--- a/content/base/public/nsIDocument.h
+++ b/content/base/public/nsIDocument.h
@@ -432,17 +432,17 @@ public:
    * shared among multiple presentation shells). The caller of this
    * method is responsible for calling BeginObservingDocument() on the
    * presshell if the presshell should observe document mutations.
    */
   virtual nsresult CreateShell(nsPresContext* aContext,
                                nsIViewManager* aViewManager,
                                nsStyleSet* aStyleSet,
                                nsIPresShell** aInstancePtrResult) = 0;
-  void DeleteShell() { mPresShell = nsnull; }
+  virtual void DeleteShell() = 0;
 
   nsIPresShell* GetShell() const
   {
     return mShellIsHidden ? nsnull : mPresShell;
   }
 
   void SetShellHidden(PRBool aHide) { mShellIsHidden = aHide; }
   PRBool ShellIsHidden() const { return mShellIsHidden; }

--- a/content/base/src/nsDocument.cpp
+++ b/content/base/src/nsDocument.cpp
@@ -778,16 +778,46 @@ ExternalResourceTraverser(nsIURI* aKey,
 void
 nsExternalResourceMap::Traverse(nsCycleCollectionTraversalCallback* aCallback) const
 {
   // mPendingLoads will get cleared out as the requests complete, so
   // no need to worry about those here.
   mMap.EnumerateRead(ExternalResourceTraverser, aCallback);
 }
 
+static PLDHashOperator
+ExternalResourceHider(nsIURI* aKey,
+                      nsExternalResourceMap::ExternalResource* aData,
+                      void* aClosure)
+{
+  aData->mViewer->Hide();
+  return PL_DHASH_NEXT;
+}
+
+void
+nsExternalResourceMap::HideViewers()
+{
+  mMap.EnumerateRead(ExternalResourceHider, nsnull);
+}
+
+static PLDHashOperator
+ExternalResourceShower(nsIURI* aKey,
+                       nsExternalResourceMap::ExternalResource* aData,
+                       void* aClosure)
+{
+  aData->mViewer->Show();
+  return PL_DHASH_NEXT;
+}
+
+void
+nsExternalResourceMap::ShowViewers()
+{
+  mMap.EnumerateRead(ExternalResourceShower, nsnull);
+}
+
 nsresult
 nsExternalResourceMap::AddExternalResource(nsIURI* aURI,
                                            nsIDocumentViewer* aViewer,
                                            nsILoadGroup* aLoadGroup,
                                            nsIDocument* aDisplayDocument)
 {
   NS_PRECONDITION(aURI, "Unexpected call");
   NS_PRECONDITION((aViewer && aLoadGroup) || (!aViewer && !aLoadGroup),
@@ -806,16 +836,19 @@ nsExternalResourceMap::AddExternalResour
 
     nsCOMPtr<nsIXULDocument> xulDoc = do_QueryInterface(doc);
     if (xulDoc) {
       // We don't handle XUL stuff here yet.
       rv = NS_ERROR_NOT_AVAILABLE;
     } else {
       doc->SetDisplayDocument(aDisplayDocument);
 
+      // Make sure that hiding our viewer will tear down its presentation.
+      aViewer->SetSticky(PR_FALSE);
+
       rv = aViewer->Init(nsnull, nsIntRect(0, 0, 0, 0));
       if (NS_SUCCEEDED(rv)) {
         rv = aViewer->Open(nsnull, nsnull);
       }
     }
     
     if (NS_FAILED(rv)) {
       doc = nsnull;
@@ -3034,21 +3067,30 @@ nsDocument::doCreateShell(nsPresContext*
   }
 
   rv = shell->Init(this, aContext, aViewManager, aStyleSet, aCompatMode);
   NS_ENSURE_SUCCESS(rv, rv);
 
   // Note: we don't hold a ref to the shell (it holds a ref to us)
   mPresShell = shell;
 
+  mExternalResourceMap.ShowViewers();
+
   shell.swap(*aInstancePtrResult);
 
   return NS_OK;
 }
 
+void
+nsDocument::DeleteShell()
+{
+  mExternalResourceMap.HideViewers();
+  mPresShell = nsnull;
+}
+
 static void
 SubDocClearEntry(PLDHashTable *table, PLDHashEntryHdr *entry)
 {
   SubDocMapEntry *e = static_cast<SubDocMapEntry *>(entry);
 
   NS_RELEASE(e->mKey);
   if (e->mSubDocument) {
     e->mSubDocument->SetParentDocument(nsnull);
@@ -7810,9 +7852,8 @@ nsIDocument::CreateStaticClone(nsISuppor
           }
         }
       }
     }
   }
   mCreatingStaticClone = PR_FALSE;
   return clonedDoc.forget();
 }
-

--- a/content/base/src/nsDocument.h
+++ b/content/base/src/nsDocument.h
@@ -370,16 +370,22 @@ public:
   struct ExternalResource
   {
     ~ExternalResource();
     nsCOMPtr<nsIDocument> mDocument;
     nsCOMPtr<nsIContentViewer> mViewer;
     nsCOMPtr<nsILoadGroup> mLoadGroup;
   };
 
+  // Hide all our viewers
+  void HideViewers();
+
+  // Show all our viewers
+  void ShowViewers();
+
 protected:
   class PendingLoad : public ExternalResourceLoad,
                       public nsIStreamListener
   {
   public:
     PendingLoad(nsDocument* aDisplayDocument) :
       mDisplayDocument(aDisplayDocument)
     {}
@@ -583,16 +589,17 @@ public:
    * Create a new presentation shell that will use aContext for
    * its presentation context (presentation context's <b>must not</b> be
    * shared among multiple presentation shell's).
    */
   virtual nsresult CreateShell(nsPresContext* aContext,
                                nsIViewManager* aViewManager,
                                nsStyleSet* aStyleSet,
                                nsIPresShell** aInstancePtrResult);
+  virtual void DeleteShell();
 
   virtual nsresult SetSubDocumentFor(nsIContent *aContent,
                                      nsIDocument* aSubDoc);
   virtual nsIDocument* GetSubDocumentFor(nsIContent *aContent) const;
   virtual nsIContent* FindContentForSubDocument(nsIDocument *aDocument) const;
   virtual Element* GetRootElementInternal() const;
 
   /**

--- a/layout/base/nsDocumentViewer.cpp
+++ b/layout/base/nsDocumentViewer.cpp
@@ -855,17 +855,19 @@ DocumentViewerImpl::InitInternal(nsIWidg
     nsresult rv = CreateDeviceContext(containerView);
     NS_ENSURE_SUCCESS(rv, rv);
 
     // XXXbz this is a nasty hack to do with the fact that we create
     // presentations both in Init() and in Show()...  Ideally we would only do
     // it in one place (Show()) and require that callers call init(), open(),
     // show() in that order or something.
     if (!mPresContext &&
-        (aParentWidget || containerView || mDocument->GetDisplayDocument())) {
+        (aParentWidget || containerView ||
+         (mDocument->GetDisplayDocument() &&
+          mDocument->GetDisplayDocument()->GetShell()))) {
       // Create presentation context
       if (mIsPageMode) {
         //Presentation context already created in SetPageMode which is calling this method
       } else {
         mPresContext = CreatePresContext(mDocument,
             nsPresContext::eContext_Galley, containerView);
       }
       NS_ENSURE_TRUE(mPresContext, NS_ERROR_OUT_OF_MEMORY);