diff --git a/layout/xul/base/src/nsMenuPopupFrame.cpp b/layout/xul/base/src/nsMenuPopupFrame.cpp
index 73a79806222..db2f74fa402 100644
--- a/layout/xul/base/src/nsMenuPopupFrame.cpp
+++ b/layout/xul/base/src/nsMenuPopupFrame.cpp
@@ -1157,7 +1157,7 @@ nsMenuPopupFrame::SetPopupPosition(nsIFrame* aAnchorFrame, PRBool aIsMove)
     hFlip = vFlip = PR_FALSE;
   }
 
-  nsRect screenRect = GetConstraintRect(anchorRect.TopLeft(), rootScreenRect);
+  nsRect screenRect = GetConstraintRect(anchorRect, rootScreenRect);
 
   // ensure that anchorRect is on screen
   if (!anchorRect.IntersectRect(anchorRect, screenRect)) {
@@ -1235,7 +1235,8 @@ nsMenuPopupFrame::GetCurrentMenuItem()
 }
 
 nsRect
-nsMenuPopupFrame::GetConstraintRect(nsPoint aAnchorPoint, nsRect& aRootScreenRect)
+nsMenuPopupFrame::GetConstraintRect(const nsRect& aAnchorRect,
+                                    const nsRect& aRootScreenRect)
 {
   nsIntRect screenRectPixels;
   nsPresContext* presContext = PresContext();
@@ -1250,10 +1251,12 @@ nsMenuPopupFrame::GetConstraintRect(nsPoint aAnchorPoint, nsRect& aRootScreenRec
     // This is because we need to constrain the content to this content area,
     // so we should use the same screen. Otherwise, use the screen where the
     // anchor is located.
-    nsPoint pnt = mInContentShell ? aRootScreenRect.TopLeft() : aAnchorPoint;
-    sm->ScreenForRect(presContext->AppUnitsToDevPixels(pnt.x),
-                      presContext->AppUnitsToDevPixels(pnt.y),
-                      1, 1, getter_AddRefs(screen));
+    nsRect rect = mInContentShell ? aRootScreenRect : aAnchorRect;
+    PRInt32 width = rect.width > 0 ? presContext->AppUnitsToDevPixels(rect.width) : 1;
+    PRInt32 height = rect.height > 0 ? presContext->AppUnitsToDevPixels(rect.height) : 1;
+    sm->ScreenForRect(presContext->AppUnitsToDevPixels(rect.x),
+                      presContext->AppUnitsToDevPixels(rect.y),
+                      width, height, getter_AddRefs(screen));
     if (screen) {
       // get the total screen area if the popup is allowed to overlap it.
       if (mMenuCanOverlapOSBar && !mInContentShell)
diff --git a/layout/xul/base/src/nsMenuPopupFrame.h b/layout/xul/base/src/nsMenuPopupFrame.h
index 2daeb98c006..bebe7723ad5 100644
--- a/layout/xul/base/src/nsMenuPopupFrame.h
+++ b/layout/xul/base/src/nsMenuPopupFrame.h
@@ -293,12 +293,12 @@ public:
 
   nsIScrollableFrame* GetScrollFrame(nsIFrame* aStart);
 
-  // For a popup that should appear at the given anchor point, determine
+  // For a popup that should appear anchored at the given rect, determine
   // the screen area that it is constrained by. This will be the available
   // area of the screen the popup should be displayed on. Content popups,
   // however, will also be constrained by the content area, given by
   // aRootScreenRect. All coordinates are in app units.
-  nsRect GetConstraintRect(nsPoint aAnchorPoint, nsRect& aRootScreenRect);
+  nsRect GetConstraintRect(const nsRect& aAnchorRect, const nsRect& aRootScreenRect);
 
   // Determines whether the given edges of the popup may be moved, where
   // aHorizontalSide and aVerticalSide are one of the NS_SIDE_* constants, or
diff --git a/layout/xul/base/src/nsResizerFrame.cpp b/layout/xul/base/src/nsResizerFrame.cpp
index da7fe4de9e0..5c955848a3b 100644
--- a/layout/xul/base/src/nsResizerFrame.cpp
+++ b/layout/xul/base/src/nsResizerFrame.cpp
@@ -227,11 +227,11 @@ nsResizerFrame::HandleEvent(nsPresContext* aPresContext,
         }
       }
       else if (menuPopupFrame) {
-        nsPoint framePoint = menuPopupFrame->GetScreenRectInAppUnits().TopLeft();
+        nsRect frameRect = menuPopupFrame->GetScreenRectInAppUnits();
         nsIFrame* rootFrame = aPresContext->PresShell()->FrameManager()->GetRootFrame();
         nsRect rootScreenRect = rootFrame->GetScreenRectInAppUnits();
 
-        nsRect screenRect = menuPopupFrame->GetConstraintRect(framePoint, rootScreenRect);
+        nsRect screenRect = menuPopupFrame->GetConstraintRect(frameRect, rootScreenRect);
         // round using ToInsidePixels as it's better to be a pixel too small
         // than be too large. If the popup is too large it could get flipped
         // to the opposite side of the anchor point while resizing.