diff --git a/xpcom/ds/nsObserverList.cpp b/xpcom/ds/nsObserverList.cpp
index 9e5e77d8863c..742ed53fd0e2 100644
--- a/xpcom/ds/nsObserverList.cpp
+++ b/xpcom/ds/nsObserverList.cpp
@@ -26,6 +26,8 @@
 #include "nsObserverList.h"
 #include "nsString.h"
 #include "nsAutoLock.h"
+#include "nsCOMPtr.h"
+#include "nsIWeakReference.h"
 
 
 #define NS_AUTOLOCK(__monitor) nsAutoLock __lock(__monitor)
@@ -33,6 +35,114 @@
 static NS_DEFINE_CID(kObserverListCID, NS_OBSERVERLIST_CID);
 
 
+class nsObserverListEnumerator : public nsIBidirectionalEnumerator
+	{
+		public:
+			nsObserverListEnumerator( nsISupportsArray* );
+
+			NS_DECL_ISUPPORTS
+			NS_DECL_NSIENUMERATOR
+			NS_DECL_NSIBIDIRECTIONALENUMERATOR
+
+		private:
+			PRUint32 GetTargetArraySize() const;
+			nsresult MoveToIndex( PRUint32 );
+
+		private:
+			nsCOMPtr<nsISupportsArray>	mTargetArray;
+			PRUint32										mCurrentItemIndex;
+	};
+
+NS_IMPL_ISUPPORTS2(nsObserverListEnumerator, nsIBidirectionalEnumerator, nsIEnumerator)
+
+nsObserverListEnumerator::nsObserverListEnumerator( nsISupportsArray* anArray )
+		: mRefCnt(0),
+			mTargetArray(anArray),
+			mCurrentItemIndex(0)
+	{
+		// nothing else to do here
+	}
+
+PRUint32
+nsObserverListEnumerator::GetTargetArraySize() const
+	{
+		PRUint32 array_size = 0;
+		mTargetArray->Count(&array_size);
+		return array_size;
+	}
+
+nsresult
+nsObserverListEnumerator::MoveToIndex( PRUint32 aNewIndex )
+	{
+		nsresult status;
+		if ( aNewIndex < GetTargetArraySize() )
+			{
+				mCurrentItemIndex = aNewIndex;
+				status = NS_OK;
+			}
+		else
+			status = NS_ERROR_FAILURE; // array bounds violation
+
+		return status;
+	}
+
+
+NS_IMETHODIMP
+nsObserverListEnumerator::First()
+	{
+		NS_ASSERTION(mTargetArray, "must enumerate over an non-null list");
+
+		return MoveToIndex(0);
+	}
+
+NS_IMETHODIMP
+nsObserverListEnumerator::Last()
+	{
+		NS_ASSERTION(mTargetArray, "must enumerate over an non-null list");
+
+		return MoveToIndex(GetTargetArraySize()-1);
+	}
+
+NS_IMETHODIMP
+nsObserverListEnumerator::Prev()
+	{
+		NS_ASSERTION(mTargetArray, "must enumerate over an non-null list");
+
+		return MoveToIndex(mCurrentItemIndex-1);
+	}
+
+NS_IMETHODIMP
+nsObserverListEnumerator::Next()
+	{
+		NS_ASSERTION(mTargetArray, "must enumerate over an non-null list");
+
+		return MoveToIndex(mCurrentItemIndex+1);
+	}
+
+NS_IMETHODIMP
+nsObserverListEnumerator::CurrentItem( nsISupports** aItemPtr )
+	{
+		NS_ASSERTION(mTargetArray, "must enumerate over an non-null list");
+		NS_ASSERTION(aItemPtr, "must supply a place to put the result");
+
+		nsWeakPtr weakPtr = getter_AddRefs(NS_REINTERPRET_CAST(nsIWeakReference*, mTargetArray->ElementAt(mCurrentItemIndex)));
+
+		if ( !aItemPtr || !weakPtr )
+			return NS_ERROR_NULL_POINTER;
+
+		return weakPtr->QueryReferent(NS_GET_IID(nsIObserver), aItemPtr);
+	}
+
+NS_IMETHODIMP
+nsObserverListEnumerator::IsDone()
+	{
+		NS_ASSERTION(mTargetArray, "must enumerate over an non-null list");
+
+		return  (mCurrentItemIndex == (GetTargetArraySize()-1)) ? NS_OK : NS_ENUMERATOR_FALSE;
+	}
+
+
+
 ////////////////////////////////////////////////////////////////////////////////
 // nsObserverList Implementation
 
@@ -87,8 +197,14 @@ nsresult nsObserverList::AddObserver(nsIObserver** anObserver)
 		if (NS_FAILED(rv)) return rv;
     }
 
+#if NS_WEAK_OBSERVERS
+	nsWeakPtr observer_ref = getter_AddRefs(NS_GetWeakReference(*anObserver));
+	if(observer_ref) {
+		inserted = mObserverList->AppendElement(observer_ref); 
+#else
 	if(*anObserver) {
-		inserted = mObserverList->AppendElement(*anObserver); 
+		inserted = mObserverList->AppendElement(*anObserver);
+#endif
 		return inserted ? NS_OK : NS_ERROR_FAILURE;
     }
 
@@ -110,8 +226,14 @@ nsresult nsObserverList::RemoveObserver(nsIObserver** anObserver)
         return NS_ERROR_FAILURE;
     }
 
+#if NS_WEAK_OBSERVERS
+	nsWeakPtr observer_ref = getter_AddRefs(NS_GetWeakReference(*anObserver));
+	if(observer_ref) {
+		removed = mObserverList->RemoveElement(observer_ref);  
+#else
 	if(*anObserver) {
-		removed = mObserverList->RemoveElement(*anObserver);  
+		removed = mObserverList->RemoveElement(*anObserver);
+#endif
 		return removed ? NS_OK : NS_ERROR_FAILURE;
     }
 
@@ -131,7 +253,15 @@ NS_IMETHODIMP nsObserverList::EnumerateObserverList(nsIEnumerator** anEnumerator
     if(!mObserverList) {
         return NS_ERROR_FAILURE;
     }
-    
- 	return mObserverList->Enumerate(anEnumerator);
+
+#if NS_WEAK_OBSERVERS
+	nsCOMPtr<nsIBidirectionalEnumerator> enumerator = new nsObserverListEnumerator(mObserverList);
+	if ( !enumerator )
+		return NS_ERROR_OUT_OF_MEMORY;
+
+	return CallQueryInterface(enumerator, anEnumerator);
+#else
+	return mObserverList->Enumerate(anEnumerator);
+#endif
 }