diff --git a/mozilla/layout/base/nsCSSFrameConstructor.cpp b/mozilla/layout/base/nsCSSFrameConstructor.cpp
index 131ef9fba68..e86f6f74853 100644
--- a/mozilla/layout/base/nsCSSFrameConstructor.cpp
+++ b/mozilla/layout/base/nsCSSFrameConstructor.cpp
@@ -668,8 +668,7 @@ DoCleanupFrameReferences(nsPresContext*  aPresContext,
   nsIFrame* frame = nsPlaceholderFrame::GetRealFrameFor(aFrameIn);
 
   // Remove the mapping from the content object to its frame
-  aFrameManager->SetPrimaryFrameFor(content, nsnull);
-  frame->RemovedAsPrimaryFrame(aPresContext);
+  aFrameManager->RemoveAsPrimaryFrame(content, frame);
   aFrameManager->ClearAllUndisplayedContentIn(content);
 
   // Recursively walk the child frames.
@@ -9725,8 +9724,7 @@ DoDeletingFrameSubtree(nsPresContext*  aPresContext,
   // Remove the mapping from the content object to its frame.
   nsIContent* content = aFrame->GetContent();
   if (content) {
-    aFrameManager->SetPrimaryFrameFor(content, nsnull);
-    aFrame->RemovedAsPrimaryFrame(aPresContext);
+    aFrameManager->RemoveAsPrimaryFrame(content, aFrame);
     aFrameManager->ClearAllUndisplayedContentIn(content);
   }
 
diff --git a/mozilla/layout/base/nsFrameManager.cpp b/mozilla/layout/base/nsFrameManager.cpp
index 5ac5b94cb2f..cb7c41476fe 100644
--- a/mozilla/layout/base/nsFrameManager.cpp
+++ b/mozilla/layout/base/nsFrameManager.cpp
@@ -417,44 +417,56 @@ nsFrameManager::SetPrimaryFrameFor(nsIContent* aContent,
                                    nsIFrame*   aPrimaryFrame)
 {
   NS_ENSURE_ARG_POINTER(aContent);
-  // it's ok if aPrimaryFrame is null
+  NS_ASSERTION(aPrimaryFrame && aPrimaryFrame->GetParent(),
+               "BOGUS!");
 
-  // If aPrimaryFrame is NULL, then remove the mapping
-  if (!aPrimaryFrame) {
-    if (mPrimaryFrameMap.ops) {
-      PL_DHashTableOperate(&mPrimaryFrameMap, aContent, PL_DHASH_REMOVE);
-    }
-  } else {
   // This code should be used if/when we switch back to a 2-word entry
   // in the primary frame map.
 #if 0
-    NS_PRECONDITION(aPrimaryFrame->GetContent() == aContent, "wrong content");
+  NS_PRECONDITION(aPrimaryFrame->GetContent() == aContent, "wrong content");
 #endif
 
-    // Create a new hashtable if necessary
-    if (!mPrimaryFrameMap.ops) {
-      if (!PL_DHashTableInit(&mPrimaryFrameMap, PL_DHashGetStubOps(), nsnull,
-                             sizeof(PrimaryFrameMapEntry), 16)) {
-        mPrimaryFrameMap.ops = nsnull;
-        return NS_ERROR_OUT_OF_MEMORY;
-      }
+  // Create a new hashtable if necessary
+  if (!mPrimaryFrameMap.ops) {
+    if (!PL_DHashTableInit(&mPrimaryFrameMap, PL_DHashGetStubOps(), nsnull,
+                           sizeof(PrimaryFrameMapEntry), 16)) {
+      mPrimaryFrameMap.ops = nsnull;
+      return NS_ERROR_OUT_OF_MEMORY;
     }
-
-    // Add a mapping to the hash table
-    PrimaryFrameMapEntry *entry = NS_STATIC_CAST(PrimaryFrameMapEntry*,
-        PL_DHashTableOperate(&mPrimaryFrameMap, aContent, PL_DHASH_ADD));
-#ifdef DEBUG_dbaron
-    if (entry->frame) {
-      NS_WARNING("already have primary frame for content");
-    }
-#endif
-    entry->frame = aPrimaryFrame;
-    entry->content = aContent;
   }
+
+  // Add a mapping to the hash table
+  PrimaryFrameMapEntry *entry = NS_STATIC_CAST(PrimaryFrameMapEntry*,
+      PL_DHashTableOperate(&mPrimaryFrameMap, aContent, PL_DHASH_ADD));
+#ifdef DEBUG_dbaron
+  if (entry->frame) {
+    NS_WARNING("already have primary frame for content");
+  }
+#endif
+  entry->frame = aPrimaryFrame;
+  entry->content = aContent;
     
   return NS_OK;
 }
 
+void
+nsFrameManager::RemoveAsPrimaryFrame(nsIContent* aContent,
+                                     nsIFrame* aPrimaryFrame)
+{
+  NS_PRECONDITION(aPrimaryFrame, "Must have a frame");
+  if (aContent && mPrimaryFrameMap.ops) {
+    PrimaryFrameMapEntry *entry = NS_STATIC_CAST(PrimaryFrameMapEntry*,
+        PL_DHashTableOperate(&mPrimaryFrameMap, aContent, PL_DHASH_LOOKUP));
+    if (PL_DHASH_ENTRY_IS_BUSY(entry) && entry->frame == aPrimaryFrame) {
+      // Don't use PL_DHashTableRawRemove, since we want the table to
+      // shrink as needed.
+      PL_DHashTableOperate(&mPrimaryFrameMap, aContent, PL_DHASH_REMOVE);
+    }
+  }
+
+  aPrimaryFrame->RemovedAsPrimaryFrame(GetPresContext());
+}
+
 void
 nsFrameManager::ClearPrimaryFrameMap()
 {
diff --git a/mozilla/layout/base/nsFrameManager.h b/mozilla/layout/base/nsFrameManager.h
index 1920e8b7733..da536912077 100644
--- a/mozilla/layout/base/nsFrameManager.h
+++ b/mozilla/layout/base/nsFrameManager.h
@@ -109,8 +109,16 @@ public:
 
   // Primary frame functions
   NS_HIDDEN_(nsIFrame*) GetPrimaryFrameFor(nsIContent* aContent);
+  // aPrimaryFrame must not be null.  If you're trying to remove a primary frame
+  // mapping, use RemoveAsPrimaryFrame.
   NS_HIDDEN_(nsresult)  SetPrimaryFrameFor(nsIContent* aContent,
                                            nsIFrame* aPrimaryFrame);
+  // If aPrimaryFrame is the current primary frame for aContent, remove the
+  // relevant hashtable entry.  If the current primary frame for aContent is
+  // null, this does nothing.  aPrimaryFrame must not be null, and this method
+  // handles calling RemovedAsPrimaryFrame on aPrimaryFrame.
+  NS_HIDDEN_(void)      RemoveAsPrimaryFrame(nsIContent* aContent,
+                                             nsIFrame* aPrimaryFrame);
   NS_HIDDEN_(void)      ClearPrimaryFrameMap();
 
   // Placeholder frame functions
diff --git a/mozilla/layout/generic/nsImageMap.cpp b/mozilla/layout/generic/nsImageMap.cpp
index a85353270ce..9c8325bb484 100644
--- a/mozilla/layout/generic/nsImageMap.cpp
+++ b/mozilla/layout/generic/nsImageMap.cpp
@@ -762,7 +762,7 @@ nsImageMap::FreeAreas()
   PRInt32 i, n = mAreas.Count();
   for (i = 0; i < n; i++) {
     Area* area = (Area*) mAreas.ElementAt(i);
-    frameManager->SetPrimaryFrameFor(area->mArea, nsnull);
+    frameManager->RemoveAsPrimaryFrame(area->mArea, mImageFrame);
 
     nsCOMPtr<nsIContent> areaContent;
     area->GetArea(getter_AddRefs(areaContent));