diff --git a/content/base/public/nsContentUtils.h b/content/base/public/nsContentUtils.h
index bbf25c512c3..aa6415e3e5d 100644
--- a/content/base/public/nsContentUtils.h
+++ b/content/base/public/nsContentUtils.h
@@ -752,42 +752,6 @@ public:
    */
   static nsIContentPolicy *GetContentPolicy();
 
-  /**
-   * Make sure that whatever value *aPtr contains at any given moment is
-   * protected from JS GC until we remove the GC root.  A call to this that
-   * succeeds MUST be matched by a call to RemoveJSGCRoot to avoid leaking.
-   */
-  static nsresult AddJSGCRoot(jsval* aPtr, const char* aName) {
-    return AddJSGCRoot((void*)aPtr, aName);
-  }
-
-  /**
-   * Make sure that whatever object *aPtr is pointing to at any given moment is
-   * protected from JS GC until we remove the GC root.  A call to this that
-   * succeeds MUST be matched by a call to RemoveJSGCRoot to avoid leaking.
-   */
-  static nsresult AddJSGCRoot(JSObject** aPtr, const char* aName) {
-    return AddJSGCRoot((void*)aPtr, aName);
-  }
-
-  /**
-   * Make sure that whatever object *aPtr is pointing to at any given moment is
-   * protected from JS GC until we remove the GC root.  A call to this that
-   * succeeds MUST be matched by a call to RemoveJSGCRoot to avoid leaking.
-   */
-  static nsresult AddJSGCRoot(void* aPtr, const char* aName);  
-
-  /**
-   * Remove aPtr as a JS GC root
-   */
-  static nsresult RemoveJSGCRoot(jsval* aPtr) {
-    return RemoveJSGCRoot((void*)aPtr);
-  }
-  static nsresult RemoveJSGCRoot(JSObject** aPtr) {
-    return RemoveJSGCRoot((void*)aPtr);
-  }
-  static nsresult RemoveJSGCRoot(void* aPtr);
-
   /**
    * Quick helper to determine whether there are any mutation listeners
    * of a given type that apply to this content or any of its ancestors.
@@ -1002,40 +966,73 @@ public:
    */
   static void DestroyAnonymousContent(nsCOMPtr<nsIContent>* aContent);
 
-  static nsresult HoldScriptObject(PRUint32 aLangID, void *aObject);
-  static nsresult DropScriptObject(PRUint32 aLangID, void *aObject);
-
-  class ScriptObjectHolder
+  /**
+   * Keep script object aNewObject, held by aScriptObjectHolder, alive.
+   *
+   * NOTE: This currently only supports objects that hold script objects of one
+   *       scripting language.
+   *
+   * @param aLangID script language ID of aNewObject
+   * @param aScriptObjectHolder the object that holds aNewObject
+   * @param aTracer the tracer for aScriptObject
+   * @param aNewObject the script object to hold
+   * @param aWasHoldingObjects whether aScriptObjectHolder was already holding
+   *                           script objects (ie. HoldScriptObject was called
+   *                           on it before, without a corresponding call to
+   *                           DropScriptObjects)
+   */
+  static nsresult HoldScriptObject(PRUint32 aLangID, void* aScriptObjectHolder,
+                                   nsScriptObjectTracer* aTracer,
+                                   void* aNewObject, PRBool aWasHoldingObjects)
   {
-  public:
-    ScriptObjectHolder(PRUint32 aLangID) : mLangID(aLangID),
-                                           mObject(nsnull)
-    {
-      MOZ_COUNT_CTOR(ScriptObjectHolder);
+    if (aLangID == nsIProgrammingLanguage::JAVASCRIPT) {
+      return aWasHoldingObjects ? NS_OK :
+                                  HoldJSObjects(aScriptObjectHolder, aTracer);
     }
-    ~ScriptObjectHolder()
-    {
-      MOZ_COUNT_DTOR(ScriptObjectHolder);
-      if (mObject)
-        DropScriptObject(mLangID, mObject);
+
+    return HoldScriptObject(aLangID, aNewObject);
+  }
+
+  /**
+   * Drop any script objects that aScriptObjectHolder is holding.
+   *
+   * NOTE: This currently only supports objects that hold script objects of one
+   *       scripting language.
+   *
+   * @param aLangID script language ID of the objects that 
+   * @param aScriptObjectHolder the object that holds script object that we want
+   *                            to drop
+   * @param aTracer the tracer for aScriptObject
+   */
+  static nsresult DropScriptObjects(PRUint32 aLangID, void* aScriptObjectHolder,
+                                    nsScriptObjectTracer* aTracer)
+  {
+    if (aLangID == nsIProgrammingLanguage::JAVASCRIPT) {
+      return DropJSObjects(aScriptObjectHolder);
     }
-    nsresult set(void *aObject)
-    {
-      NS_ASSERTION(aObject, "unexpected null object");
-      NS_ASSERTION(!mObject, "already have an object");
-      nsresult rv = HoldScriptObject(mLangID, aObject);
-      if (NS_SUCCEEDED(rv)) {
-        mObject = aObject;
-      }
-      return rv;
-    }
-    void traverse(nsCycleCollectionTraversalCallback &cb)
-    {
-      cb.NoteScriptChild(mLangID, mObject);
-    }
-    PRUint32 mLangID;
-    void *mObject;
-  };
+
+    aTracer->Trace(aScriptObjectHolder, DropScriptObject, nsnull);
+
+    return NS_OK;
+  }
+
+  /**
+   * Keep the JS objects held by aScriptObjectHolder alive.
+   *
+   * @param aScriptObjectHolder the object that holds JS objects that we want to
+   *                            keep alive
+   * @param aTracer the tracer for aScriptObject
+   */
+  static nsresult HoldJSObjects(void* aScriptObjectHolder,
+                                nsScriptObjectTracer* aTracer);
+
+  /**
+   * Drop the JS objects held by aScriptObjectHolder.
+   *
+   * @param aScriptObjectHolder the object that holds JS objects that we want to
+   *                            drop
+   */
+  static nsresult DropJSObjects(void* aScriptObjectHolder);
 
   /**
    * Convert nsIContent::IME_STATUS_* to nsIKBStateControll::IME_STATUS_*
@@ -1122,6 +1119,10 @@ private:
 
   static nsIDOMScriptObjectFactory *GetDOMScriptObjectFactory();
 
+  static nsresult HoldScriptObject(PRUint32 aLangID, void* aObject);
+  PR_STATIC_CALLBACK(void) DropScriptObject(PRUint32 aLangID, void *aObject,
+                                            void *aClosure);
+
   static nsIDOMScriptObjectFactory *sDOMScriptObjectFactory;
 
   static nsIXPConnect *sXPConnect;
@@ -1163,14 +1164,9 @@ private:
   // Holds pointers to nsISupports* that should be released at shutdown
   static nsVoidArray* sPtrsToPtrsToRelease;
 
-  // For now, we don't want to automatically clean this up in Shutdown(), since
-  // consumers might unfortunately end up wanting to use it after that
-  static nsIJSRuntimeService* sJSRuntimeService;
-  static JSRuntime* sJSScriptRuntime;
-  static PRInt32 sJSScriptRootCount;
-
   static nsIScriptRuntime* sScriptRuntimes[NS_STID_ARRAY_UBOUND];
   static PRInt32 sScriptRootCount[NS_STID_ARRAY_UBOUND];
+  static PRUint32 sJSGCThingRootCount;
 
 #ifdef IBMBIDI
   static nsIBidiKeyboard* sBidiKeyboard;
@@ -1180,6 +1176,14 @@ private:
 };
 
 
+#define NS_HOLD_JS_OBJECTS(obj, clazz)                                         \
+  nsContentUtils::HoldJSObjects(NS_CYCLE_COLLECTION_UPCAST(obj, clazz),        \
+                                &NS_CYCLE_COLLECTION_NAME(clazz))
+
+#define NS_DROP_JS_OBJECTS(obj, clazz)                                         \
+  nsContentUtils::DropJSObjects(NS_CYCLE_COLLECTION_UPCAST(obj, clazz))
+
+
 class nsCxPusher
 {
 public:
@@ -1202,33 +1206,38 @@ public:
   nsAutoGCRoot(jsval* aPtr, nsresult* aResult) :
     mPtr(aPtr)
   {
-    mResult = *aResult =
-      nsContentUtils::AddJSGCRoot(aPtr, "nsAutoGCRoot");
+    mResult = *aResult = AddJSGCRoot(aPtr, "nsAutoGCRoot");
   }
 
   // aPtr should be the pointer to the JSObject* we want to protect
   nsAutoGCRoot(JSObject** aPtr, nsresult* aResult) :
     mPtr(aPtr)
   {
-    mResult = *aResult =
-      nsContentUtils::AddJSGCRoot(aPtr, "nsAutoGCRoot");
+    mResult = *aResult = AddJSGCRoot(aPtr, "nsAutoGCRoot");
   }
 
   // aPtr should be the pointer to the thing we want to protect
   nsAutoGCRoot(void* aPtr, nsresult* aResult) :
     mPtr(aPtr)
   {
-    mResult = *aResult =
-      nsContentUtils::AddJSGCRoot(aPtr, "nsAutoGCRoot");
+    mResult = *aResult = AddJSGCRoot(aPtr, "nsAutoGCRoot");
   }
 
   ~nsAutoGCRoot() {
     if (NS_SUCCEEDED(mResult)) {
-      nsContentUtils::RemoveJSGCRoot(mPtr);
+      RemoveJSGCRoot(mPtr);
     }
   }
 
+  static void Shutdown();
+
 private:
+  static nsresult AddJSGCRoot(void *aPtr, const char* aName);
+  static nsresult RemoveJSGCRoot(void *aPtr);
+
+  static nsIJSRuntimeService* sJSRuntimeService;
+  static JSRuntime* sJSScriptRuntime;
+
   void* mPtr;
   nsresult mResult;
 };
diff --git a/content/base/src/nsContentUtils.cpp b/content/base/src/nsContentUtils.cpp
index 827e66bed16..6957e21c3d7 100644
--- a/content/base/src/nsContentUtils.cpp
+++ b/content/base/src/nsContentUtils.cpp
@@ -180,15 +180,15 @@ nsILineBreaker *nsContentUtils::sLineBreaker;
 nsIWordBreaker *nsContentUtils::sWordBreaker;
 nsICaseConversion *nsContentUtils::sCaseConv;
 nsVoidArray *nsContentUtils::sPtrsToPtrsToRelease;
-nsIJSRuntimeService *nsContentUtils::sJSRuntimeService;
-JSRuntime *nsContentUtils::sJSScriptRuntime;
-PRInt32 nsContentUtils::sJSScriptRootCount = 0;
 nsIScriptRuntime *nsContentUtils::sScriptRuntimes[NS_STID_ARRAY_UBOUND];
 PRInt32 nsContentUtils::sScriptRootCount[NS_STID_ARRAY_UBOUND];
+PRUint32 nsContentUtils::sJSGCThingRootCount;
 #ifdef IBMBIDI
 nsIBidiKeyboard *nsContentUtils::sBidiKeyboard = nsnull;
 #endif
 
+nsIJSRuntimeService *nsAutoGCRoot::sJSRuntimeService;
+JSRuntime *nsAutoGCRoot::sJSScriptRuntime;
 
 PRBool nsContentUtils::sInitialized = PR_FALSE;
 
@@ -671,7 +671,8 @@ nsContentUtils::Shutdown()
   NS_IF_RELEASE(sStringBundleService);
   NS_IF_RELEASE(sConsoleService);
   NS_IF_RELEASE(sDOMScriptObjectFactory);
-  NS_IF_RELEASE(sXPConnect);
+  if (sJSGCThingRootCount == 0 && sXPConnect)
+    NS_RELEASE(sXPConnect);
   NS_IF_RELEASE(sSecurityManager);
   NS_IF_RELEASE(sThreadJSContextStack);
   NS_IF_RELEASE(sNameSpaceManager);
@@ -721,6 +722,8 @@ nsContentUtils::Shutdown()
       sEventListenerManagersHash.ops = nsnull;
     }
   }
+
+  nsAutoGCRoot::Shutdown();
 }
 
 static PRBool IsCallerTrustedForCapability(const char* aCapability)
@@ -2672,7 +2675,7 @@ nsContentUtils::GetContentPolicy()
 
 // static
 nsresult
-nsContentUtils::AddJSGCRoot(void* aPtr, const char* aName)
+nsAutoGCRoot::AddJSGCRoot(void* aPtr, const char* aName)
 {
   if (!sJSScriptRuntime) {
     nsresult rv = CallGetService("@mozilla.org/js/xpc/RuntimeService;1",
@@ -2690,25 +2693,16 @@ nsContentUtils::AddJSGCRoot(void* aPtr, const char* aName)
   PRBool ok;
   ok = ::JS_AddNamedRootRT(sJSScriptRuntime, aPtr, aName);
   if (!ok) {
-    if (sJSScriptRootCount == 0) {
-      // We just got the runtime... Just null things out, since no
-      // one's expecting us to have a runtime yet
-      NS_RELEASE(sJSRuntimeService);
-      sJSScriptRuntime = nsnull;
-    }
     NS_WARNING("JS_AddNamedRootRT failed");
     return NS_ERROR_OUT_OF_MEMORY;
   }
 
-  // We now have one more root we added to the runtime
-  ++sJSScriptRootCount;
-
   return NS_OK;
 }
 
 /* static */
 nsresult
-nsContentUtils::RemoveJSGCRoot(void* aPtr)
+nsAutoGCRoot::RemoveJSGCRoot(void* aPtr)
 {
   if (!sJSScriptRuntime) {
     NS_NOTREACHED("Trying to remove a JS GC root when none were added");
@@ -2717,11 +2711,6 @@ nsContentUtils::RemoveJSGCRoot(void* aPtr)
 
   ::JS_RemoveRootRT(sJSScriptRuntime, aPtr);
 
-  if (--sJSScriptRootCount == 0) {
-    NS_RELEASE(sJSRuntimeService);
-    sJSScriptRuntime = nsnull;
-  }
-
   return NS_OK;
 }
 
@@ -3525,6 +3514,8 @@ nsresult
 nsContentUtils::HoldScriptObject(PRUint32 aLangID, void *aObject)
 {
   NS_ASSERTION(aObject, "unexpected null object");
+  NS_ASSERTION(aLangID != nsIProgrammingLanguage::JAVASCRIPT,
+               "Should use HoldJSObjects.");
   nsresult rv;
 
   PRUint32 langIndex = NS_STID_INDEX(aLangID);
@@ -3551,17 +3542,47 @@ nsContentUtils::HoldScriptObject(PRUint32 aLangID, void *aObject)
 }
 
 /* static */
-nsresult
-nsContentUtils::DropScriptObject(PRUint32 aLangID, void *aObject)
+void
+nsContentUtils::DropScriptObject(PRUint32 aLangID, void *aObject,
+                                 void *aClosure)
 {
   NS_ASSERTION(aObject, "unexpected null object");
+  NS_ASSERTION(aLangID != nsIProgrammingLanguage::JAVASCRIPT,
+               "Should use DropJSObjects.");
   PRUint32 langIndex = NS_STID_INDEX(aLangID);
   NS_LOG_RELEASE(sScriptRuntimes[langIndex], sScriptRootCount[langIndex] - 1,
                  "HoldScriptObject");
-  nsresult rv = sScriptRuntimes[langIndex]->DropScriptObject(aObject);
+  sScriptRuntimes[langIndex]->DropScriptObject(aObject);
   if (--sScriptRootCount[langIndex] == 0) {
     NS_RELEASE(sScriptRuntimes[langIndex]);
   }
+}
+
+/* static */
+nsresult
+nsContentUtils::HoldJSObjects(void* aScriptObjectHolder,
+                              nsScriptObjectTracer* aTracer)
+{
+  PRBool newHolder;
+  nsresult rv = sXPConnect->AddJSHolder(aScriptObjectHolder, aTracer);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  ++sJSGCThingRootCount;
+  NS_LOG_ADDREF(sXPConnect, sJSGCThingRootCount, "HoldJSObjects",
+                sizeof(void*));
+
+  return NS_OK;
+}
+
+/* static */
+nsresult
+nsContentUtils::DropJSObjects(void* aScriptObjectHolder)
+{
+  NS_LOG_RELEASE(sXPConnect, sJSGCThingRootCount - 1, "HoldJSObjects");
+  nsresult rv = sXPConnect->RemoveJSHolder(aScriptObjectHolder);
+  if (--sJSGCThingRootCount == 0 && !sInitialized) {
+    NS_RELEASE(sXPConnect);
+  }
   return rv;
 }
 
@@ -3717,3 +3738,10 @@ nsContentUtils::IsNativeAnonymous(nsIContent* aContent)
 
   return PR_FALSE;
 }
+
+/* static */
+void
+nsAutoGCRoot::Shutdown()
+{
+  NS_IF_RELEASE(sJSRuntimeService);
+}
diff --git a/content/xbl/src/nsXBLBinding.cpp b/content/xbl/src/nsXBLBinding.cpp
index 1b94a9f7c93..611519fccf6 100644
--- a/content/xbl/src/nsXBLBinding.cpp
+++ b/content/xbl/src/nsXBLBinding.cpp
@@ -306,7 +306,7 @@ TraverseKey(nsISupports* aKey, nsInsertionPointList* aData, void* aClosure)
   return PL_DHASH_NEXT;
 }
 
-NS_IMPL_CYCLE_COLLECTION_NATIVE_CLASS(nsXBLBinding)
+NS_IMPL_CYCLE_COLLECTION_CLASS(nsXBLBinding)
 NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_NATIVE(nsXBLBinding)
   // XXX Probably can't unlink mPrototypeBinding->XBLDocumentInfo(), because
   //     mPrototypeBinding is weak.
diff --git a/content/xbl/src/nsXBLDocumentInfo.cpp b/content/xbl/src/nsXBLDocumentInfo.cpp
index 4da0e377fb1..5b4007f0deb 100644
--- a/content/xbl/src/nsXBLDocumentInfo.cpp
+++ b/content/xbl/src/nsXBLDocumentInfo.cpp
@@ -452,6 +452,21 @@ UnlinkProtos(nsHashKey *aKey, void *aData, void* aClosure)
   return kHashEnumerateNext;
 }
 
+struct ProtoTracer
+{
+  TraceCallback mCallback;
+  void *mClosure;
+};
+
+static PRIntn PR_CALLBACK
+TraceProtos(nsHashKey *aKey, void *aData, void* aClosure)
+{
+  ProtoTracer* closure = static_cast<ProtoTracer*>(aClosure);
+  nsXBLPrototypeBinding *proto = static_cast<nsXBLPrototypeBinding*>(aData);
+  proto->Trace(closure->mCallback, closure->mClosure);
+  return kHashEnumerateNext;
+}
+
 NS_IMPL_CYCLE_COLLECTION_CLASS(nsXBLDocumentInfo)
 NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(nsXBLDocumentInfo)
   if (tmp->mBindingTable) {
@@ -466,7 +481,14 @@ NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(nsXBLDocumentInfo)
     tmp->mBindingTable->Enumerate(TraverseProtos, &cb);
   }
   cb.NoteXPCOMChild(static_cast<nsIScriptGlobalObject*>(tmp->mGlobalObject));
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_SCRIPT_OBJECTS
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN(nsXBLDocumentInfo)
+  if (tmp->mBindingTable) {
+    ProtoTracer closure = { aCallback, aClosure };
+    tmp->mBindingTable->Enumerate(TraceProtos, &closure);
+  }
+NS_IMPL_CYCLE_COLLECTION_TRACE_END
 
 NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(nsXBLDocumentInfo)
   NS_INTERFACE_MAP_ENTRY(nsIXBLDocumentInfo)
@@ -507,7 +529,10 @@ nsXBLDocumentInfo::~nsXBLDocumentInfo()
     mGlobalObject->SetScriptContext(nsIProgrammingLanguage::JAVASCRIPT, nsnull);
     mGlobalObject->ClearGlobalObjectOwner(); // just in case
   }
-  delete mBindingTable;
+  if (mBindingTable) {
+    NS_DROP_JS_OBJECTS(this, nsXBLDocumentInfo);
+    delete mBindingTable;
+  }
 }
 
 NS_IMETHODIMP
@@ -541,8 +566,13 @@ DeletePrototypeBinding(nsHashKey* aKey, void* aData, void* aClosure)
 NS_IMETHODIMP
 nsXBLDocumentInfo::SetPrototypeBinding(const nsACString& aRef, nsXBLPrototypeBinding* aBinding)
 {
-  if (!mBindingTable)
+  if (!mBindingTable) {
     mBindingTable = new nsObjectHashtable(nsnull, nsnull, DeletePrototypeBinding, nsnull);
+    if (!mBindingTable)
+      return NS_ERROR_OUT_OF_MEMORY;
+
+    NS_HOLD_JS_OBJECTS(this, nsXBLDocumentInfo);
+  }
 
   const nsPromiseFlatCString& flat = PromiseFlatCString(aRef);
   nsCStringKey key(flat.get());
diff --git a/content/xbl/src/nsXBLDocumentInfo.h b/content/xbl/src/nsXBLDocumentInfo.h
index 1f65e7168d6..29054dd1e2b 100644
--- a/content/xbl/src/nsXBLDocumentInfo.h
+++ b/content/xbl/src/nsXBLDocumentInfo.h
@@ -72,8 +72,8 @@ public:
   // nsIScriptGlobalObjectOwner methods
   virtual nsIScriptGlobalObject* GetScriptGlobalObject();
 
-  NS_DECL_CYCLE_COLLECTION_CLASS_AMBIGUOUS(nsXBLDocumentInfo,
-                                           nsIXBLDocumentInfo)
+  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS_AMBIGUOUS(nsXBLDocumentInfo,
+                                                         nsIXBLDocumentInfo)
 
 private:
   nsCOMPtr<nsIDocument> mDocument;
diff --git a/content/xbl/src/nsXBLInsertionPoint.cpp b/content/xbl/src/nsXBLInsertionPoint.cpp
index c3c6dd6b500..56d86fccaba 100644
--- a/content/xbl/src/nsXBLInsertionPoint.cpp
+++ b/content/xbl/src/nsXBLInsertionPoint.cpp
@@ -64,7 +64,7 @@ nsXBLInsertionPoint::Release()
   return mRefCnt;
 }
 
-NS_IMPL_CYCLE_COLLECTION_NATIVE_CLASS(nsXBLInsertionPoint)
+NS_IMPL_CYCLE_COLLECTION_CLASS(nsXBLInsertionPoint)
 NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_NATIVE(nsXBLInsertionPoint)
   NS_IMPL_CYCLE_COLLECTION_UNLINK_NSCOMARRAY(mElements)
   NS_IMPL_CYCLE_COLLECTION_UNLINK_NSCOMPTR(mDefaultContentTemplate)
diff --git a/content/xbl/src/nsXBLProtoImpl.cpp b/content/xbl/src/nsXBLProtoImpl.cpp
index 2cd34154537..a1860f98ded 100644
--- a/content/xbl/src/nsXBLProtoImpl.cpp
+++ b/content/xbl/src/nsXBLProtoImpl.cpp
@@ -200,7 +200,7 @@ nsXBLProtoImpl::CompilePrototypeMembers(nsXBLPrototypeBinding* aBinding)
 }
 
 void
-nsXBLProtoImpl::Traverse(nsCycleCollectionTraversalCallback &cb) const
+nsXBLProtoImpl::Trace(TraceCallback aCallback, void *aClosure) const
 {
   // If we don't have a class object then we either didn't compile members
   // or we only have fields, in both cases there are no cycles through our
@@ -211,7 +211,7 @@ nsXBLProtoImpl::Traverse(nsCycleCollectionTraversalCallback &cb) const
 
   nsXBLProtoImplMember *member;
   for (member = mMembers; member; member = member->GetNext()) {
-    member->Traverse(cb);
+    member->Trace(aCallback, aClosure);
   }
 }
 
diff --git a/content/xbl/src/nsXBLProtoImpl.h b/content/xbl/src/nsXBLProtoImpl.h
index e9989f1e437..caa26436044 100644
--- a/content/xbl/src/nsXBLProtoImpl.h
+++ b/content/xbl/src/nsXBLProtoImpl.h
@@ -90,7 +90,7 @@ public:
     mFields = aFieldList;
   }
 
-  void Traverse(nsCycleCollectionTraversalCallback &cb) const;
+  void Trace(TraceCallback aCallback, void *aClosure) const;
   void Unlink();
 
   nsXBLProtoImplField* FindField(const nsString& aFieldName) const;
diff --git a/content/xbl/src/nsXBLProtoImplMember.h b/content/xbl/src/nsXBLProtoImplMember.h
index 0ca62573a13..d8e12cd3181 100644
--- a/content/xbl/src/nsXBLProtoImplMember.h
+++ b/content/xbl/src/nsXBLProtoImplMember.h
@@ -47,11 +47,11 @@
 #include "nsIJSRuntimeService.h"
 #include "nsIServiceManager.h"
 #include "nsReadableUtils.h"
+#include "nsCycleCollectionParticipant.h"
 
 class nsIScriptContext;
 struct JSRuntime;
 class nsIJSRuntimeService;
-class nsCycleCollectionTraversalCallback;
 
 struct nsXBLTextWithLineNumber
 {
@@ -114,7 +114,7 @@ public:
                                  const nsCString& aClassStr,
                                  void* aClassObject)=0;
 
-  virtual void Traverse(nsCycleCollectionTraversalCallback &cb) const = 0;
+  virtual void Trace(TraceCallback aCallback, void *aClosure) const = 0;
 
 protected:
   friend class nsAutoGCRoot;
diff --git a/content/xbl/src/nsXBLProtoImplMethod.cpp b/content/xbl/src/nsXBLProtoImplMethod.cpp
index d1876811831..3da1692c64c 100644
--- a/content/xbl/src/nsXBLProtoImplMethod.cpp
+++ b/content/xbl/src/nsXBLProtoImplMethod.cpp
@@ -72,8 +72,6 @@ nsXBLProtoImplMethod::Destroy(PRBool aIsCompiled)
   NS_PRECONDITION(aIsCompiled == mIsCompiled,
                   "Incorrect aIsCompiled in nsXBLProtoImplMethod::Destroy");
   if (aIsCompiled) {
-    if (mJSMethodObject)
-      nsContentUtils::RemoveJSGCRoot(&mJSMethodObject);
     mJSMethodObject = nsnull;
   }
   else {
@@ -263,8 +261,6 @@ nsXBLProtoImplMethod::CompileMember(nsIScriptContext* aContext, const nsCString&
 
   if (methodObject) {
     // Root the compiled prototype script object.
-    rv = nsContentUtils::AddJSGCRoot(&mJSMethodObject,
-                                     "nsXBLProtoImplMethod::mJSMethodObject");
     if (NS_FAILED(rv)) {
       mJSMethodObject = nsnull;
     }
@@ -277,11 +273,13 @@ nsXBLProtoImplMethod::CompileMember(nsIScriptContext* aContext, const nsCString&
 }
 
 void
-nsXBLProtoImplMethod::Traverse(nsCycleCollectionTraversalCallback &cb) const
+nsXBLProtoImplMethod::Trace(TraceCallback aCallback, void *aClosure) const
 {
   NS_ASSERTION(mIsCompiled, "Shouldn't traverse uncompiled method");
 
-  cb.NoteScriptChild(nsIProgrammingLanguage::JAVASCRIPT, mJSMethodObject);
+  if (mJSMethodObject) {
+    aCallback(nsIProgrammingLanguage::JAVASCRIPT, mJSMethodObject, aClosure);
+  }
 }
 
 nsresult
diff --git a/content/xbl/src/nsXBLProtoImplMethod.h b/content/xbl/src/nsXBLProtoImplMethod.h
index a1e66583639..bac2927b56f 100644
--- a/content/xbl/src/nsXBLProtoImplMethod.h
+++ b/content/xbl/src/nsXBLProtoImplMethod.h
@@ -129,7 +129,7 @@ public:
                                  const nsCString& aClassStr,
                                  void* aClassObject);
 
-  virtual void Traverse(nsCycleCollectionTraversalCallback &cb) const;
+  virtual void Trace(TraceCallback aCallback, void *aClosure) const;
 
 protected:
   union {
diff --git a/content/xbl/src/nsXBLProtoImplProperty.cpp b/content/xbl/src/nsXBLProtoImplProperty.cpp
index 76a5b44bec0..407265f8acf 100644
--- a/content/xbl/src/nsXBLProtoImplProperty.cpp
+++ b/content/xbl/src/nsXBLProtoImplProperty.cpp
@@ -87,14 +87,14 @@ nsXBLProtoImplProperty::Destroy(PRBool aIsCompiled)
                   "Incorrect aIsCompiled in nsXBLProtoImplProperty::Destroy");
 
   if ((mJSAttributes & JSPROP_GETTER) && mJSGetterObject) {
-    nsContentUtils::RemoveJSGCRoot(&mJSGetterObject);
+    mJSGetterObject = nsnull;
   }
   else {
     delete mGetterText;
   }
 
   if ((mJSAttributes & JSPROP_SETTER) && mJSSetterObject) {
-    nsContentUtils::RemoveJSGCRoot(&mJSSetterObject);
+    mJSSetterObject = nsnull;
   }
   else {
     delete mSetterText;
@@ -268,9 +268,6 @@ nsXBLProtoImplProperty::CompileMember(nsIScriptContext* aContext, const nsCStrin
     
       if (mJSGetterObject && NS_SUCCEEDED(rv)) {
         mJSAttributes |= JSPROP_GETTER | JSPROP_SHARED;
-        // Root the compiled prototype script object.
-        rv = nsContentUtils::AddJSGCRoot(&mJSGetterObject,
-                                         "nsXBLProtoImplProperty::mJSGetterObject");
       }
       if (NS_FAILED(rv)) {
         mJSGetterObject = nsnull;
@@ -320,9 +317,6 @@ nsXBLProtoImplProperty::CompileMember(nsIScriptContext* aContext, const nsCStrin
 
       if (mJSSetterObject && NS_SUCCEEDED(rv)) {
         mJSAttributes |= JSPROP_SETTER | JSPROP_SHARED;
-        // Root the compiled prototype script object.
-        rv = nsContentUtils::AddJSGCRoot(&mJSSetterObject,
-                                         "nsXBLProtoImplProperty::mJSSetterObject");
       }
       if (NS_FAILED(rv)) {
         mJSSetterObject = nsnull;
@@ -345,15 +339,15 @@ nsXBLProtoImplProperty::CompileMember(nsIScriptContext* aContext, const nsCStrin
 }
 
 void
-nsXBLProtoImplProperty::Traverse(nsCycleCollectionTraversalCallback &cb) const
+nsXBLProtoImplProperty::Trace(TraceCallback aCallback, void *aClosure) const
 {
   NS_ASSERTION(mIsCompiled, "Shouldn't traverse uncompiled method");
 
-  if (mJSAttributes & JSPROP_GETTER) {
-    cb.NoteScriptChild(nsIProgrammingLanguage::JAVASCRIPT, mJSGetterObject);
+  if ((mJSAttributes & JSPROP_GETTER) && mJSGetterObject) {
+    aCallback(nsIProgrammingLanguage::JAVASCRIPT, mJSGetterObject, aClosure);
   }
 
-  if (mJSAttributes & JSPROP_SETTER) {
-    cb.NoteScriptChild(nsIProgrammingLanguage::JAVASCRIPT, mJSSetterObject);
+  if ((mJSAttributes & JSPROP_SETTER) && mJSSetterObject) {
+    aCallback(nsIProgrammingLanguage::JAVASCRIPT, mJSSetterObject, aClosure);
   }
 }
diff --git a/content/xbl/src/nsXBLProtoImplProperty.h b/content/xbl/src/nsXBLProtoImplProperty.h
index f5ab70c79ac..9c10326c43d 100644
--- a/content/xbl/src/nsXBLProtoImplProperty.h
+++ b/content/xbl/src/nsXBLProtoImplProperty.h
@@ -72,7 +72,7 @@ public:
                                  const nsCString& aClassStr,
                                  void* aClassObject);
 
-  virtual void Traverse(nsCycleCollectionTraversalCallback &cb) const;
+  virtual void Trace(TraceCallback aCallback, void *aClosure) const;
 
 protected:
   union {
diff --git a/content/xbl/src/nsXBLPrototypeBinding.cpp b/content/xbl/src/nsXBLPrototypeBinding.cpp
index 568945789b4..725ec9a755f 100644
--- a/content/xbl/src/nsXBLPrototypeBinding.cpp
+++ b/content/xbl/src/nsXBLPrototypeBinding.cpp
@@ -244,7 +244,7 @@ private:
 PRUint32 nsXBLInsertionPointEntry::gRefCnt = 0;
 nsFixedSizeAllocator* nsXBLInsertionPointEntry::kPool;
 
-NS_IMPL_CYCLE_COLLECTION_NATIVE_CLASS(nsXBLInsertionPointEntry)
+NS_IMPL_CYCLE_COLLECTION_CLASS(nsXBLInsertionPointEntry)
 NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_NATIVE(nsXBLInsertionPointEntry)
   NS_IMPL_CYCLE_COLLECTION_UNLINK_NSCOMPTR(mInsertionParent)
   if (tmp->mDefaultContent) {
@@ -355,8 +355,6 @@ void
 nsXBLPrototypeBinding::Traverse(nsCycleCollectionTraversalCallback &cb) const
 {
   cb.NoteXPCOMChild(mBinding);
-  if (mImplementation)
-    mImplementation->Traverse(cb);
   if (mResources)
     cb.NoteXPCOMChild(mResources->mLoader);
   if (mInsertionPointTable)
@@ -372,6 +370,13 @@ nsXBLPrototypeBinding::Unlink()
     mImplementation->Unlink();
 }
 
+void
+nsXBLPrototypeBinding::Trace(TraceCallback aCallback, void *aClosure) const
+{
+  if (mImplementation)
+    mImplementation->Trace(aCallback, aClosure);
+}
+
 void
 nsXBLPrototypeBinding::Initialize()
 {
diff --git a/content/xbl/src/nsXBLPrototypeBinding.h b/content/xbl/src/nsXBLPrototypeBinding.h
index 83ced720db4..3243bd25490 100644
--- a/content/xbl/src/nsXBLPrototypeBinding.h
+++ b/content/xbl/src/nsXBLPrototypeBinding.h
@@ -198,6 +198,7 @@ public:
 
   void Traverse(nsCycleCollectionTraversalCallback &cb) const;
   void Unlink();
+  void Trace(TraceCallback aCallback, void *aClosure) const;
 
 // Static members
   static PRUint32 gRefCnt;
diff --git a/content/xul/content/src/nsXULElement.cpp b/content/xul/content/src/nsXULElement.cpp
index cc28aeda511..2cc482e868c 100644
--- a/content/xul/content/src/nsXULElement.cpp
+++ b/content/xul/content/src/nsXULElement.cpp
@@ -55,7 +55,6 @@
  *                               use in OS2
  */
 
-#include "jsapi.h"      // for JS_AddNamedRoot and JS_RemoveRootRT
 #include "nsCOMPtr.h"
 #include "nsDOMCID.h"
 #include "nsDOMError.h"
@@ -702,7 +701,8 @@ nsScriptEventHandlerOwnerTearoff::CompileEventHandler(
     nsCOMPtr<nsIXULDocument> xuldoc = do_QueryInterface(mElement->GetOwnerDoc());
 
     nsIScriptContext *context;
-    if (mElement->mPrototype && xuldoc) {
+    nsXULPrototypeElement *elem = mElement->mPrototype;
+    if (elem && xuldoc) {
         // It'll be shared among the instances of the prototype.
 
         // Use the prototype document's special context.  Because
@@ -755,9 +755,16 @@ nsScriptEventHandlerOwnerTearoff::CompileEventHandler(
         XUL_PROTOTYPE_ATTRIBUTE_METER(gNumCacheFills);
         // take a copy of the event handler, and tell the language about it.
         if (aHandler) {
+            NS_ASSERTION(!attr->mEventHandler, "Leaking handler.");
+
             rv = nsContentUtils::HoldScriptObject(aContext->GetScriptTypeID(),
-                                                  aHandler);
+                                                  elem,
+                                                  &NS_CYCLE_COLLECTION_NAME(nsXULPrototypeNode),
+                                                  aHandler,
+                                                  elem->mHoldsScriptObject);
             if (NS_FAILED(rv)) return rv;
+
+            elem->mHoldsScriptObject = PR_TRUE;
         }
         attr->mEventHandler = (void *)aHandler;
     }
@@ -2351,26 +2358,40 @@ nsXULElement::RecompileScriptEventListeners()
     }
 }
 
-NS_IMPL_CYCLE_COLLECTION_NATIVE_CLASS(nsXULPrototypeNode)
+NS_IMPL_CYCLE_COLLECTION_CLASS(nsXULPrototypeNode)
 NS_IMPL_CYCLE_COLLECTION_UNLINK_NATIVE_0(nsXULPrototypeNode)
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_NATIVE_BEGIN(nsXULPrototypeNode)
     if (tmp->mType == nsXULPrototypeNode::eType_Element) {
         nsXULPrototypeElement *elem =
             static_cast<nsXULPrototypeElement*>(tmp);
         PRUint32 i;
-        for (i = 0; i < elem->mNumAttributes; ++i) {
-            cb.NoteScriptChild(elem->mScriptTypeID,
-                               elem->mAttributes[i].mEventHandler);
-        }
         for (i = 0; i < elem->mNumChildren; ++i) {
             NS_IMPL_CYCLE_COLLECTION_TRAVERSE_NATIVE_PTR(elem->mChildren[i],
                                                          nsXULPrototypeNode)
         }
     }
-    else if (tmp->mType == nsXULPrototypeNode::eType_Script) {
-        static_cast<nsXULPrototypeScript*>(tmp)->mScriptObject.traverse(cb);
-    }
+    NS_IMPL_CYCLE_COLLECTION_TRAVERSE_SCRIPT_OBJECTS
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+NS_IMPL_CYCLE_COLLECTION_TRACE_NATIVE_BEGIN(nsXULPrototypeNode)
+    if (tmp->mType == nsXULPrototypeNode::eType_Element) {
+        nsXULPrototypeElement *elem =
+            static_cast<nsXULPrototypeElement*>(tmp);
+        if (elem->mHoldsScriptObject) {
+            PRUint32 i;
+            for (i = 0; i < elem->mNumAttributes; ++i) {
+                void *handler = elem->mAttributes[i].mEventHandler;
+                NS_IMPL_CYCLE_COLLECTION_TRACE_CALLBACK(elem->mScriptTypeID,
+                                                        handler)
+            }
+        }
+    }
+    else if (tmp->mType == nsXULPrototypeNode::eType_Script) {
+        nsXULPrototypeScript *script =
+            static_cast<nsXULPrototypeScript*>(tmp);
+        NS_IMPL_CYCLE_COLLECTION_TRACE_CALLBACK(script->mScriptObject.mLangID,
+                                                script->mScriptObject.mObject)
+    }
+NS_IMPL_CYCLE_COLLECTION_TRACE_END
 NS_IMPL_CYCLE_COLLECTION_ROOT_NATIVE(nsXULPrototypeNode, AddRef)
 NS_IMPL_CYCLE_COLLECTION_UNROOT_NATIVE(nsXULPrototypeNode, Release)
 
@@ -2382,17 +2403,6 @@ NS_IMPL_CYCLE_COLLECTION_UNROOT_NATIVE(nsXULPrototypeNode, Release)
 nsXULPrototypeAttribute::~nsXULPrototypeAttribute()
 {
     MOZ_COUNT_DTOR(nsXULPrototypeAttribute);
-    NS_ASSERTION(!mEventHandler, "Finalize not called - language object leak!");
-}
-
-void
-nsXULPrototypeAttribute::Finalize(PRUint32 aLangID)
-{
-    if (mEventHandler) {
-        if (NS_FAILED(nsContentUtils::DropScriptObject(aLangID, mEventHandler)))
-            NS_ERROR("Failed to drop script object");
-        mEventHandler = nsnull;
-    }
 }
 
 
@@ -2679,6 +2689,19 @@ nsXULPrototypeElement::SetAttrAt(PRUint32 aPos, const nsAString& aValue,
     return NS_OK;
 }
 
+void
+nsXULPrototypeElement::Unlink()
+{
+    if (mHoldsScriptObject) {
+        nsContentUtils::DropScriptObjects(mScriptTypeID, this,
+                                          &NS_CYCLE_COLLECTION_NAME(nsXULPrototypeNode));
+        mHoldsScriptObject = PR_FALSE;
+    }
+    mNumAttributes = 0;
+    delete[] mAttributes;
+    mAttributes = nsnull;
+}
+
 //----------------------------------------------------------------------
 //
 // nsXULPrototypeScript
@@ -2701,6 +2724,7 @@ nsXULPrototypeScript::nsXULPrototypeScript(PRUint32 aLangID, PRUint32 aLineNo, P
 
 nsXULPrototypeScript::~nsXULPrototypeScript()
 {
+    Unlink();
 }
 
 nsresult
@@ -2818,7 +2842,7 @@ nsXULPrototypeScript::Deserialize(nsIObjectInputStream* aStream,
         NS_WARNING("Language deseralization failed");
         return rv;
     }
-    mScriptObject.set(newScriptObject);
+    Set(newScriptObject);
     return NS_OK;
 }
 
@@ -2871,7 +2895,7 @@ nsXULPrototypeScript::DeserializeOutOfLine(nsIObjectInputStream* aInput,
                         NS_ERROR("XUL cache gave different language?");
                         return NS_ERROR_UNEXPECTED;
                     }
-                    mScriptObject.set(newScriptObject);
+                    Set(newScriptObject);
                 }
             }
         }
@@ -2997,7 +3021,7 @@ nsXULPrototypeScript::Compile(const PRUnichar* aText,
     if (NS_FAILED(rv))
         return rv;
 
-    mScriptObject.set(newScriptObject);
+    Set(newScriptObject);
     return rv;
 }
 
diff --git a/content/xul/content/src/nsXULElement.h b/content/xul/content/src/nsXULElement.h
index aed4c073b3b..aa3af24903a 100644
--- a/content/xul/content/src/nsXULElement.h
+++ b/content/xul/content/src/nsXULElement.h
@@ -124,9 +124,6 @@ public:
     // nsScriptObjectHolder, but want to avoid the extra lang ID.
     void* mEventHandler;
 
-    // Containing element must tell us the langID so we can cleanup.
-    void Finalize(PRUint32 aLangID);
-
 #ifdef XUL_PROTOTYPE_ATTRIBUTE_METERING
     /**
       If enough attributes, on average, are event handlers, it pays to keep
@@ -230,7 +227,7 @@ public:
      */
     virtual void ReleaseSubtree() { Release(); }
 
-    NS_DECL_CYCLE_COLLECTION_NATIVE_CLASS(nsXULPrototypeNode)
+    NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_NATIVE_CLASS(nsXULPrototypeNode)
 
 protected:
     nsXULPrototypeNode(Type aType)
@@ -249,6 +246,7 @@ public:
           mHasIdAttribute(PR_FALSE),
           mHasClassAttribute(PR_FALSE),
           mHasStyleAttribute(PR_FALSE),
+          mHoldsScriptObject(PR_FALSE),
           mScriptTypeID(nsIProgrammingLanguage::UNKNOWN)
     {
         NS_LOG_ADDREF(this, 1, ClassName(), ClassSize());
@@ -256,10 +254,7 @@ public:
 
     virtual ~nsXULPrototypeElement()
     {
-        PRUint32 i;
-        for (i = 0; i < mNumAttributes; i++)
-            mAttributes[i].Finalize(mScriptTypeID);
-        delete[] mAttributes;
+        Unlink();
         NS_ASSERTION(!mChildren && mNumChildren == 0,
                      "ReleaseSubtree not called");
     }
@@ -294,6 +289,8 @@ public:
 
     nsresult SetAttrAt(PRUint32 aPos, const nsAString& aValue, nsIURI* aDocumentURI);
 
+    void Unlink();
+
     PRUint32                 mNumChildren;
     nsXULPrototypeNode**     mChildren;           // [OWNER]
 
@@ -305,6 +302,7 @@ public:
     PRPackedBool             mHasIdAttribute:1;
     PRPackedBool             mHasClassAttribute:1;
     PRPackedBool             mHasStyleAttribute:1;
+    PRPackedBool             mHoldsScriptObject:1;
 
     // The language ID can not be set on a per-node basis, but is tracked
     // so that the language ID from the originating root can be used
@@ -361,13 +359,52 @@ public:
                      nsIDocument* aDocument,
                      nsIScriptGlobalObjectOwner* aGlobalOwner);
 
+    void Unlink()
+    {
+        if (mScriptObject.mObject) {
+            nsContentUtils::DropScriptObjects(mScriptObject.mLangID, this,
+                                              &NS_CYCLE_COLLECTION_NAME(nsXULPrototypeNode));
+            mScriptObject.mObject = nsnull;
+        }
+    }
+
+    void Set(nsScriptObjectHolder &aHolder)
+    {
+        NS_ASSERTION(mScriptObject.mLangID == aHolder.getScriptTypeID(),
+                     "Wrong language, this will leak the previous object.");
+
+        mScriptObject.mLangID = aHolder.getScriptTypeID();
+        Set((void*)aHolder);
+    }
+    void Set(void *aObject)
+    {
+        NS_ASSERTION(!mScriptObject.mObject, "Leaking script object.");
+
+        nsresult rv = nsContentUtils::HoldScriptObject(mScriptObject.mLangID,
+                                                       this,
+                                                       &NS_CYCLE_COLLECTION_NAME(nsXULPrototypeNode),
+                                                       aObject, PR_FALSE);
+        if (NS_SUCCEEDED(rv)) {
+            mScriptObject.mObject = aObject;
+        }
+    }
+
+    struct ScriptObjectHolder
+    {
+        ScriptObjectHolder(PRUint32 aLangID) : mLangID(aLangID),
+                                               mObject(nsnull)
+        {
+        }
+        PRUint32 mLangID;
+        void* mObject;
+    };
     nsCOMPtr<nsIURI>         mSrcURI;
     PRUint32                 mLineNo;
     PRPackedBool             mSrcLoading;
     PRPackedBool             mOutOfLine;
     nsXULDocument*           mSrcLoadWaiters;   // [OWNER] but not COMPtr
     PRUint32                 mLangVersion;
-    nsContentUtils::ScriptObjectHolder mScriptObject;
+    ScriptObjectHolder       mScriptObject;
 };
 
 class nsXULPrototypeText : public nsXULPrototypeNode
diff --git a/content/xul/document/src/nsXULDocument.cpp b/content/xul/document/src/nsXULDocument.cpp
index 8b5dded271a..f5b2a1e9b09 100644
--- a/content/xul/document/src/nsXULDocument.cpp
+++ b/content/xul/document/src/nsXULDocument.cpp
@@ -3209,7 +3209,7 @@ nsXULDocument::LoadScript(nsXULPrototypeScript* aScriptProto, PRBool* aBlock)
                 NS_ERROR("XUL cache gave me an incorrect script language");
                 return NS_ERROR_UNEXPECTED;
             }
-            aScriptProto->mScriptObject.set(newScriptObject);
+            aScriptProto->Set(newScriptObject);
         }
 
         if (aScriptProto->mScriptObject.mObject) {
diff --git a/dom/src/base/nsJSEnvironment.cpp b/dom/src/base/nsJSEnvironment.cpp
index 442fe2e28e3..25a337ff2ad 100644
--- a/dom/src/base/nsJSEnvironment.cpp
+++ b/dom/src/base/nsJSEnvironment.cpp
@@ -3729,7 +3729,8 @@ public:
   ~nsJSArgArray();
   // nsISupports
   NS_DECL_CYCLE_COLLECTING_ISUPPORTS
-  NS_DECL_CYCLE_COLLECTION_CLASS_AMBIGUOUS(nsJSArgArray, nsIJSArgArray)
+  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS_AMBIGUOUS(nsJSArgArray,
+                                                         nsIJSArgArray)
 
   // nsIArray
   NS_DECL_NSIARRAY
@@ -3759,16 +3760,14 @@ nsJSArgArray::nsJSArgArray(JSContext *aContext, PRUint32 argc, jsval *argv,
     return;
   }
 
-  JSAutoRequest ar(aContext);
-  for (PRUint32 i = 0; i < argc; ++i) {
-    if (argv)
+  // Callers are allowed to pass in a null argv even for argc > 0. They can
+  // then use GetArgs to initialize the values.
+  if (argv) {
+    for (PRUint32 i = 0; i < argc; ++i)
       mArgv[i] = argv[i];
-    if (!::JS_AddNamedRoot(aContext, &mArgv[i], "nsJSArgArray.mArgv[i]")) {
-      *prv = NS_ERROR_UNEXPECTED;
-      return;
-    }
   }
-  *prv = NS_OK;
+  if (argc > 0)
+    *prv = NS_HOLD_JS_OBJECTS(this, nsJSArgArray);
 }
 
 nsJSArgArray::~nsJSArgArray()
@@ -3779,13 +3778,9 @@ nsJSArgArray::~nsJSArgArray()
 void
 nsJSArgArray::ReleaseJSObjects()
 {
+  if (mArgc > 0)
+    NS_DROP_JS_OBJECTS(this, nsJSArgArray);
   if (mArgv) {
-    NS_ASSERTION(nsJSRuntime::sRuntime, "Where's the runtime gone?");
-    if (nsJSRuntime::sRuntime) {
-      for (PRUint32 i = 0; i < mArgc; ++i) {
-        ::JS_RemoveRootRT(nsJSRuntime::sRuntime, &mArgv[i]);
-      }
-    }
     PR_DELETE(mArgv);
   }
   mArgc = 0;
@@ -3797,17 +3792,20 @@ NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(nsJSArgArray)
   tmp->ReleaseJSObjects();
 NS_IMPL_CYCLE_COLLECTION_UNLINK_END
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(nsJSArgArray)
-  {
-    jsval *argv = tmp->mArgv;
-    if (argv) {
-      jsval *end;
-      for (end = argv + tmp->mArgc; argv < end; ++argv) {
-        if (JSVAL_IS_OBJECT(*argv))
-          cb.NoteScriptChild(JAVASCRIPT, JSVAL_TO_OBJECT(*argv));
-      }
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_SCRIPT_OBJECTS
+NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+
+NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN(nsJSArgArray)
+  jsval *argv = tmp->mArgv;
+  if (argv) {
+    jsval *end;
+    for (end = argv + tmp->mArgc; argv < end; ++argv) {
+	    if (JSVAL_IS_GCTHING(*argv))
+        NS_IMPL_CYCLE_COLLECTION_TRACE_CALLBACK(JAVASCRIPT,
+                                                JSVAL_TO_GCTHING(*argv))
     }
   }
-NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
+NS_IMPL_CYCLE_COLLECTION_TRACE_END
 
 NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(nsJSArgArray)
   NS_INTERFACE_MAP_ENTRY(nsIArray)
diff --git a/dom/src/base/nsJSTimeoutHandler.cpp b/dom/src/base/nsJSTimeoutHandler.cpp
index b2dd3e89eb7..989f4dd3c0c 100644
--- a/dom/src/base/nsJSTimeoutHandler.cpp
+++ b/dom/src/base/nsJSTimeoutHandler.cpp
@@ -59,7 +59,7 @@ class nsJSScriptTimeoutHandler: public nsIScriptTimeoutHandler
 public:
   // nsISupports
   NS_DECL_CYCLE_COLLECTING_ISUPPORTS
-  NS_DECL_CYCLE_COLLECTION_CLASS(nsJSScriptTimeoutHandler)
+  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS(nsJSScriptTimeoutHandler)
 
   nsJSScriptTimeoutHandler();
   ~nsJSScriptTimeoutHandler();
@@ -118,9 +118,14 @@ NS_IMPL_CYCLE_COLLECTION_UNLINK_END
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(nsJSScriptTimeoutHandler)
   NS_IMPL_CYCLE_COLLECTION_TRAVERSE_NSCOMPTR(mContext)
   NS_IMPL_CYCLE_COLLECTION_TRAVERSE_NSCOMPTR(mArgv)
-  cb.NoteScriptChild(nsIProgrammingLanguage::JAVASCRIPT, tmp->mFunObj);
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_SCRIPT_OBJECTS
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
 
+NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN(nsJSScriptTimeoutHandler)
+  NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBER_CALLBACK(mExpr)
+  NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBER_CALLBACK(mFunObj)
+NS_IMPL_CYCLE_COLLECTION_TRACE_END
+
 NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(nsJSScriptTimeoutHandler)
   NS_INTERFACE_MAP_ENTRY(nsIScriptTimeoutHandler)
   NS_INTERFACE_MAP_ENTRY(nsISupports)
@@ -146,49 +151,11 @@ void
 nsJSScriptTimeoutHandler::ReleaseJSObjects()
 {
   if (mExpr || mFunObj) {
-    nsCOMPtr<nsIScriptContext> scx = mContext;
-    JSRuntime *rt = nsnull;
-
-    if (scx) {
-      JSContext *cx;
-      cx = (JSContext *)scx->GetNativeContext();
-      rt = ::JS_GetRuntime(cx);
-      mContext = nsnull;
-    } else {
-      // XXX The timeout *must* be unrooted, even if !scx. This can be
-      // done without a JS context using the JSRuntime. This is safe
-      // enough, but it would be better to drop all a window's
-      // timeouts before its context is cleared. Bug 50705 describes a
-      // situation where we're not. In that case, at the time the
-      // context is cleared, a timeout (actually an Interval) is still
-      // active, but temporarily removed from the window's list of
-      // timers (placed instead on the timer manager's list). This
-      // makes the nearly handy ClearAllTimeouts routine useless, so
-      // we settled on using the JSRuntime rather than relying on the
-      // window having a context. It would be good to remedy this
-      // workable but clumsy situation someday.
-
-      nsCOMPtr<nsIJSRuntimeService> rtsvc =
-        do_GetService("@mozilla.org/js/xpc/RuntimeService;1");
-
-      if (rtsvc) {
-        rtsvc->GetRuntime(&rt);
-      }
-    }
-
-    if (!rt) {
-      // most unexpected. not much choice but to bail.
-
-      NS_ERROR("nsTimeout::Release() with no JSRuntime. eek!");
-
-      return;
-    }
-
     if (mExpr) {
-      ::JS_RemoveRootRT(rt, &mExpr);
+      NS_DROP_JS_OBJECTS(this, nsJSScriptTimeoutHandler);
       mExpr = nsnull;
     } else if (mFunObj) {
-      ::JS_RemoveRootRT(rt, &mFunObj);
+      NS_DROP_JS_OBJECTS(this, nsJSScriptTimeoutHandler);
       mFunObj = nsnull;
     } else {
       NS_WARNING("No func and no expr - roots may not have been removed");
@@ -280,9 +247,8 @@ nsJSScriptTimeoutHandler::Init(nsIScriptContext *aContext, PRBool *aIsInterval,
   }
 
   if (expr) {
-    if (!::JS_AddNamedRoot(cx, &mExpr, "timeout.mExpr")) {
-      return NS_ERROR_OUT_OF_MEMORY;
-    }
+    rv = NS_HOLD_JS_OBJECTS(this, nsJSScriptTimeoutHandler);
+    NS_ENSURE_SUCCESS(rv, rv);
 
     mExpr = expr;
 
@@ -292,9 +258,8 @@ nsJSScriptTimeoutHandler::Init(nsIScriptContext *aContext, PRBool *aIsInterval,
       mFileName.Assign(filename);
     }
   } else if (funobj) {
-    if (!::JS_AddNamedRoot(cx, &mFunObj, "timeout.mFunObj")) {
-      return NS_ERROR_OUT_OF_MEMORY;
-    }
+    rv = NS_HOLD_JS_OBJECTS(this, nsJSScriptTimeoutHandler);
+    NS_ENSURE_SUCCESS(rv, rv);
 
     mFunObj = funobj;
 
diff --git a/dom/src/events/nsJSEventListener.cpp b/dom/src/events/nsJSEventListener.cpp
index 414da25a809..46ae7c366ce 100644
--- a/dom/src/events/nsJSEventListener.cpp
+++ b/dom/src/events/nsJSEventListener.cpp
@@ -81,12 +81,13 @@ nsJSEventListener::nsJSEventListener(nsIScriptContext *aContext,
   // until we are done with it.
   NS_ASSERTION(aScopeObject && aContext,
                "EventListener with no context or scope?");
-  aContext->HoldScriptObject(aScopeObject);
+  NS_HOLD_JS_OBJECTS(this, nsJSEventListener);
 }
 
 nsJSEventListener::~nsJSEventListener() 
 {
-  mContext->DropScriptObject(mScopeObject);
+  if (mContext)
+    NS_DROP_JS_OBJECTS(this, nsJSEventListener);
 }
 
 NS_IMPL_CYCLE_COLLECTION_CLASS(nsJSEventListener)
@@ -96,9 +97,14 @@ NS_IMPL_CYCLE_COLLECTION_UNLINK_END
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(nsJSEventListener)
   NS_IMPL_CYCLE_COLLECTION_TRAVERSE_NSCOMPTR(mTarget)
   NS_IMPL_CYCLE_COLLECTION_TRAVERSE_NSCOMPTR(mContext)
-  cb.NoteScriptChild(nsIProgrammingLanguage::JAVASCRIPT, tmp->mScopeObject);
+  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_SCRIPT_OBJECTS
 NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
 
+NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN(nsJSEventListener)
+  NS_IMPL_CYCLE_COLLECTION_TRACE_MEMBER_CALLBACK(tmp->mContext->GetScriptTypeID(),
+                                                 mScopeObject)
+NS_IMPL_CYCLE_COLLECTION_TRACE_END
+
 NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(nsJSEventListener)
   NS_INTERFACE_MAP_ENTRY(nsIDOMEventListener)
   NS_INTERFACE_MAP_ENTRY(nsIJSEventListener)
diff --git a/dom/src/events/nsJSEventListener.h b/dom/src/events/nsJSEventListener.h
index 542d113d838..d7de952c180 100644
--- a/dom/src/events/nsJSEventListener.h
+++ b/dom/src/events/nsJSEventListener.h
@@ -65,8 +65,8 @@ public:
   // nsIJSEventListener interface
   virtual void SetEventName(nsIAtom* aName);
 
-  NS_DECL_CYCLE_COLLECTION_CLASS_AMBIGUOUS(nsJSEventListener,
-                                           nsIDOMEventListener)
+  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS_AMBIGUOUS(nsJSEventListener,
+                                                         nsIDOMEventListener)
 protected:
   nsCOMPtr<nsIAtom> mEventName;
   
diff --git a/js/src/xpconnect/idl/nsIXPCScriptable.idl b/js/src/xpconnect/idl/nsIXPCScriptable.idl
index 7c37283480e..00c8edd905c 100644
--- a/js/src/xpconnect/idl/nsIXPCScriptable.idl
+++ b/js/src/xpconnect/idl/nsIXPCScriptable.idl
@@ -41,6 +41,8 @@
 #include "nsISupports.idl"
 #include "nsIXPConnect.idl"
 
+[ptr] native JSTracerPtr(JSTracer);
+
 %{ C++
 #define NS_SUCCESS_I_DID_SOMETHING \
    (NS_ERROR_GENERATE_SUCCESS(NS_ERROR_MODULE_XPCONNECT,1))
diff --git a/js/src/xpconnect/idl/nsIXPConnect.idl b/js/src/xpconnect/idl/nsIXPConnect.idl
index a523c7c7c10..beecc437481 100644
--- a/js/src/xpconnect/idl/nsIXPConnect.idl
+++ b/js/src/xpconnect/idl/nsIXPConnect.idl
@@ -64,7 +64,7 @@
       native JSVal(jsval);
       native JSID(jsid);
 [ptr] native voidPtrPtr(void*);
-[ptr] native JSTracerPtr(JSTracer);
+[ptr] native nsScriptObjectTracerPtr(nsScriptObjectTracer);
 
 /***************************************************************************/
 
@@ -150,7 +150,7 @@ interface nsIXPCSecurityManager;
 interface nsIPrincipal;
 
 %{C++
-class nsCycleCollectionTraversalCallback;
+class nsScriptObjectTracer;
 %}
 
 /***************************************************************************/
@@ -443,7 +443,7 @@ interface nsIXPCFunctionThisTranslator : nsISupports
     { 0xbd, 0xd6, 0x0, 0x0, 0x64, 0x65, 0x73, 0x74 } }
 %}
 
-[uuid(52fc2ff3-c0ea-46c1-9105-655283c361ff)]
+[uuid(3eb7f5fc-1325-43af-aead-6033162e04af)]
 interface nsIXPConnect : nsISupports
 {
 %{ C++
@@ -727,4 +727,18 @@ interface nsIXPConnect : nsISupports
     [noscript] JSVal getCrossOriginWrapperForObject(in JSContextPtr aJSContext,
                                                     in JSObjectPtr aParent,
                                                     in JSObjectPtr aWrappedObj);
+
+    /**
+     * Root JS objects held by aHolder.
+     * @param aHolder The object that hold the JS objects that should be rooted.
+     * @param aTrace The tracer for aHolder.
+     */
+    [noscript] void addJSHolder(in voidPtr aHolder,
+                                in nsScriptObjectTracerPtr aTracer);
+
+    /**
+     * Stop rooting the JS objects held by aHolder.
+     * @param aHolder The object that hold the rooted JS objects.
+     */
+    [noscript] void removeJSHolder(in voidPtr aHolder);
 };
diff --git a/js/src/xpconnect/src/nsXPConnect.cpp b/js/src/xpconnect/src/nsXPConnect.cpp
index 91e9f94551d..839c6a3efb0 100644
--- a/js/src/xpconnect/src/nsXPConnect.cpp
+++ b/js/src/xpconnect/src/nsXPConnect.cpp
@@ -695,16 +695,31 @@ NoteJSChild(JSTracer *trc, void *thing, uint32 kind)
 
 static uint8 GCTypeToTraceKindMap[GCX_NTYPES] = {
     JSTRACE_OBJECT,     /* GCX_OBJECT */
-    JSTRACE_STRING,     /* GCX_STRING (unused) */
-    JSTRACE_DOUBLE,     /* GCX_DOUBLE (unused) */
-    JSTRACE_STRING,     /* GCX_MUTABLE_STRING (unused) */
-    JSTRACE_FUNCTION,   /* GCX_FUNCTION (unused) */
+    JSTRACE_STRING,     /* GCX_STRING */
+    JSTRACE_DOUBLE,     /* GCX_DOUBLE */
+    JSTRACE_FUNCTION,   /* GCX_FUNCTION */
     JSTRACE_NAMESPACE,  /* GCX_NAMESPACE */
     JSTRACE_QNAME,      /* GCX_QNAME */
-    JSTRACE_XML         /* GCX_XML */
-    // We don't care about JSTRACE_STRING, so stop here
+    JSTRACE_XML,        /* GCX_XML */
+    (uint8)-1,         /* unused */
+    JSTRACE_STRING,     /* GCX_EXTERNAL_STRING + 0 */
+    JSTRACE_STRING,     /* GCX_EXTERNAL_STRING + 1 */
+    JSTRACE_STRING,     /* GCX_EXTERNAL_STRING + 2 */
+    JSTRACE_STRING,     /* GCX_EXTERNAL_STRING + 3 */
+    JSTRACE_STRING,     /* GCX_EXTERNAL_STRING + 4 */
+    JSTRACE_STRING,     /* GCX_EXTERNAL_STRING + 5 */
+    JSTRACE_STRING,     /* GCX_EXTERNAL_STRING + 6 */
+    JSTRACE_STRING,     /* GCX_EXTERNAL_STRING + 7 */
 };
 
+// static
+uint8
+nsXPConnect::GetTraceKind(void *thing)
+{
+    uint8 type = *js_GetGCThingFlags(thing) & GCF_TYPEMASK;
+    return GCTypeToTraceKindMap[type];
+}
+
 NS_IMETHODIMP
 nsXPConnect::Traverse(void *p, nsCycleCollectionTraversalCallback &cb)
 {
@@ -716,7 +731,7 @@ nsXPConnect::Traverse(void *p, nsCycleCollectionTraversalCallback &cb)
     PRUint32 refcount = mObjRefcounts->Get(p);
     NS_ASSERTION(refcount > 0, "JS object but unknown to the JS GC?");
 
-    uint8 ty = *js_GetGCThingFlags(p) & GCF_TYPEMASK;
+    uint8 ty = GetTraceKind(p);
     if(ty != GCX_OBJECT && ty != GCX_NAMESPACE && ty != GCX_QNAME &&
        ty != GCX_XML)
         return NS_OK;
@@ -2097,6 +2112,18 @@ nsXPConnect::OnDispatchedEvent(nsIThreadInternal* aThread)
     return NS_ERROR_UNEXPECTED;
 }
 
+NS_IMETHODIMP
+nsXPConnect::AddJSHolder(void* aHolder, nsScriptObjectTracer* aTracer)
+{
+    return mRuntime->AddJSHolder(aHolder, aTracer);
+}
+
+NS_IMETHODIMP
+nsXPConnect::RemoveJSHolder(void* aHolder)
+{
+    return mRuntime->RemoveJSHolder(aHolder);
+}
+
 #ifdef DEBUG
 /* These are here to be callable from a debugger */
 JS_BEGIN_EXTERN_C
diff --git a/js/src/xpconnect/src/xpcjsruntime.cpp b/js/src/xpconnect/src/xpcjsruntime.cpp
index b02612fc5ad..ced529b9ae7 100644
--- a/js/src/xpconnect/src/xpcjsruntime.cpp
+++ b/js/src/xpconnect/src/xpcjsruntime.cpp
@@ -251,6 +251,42 @@ ContextCallback(JSContext *cx, uintN operation)
            : JS_TRUE;
 }
 
+struct ObjectHolder : public JSDHashEntryHdr
+{
+    void *holder;
+    nsScriptObjectTracer* tracer;
+};
+
+nsresult
+XPCJSRuntime::AddJSHolder(void* aHolder, nsScriptObjectTracer* aTracer)
+{
+    if(!mJSHolders.ops)
+        return NS_ERROR_OUT_OF_MEMORY;
+
+    ObjectHolder *entry =
+        reinterpret_cast<ObjectHolder*>(JS_DHashTableOperate(&mJSHolders,
+                                                             aHolder,
+                                                             JS_DHASH_ADD));
+    if(!entry)
+        return NS_ERROR_OUT_OF_MEMORY;
+
+    entry->holder = aHolder;
+    entry->tracer = aTracer;
+
+    return NS_OK;
+}
+
+nsresult
+XPCJSRuntime::RemoveJSHolder(void* aHolder)
+{
+    if(!mJSHolders.ops)
+        return NS_ERROR_OUT_OF_MEMORY;
+
+    JS_DHashTableOperate(&mJSHolders, aHolder, JS_DHASH_REMOVE);
+
+    return NS_OK;
+}
+
 // static
 void XPCJSRuntime::TraceJS(JSTracer* trc, void* data)
 {
@@ -277,16 +313,48 @@ void XPCJSRuntime::TraceJS(JSTracer* trc, void* data)
         }
     }
 
-    XPCWrappedNativeScope::TraceJS(trc, self);
+    // XPCJSObjectHolders don't participate in cycle collection, so always trace
+    // them here.
+    for(XPCRootSetElem *e = self->mObjectHolderRoots; e ; e = e->GetNextRoot())
+        static_cast<XPCJSObjectHolder*>(e)->TraceJS(trc);
+        
+    self->TraceXPConnectRoots(trc);
+}
 
-    for (XPCRootSetElem *e = self->mVariantRoots; e ; e = e->GetNextRoot())
+PR_STATIC_CALLBACK(void)
+TraceJSObject(PRUint32 aLangID, void *aScriptThing, void *aClosure)
+{
+    if(aLangID == nsIProgrammingLanguage::JAVASCRIPT)
+    {
+        JS_CALL_TRACER(static_cast<JSTracer*>(aClosure), aScriptThing,
+                       nsXPConnect::GetXPConnect()->GetTraceKind(aScriptThing),
+                       "JSObjectHolder");
+    }
+}
+
+JS_STATIC_DLL_CALLBACK(JSDHashOperator)
+TraceJSHolder(JSDHashTable *table, JSDHashEntryHdr *hdr, uint32 number,
+              void *arg)
+{
+    ObjectHolder* entry = reinterpret_cast<ObjectHolder*>(hdr);
+
+    entry->tracer->Trace(entry->holder, TraceJSObject, arg);
+
+    return JS_DHASH_NEXT;
+}
+
+void XPCJSRuntime::TraceXPConnectRoots(JSTracer *trc)
+{
+    XPCWrappedNativeScope::TraceJS(trc, this);
+
+    for(XPCRootSetElem *e = mVariantRoots; e ; e = e->GetNextRoot())
         static_cast<XPCTraceableVariant*>(e)->TraceJS(trc);
 
-    for (XPCRootSetElem *e = self->mWrappedJSRoots; e ; e = e->GetNextRoot())
+    for(XPCRootSetElem *e = mWrappedJSRoots; e ; e = e->GetNextRoot())
         static_cast<nsXPCWrappedJS*>(e)->TraceJS(trc);
 
-    for (XPCRootSetElem *e = self->mObjectHolderRoots; e ; e = e->GetNextRoot())
-        static_cast<XPCJSObjectHolder*>(e)->TraceJS(trc);
+    if(mJSHolders.ops)
+        JS_DHashTableEnumerate(&mJSHolders, TraceJSHolder, trc);
 }
 
 // static
@@ -809,6 +877,12 @@ XPCJSRuntime::~XPCJSRuntime()
 
     gOldJSGCCallback = NULL;
     gOldJSContextCallback = NULL;
+
+    if(mJSHolders.ops)
+    {
+        JS_DHashTableFinish(&mJSHolders);
+        mJSHolders.ops = nsnull;
+    }
 }
 
 XPCJSRuntime::XPCJSRuntime(nsXPConnect* aXPConnect,
@@ -862,6 +936,10 @@ XPCJSRuntime::XPCJSRuntime(nsXPConnect* aXPConnect,
         JS_SetExtraGCRoots(mJSRuntime, TraceJS, this);
     }
 
+    if(!JS_DHashTableInit(&mJSHolders, JS_DHashGetStubOps(), nsnull,
+                          sizeof(ObjectHolder), 512))
+        mJSHolders.ops = nsnull;
+
     // Install a JavaScript 'debugger' keyword handler in debug builds only
 #ifdef DEBUG
     if(mJSRuntime && !JS_GetGlobalDebugHooks(mJSRuntime)->debuggerHandler)
diff --git a/js/src/xpconnect/src/xpcprivate.h b/js/src/xpconnect/src/xpcprivate.h
index 0bcc64caaf1..31ed95b2e08 100644
--- a/js/src/xpconnect/src/xpcprivate.h
+++ b/js/src/xpconnect/src/xpcprivate.h
@@ -498,6 +498,9 @@ public:
 #endif
 
     JSObjectRefcounts* GetJSObjectRefcounts() {return mObjRefcounts;}
+
+    static uint8 GetTraceKind(void *thing);
+
 #ifndef XPCONNECT_STANDALONE
     void RecordTraversal(void *p, nsISupports *s);
 #endif
@@ -676,6 +679,9 @@ public:
     }
 
     static void JS_DLL_CALLBACK TraceJS(JSTracer* trc, void* data);
+    void TraceXPConnectRoots(JSTracer *trc);
+    void AddXPConnectRoots(JSContext* cx,
+                           nsCycleCollectionTraversalCallback& cb);
 
     static JSBool JS_DLL_CALLBACK GCCallback(JSContext *cx, JSGCStatus status);
 
@@ -683,6 +689,9 @@ public:
     inline void AddWrappedJSRoot(nsXPCWrappedJS* wrappedJS);
     inline void AddObjectHolderRoot(XPCJSObjectHolder* holder);
 
+    nsresult AddJSHolder(void* aHolder, nsScriptObjectTracer* aTracer);
+    nsresult RemoveJSHolder(void* aHolder);
+
     void DebugDump(PRInt16 depth);
 
     void SystemIsBeingShutDown(JSContext* cx);
@@ -746,6 +755,7 @@ private:
     XPCRootSetElem *mVariantRoots;
     XPCRootSetElem *mWrappedJSRoots;
     XPCRootSetElem *mObjectHolderRoots;
+    JSDHashTable mJSHolders;
 };
 
 /***************************************************************************/
@@ -1191,8 +1201,6 @@ public:
 
     static void InitStatics() { gScopes = nsnull; gDyingScopes = nsnull; }
 
-    void Traverse(nsCycleCollectionTraversalCallback &cb);
-
 #ifndef XPCONNECT_STANDALONE
     /**
      * Fills the hash mapping global object to principal.
@@ -1931,10 +1939,11 @@ private:
 class XPCWrappedNative : public nsIXPConnectWrappedNative
 {
 public:
-    NS_DECL_CYCLE_COLLECTING_ISUPPORTS
+    NS_DECL_ISUPPORTS
     NS_DECL_NSIXPCONNECTJSOBJECTHOLDER
     NS_DECL_NSIXPCONNECTWRAPPEDNATIVE
     NS_DECL_CYCLE_COLLECTION_CLASS(XPCWrappedNative)
+    NS_DECL_CYCLE_COLLECTION_UNMARK_PURPLE_STUB(XPCWrappedNative)
 
 #ifndef XPCONNECT_STANDALONE
     virtual nsIPrincipal* GetObjectPrincipal() const;
@@ -2044,7 +2053,7 @@ public:
                            nsISupports* aCOMObj,
                            XPCWrappedNative** aWrapper);
 
-    void FlatJSObjectFinalized(JSContext *cx, JSObject *obj);
+    void FlatJSObjectFinalized(JSContext *cx);
 
     void SystemIsBeingShutDown(JSContext* cx);
 
@@ -2196,8 +2205,10 @@ private:
     XPCWrappedNativeTearOffChunk mFirstChunk;
     JSObject*                    mWrapper;
 
+#ifdef XPC_CHECK_WRAPPER_THREADSAFETY
 public:
     nsCOMPtr<nsIThread>          mThread; // Don't want to overload _mOwningThread
+#endif
 };
 
 /***************************************************************************
@@ -3028,7 +3039,6 @@ private:
     JSUint32             mWrappedNativeThreadsafetyReportDepth;
 #endif
     PRThread*            mThread;
-    nsVoidArray          mNativesToReleaseArray;
 
     static PRLock*           gLock;
     static XPCPerThreadData* gThreads;
diff --git a/js/src/xpconnect/src/xpcwrappedjs.cpp b/js/src/xpconnect/src/xpcwrappedjs.cpp
index 32cd5edcf71..8eed14c1d4f 100644
--- a/js/src/xpconnect/src/xpcwrappedjs.cpp
+++ b/js/src/xpconnect/src/xpcwrappedjs.cpp
@@ -589,10 +589,6 @@ nsXPCWrappedJS::SystemIsBeingShutDown(JSRuntime* rt)
     // work (and avoid crashing some platforms).
     mJSObj = nsnull;
 
-    // There is no reason to keep this root any longer. Since we've cleared
-    // mJSObj our dtor will not remove the root later. So, we do it now.
-    JS_RemoveRootRT(rt, &mJSObj);
-
     // Notify other wrappers in the chain.
     if(mNext)
         mNext->SystemIsBeingShutDown(rt);
diff --git a/js/src/xpconnect/src/xpcwrappednative.cpp b/js/src/xpconnect/src/xpcwrappednative.cpp
index 2b1d3e88b82..ed78d2add53 100644
--- a/js/src/xpconnect/src/xpcwrappednative.cpp
+++ b/js/src/xpconnect/src/xpcwrappednative.cpp
@@ -961,7 +961,7 @@ NS_IMPL_THREADSAFE_RELEASE(XPCWrappedNative)
  */
 
 void
-XPCWrappedNative::FlatJSObjectFinalized(JSContext *cx, JSObject *obj)
+XPCWrappedNative::FlatJSObjectFinalized(JSContext *cx)
 {
     if(!IsValid())
         return;
diff --git a/js/src/xpconnect/src/xpcwrappednativejsops.cpp b/js/src/xpconnect/src/xpcwrappednativejsops.cpp
index 32d084a7cb6..674e457af3c 100644
--- a/js/src/xpconnect/src/xpcwrappednativejsops.cpp
+++ b/js/src/xpconnect/src/xpcwrappednativejsops.cpp
@@ -647,7 +647,7 @@ XPC_WN_NoHelper_Finalize(JSContext *cx, JSObject *obj)
     XPCWrappedNative* p = (XPCWrappedNative*) JS_GetPrivate(cx, obj);
     if(!p)
         return;
-    p->FlatJSObjectFinalized(cx, obj);
+    p->FlatJSObjectFinalized(cx);
 }
 
 static void
@@ -658,7 +658,7 @@ TraceScopeJSObjects(JSTracer *trc, XPCWrappedNativeScope* scope)
     JSObject* obj;
 
     obj = scope->GetGlobalJSObject();
-    NS_ASSERTION(scope, "bad scope JSObject");
+    NS_ASSERTION(obj, "bad scope JSObject");
     JS_CALL_OBJECT_TRACER(trc, obj, "XPCWrappedNativeScope::mGlobalJSObject");
 
     obj = scope->GetPrototypeJSObject();
@@ -1035,7 +1035,7 @@ XPC_WN_Helper_Finalize(JSContext *cx, JSObject *obj)
     if(!wrapper)
         return;
     wrapper->GetScriptableCallback()->Finalize(wrapper, cx, obj);
-    wrapper->FlatJSObjectFinalized(cx, obj);
+    wrapper->FlatJSObjectFinalized(cx);
 }
 
 JS_STATIC_DLL_CALLBACK(void)
diff --git a/js/src/xpconnect/src/xpcwrappednativescope.cpp b/js/src/xpconnect/src/xpcwrappednativescope.cpp
index ea9c5b6d588..e167780f016 100644
--- a/js/src/xpconnect/src/xpcwrappednativescope.cpp
+++ b/js/src/xpconnect/src/xpcwrappednativescope.cpp
@@ -851,16 +851,6 @@ XPCWrappedNativeScope::DebugDump(PRInt16 depth)
 #endif
 }
 
-void
-XPCWrappedNativeScope::Traverse(nsCycleCollectionTraversalCallback &cb)
-{
-    // See TraceScopeJSObjects.
-    cb.NoteScriptChild(nsIProgrammingLanguage::JAVASCRIPT, mGlobalJSObject);
-    cb.NoteScriptChild(nsIProgrammingLanguage::JAVASCRIPT, mPrototypeJSObject);
-    cb.NoteScriptChild(nsIProgrammingLanguage::JAVASCRIPT,
-                       mPrototypeJSFunction);
-}
-
 #ifndef XPCONNECT_STANDALONE
 // static
 void
diff --git a/xpcom/base/nsAgg.h b/xpcom/base/nsAgg.h
index 2ba68b5477c..294a50d97d7 100644
--- a/xpcom/base/nsAgg.h
+++ b/xpcom/base/nsAgg.h
@@ -118,7 +118,8 @@ public:                                                                     \
   {                                                                         \
     return p->InnerObject();                                                \
   }                                                                         \
-};                                                           
+};                                                                          \
+NS_CYCLE_COLLECTION_PARTICIPANT_INSTANCE
 
 // Put this in your class's constructor:
 #define NS_INIT_AGGREGATED(outer)                                           \
diff --git a/xpcom/glue/nsCycleCollectionParticipant.cpp b/xpcom/glue/nsCycleCollectionParticipant.cpp
index 5a90aaf536c..4e0e3a2a3e7 100644
--- a/xpcom/glue/nsCycleCollectionParticipant.cpp
+++ b/xpcom/glue/nsCycleCollectionParticipant.cpp
@@ -38,6 +38,21 @@
 #include "nsCycleCollectionParticipant.h"
 #include "nsCOMPtr.h"
 
+PR_STATIC_CALLBACK(void)
+NoteChild(PRUint32 aLangID, void *aScriptThing, void *aClosure)
+{
+  nsCycleCollectionTraversalCallback *cb =
+    static_cast<nsCycleCollectionTraversalCallback*>(aClosure);
+  cb->NoteScriptChild(aLangID, aScriptThing);
+}
+
+void
+nsScriptObjectTracer::TraverseScriptObjects(void *p,
+                                        nsCycleCollectionTraversalCallback &cb)
+{
+  Trace(p, NoteChild, &cb);
+}
+
 nsresult
 nsXPCOMCycleCollectionParticipant::Root(void *p)
 {
@@ -72,6 +87,12 @@ nsXPCOMCycleCollectionParticipant::UnmarkPurple(nsISupports *n)
 {
 }
 
+NS_IMETHODIMP_(void)
+nsXPCOMCycleCollectionParticipant::Trace(void *p, TraceCallback cb,
+                                         void *closure)
+{
+}
+
 PRBool
 nsXPCOMCycleCollectionParticipant::CheckForRightISupports(nsISupports *s)
 {
diff --git a/xpcom/glue/nsCycleCollectionParticipant.h b/xpcom/glue/nsCycleCollectionParticipant.h
index fdb54f2292d..9f5ed2a9d75 100644
--- a/xpcom/glue/nsCycleCollectionParticipant.h
+++ b/xpcom/glue/nsCycleCollectionParticipant.h
@@ -125,8 +125,19 @@ NS_DEFINE_STATIC_IID_ACCESSOR(nsCycleCollectionParticipant,
 #undef IMETHOD_VISIBILITY
 #define IMETHOD_VISIBILITY NS_COM_GLUE
 
+typedef void
+(* PR_CALLBACK TraceCallback)(PRUint32 langID, void *p, void *closure);
+
+class NS_NO_VTABLE nsScriptObjectTracer : public nsCycleCollectionParticipant
+{
+public:
+    NS_IMETHOD_(void) Trace(void *p, TraceCallback cb, void *closure) = 0;
+    void NS_COM_GLUE TraverseScriptObjects(void *p,
+                                        nsCycleCollectionTraversalCallback &cb);
+};
+
 class NS_COM_GLUE nsXPCOMCycleCollectionParticipant
-    : public nsCycleCollectionParticipant
+    : public nsScriptObjectTracer
 {
 public:
     NS_IMETHOD Traverse(void *p, nsCycleCollectionTraversalCallback &cb);
@@ -135,6 +146,8 @@ public:
     NS_IMETHOD Unlink(void *p);
     NS_IMETHOD Unroot(void *p);
 
+    NS_IMETHOD_(void) Trace(void *p, TraceCallback cb, void *closure);
+
     NS_IMETHOD_(void) UnmarkPurple(nsISupports *p);
 
     PRBool CheckForRightISupports(nsISupports *s);
@@ -153,8 +166,11 @@ public:
 #define NS_CYCLE_COLLECTION_CLASSNAME(_class)                                  \
         _class::NS_CYCLE_COLLECTION_INNERCLASS
 
+#define NS_CYCLE_COLLECTION_INNERNAME                                          \
+        _cycleCollectorGlobal
+
 #define NS_CYCLE_COLLECTION_NAME(_class)                                       \
-        _class##_cycleCollectorGlobal
+        _class::NS_CYCLE_COLLECTION_INNERNAME
 
 #define NS_IMPL_QUERY_CYCLE_COLLECTION(_class)                                 \
   if ( aIID.Equals(NS_GET_IID(nsXPCOMCycleCollectionParticipant)) ) {          \
@@ -201,6 +217,8 @@ public:
     }                                                                         \
     nsresult rv;
 
+#define NS_CYCLE_COLLECTION_UPCAST(obj, clazz)                                 \
+  NS_CYCLE_COLLECTION_CLASSNAME(clazz)::Upcast(obj)
 
 ///////////////////////////////////////////////////////////////////////////////
 // Helpers for implementing nsCycleCollectionParticipant::Unlink
@@ -323,7 +341,7 @@ public:
     }
 
 #define NS_IMPL_CYCLE_COLLECTION_TRAVERSE_NATIVE_PTR(_ptr, _ptr_class)         \
-  cb.NoteNativeChild(_ptr, &NS_CYCLE_COLLECTION_NATIVE_NAME(_ptr_class));
+  cb.NoteNativeChild(_ptr, &NS_CYCLE_COLLECTION_NAME(_ptr_class));
 
 #define NS_IMPL_CYCLE_COLLECTION_TRAVERSE_NATIVE_MEMBER(_field, _field_class)  \
   NS_IMPL_CYCLE_COLLECTION_TRAVERSE_NATIVE_PTR(tmp->_field, _field_class)
@@ -340,18 +358,61 @@ public:
                                                           _element_class)      \
     NS_IMPL_CYCLE_COLLECTION_TRAVERSE_NSTARRAY(tmp->_field, _element_class)
 
+#define NS_IMPL_CYCLE_COLLECTION_TRAVERSE_SCRIPT_OBJECTS                       \
+    TraverseScriptObjects(tmp, cb);
+
 #define NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END                                  \
     return NS_OK;                                                              \
   }
 
+///////////////////////////////////////////////////////////////////////////////
+// Helpers for implementing nsScriptObjectTracer::Trace
+///////////////////////////////////////////////////////////////////////////////
+
+#define NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN(_class)                           \
+  void                                                                         \
+  NS_CYCLE_COLLECTION_CLASSNAME(_class)::Trace(void *p,                        \
+                                               TraceCallback aCallback,        \
+                                               void *aClosure)                 \
+  {                                                                            \
+    nsISupports *s = static_cast<nsISupports*>(p);                             \
+    NS_ASSERTION(CheckForRightISupports(s),                                    \
+                 "not the nsISupports pointer we expect");                     \
+    _class *tmp = Downcast(s);
+
+#define NS_IMPL_CYCLE_COLLECTION_TRACE_NATIVE_BEGIN(_class)                    \
+  void                                                                         \
+  NS_CYCLE_COLLECTION_CLASSNAME(_class)::Trace(void *p,                        \
+                                               TraceCallback aCallback,        \
+                                               void *aClosure)                 \
+  {                                                                            \
+    _class *tmp = static_cast<_class*>(p);
+
+#define NS_IMPL_CYCLE_COLLECTION_TRACE_CALLBACK(_langID, _object)              \
+  if (_object)                                                                 \
+    aCallback(_langID, _object, aClosure);
+
+#define NS_IMPL_CYCLE_COLLECTION_TRACE_MEMBER_CALLBACK(_langID, _field)        \
+  NS_IMPL_CYCLE_COLLECTION_TRACE_CALLBACK(_langID, tmp->_field)
+
+#define NS_IMPL_CYCLE_COLLECTION_TRACE_JS_CALLBACK(_object)                    \
+  NS_IMPL_CYCLE_COLLECTION_TRACE_CALLBACK(nsIProgrammingLanguage::JAVASCRIPT,  \
+                                          _object)
+
+#define NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBER_CALLBACK(_field)              \
+  NS_IMPL_CYCLE_COLLECTION_TRACE_JS_CALLBACK(tmp->_field)
+
+#define NS_IMPL_CYCLE_COLLECTION_TRACE_END                                     \
+  }
+
 ///////////////////////////////////////////////////////////////////////////////
 // Helpers for implementing a concrete nsCycleCollectionParticipant 
 ///////////////////////////////////////////////////////////////////////////////
 
-#define NS_DECL_CYCLE_COLLECTION_CLASS_AMBIGUOUS(_class, _base)                \
-class NS_CYCLE_COLLECTION_INNERCLASS                                           \
- : public nsXPCOMCycleCollectionParticipant                                    \
-{                                                                              \
+#define NS_CYCLE_COLLECTION_PARTICIPANT_INSTANCE                               \
+  static NS_CYCLE_COLLECTION_INNERCLASS NS_CYCLE_COLLECTION_INNERNAME;
+
+#define NS_DECL_CYCLE_COLLECTION_CLASS_BODY(_class, _base)                     \
 public:                                                                        \
   NS_IMETHOD Unlink(void *p);                                                  \
   NS_IMETHOD Traverse(void *p,                                                 \
@@ -367,12 +428,31 @@ public:                                                                        \
   static nsISupports* Upcast(_class *p)                                        \
   {                                                                            \
     return NS_ISUPPORTS_CAST(_base*, p);                                       \
-  }                                                                            \
-};                                                           
+  }
+
+#define NS_DECL_CYCLE_COLLECTION_CLASS_AMBIGUOUS(_class, _base)                \
+class NS_CYCLE_COLLECTION_INNERCLASS                                           \
+ : public nsXPCOMCycleCollectionParticipant                                    \
+{                                                                              \
+  NS_DECL_CYCLE_COLLECTION_CLASS_BODY(_class, _base)                           \
+};                                                                             \
+NS_CYCLE_COLLECTION_PARTICIPANT_INSTANCE
 
 #define NS_DECL_CYCLE_COLLECTION_CLASS(_class)                                 \
   NS_DECL_CYCLE_COLLECTION_CLASS_AMBIGUOUS(_class, _class)
 
+#define NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS_AMBIGUOUS(_class, _base)  \
+class NS_CYCLE_COLLECTION_INNERCLASS                                           \
+ : public nsXPCOMCycleCollectionParticipant                                    \
+{                                                                              \
+  NS_DECL_CYCLE_COLLECTION_CLASS_BODY(_class, _base)                           \
+  NS_IMETHOD_(void) Trace(void *p, TraceCallback cb, void *closure);           \
+};                                                                             \
+NS_CYCLE_COLLECTION_PARTICIPANT_INSTANCE
+
+#define NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS(_class)  \
+  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS_AMBIGUOUS(_class, _class)
+
 #define NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(_class, _base_class)          \
 class NS_CYCLE_COLLECTION_INNERCLASS                                           \
  : public NS_CYCLE_COLLECTION_CLASSNAME(_base_class)                           \
@@ -386,7 +466,8 @@ public:                                                                        \
     return static_cast<_class*>(static_cast<_base_class*>(                     \
       NS_CYCLE_COLLECTION_CLASSNAME(_base_class)::Downcast(s)));               \
   }                                                                            \
-};
+};                                                                             \
+NS_CYCLE_COLLECTION_PARTICIPANT_INSTANCE
 
 #define NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED_NO_UNLINK(_class,             \
                                                            _base_class)        \
@@ -401,7 +482,8 @@ public:                                                                        \
     return static_cast<_class*>(static_cast<_base_class*>(                     \
       NS_CYCLE_COLLECTION_CLASSNAME(_base_class)::Downcast(s)));               \
   }                                                                            \
-};
+};                                                                             \
+NS_CYCLE_COLLECTION_PARTICIPANT_INSTANCE
 
 /**
  * This implements a stub UnmarkPurple function for classes that want to be
@@ -415,31 +497,32 @@ public:                                                                        \
   }                                                                            \
 
 #define NS_IMPL_CYCLE_COLLECTION_CLASS(_class)                                 \
-  static NS_CYCLE_COLLECTION_CLASSNAME(_class)                                 \
-    NS_CYCLE_COLLECTION_NAME(_class);
+  NS_CYCLE_COLLECTION_CLASSNAME(_class) NS_CYCLE_COLLECTION_NAME(_class);
 
-#define NS_CYCLE_COLLECTION_NATIVE_INNERNAME                                   \
-        _cycleCollectorGlobal
-
-#define NS_CYCLE_COLLECTION_NATIVE_NAME(_class)                                \
-        _class::NS_CYCLE_COLLECTION_NATIVE_INNERNAME
-
-#define NS_DECL_CYCLE_COLLECTION_NATIVE_CLASS(_class)                          \
-  class NS_CYCLE_COLLECTION_INNERCLASS                                         \
-   : public nsCycleCollectionParticipant                                       \
-  {                                                                            \
+#define NS_DECL_CYCLE_COLLECTION_NATIVE_CLASS_BODY                             \
   public:                                                                      \
     NS_IMETHOD Root(void *n);                                                  \
     NS_IMETHOD Unlink(void *n);                                                \
     NS_IMETHOD Unroot(void *n);                                                \
     NS_IMETHOD Traverse(void *n,                                               \
-                      nsCycleCollectionTraversalCallback &cb);                 \
-  };                                                                           \
-  static NS_CYCLE_COLLECTION_INNERCLASS                                        \
-      NS_CYCLE_COLLECTION_NATIVE_INNERNAME;
+                      nsCycleCollectionTraversalCallback &cb);
 
-#define NS_IMPL_CYCLE_COLLECTION_NATIVE_CLASS(_class)                          \
-  NS_CYCLE_COLLECTION_CLASSNAME(_class) NS_CYCLE_COLLECTION_NATIVE_NAME(_class);
+#define NS_DECL_CYCLE_COLLECTION_NATIVE_CLASS(_class)                          \
+  class NS_CYCLE_COLLECTION_INNERCLASS                                         \
+   : public nsCycleCollectionParticipant                                       \
+  {                                                                            \
+     NS_DECL_CYCLE_COLLECTION_NATIVE_CLASS_BODY                                \
+  };                                                                           \
+  NS_CYCLE_COLLECTION_PARTICIPANT_INSTANCE
+
+#define NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_NATIVE_CLASS(_class)            \
+  class NS_CYCLE_COLLECTION_INNERCLASS                                         \
+   : public nsScriptObjectTracer                                               \
+  {                                                                            \
+    NS_DECL_CYCLE_COLLECTION_NATIVE_CLASS_BODY                                 \
+    NS_IMETHOD_(void) Trace(void *p, TraceCallback cb, void *closure);         \
+  };                                                                           \
+  NS_CYCLE_COLLECTION_PARTICIPANT_INSTANCE
 
 #define NS_IMPL_CYCLE_COLLECTION_ROOT_NATIVE(_class, _root_function)           \
   NS_IMETHODIMP                                                                \