diff --git a/dom/base/nsGlobalWindow.cpp b/dom/base/nsGlobalWindow.cpp
index 4e384c4d21..884ad69ca5 100644
--- a/dom/base/nsGlobalWindow.cpp
+++ b/dom/base/nsGlobalWindow.cpp
@@ -14633,7 +14633,9 @@ nsGlobalWindow::NotifyDefaultButtonLoaded(Element& aDefaultButton,
     return;
   }
   LayoutDeviceIntRect buttonRect =
-    LayoutDeviceIntRect::FromUnknownRect(frame->GetScreenRect());
+    LayoutDeviceIntRect::FromAppUnitsToNearest(
+      frame->GetScreenRectInAppUnits(),
+      frame->PresContext()->AppUnitsPerDevPixel());
 
   // Get the widget rect in screen coordinates.
   nsIWidget *widget = GetNearestWidget();