diff --git a/gfx/layers/apz/util/ChromeProcessController.cpp b/gfx/layers/apz/util/ChromeProcessController.cpp
index 333b7e27953..f60cae1f30a 100644
--- a/gfx/layers/apz/util/ChromeProcessController.cpp
+++ b/gfx/layers/apz/util/ChromeProcessController.cpp
@@ -59,6 +59,8 @@ ChromeProcessController::InitializeRoot()
   uint32_t presShellId;
   FrameMetrics::ViewID viewId;
   if (APZCCallbackHelper::GetOrCreateScrollIdentifiers(content, &presShellId, &viewId)) {
+    // Note that the base rect that goes with these margins is set in
+    // nsRootBoxFrame::BuildDisplayList.
     nsLayoutUtils::SetDisplayPortMargins(content, presShell, ScreenMargin(), 0,
         nsLayoutUtils::RepaintMode::DoNotRepaint);
   }
diff --git a/layout/xul/nsRootBoxFrame.cpp b/layout/xul/nsRootBoxFrame.cpp
index 11fb77b2024..32ef238a797 100644
--- a/layout/xul/nsRootBoxFrame.cpp
+++ b/layout/xul/nsRootBoxFrame.cpp
@@ -179,6 +179,14 @@ nsRootBoxFrame::BuildDisplayList(nsDisplayListBuilder*   aBuilder,
                                  const nsRect&           aDirtyRect,
                                  const nsDisplayListSet& aLists)
 {
+  if (mContent && mContent->GetProperty(nsGkAtoms::DisplayPortMargins)) {
+    // The XUL document's root element may have displayport margins set in
+    // ChromeProcessController::InitializeRoot, and we should to supply the
+    // base rect.
+    nsRect displayPortBase = aDirtyRect.Intersect(nsRect(nsPoint(0, 0), GetSize()));
+    nsLayoutUtils::SetDisplayPortBase(mContent, displayPortBase);
+  }
+
   // root boxes don't need a debug border/outline or a selection overlay...
   // They *may* have a background propagated to them, so force creation
   // of a background display list element.