diff --git a/mozilla/base/public/nsIProperties.h b/mozilla/base/public/nsIProperties.h
new file mode 100644
index 00000000000..52e2e4fa41e
--- /dev/null
+++ b/mozilla/base/public/nsIProperties.h
@@ -0,0 +1,48 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ *
+ * The contents of this file are subject to the Netscape Public License
+ * Version 1.0 (the "NPL"); you may not use this file except in
+ * compliance with the NPL. You may obtain a copy of the NPL at
+ * http://www.mozilla.org/NPL/
+ *
+ * Software distributed under the NPL is distributed on an "AS IS" basis,
+ * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the NPL
+ * for the specific language governing rights and limitations under the
+ * NPL.
+ *
+ * The Initial Developer of this code under the NPL is Netscape
+ * Communications Corporation. Portions created by Netscape are
+ * Copyright (C) 1998 Netscape Communications Corporation. All Rights
+ * Reserved.
+ */
+
+#ifndef nsIProperties_h___
+#define nsIProperties_h___
+
+#include "nsID.h"
+#include "nsIInputStream.h"
+#include "nsIOutputStream.h"
+#include "nsISupports.h"
+#include "nsString.h"
+
+// {1A180F60-93B2-11d2-9B8B-00805F8A16D9}
+#define NS_IPROPERTIES_IID \
+{ 0x1a180f60, 0x93b2, 0x11d2, \
+  { 0x9b, 0x8b, 0x0, 0x80, 0x5f, 0x8a, 0x16, 0xd9 } }
+
+// {2245E573-9464-11d2-9B8B-00805F8A16D9}
+NS_DECLARE_ID(kPropertiesCID,
+  0x2245e573, 0x9464, 0x11d2, 0x9b, 0x8b, 0x0, 0x80, 0x5f, 0x8a, 0x16, 0xd9);
+
+class nsIProperties : public nsISupports
+{
+public:
+  NS_IMETHOD Load(nsIInputStream* aIn) = 0;
+  NS_IMETHOD GetProperty(const nsString& aKey, nsString& aValue) = 0;
+  NS_IMETHOD SetProperty(const nsString& aKey, nsString& aNewValue,
+                         nsString& aOldValue) = 0;
+  NS_IMETHOD Save(nsIOutputStream* aOut, const nsString& aHeader) = 0;
+  NS_IMETHOD Subclass(nsIProperties* aSubclass) = 0;
+};
+
+#endif /* nsIProperties_h___ */
diff --git a/mozilla/xpcom/ds/nsIProperties.h b/mozilla/xpcom/ds/nsIProperties.h
new file mode 100644
index 00000000000..52e2e4fa41e
--- /dev/null
+++ b/mozilla/xpcom/ds/nsIProperties.h
@@ -0,0 +1,48 @@
+/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ *
+ * The contents of this file are subject to the Netscape Public License
+ * Version 1.0 (the "NPL"); you may not use this file except in
+ * compliance with the NPL. You may obtain a copy of the NPL at
+ * http://www.mozilla.org/NPL/
+ *
+ * Software distributed under the NPL is distributed on an "AS IS" basis,
+ * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the NPL
+ * for the specific language governing rights and limitations under the
+ * NPL.
+ *
+ * The Initial Developer of this code under the NPL is Netscape
+ * Communications Corporation. Portions created by Netscape are
+ * Copyright (C) 1998 Netscape Communications Corporation. All Rights
+ * Reserved.
+ */
+
+#ifndef nsIProperties_h___
+#define nsIProperties_h___
+
+#include "nsID.h"
+#include "nsIInputStream.h"
+#include "nsIOutputStream.h"
+#include "nsISupports.h"
+#include "nsString.h"
+
+// {1A180F60-93B2-11d2-9B8B-00805F8A16D9}
+#define NS_IPROPERTIES_IID \
+{ 0x1a180f60, 0x93b2, 0x11d2, \
+  { 0x9b, 0x8b, 0x0, 0x80, 0x5f, 0x8a, 0x16, 0xd9 } }
+
+// {2245E573-9464-11d2-9B8B-00805F8A16D9}
+NS_DECLARE_ID(kPropertiesCID,
+  0x2245e573, 0x9464, 0x11d2, 0x9b, 0x8b, 0x0, 0x80, 0x5f, 0x8a, 0x16, 0xd9);
+
+class nsIProperties : public nsISupports
+{
+public:
+  NS_IMETHOD Load(nsIInputStream* aIn) = 0;
+  NS_IMETHOD GetProperty(const nsString& aKey, nsString& aValue) = 0;
+  NS_IMETHOD SetProperty(const nsString& aKey, nsString& aNewValue,
+                         nsString& aOldValue) = 0;
+  NS_IMETHOD Save(nsIOutputStream* aOut, const nsString& aHeader) = 0;
+  NS_IMETHOD Subclass(nsIProperties* aSubclass) = 0;
+};
+
+#endif /* nsIProperties_h___ */