--- a/layout/xul/nsMenuPopupFrame.cpp
+++ b/layout/xul/nsMenuPopupFrame.cpp
@@ -1412,19 +1412,16 @@ nsMenuPopupFrame::GetConstraintRect(cons
         screen->GetRect(&screenRectPixels.x, &screenRectPixels.y,
                         &screenRectPixels.width, &screenRectPixels.height);
       else
         screen->GetAvailRect(&screenRectPixels.x, &screenRectPixels.y,
                              &screenRectPixels.width, &screenRectPixels.height);
     }
   }
 
-  // keep a 3 pixel margin to the right and bottom of the screen for the WinXP dropshadow
-  screenRectPixels.SizeTo(screenRectPixels.width - 3, screenRectPixels.height - 3);
-
   nsRect screenRect = screenRectPixels.ToAppUnits(presContext->AppUnitsPerDevPixel());
   if (mInContentShell) {
     // for content shells, clip to the client area rather than the screen area
     screenRect.IntersectRect(screenRect, aRootScreenRect);
   }
 
   return screenRect;
 }

--- a/toolkit/content/tests/chrome/window_largemenu.xul
+++ b/toolkit/content/tests/chrome/window_largemenu.xul
@@ -106,17 +106,17 @@ function popupShown()
     ok(Math.round(rect.top) + gScreenY >= screen.top, gTests[gTestIndex] + " top");
     is(Math.round(rect.bottom) + gScreenY, screen.height - 100,
                                 gTests[gTestIndex] + " bottom");
     ok(!gOverflowed && !gUnderflowed, gTests[gTestIndex] + " overflow")
   }
   else if (gTestIndex == 2) {
     // the popup is too large so ensure that it is on screen
     ok(Math.round(rect.top) + gScreenY >= screen.top, gTests[gTestIndex] + " top");
-    ok(Math.round(rect.bottom) + gScreenY < screen.height, gTests[gTestIndex] + " bottom");
+    ok(Math.round(rect.bottom) + gScreenY <= screen.height, gTests[gTestIndex] + " bottom");
     ok(gOverflowed && !gUnderflowed, gTests[gTestIndex] + " overflow")
 
     sbo.scrollTo(0, 40);
     expectedScrollPos = 40;
   }
   else if (gTestIndex == 3) {
     expectedScrollPos = 40;
   }
@@ -209,20 +209,18 @@ function contextMenuPopupShown()
       break;
     case "context menu more space above":
       is(rect.top, labelrect.top - rect.height + 2, gTests[gTestIndex] + " top");
       break;
     case "context menu too big either side":
       [, gScreenY] = getScreenXY(document.documentElement);
       // compare against the available size as well as the total size, as some
       // platforms allow the menu to overlap os chrome and others do not
-      // the - 3 here is to account for 3 pixels that are subtracted from the
-      // screen size when sizing a popup for the popup shadow
-      var pos = (screen.availTop + screen.availHeight - 3 - rect.height) - gScreenY;
-      var availPos = (screen.top + screen.height - 3 - rect.height) - gScreenY;
+      var pos = (screen.availTop + screen.availHeight - rect.height) - gScreenY;
+      var availPos = (screen.top + screen.height - rect.height) - gScreenY;
       ok(rect.top == pos || rect.top == availPos,
          gTests[gTestIndex] + " top");
       break;
     case "context menu larger than screen":
       ok(rect.top == -(gScreenY - screen.availTop) || rect.top == -(gScreenY - screen.top), gTests[gTestIndex] + " top");
       break;
   }
 
@@ -283,31 +281,31 @@ function testPopupMovement()
   is(screenY, expectedy, gTests[gTestIndex] + " (1, 1) y");
 
   popup.moveTo(100, 8000);
   if (isPanelTest) {
     expectedy = 8000;
   }
   else {
     expectedy = (overlapOSChrome ? screen.height + screen.top : screen.availHeight + screen.availTop) -
-                Math.round(rect.height) - 3;
+                Math.round(rect.height);
   }
 
   [screenX, screenY] = getScreenXY(popup);
   is(screenX, 100, gTests[gTestIndex] + " (100, 8000) x");
   is(screenY, expectedy, gTests[gTestIndex] + " (100, 8000) y");
 
   popup.moveTo(6000, 100);
 
   if (isPanelTest) {
     expectedx = 6000;
   }
   else {
     expectedx = (overlapOSChrome ? screen.width + screen.left : screen.availWidth + screen.availLeft) -
-                Math.round(rect.width) - 3;
+                Math.round(rect.width);
   }
 
   [screenX, screenY] = getScreenXY(popup);
   is(screenX, expectedx, gTests[gTestIndex] + " (6000, 100) x");
   is(screenY, 100, gTests[gTestIndex] + " (6000, 100) y");
 
   is(popup.left, "", gTests[gTestIndex] + " left is empty after moving");
   is(popup.top, "", gTests[gTestIndex] + " top is empty after moving");