diff --git a/layout/xul/base/src/nsBoxLayout.h b/layout/xul/base/src/nsBoxLayout.h
new file mode 100644
index 00000000000..b9e67a65954
--- /dev/null
+++ b/layout/xul/base/src/nsBoxLayout.h
@@ -0,0 +1,70 @@
+/* -*- 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 1.1 (the "License"); you may not use this file
+ * except in compliance with the License. You may obtain a copy of
+ * the License at http://www.mozilla.org/NPL/
+ *
+ * Software distributed under the License is distributed on an "AS
+ * IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or
+ * implied. See the License for the specific language governing
+ * rights and limitations under the License.
+ *
+ * The Original Code is Mozilla Communicator client code.
+ *
+ * The Initial Developer of the Original Code is Netscape Communications
+ * Corporation.  Portions created by Netscape are
+ * Copyright (C) 1998 Netscape Communications Corporation. All
+ * Rights Reserved.
+ *
+ * Author:
+ * Eric D Vaughan
+ *
+ * Contributor(s): 
+ */
+
+#ifndef nsBoxLayout_h___
+#define nsBoxLayout_h___
+
+#include "nsIBoxLayout.h"
+
+class nsBoxLayout : public nsIBoxLayout {
+
+public:
+
+  nsBoxLayout();
+
+  NS_DECL_ISUPPORTS
+
+  NS_IMETHOD Layout(nsIBox* aBox, nsBoxLayoutState& aState);
+
+  NS_IMETHOD PaintDebug(nsIBox* aBox, 
+                        nsIPresContext* aPresContext,
+                        nsIRenderingContext& aRenderingContext,
+                        const nsRect& aDirtyRect,
+                        nsFramePaintLayer aWhichLayer);
+
+  NS_IMETHOD DisplayDebugInfoFor(nsIBox* aBox, 
+                                 nsIPresContext* aPresContext,
+                                 nsPoint&        aPoint,
+                                 PRInt32&        aCursor);
+
+
+  NS_IMETHOD GetPrefSize(nsIBox* aBox, nsBoxLayoutState& aBoxLayoutState, nsSize& aSize);
+  NS_IMETHOD GetMinSize(nsIBox* aBox, nsBoxLayoutState& aBoxLayoutState, nsSize& aSize);
+  NS_IMETHOD GetMaxSize(nsIBox* aBox, nsBoxLayoutState& aBoxLayoutState, nsSize& aSize);
+  NS_IMETHOD GetFlex(nsIBox* aBox, nsBoxLayoutState& aBoxLayoutState, nscoord& aFlex);
+  NS_IMETHOD GetAscent(nsIBox* aBox, nsBoxLayoutState& aBoxLayoutState, nscoord& aAscent);
+  NS_IMETHOD IsCollapsed(nsIBox* aBox, nsBoxLayoutState& aBoxLayoutState, PRBool& aCollapsed);
+
+  virtual void AddBorderAndPadding(nsIBox* aBox, nsSize& aSize);
+  virtual void AddInset(nsIBox* aBox, nsSize& aSize);
+  virtual void AddMargin(nsIBox* aChild, nsSize& aSize);
+  virtual void AddMargin(nsSize& aSize, const nsMargin& aMargin);
+
+  virtual void AddLargestSize(nsSize& aSize, const nsSize& aToAdd);
+  virtual void AddSmallestSize(nsSize& aSize, const nsSize& aToAdd);
+};
+
+#endif
+
diff --git a/layout/xul/base/src/nsIBoxLayout.h b/layout/xul/base/src/nsIBoxLayout.h
new file mode 100644
index 00000000000..9f0cc08710f
--- /dev/null
+++ b/layout/xul/base/src/nsIBoxLayout.h
@@ -0,0 +1,60 @@
+/* -*- 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 1.1 (the "License"); you may not use this file
+ * except in compliance with the License. You may obtain a copy of
+ * the License at http://www.mozilla.org/NPL/
+ *
+ * Software distributed under the License is distributed on an "AS
+ * IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or
+ * implied. See the License for the specific language governing
+ * rights and limitations under the License.
+ *
+ * The Original Code is Mozilla Communicator client code.
+ *
+ * The Initial Developer of the Original Code is Netscape Communications
+ * Corporation.  Portions created by Netscape are
+ * Copyright (C) 1998 Netscape Communications Corporation. All
+ * Rights Reserved.
+ *
+ * Author:
+ * Eric D Vaughan
+ *
+ * Contributor(s): 
+ */
+
+#ifndef nsIBoxLayout_h___
+#define nsIBoxLayout_h___
+
+#include "nsISupports.h"
+#include "nsIFrame.h"
+
+class nsIPresContext;
+class nsIBox;
+class nsBoxLayout;
+class nsBoxLayoutState;
+class nsIRenderingContext;
+struct nsRect;
+
+// {162F6B5F-F926-11d3-BA06-001083023C1E}
+#define NS_IBOX_LAYOUT_IID { 0x162f6b5f, 0xf926, 0x11d3, { 0xba, 0x6, 0x0, 0x10, 0x83, 0x2, 0x3c, 0x1e } }
+
+class nsIBoxLayout : public nsISupports {
+
+public:
+
+  static const nsIID& GetIID() { static nsIID iid = NS_IBOX_LAYOUT_IID; return iid; }
+
+  NS_IMETHOD Layout(nsIBox* aBox, nsBoxLayoutState& aState)=0;
+
+  NS_IMETHOD GetPrefSize(nsIBox* aBox, nsBoxLayoutState& aBoxLayoutState, nsSize& aSize)=0;
+  NS_IMETHOD GetMinSize(nsIBox* aBox, nsBoxLayoutState& aBoxLayoutState, nsSize& aSize)=0;
+  NS_IMETHOD GetMaxSize(nsIBox* aBox, nsBoxLayoutState& aBoxLayoutState, nsSize& aSize)=0;
+  NS_IMETHOD GetFlex(nsIBox* aBox, nsBoxLayoutState& aBoxLayoutState, nscoord& aFlex)=0;
+  NS_IMETHOD GetAscent(nsIBox* aBox, nsBoxLayoutState& aBoxLayoutState, nscoord& aAscent)=0;
+  NS_IMETHOD IsCollapsed(nsIBox* aBox, nsBoxLayoutState& aBoxLayoutState, PRBool& aCollapsed)=0;
+
+};
+
+#endif
+