diff --git a/mozilla/content/base/src/nsContentList.cpp b/mozilla/content/base/src/nsContentList.cpp
index e6088561fba..7f52caadcc6 100644
--- a/mozilla/content/base/src/nsContentList.cpp
+++ b/mozilla/content/base/src/nsContentList.cpp
@@ -52,6 +52,8 @@
 #include "nsIDOMHTMLFormElement.h"
 #include "nsIContentList.h"
 
+#include "pldhash.h"
+
 nsBaseContentList::nsBaseContentList()
 {
   NS_INIT_REFCNT();
@@ -272,15 +274,117 @@ nsFormContentList::Reset()
   return nsBaseContentList::Reset();
 }
 
+// Hashtable for storing nsContentLists
+static PLDHashTable gContentListHashTable;
+
+struct ContentListHashEntry : public PLDHashEntryHdr
+{
+  nsContentList* mContentList;
+};
+
+PR_STATIC_CALLBACK(const void *)
+ContentListHashtableGetKey(PLDHashTable *table, PLDHashEntryHdr *entry)
+{
+  ContentListHashEntry *e = NS_STATIC_CAST(ContentListHashEntry *, entry);
+  return e->mContentList->GetKey();
+}
+
+PR_STATIC_CALLBACK(PLDHashNumber)
+ContentListHashtableHashKey(PLDHashTable *table, const void *key)
+{
+  const nsContentListKey* list = NS_STATIC_CAST(const nsContentListKey *, key);
+  return list->GetHash();
+}
+
+PR_STATIC_CALLBACK(PRBool)
+ContentListHashtableMatchEntry(PLDHashTable *table,
+                               const PLDHashEntryHdr *entry,
+                               const void *key)
+{
+  const ContentListHashEntry *e =
+    NS_STATIC_CAST(const ContentListHashEntry *, entry);
+  const nsContentListKey* list1 = e->mContentList->GetKey();
+  const nsContentListKey* list2 = NS_STATIC_CAST(const nsContentListKey *, key);
+
+  return list1->Equals(*list2);
+}
+
+nsresult
+NS_GetContentList(nsIDocument* aDocument, nsIAtom* aMatchAtom,
+                  PRInt32 aMatchNameSpaceId, nsIContent* aRootContent,
+                  nsIContentList** aInstancePtrResult)
+{
+  *aInstancePtrResult = nsnull;
+  nsContentList* list = nsnull;
+
+  static PLDHashTableOps hash_table_ops =
+  {
+    PL_DHashAllocTable,
+    PL_DHashFreeTable,
+    ContentListHashtableGetKey,
+    ContentListHashtableHashKey,
+    ContentListHashtableMatchEntry,
+    PL_DHashMoveEntryStub,
+    PL_DHashClearEntryStub,
+    PL_DHashFinalizeStub
+  };
+
+  // Initialize the hashtable if needed.
+  if (!gContentListHashTable.ops) {
+    PRBool success = PL_DHashTableInit(&gContentListHashTable,
+                                       &hash_table_ops, nsnull,
+                                       sizeof(ContentListHashEntry),
+                                       16);
+
+    if (!success) {
+      gContentListHashTable.ops = nsnull;
+    }
+  }
+  
+  ContentListHashEntry *entry = nsnull;
+  // First we look in our hashtable.  Then we create a content list if needed
+  if (gContentListHashTable.ops) {
+    nsContentListKey hashKey(aDocument, aMatchAtom,
+                             aMatchNameSpaceId, aRootContent);
+    
+    // A PL_DHASH_ADD is equivalent to a PL_DHASH_LOOKUP for cases
+    // when the entry is already in the hashtable.
+    entry = NS_STATIC_CAST(ContentListHashEntry *,
+                           PL_DHashTableOperate(&gContentListHashTable,
+                                                &hashKey,
+                                                PL_DHASH_ADD));
+    if (entry)
+      list = entry->mContentList;
+  }
+
+  if (!list) {
+    // We need to create a ContentList and add it to our new entry, if
+    // we have an entry
+    list = new nsContentList(aDocument, aMatchAtom,
+                             aMatchNameSpaceId, aRootContent);
+    if (entry) {
+      if (list)
+        entry->mContentList = list;
+      else
+        PL_DHashTableRawRemove(&gContentListHashTable, entry);
+    }
+  }
+
+  NS_ENSURE_TRUE(list, NS_ERROR_OUT_OF_MEMORY);
+
+  *aInstancePtrResult = list;
+  NS_ADDREF(*aInstancePtrResult);
+                               
+  return NS_OK;
+}
+
 
 // nsContentList implementation
 
 nsContentList::nsContentList(const nsContentList& aContentList)
-  : nsBaseContentList()
+  : nsBaseContentList(), nsContentListKey(aContentList)
 {
   mFunc = aContentList.mFunc;
-  mMatchAtom = aContentList.mMatchAtom;
-  mDocument = aContentList.mDocument;
 
   if (aContentList.mData) {
     mData = new nsString(*aContentList.mData);
@@ -289,39 +393,31 @@ nsContentList::nsContentList(const nsContentList& aContentList)
   }
 
   mMatchAll = aContentList.mMatchAll;
-  mRootContent = aContentList.mRootContent;
   mElements = aContentList.mElements;
 }
 
 nsContentList::nsContentList(nsIDocument *aDocument)
-  : nsBaseContentList()
+  : nsBaseContentList(), nsContentListKey(aDocument, nsnull, kNameSpaceID_Unknown, nsnull)
 {
   mFunc = nsnull;
-  mMatchAtom = nsnull;
-  mDocument = aDocument;
   mData = nsnull;
   mMatchAll = PR_FALSE;
-  mRootContent = nsnull;
 }
 
 nsContentList::nsContentList(nsIDocument *aDocument,
                              nsIAtom* aMatchAtom,
                              PRInt32 aMatchNameSpaceId,
                              nsIContent* aRootContent)
-  : nsBaseContentList()
+  : nsBaseContentList(), nsContentListKey(aDocument, aMatchAtom, aMatchNameSpaceId, aRootContent)
 {
-  mMatchAtom = aMatchAtom;
-  NS_IF_ADDREF(mMatchAtom);
   if (nsLayoutAtoms::wildcard == mMatchAtom) {
     mMatchAll = PR_TRUE;
   }
   else {
     mMatchAll = PR_FALSE;
   }
-  mMatchNameSpaceId = aMatchNameSpaceId;
   mFunc = nsnull;
   mData = nsnull;
-  mRootContent = aRootContent;
   Init(aDocument);
 }
 
@@ -329,7 +425,7 @@ nsContentList::nsContentList(nsIDocument *aDocument,
                              nsContentListMatchFunc aFunc,
                              const nsAString& aData,
                              nsIContent* aRootContent)
-  : nsBaseContentList()
+  : nsBaseContentList(), nsContentListKey(aDocument, nsnull, kNameSpaceID_Unknown, aRootContent)
 {
   mFunc = aFunc;
   if (!aData.IsEmpty()) {
@@ -361,12 +457,11 @@ void nsContentList::Init(nsIDocument *aDocument)
 
 nsContentList::~nsContentList()
 {
+  RemoveFromHashtable();
   if (mDocument) {
     mDocument->RemoveObserver(this);
   }
   
-  NS_IF_RELEASE(mMatchAtom);
-
   delete mData;
 }
 
@@ -567,6 +662,8 @@ NS_IMETHODIMP
 nsContentList::DocumentWillBeDestroyed(nsIDocument *aDocument)
 {
   if (mDocument) {
+    // Our key will change... Best remove ourselves before that happens.
+    RemoveFromHashtable();
     aDocument->RemoveObserver(this);
     mDocument = nsnull;
   }
@@ -653,14 +750,12 @@ nsContentList::MatchSelf(nsIContent *aContent)
   }
   
   aContent->ChildCount(count);
+  nsCOMPtr<nsIContent> child;
   for (i = 0; i < count; i++) {
-    nsIContent *child;
-    aContent->ChildAt(i, child);
+    aContent->ChildAt(i, *getter_AddRefs(child));
     if (MatchSelf(child)) {
-      NS_RELEASE(child);
       return PR_TRUE;
     }
-    NS_RELEASE(child);
   }
   
   return PR_FALSE;
@@ -681,11 +776,10 @@ nsContentList::PopulateWith(nsIContent *aContent, PRBool aIncludeRoot)
   }
   
   aContent->ChildCount(count);
+  nsCOMPtr<nsIContent> child;
   for (i = 0; i < count; i++) {
-    nsIContent *child;
-    aContent->ChildAt(i, child);
+    aContent->ChildAt(i, *getter_AddRefs(child));
     PopulateWith(child, PR_TRUE);
-    NS_RELEASE(child);
   }
 }
 
@@ -698,11 +792,10 @@ nsContentList::PopulateSelf()
     PopulateWith(mRootContent, PR_FALSE);
   }
   else if (mDocument) {
-    nsIContent *root = nsnull;
-    mDocument->GetRootContent(&root);
+    nsCOMPtr<nsIContent> root;
+    mDocument->GetRootContent(getter_AddRefs(root));
     if (root) {
       PopulateWith(root, PR_TRUE);
-      NS_RELEASE(root);
     }
   }
 }
@@ -769,7 +862,26 @@ void
 nsContentList::DisconnectFromDocument()
 {
   if (mDocument) {
+    // Our key will change... Best remove ourselves before that happens.
+    RemoveFromHashtable();
     mDocument->RemoveObserver(this);
     mDocument = nsnull;
   }
 }
+
+void
+nsContentList::RemoveFromHashtable()
+{
+  if (!gContentListHashTable.ops)
+    return;
+    
+  PL_DHashTableOperate(&gContentListHashTable,
+                       GetKey(),
+                       PL_DHASH_REMOVE);
+
+  if (gContentListHashTable.entryCount == 0) {
+    PL_DHashTableFinish(&gContentListHashTable);
+    gContentListHashTable.ops = nsnull;
+  }
+}
+
diff --git a/mozilla/content/base/src/nsContentList.h b/mozilla/content/base/src/nsContentList.h
index 787dd649c0c..13db1861d58 100644
--- a/mozilla/content/base/src/nsContentList.h
+++ b/mozilla/content/base/src/nsContentList.h
@@ -90,7 +90,54 @@ public:
   NS_IMETHOD Reset();
 };
 
+class nsContentListKey
+{
+public:
+  nsContentListKey(nsIDocument *aDocument,
+                   nsIAtom* aMatchAtom, 
+                   PRInt32 aMatchNameSpaceId,
+                   nsIContent* aRootContent)
+    : mMatchAtom(aMatchAtom),
+      mMatchNameSpaceId(aMatchNameSpaceId),
+      mDocument(aDocument),
+      mRootContent(aRootContent)
+  {
+  }
+  
+  nsContentListKey(const nsContentListKey& aContentListKey)
+    : mMatchAtom(aContentListKey.mMatchAtom),
+      mMatchNameSpaceId(aContentListKey.mMatchNameSpaceId),
+      mDocument(aContentListKey.mDocument),
+      mRootContent(aContentListKey.mRootContent)
+  {
+  }
+
+  PRBool Equals(const nsContentListKey& aContentListKey) const
+  {
+    return
+      mMatchAtom == aContentListKey.mMatchAtom &&
+      mMatchNameSpaceId == aContentListKey.mMatchNameSpaceId &&
+      mDocument == aContentListKey.mDocument &&
+      mRootContent == aContentListKey.mRootContent;
+  }
+  inline PRUint32 GetHash(void) const
+  {
+    return
+      NS_PTR_TO_INT32(mMatchAtom.get()) ^
+      (NS_PTR_TO_INT32(mRootContent) << 8) ^
+      (NS_PTR_TO_INT32(mDocument) << 16) ^
+      (mMatchNameSpaceId << 24);
+  }
+  
+protected:
+  nsCOMPtr<nsIAtom> mMatchAtom;
+  PRInt32 mMatchNameSpaceId;
+  nsIDocument* mDocument;   // Weak ref
+  nsIContent* mRootContent; // Weak ref
+};
+
 class nsContentList : public nsBaseContentList,
+                      protected nsContentListKey,
                       public nsIDOMHTMLCollection,
                       public nsIDocumentObserver,
                       public nsIContentList
@@ -181,6 +228,11 @@ public:
                               nsIStyleRule* aStyleRule) { return NS_OK; }
   NS_IMETHOD DocumentWillBeDestroyed(nsIDocument *aDocument);
 
+  // Other public methods
+  nsContentListKey* GetKey() {
+    return NS_STATIC_CAST(nsContentListKey*, this);
+  }
+  
 protected:
   nsresult Match(nsIContent *aContent, PRBool *aMatch);
   void Init(nsIDocument *aDocument);
@@ -191,14 +243,16 @@ protected:
   PRBool IsDescendantOfRoot(nsIContent* aContainer);
   PRBool ContainsRoot(nsIContent* aContent);
   nsresult CheckDocumentExistence();
+  void RemoveFromHashtable();
 
-  nsIAtom* mMatchAtom;
-  PRInt32 mMatchNameSpaceId;
   nsContentListMatchFunc mFunc;
   nsString* mData;
-  nsIDocument* mDocument;
-  nsIContent* mRootContent;
   PRBool mMatchAll;
 };
 
+extern nsresult
+NS_GetContentList(nsIDocument* aDocument, nsIAtom* aMatchAtom,
+                  PRInt32 aMatchNameSpaceId, nsIContent* aRootContent,
+                  nsIContentList** aInstancePtrResult);
+
 #endif // nsContentList_h___
diff --git a/mozilla/content/base/src/nsDocument.cpp b/mozilla/content/base/src/nsDocument.cpp
index d2f2ac99f8d..35f79ac452e 100644
--- a/mozilla/content/base/src/nsDocument.cpp
+++ b/mozilla/content/base/src/nsDocument.cpp
@@ -2444,10 +2444,12 @@ nsDocument::GetElementsByTagName(const nsAString& aTagname,
 {
   nsCOMPtr<nsIAtom> nameAtom(dont_AddRef(NS_NewAtom(aTagname)));
 
-  nsContentList* list = new nsContentList(this, nameAtom, kNameSpaceID_Unknown);
+  nsCOMPtr<nsIContentList> list;
+  NS_GetContentList(this, nameAtom, kNameSpaceID_Unknown, nsnull,
+                    getter_AddRefs(list));
   NS_ENSURE_TRUE(list, NS_ERROR_OUT_OF_MEMORY);
 
-  return list->QueryInterface(NS_GET_IID(nsIDOMNodeList), (void **)aReturn);
+  return CallQueryInterface(list, aReturn);
 }
 
 NS_IMETHODIMP    
@@ -2458,25 +2460,27 @@ nsDocument::GetElementsByTagNameNS(const nsAString& aNamespaceURI,
 
   PRInt32 nameSpaceId = kNameSpaceID_Unknown;
 
-  nsContentList* list = nsnull;
+  nsCOMPtr<nsIContentList> list;
 
   if (!aNamespaceURI.Equals(NS_LITERAL_STRING("*"))) {
     mNameSpaceManager->GetNameSpaceID(aNamespaceURI, nameSpaceId);
 
     if (nameSpaceId == kNameSpaceID_Unknown) {
       // Unkonwn namespace means no matches, we create an empty list...
-      list = new nsContentList(this, nsnull, kNameSpaceID_None);
+      NS_GetContentList(this, nsnull, kNameSpaceID_None, nsnull,
+                        getter_AddRefs(list));
       NS_ENSURE_TRUE(list, NS_ERROR_OUT_OF_MEMORY);
     }
   }
 
   if (!list) {
     nsCOMPtr<nsIAtom> nameAtom(dont_AddRef(NS_NewAtom(aLocalName)));
-    list = new nsContentList(this, nameAtom, nameSpaceId);
+    NS_GetContentList(this, nameAtom, nameSpaceId, nsnull,
+                      getter_AddRefs(list));
     NS_ENSURE_TRUE(list, NS_ERROR_OUT_OF_MEMORY);
   }
 
-  return list->QueryInterface(NS_GET_IID(nsIDOMNodeList), (void **)aReturn);
+  return CallQueryInterface(list, aReturn);
 }
 
 NS_IMETHODIMP    
diff --git a/mozilla/content/base/src/nsGenericElement.cpp b/mozilla/content/base/src/nsGenericElement.cpp
index fcb1edd318e..98e587c2215 100644
--- a/mozilla/content/base/src/nsGenericElement.cpp
+++ b/mozilla/content/base/src/nsGenericElement.cpp
@@ -1075,16 +1075,15 @@ nsGenericElement::GetElementsByTagName(const nsAString& aTagname,
 
   nameAtom = dont_AddRef(NS_NewAtom(aTagname));
 
-  nsContentList* list = new nsContentList(mDocument,
-                                          nameAtom,
-                                          kNameSpaceID_Unknown,
-                                          this);
+  nsCOMPtr<nsIContentList> list;
+  NS_GetContentList(mDocument, nameAtom, kNameSpaceID_Unknown, this,
+                    getter_AddRefs(list));
 
   if (!list) {
     return NS_ERROR_OUT_OF_MEMORY;
   }
 
-  return list->QueryInterface(NS_GET_IID(nsIDOMNodeList), (void **)aReturn);
+  return CallQueryInterface(list, aReturn);
 }
 
 nsresult
@@ -1224,7 +1223,7 @@ nsGenericElement::GetElementsByTagNameNS(const nsAString& aNamespaceURI,
   nsCOMPtr<nsIAtom> nameAtom(dont_AddRef(NS_NewAtom(aLocalName)));
   PRInt32 nameSpaceId = kNameSpaceID_Unknown;
 
-  nsContentList* list = nsnull;
+  nsCOMPtr<nsIContentList> list;
 
   if (!aNamespaceURI.Equals(NS_LITERAL_STRING("*"))) {
     nsCOMPtr<nsINodeInfoManager> nimgr;
@@ -1238,18 +1237,20 @@ nsGenericElement::GetElementsByTagNameNS(const nsAString& aNamespaceURI,
     nsmgr->GetNameSpaceID(aNamespaceURI, nameSpaceId);
 
     if (nameSpaceId == kNameSpaceID_Unknown) {
-      // Unkonwn namespace means no matches, we create an empty list...
-      list = new nsContentList(mDocument, nsnull, kNameSpaceID_None);
+      // Unknown namespace means no matches, we create an empty list...
+      NS_GetContentList(mDocument, nsnull, kNameSpaceID_None, nsnull,
+                        getter_AddRefs(list));
       NS_ENSURE_TRUE(list, NS_ERROR_OUT_OF_MEMORY);
     }
   }
 
   if (!list) {
-    list = new nsContentList(mDocument, nameAtom, nameSpaceId, this);
+    NS_GetContentList(mDocument, nameAtom, nameSpaceId, this,
+                      getter_AddRefs(list));
     NS_ENSURE_TRUE(list, NS_ERROR_OUT_OF_MEMORY);
   }
 
-  return list->QueryInterface(NS_GET_IID(nsIDOMNodeList), (void **)aReturn);
+  return CallQueryInterface(list, aReturn);
 }
 
 nsresult