diff --git a/layout/base/nsLayoutUtils.cpp b/layout/base/nsLayoutUtils.cpp
index 7e8e8ea88de2..90d073b83e3e 100644
--- a/layout/base/nsLayoutUtils.cpp
+++ b/layout/base/nsLayoutUtils.cpp
@@ -89,6 +89,7 @@
 #include "imgIContainer.h"
 #include "nsIImageLoadingContent.h"
 #include "nsCOMPtr.h"
+#include "nsListControlFrame.h"
 
 #ifdef MOZ_SVG
 #include "nsSVGUtils.h"
@@ -3233,6 +3234,38 @@ nsLayoutUtils::GetFrameTransparency(nsIFrame* aBackgroundFrame,
   return eTransparencyOpaque;
 }
 
+/* static */ PRBool
+nsLayoutUtils::IsPopup(nsIFrame* aFrame)
+{
+  nsIAtom* frameType = aFrame->GetType();
+
+  // We're a popup if we're the list control frame dropdown for a combobox.
+  if (frameType == nsGkAtoms::listControlFrame) {
+    nsListControlFrame* listControlFrame = static_cast<nsListControlFrame*>(aFrame);
+      
+    if (listControlFrame) {
+      return listControlFrame->IsInDropDownMode();
+    }
+  }
+
+  // ... or if we're a XUL menupopup frame.
+  return (frameType == nsGkAtoms::menuPopupFrame);
+}
+
+/* static */ nsIFrame*
+nsLayoutUtils::GetDisplayRootFrame(nsIFrame* aFrame)
+{
+  nsIFrame* f = aFrame;
+  for (;;) {
+    if (IsPopup(f))
+      return f;
+    nsIFrame* parent = GetCrossDocParentFrame(f);
+    if (!parent)
+      return f;
+    f = parent;
+  }
+}
+
 static PRBool
 IsNonzeroCoord(const nsStyleCoord& aCoord)
 {
diff --git a/layout/base/nsLayoutUtils.h b/layout/base/nsLayoutUtils.h
index 90dafda63ab6..cea1328f953d 100644
--- a/layout/base/nsLayoutUtils.h
+++ b/layout/base/nsLayoutUtils.h
@@ -1019,6 +1019,18 @@ public:
   static nsTransparencyMode GetFrameTransparency(nsIFrame* aBackgroundFrame,
                                                  nsIFrame* aCSSRootFrame);
 
+  /**
+   * A frame is a popup if it has its own floating window. Menus, panels
+   * and combobox dropdowns are popups.
+   */
+  static PRBool IsPopup(nsIFrame* aFrame);
+
+  /**
+   * Find the nearest "display root". This is the nearest enclosing
+   * popup frame or the root prescontext's root frame.
+   */
+  static nsIFrame* GetDisplayRootFrame(nsIFrame* aFrame);
+
   /**
    * Get textrun construction flags determined by a given style; in particular
    * some combination of:
diff --git a/layout/forms/nsListControlFrame.cpp b/layout/forms/nsListControlFrame.cpp
index 9de54442c354..c9ea5369cb10 100644
--- a/layout/forms/nsListControlFrame.cpp
+++ b/layout/forms/nsListControlFrame.cpp
@@ -1020,12 +1020,6 @@ nsListControlFrame::CaptureMouseEvents(PRBool aGrabMouseEvents)
   // code paths, if any exist).
   if (aGrabMouseEvents && IsInDropDownMode() && nsComboboxControlFrame::ToolkitHasNativePopup())
     return;
-  
-  nsIView* view = GetScrolledFrame()->GetView();
-
-  NS_ASSERTION(view, "no view???");
-  if (NS_UNLIKELY(!view))
-    return;
 
   if (aGrabMouseEvents) {
     nsIPresShell::SetCapturingContent(mContent, CAPTURE_IGNOREALLOWED);
diff --git a/layout/generic/nsFrame.cpp b/layout/generic/nsFrame.cpp
index 6f83a7e2a70e..1fb3d03bfe65 100644
--- a/layout/generic/nsFrame.cpp
+++ b/layout/generic/nsFrame.cpp
@@ -1422,7 +1422,7 @@ nsIFrame::BuildDisplayListForChild(nsDisplayListBuilder*   aBuilder,
     nsPlaceholderFrame* placeholder = static_cast<nsPlaceholderFrame*>(aChild);
     aChild = placeholder->GetOutOfFlowFrame();
     NS_ASSERTION(aChild, "No out of flow frame?");
-    if (!aChild || aChild->GetType() == nsGkAtoms::menuPopupFrame)
+    if (!aChild || nsLayoutUtils::IsPopup(aChild))
       return NS_OK;
     // update for the new child
     disp = aChild->GetStyleDisplay();