::GetRealFrameForPlaceholder(child);
-                  NS_ASSERTION(outOfFlowFrame, "no out-of-flow frame");
+        do {
+          child = aFrame->GetFirstChild(childList);
+          while (child) {
+            // only do frames that are in flow
+            if (!(child->GetStateBits() & NS_FRAME_OUT_OF_FLOW)) {
+              if (nsLayoutAtoms::placeholderFrame == child->GetType()) {
+                // get out of flow frame and recurse there
+                nsIFrame* outOfFlowFrame =
+                  nsPlaceholderFrame::GetRealFrameForPlaceholder(child);
+                NS_ASSERTION(outOfFlowFrame, "no out-of-flow frame");
 
-                  result = ReParentStyleContext(outOfFlowFrame, newContext);
+                NS_ASSERTION(outOfFlowFrame != providerChild,
+                             "Out of flow provider?");
 
-                  // reparent placeholder's context under out of flow frame
-                  nsStyleContext* outOfFlowContext = outOfFlowFrame->GetStyleContext();
-                  ReParentStyleContext(child, outOfFlowContext);
-                }
-                else { // regular frame
-                  result = ReParentStyleContext(child, newContext);
-                }
+                ReParentStyleContext(outOfFlowFrame);
+
+                // reparent placeholder too
+                ReParentStyleContext(child);
               }
-
-              child = child->GetNextSibling();
-            }
-
-            childList = aFrame->GetAdditionalChildListName(listIndex++);
-          } while (childList);
-
-          // do additional contexts 
-          PRInt32 contextIndex = -1;
-          while (1) {
-            nsStyleContext* oldExtraContext = aFrame->GetAdditionalStyleContext(++contextIndex);
-            if (oldExtraContext) {
-              nsRefPtr<nsStyleContext> newExtraContext;
-              newExtraContext = mStyleSet->ReParentStyleContext(presContext,
-                                                                oldExtraContext,
-                                                                newContext);
-              if (newExtraContext) {
-                aFrame->SetAdditionalStyleContext(contextIndex, newExtraContext);
+              else if (child != providerChild) {
+                // regular frame, not reparented yet
+                ReParentStyleContext(child);
               }
             }
-            else {
-              result = NS_OK; // ok not to have extras (or run out)
-              break;
+
+            child = child->GetNextSibling();
+          }
+
+          childList = aFrame->GetAdditionalChildListName(listIndex++);
+        } while (childList);
+
+        // do additional contexts 
+        PRInt32 contextIndex = -1;
+        while (1) {
+          nsStyleContext* oldExtraContext =
+            aFrame->GetAdditionalStyleContext(++contextIndex);
+          if (oldExtraContext) {
+            nsRefPtr<nsStyleContext> newExtraContext;
+            newExtraContext = mStyleSet->ReParentStyleContext(presContext,
+                                                              oldExtraContext,
+                                                              newContext);
+            if (newExtraContext) {
+              aFrame->SetAdditionalStyleContext(contextIndex, newExtraContext);
             }
           }
-#ifdef DEBUG
-          VerifyStyleTree(GetPresContext(), aFrame, aNewParentContext);
-#endif
+          else {
+            break;
+          }
         }
+#ifdef DEBUG
+        VerifyStyleTree(GetPresContext(), aFrame, newParentContext);
+#endif
       }
     }
   }
-  return result;
+  return NS_OK;
 }
 
 static nsChangeHint
diff --git a/mozilla/layout/base/nsFrameManager.h b/mozilla/layout/base/nsFrameManager.h
index da11a593084..1920e8b7733 100644
--- a/mozilla/layout/base/nsFrameManager.h
+++ b/mozilla/layout/base/nsFrameManager.h
@@ -166,13 +166,14 @@ public:
   NS_HIDDEN_(void)     NotifyDestroyingFrame(nsIFrame* aFrame);
 
   /*
-   * Reparent the style contexts of this frame subtree to live under the new
-   * given parent style context.  The StyleContextParent of aFrame should be
-   * changed _before_ this method is called, so that style tree verification
-   * can take place correctly.
+   * Reparent the style contexts of this frame subtree.  The parent frame of
+   * aFrame must be changed to the new parent before this function is called;
+   * the new parent style context will be automatically computed based on the
+   * new position in the frame tree.
+   *
+   * @param aFrame the root of the subtree to reparent.  Must not be null.
    */
-  NS_HIDDEN_(nsresult) ReParentStyleContext(nsIFrame* aFrame, 
-                                            nsStyleContext* aNewParentContext);
+  NS_HIDDEN_(nsresult) ReParentStyleContext(nsIFrame* aFrame);
 
   /*
    * Re-resolve the style contexts for a frame tree.  Returns the top-level
diff --git a/mozilla/layout/forms/nsFieldSetFrame.cpp b/mozilla/layout/forms/nsFieldSetFrame.cpp
index f48e214d877..babe91fd1a4 100644
--- a/mozilla/layout/forms/nsFieldSetFrame.cpp
+++ b/mozilla/layout/forms/nsFieldSetFrame.cpp
@@ -708,11 +708,10 @@ nsFieldSetFrame::MaybeSetLegend(nsIFrame* aFrameList, nsIAtom* aListName)
 void
 nsFieldSetFrame::ReParentFrameList(nsIFrame* aFrameList)
 {
-  nsFrameManager* frameManager = mContentFrame->GetPresContext()->FrameManager();
-  nsStyleContext* newParentContext = mContentFrame->GetStyleContext();
+  nsFrameManager* frameManager = GetPresContext()->FrameManager();
   for (nsIFrame* frame = aFrameList; frame; frame = frame->GetNextSibling()) {
     frame->SetParent(mContentFrame);
-    frameManager->ReParentStyleContext(frame, newParentContext);
+    frameManager->ReParentStyleContext(frame);
   }
   mContentFrame->AddStateBits(GetStateBits() & NS_FRAME_HAS_CHILD_WITH_VIEW);
 }
diff --git a/mozilla/layout/forms/nsHTMLButtonControlFrame.cpp b/mozilla/layout/forms/nsHTMLButtonControlFrame.cpp
index c90bb77138c..c70cf8387a6 100644
--- a/mozilla/layout/forms/nsHTMLButtonControlFrame.cpp
+++ b/mozilla/layout/forms/nsHTMLButtonControlFrame.cpp
@@ -217,7 +217,7 @@ nsHTMLButtonControlFrame::ReParentFrameList(nsFrameManager* aFrameManager,
   for (nsIFrame* frame = aFrameList; frame; frame = frame->GetNextSibling()) {
     frame->SetParent(mFrames.FirstChild());
     // now reparent the contexts for the reparented frame too
-    aFrameManager->ReParentStyleContext(frame, newParentContext);
+    aFrameManager->ReParentStyleContext(frame);
   }
 
   // Set NS_FRAME_HAS_CHILD_WITH_VIEW on the area frame if needed, bug 276236.
diff --git a/mozilla/layout/generic/nsFirstLetterFrame.cpp b/mozilla/layout/generic/nsFirstLetterFrame.cpp
index 11a672dce8e..a37f8384b41 100644
--- a/mozilla/layout/generic/nsFirstLetterFrame.cpp
+++ b/mozilla/layout/generic/nsFirstLetterFrame.cpp
@@ -164,7 +164,8 @@ nsFirstLetterFrame::SetInitialChildList(nsPresContext* aPresContext,
   nsFrameManager *frameManager = aPresContext->FrameManager();
 
   for (nsIFrame* frame = aChildList; frame; frame = frame->GetNextSibling()) {
-    frameManager->ReParentStyleContext(frame, mStyleContext);
+    NS_ASSERTION(frame->GetParent() == this, "Unexpected parent");
+    frameManager->ReParentStyleContext(frame);
   }
   return NS_OK;
 }
diff --git a/mozilla/layout/generic/nsInlineFrame.cpp b/mozilla/layout/generic/nsInlineFrame.cpp
index b756d82659a..0a015dd96b7 100644
--- a/mozilla/layout/generic/nsInlineFrame.cpp
+++ b/mozilla/layout/generic/nsInlineFrame.cpp
@@ -884,14 +884,15 @@ NS_IMETHODIMP nsInlineFrame::GetAccessible(nsIAccessible** aAccessible)
 
 static void
 ReParentChildListStyle(nsPresContext* aPresContext,
-                       nsStyleContext* aParentStyleContext,
-                       nsFrameList& aFrameList)
+                       nsFrameList& aFrameList,
+                       nsIFrame* aParentFrame)
 {
   nsFrameManager *frameManager = aPresContext->FrameManager();
 
   for (nsIFrame* kid = aFrameList.FirstChild(); kid;
        kid = kid->GetNextSibling()) {
-    frameManager->ReParentStyleContext(kid, aParentStyleContext);
+    NS_ASSERTION(kid->GetParent() == aParentFrame, "Bogus parentage");
+    frameManager->ReParentStyleContext(kid);
   }
 }
 
@@ -947,7 +948,8 @@ nsFirstLineFrame::PullOneFrame(nsPresContext* aPresContext, InlineReflowState& i
   if (frame && !mPrevInFlow) {
     // We are a first-line frame. Fixup the child frames
     // style-context that we just pulled.
-    aPresContext->FrameManager()->ReParentStyleContext(frame, mStyleContext);
+    NS_ASSERTION(frame->GetParent() == this, "Incorrect parent?");
+    aPresContext->FrameManager()->ReParentStyleContext(frame);
   }
   return frame;
 }
@@ -970,7 +972,7 @@ nsFirstLineFrame::Reflow(nsPresContext* aPresContext,
       nsFrameList frames(prevOverflowFrames);
       
       mFrames.InsertFrames(this, nsnull, prevOverflowFrames);
-      ReParentChildListStyle(aPresContext, mStyleContext, frames);
+      ReParentChildListStyle(aPresContext, frames, this);
     }
   }
 
@@ -981,7 +983,7 @@ nsFirstLineFrame::Reflow(nsPresContext* aPresContext,
     nsFrameList frames(overflowFrames);
 
     mFrames.AppendFrames(nsnull, overflowFrames);
-    ReParentChildListStyle(aPresContext, mStyleContext, frames);
+    ReParentChildListStyle(aPresContext, frames, this);
   }
 
   // Set our own reflow state (additional state above and beyond
@@ -1042,7 +1044,7 @@ nsFirstLineFrame::Reflow(nsPresContext* aPresContext,
           SetStyleContext(aPresContext, newSC);
 
           // Re-resolve all children
-          ReParentChildListStyle(aPresContext, mStyleContext, mFrames);
+          ReParentChildListStyle(aPresContext, mFrames, this);
         }
       }
     }