diff --git a/docshell/build/nsDocShellModule.cpp b/docshell/build/nsDocShellModule.cpp
index 75e2f63c4472..fb4acaed0324 100644
--- a/docshell/build/nsDocShellModule.cpp
+++ b/docshell/build/nsDocShellModule.cpp
@@ -80,12 +80,16 @@ Initialize(nsIModule* aSelf)
   gInitialized = PR_TRUE;
 
   nsresult rv = nsSHistory::Startup();
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  rv = nsSHEntry::Startup();
   return rv;
 }
 
 PR_STATIC_CALLBACK(void)
 Shutdown(nsIModule* aSelf)
 {
+  nsSHEntry::Shutdown();
   gInitialized = PR_FALSE;
 }
 
diff --git a/docshell/shistory/public/nsISHistoryInternal.idl b/docshell/shistory/public/nsISHistoryInternal.idl
index 1dfd5961c6bf..ea35fc2d5886 100644
--- a/docshell/shistory/public/nsISHistoryInternal.idl
+++ b/docshell/shistory/public/nsISHistoryInternal.idl
@@ -46,12 +46,13 @@ interface nsIDocShell;
 
 %{C++
 #define NS_SHISTORY_INTERNAL_CID \
-{0x5b4cba4c, 0xbf67, 0x499a, {0xae, 0x2c, 0x3f, 0x76, 0x65, 0x6f, 0x4a, 0x4e}}
+{ 0x9c47c121, 0x1c6e, 0x4d8f, \
+  { 0xb9, 0x04, 0x3a, 0xc9, 0x68, 0x11, 0x6e, 0x88 } }
 
 #define NS_SHISTORY_INTERNAL_CONTRACTID "@mozilla.org/browser/shistory-internal;1"
 %}
 
-[scriptable, uuid(df8788d6-c0ed-4517-b47e-c719afc94284)]
+[scriptable, uuid(9c47c121-1c6e-4d8f-b904-3ac968116e88)]
 interface nsISHistoryInternal: nsISupports
 {
   /**
@@ -98,4 +99,10 @@ interface nsISHistoryInternal: nsISupports
    * the previous viewer.
    */
    void evictContentViewers(in long previousIndex, in long index);
+   
+   /**
+    * Evict the content viewer associated with a session history entry
+    * that has timed out.
+    */
+   void evictExpiredContentViewerForEntry(in nsISHEntry aEntry);
 };
diff --git a/docshell/shistory/src/nsSHEntry.cpp b/docshell/shistory/src/nsSHEntry.cpp
index 9095d1ae26e5..32a8bc87afa2 100644
--- a/docshell/shistory/src/nsSHEntry.cpp
+++ b/docshell/shistory/src/nsSHEntry.cpp
@@ -51,14 +51,53 @@
 #include "nsIDOMDocument.h"
 #include "nsAutoPtr.h"
 #include "nsThreadUtils.h"
+#include "nsIWebNavigation.h"
+#include "nsISHistory.h"
+#include "nsISHistoryInternal.h"
 
+// Hardcode this to time out unused content viewers after 30 minutes
+#define CONTENT_VIEWER_TIMEOUT_SECONDS 30*60
 
+typedef nsExpirationTracker<nsSHEntry,3> HistoryTrackerBase;
+class HistoryTracker : public HistoryTrackerBase {
+public:
+  // Expire cached contentviewers after 20-30 minutes in the cache.
+  HistoryTracker() : HistoryTrackerBase((CONTENT_VIEWER_TIMEOUT_SECONDS/2)*1000) {}
+  
+protected:
+  virtual void NotifyExpired(nsSHEntry* aObj) {
+    RemoveObject(aObj);
+    aObj->Expire();
+  }
+};
+
+static HistoryTracker *gHistoryTracker = nsnull;
 static PRUint32 gEntryID = 0;
 
+nsresult nsSHEntry::Startup()
+{
+  gHistoryTracker = new HistoryTracker();
+  return gHistoryTracker ? NS_OK : NS_ERROR_OUT_OF_MEMORY;
+}
+
+void nsSHEntry::Shutdown()
+{
+  delete gHistoryTracker;
+  gHistoryTracker = nsnull;
+}
+
+static void StopTrackingEntry(nsSHEntry *aEntry)
+{
+  if (aEntry->GetExpirationState()->IsTracked()) {
+    gHistoryTracker->RemoveObject(aEntry);
+  }
+}
+
 //*****************************************************************************
 //***    nsSHEntry: Object Management
 //*****************************************************************************
 
+
 nsSHEntry::nsSHEntry() 
   : mLoadType(0)
   , mID(gEntryID++)
@@ -109,6 +148,8 @@ ClearParentPtr(nsISHEntry* aEntry, void* /* aData */)
 
 nsSHEntry::~nsSHEntry()
 {
+  StopTrackingEntry(this);
+
   // Since we never really remove kids from SHEntrys, we need to null
   // out the mParent pointers on all our kids.
   mChildren.EnumerateForwards(ClearParentPtr, nsnull);
@@ -193,6 +234,8 @@ nsSHEntry::SetContentViewer(nsIContentViewer *aViewer)
       mDocument->SetShellsHidden(PR_TRUE);
       mDocument->AddMutationObserver(this);
     }
+    
+    gHistoryTracker->AddObject(this);
   }
 
   return NS_OK;
@@ -637,6 +680,7 @@ nsSHEntry::DropPresentationState()
   if (mContentViewer)
     mContentViewer->ClearHistoryEntry();
 
+  StopTrackingEntry(this);
   mContentViewer = nsnull;
   mSticky = PR_TRUE;
   mWindowState = nsnull;
@@ -645,6 +689,31 @@ nsSHEntry::DropPresentationState()
   mRefreshURIList = nsnull;
 }
 
+void
+nsSHEntry::Expire()
+{
+  // This entry has timed out. If we still have a content viewer, we need to
+  // get it evicted.
+  if (!mContentViewer)
+    return;
+  nsCOMPtr<nsISupports> container;
+  mContentViewer->GetContainer(getter_AddRefs(container));
+  nsCOMPtr<nsIDocShellTreeItem> treeItem = do_QueryInterface(container);
+  if (!treeItem)
+    return;
+  // We need to find the root DocShell since only that object has an
+  // SHistory and we need the SHistory to evict content viewers
+  nsCOMPtr<nsIDocShellTreeItem> root;
+  treeItem->GetSameTypeRootTreeItem(getter_AddRefs(root));
+  nsCOMPtr<nsIWebNavigation> webNav = do_QueryInterface(root);
+  nsCOMPtr<nsISHistory> history;
+  webNav->GetSessionHistory(getter_AddRefs(history));
+  nsCOMPtr<nsISHistoryInternal> historyInt = do_QueryInterface(history);
+  if (!historyInt)
+    return;
+  historyInt->EvictExpiredContentViewerForEntry(this);
+}
+
 //*****************************************************************************
 //    nsSHEntry: nsIMutationObserver
 //*****************************************************************************
diff --git a/docshell/shistory/src/nsSHEntry.h b/docshell/shistory/src/nsSHEntry.h
index 6819e7db6636..95de45337fd9 100644
--- a/docshell/shistory/src/nsSHEntry.h
+++ b/docshell/shistory/src/nsSHEntry.h
@@ -58,6 +58,7 @@
 #include "nsRect.h"
 #include "nsSupportsArray.h"
 #include "nsIMutationObserver.h"
+#include "nsExpirationTracker.h"
 
 class nsSHEntry : public nsISHEntry,
                   public nsISHContainer,
@@ -75,6 +76,13 @@ public:
 
   void DropPresentationState();
 
+  void Expire();
+  
+  nsExpirationState *GetExpirationState() { return &mExpirationState; }
+  
+  static nsresult Startup();
+  static void Shutdown();
+  
 private:
   ~nsSHEntry();
   void DocumentMutated();
@@ -104,6 +112,7 @@ private:
   nsCOMArray<nsIDocShellTreeItem> mChildShells;
   nsCOMPtr<nsISupportsArray>      mRefreshURIList;
   nsCOMPtr<nsISupports>           mOwner;
+  nsExpirationState               mExpirationState;
 };
 
 #endif /* nsSHEntry_h */
diff --git a/docshell/shistory/src/nsSHistory.cpp b/docshell/shistory/src/nsSHistory.cpp
index b3443fff4ad5..fd231b6f9000 100644
--- a/docshell/shistory/src/nsSHistory.cpp
+++ b/docshell/shistory/src/nsSHistory.cpp
@@ -789,11 +789,17 @@ nsSHistory::EvictWindowContentViewers(PRInt32 aFromIndex, PRInt32 aToIndex)
     }
     endIndex = PR_MIN(mLength, aFromIndex + gHistoryMaxViewers);
   }
+  
+  EvictContentViewersInRange(startIndex, endIndex);
+}
 
+void
+nsSHistory::EvictContentViewersInRange(PRInt32 aStart, PRInt32 aEnd)
+{
   nsCOMPtr<nsISHTransaction> trans;
-  GetTransactionAtIndex(startIndex, getter_AddRefs(trans));
+  GetTransactionAtIndex(aStart, getter_AddRefs(trans));
 
-  for (PRInt32 i = startIndex; i < endIndex; ++i) {
+  for (PRInt32 i = aStart; i < aEnd; ++i) {
     nsCOMPtr<nsISHEntry> entry;
     trans->GetSHEntry(getter_AddRefs(entry));
     nsCOMPtr<nsIContentViewer> viewer;
@@ -941,6 +947,46 @@ nsSHistory::EvictGlobalContentViewer()
   }  // while shouldTryEviction
 }
 
+NS_IMETHODIMP
+nsSHistory::EvictExpiredContentViewerForEntry(nsISHEntry *aEntry)
+{
+  PRInt32 startIndex = PR_MAX(0, mIndex - gHistoryMaxViewers);
+  PRInt32 endIndex = PR_MIN(mLength - 1,
+                            mIndex + gHistoryMaxViewers);
+  nsCOMPtr<nsISHTransaction> trans;
+  GetTransactionAtIndex(startIndex, getter_AddRefs(trans));
+
+  PRInt32 i;
+  for (i = startIndex; i <= endIndex; ++i) {
+    nsCOMPtr<nsISHEntry> entry;
+    trans->GetSHEntry(getter_AddRefs(entry));
+    if (entry == aEntry)
+      break;
+
+    nsISHTransaction *temp = trans;
+    temp->GetNext(getter_AddRefs(trans));
+  }
+  if (i > endIndex)
+    return NS_OK;
+  
+  NS_ASSERTION(i != mIndex, "How did the current session entry expire?");
+  if (i == mIndex)
+    return NS_OK;
+  
+  // We evict content viewers for the expired entry and any other entries that
+  // we would have to go through the expired entry to get to (i.e. the entries
+  // that have the expired entry between them and the current entry). Those
+  // other entries should have timed out already, actually, but this is just
+  // to be on the safe side.
+  if (i < mIndex) {
+    EvictContentViewersInRange(startIndex, i + 1);
+  } else {
+    EvictContentViewersInRange(i, endIndex + 1);
+  }
+  
+  return NS_OK;
+}
+
 // Evicts all content viewers in all history objects.  This is very
 // inefficient, because it requires a linear search through all SHistory
 // objects for each viewer to be evicted.  However, this method is called
diff --git a/docshell/shistory/src/nsSHistory.h b/docshell/shistory/src/nsSHistory.h
index 4bd252eb84c0..f5298d702a90 100644
--- a/docshell/shistory/src/nsSHistory.h
+++ b/docshell/shistory/src/nsSHistory.h
@@ -99,6 +99,7 @@ protected:
    nsresult PrintHistory();
 #endif
 
+  void EvictContentViewersInRange(PRInt32 aStartIndex, PRInt32 aEndIndex);
   void EvictWindowContentViewers(PRInt32 aFromIndex, PRInt32 aToIndex);
   static void EvictGlobalContentViewer();
   static void EvictAllContentViewers();