diff --git a/widget/public/nsIWidget.h b/widget/public/nsIWidget.h
index 6ae095db8058..07612abea564 100644
--- a/widget/public/nsIWidget.h
+++ b/widget/public/nsIWidget.h
@@ -352,6 +352,10 @@ class nsIWidget : public nsISupports {
      * Perform platform-dependent sanity check on a potential window position.
      * This is guaranteed to work only for top-level windows.
      *
+     * @param aAllowSlop: if true, allow the window to slop offscreen;
+     *                    the window should be partially visible. if false,
+     *                    force the entire window onscreen (or at least
+     *                    the upper-left corner, if it's too large).
      * @param aX in: an x position expressed in screen coordinates.
      *           out: the x position constrained to fit on the screen(s).
      * @param aY in: an y position expressed in screen coordinates.
@@ -359,7 +363,9 @@ class nsIWidget : public nsISupports {
      * @return vapid success indication. but see also the parameters.
      *
      **/
-    NS_IMETHOD ConstrainPosition(PRInt32 *aX, PRInt32 *aY) = 0;
+    NS_IMETHOD ConstrainPosition(PRBool aAllowSlop,
+                                 PRInt32 *aX,
+                                 PRInt32 *aY) = 0;
 
     /**
      * Move this widget.
diff --git a/widget/src/beos/nsWindow.cpp b/widget/src/beos/nsWindow.cpp
index 805f57a46965..f5994c040255 100644
--- a/widget/src/beos/nsWindow.cpp
+++ b/widget/src/beos/nsWindow.cpp
@@ -981,7 +981,7 @@ NS_METHOD nsWindow::IsVisible(PRBool & bState)
 // Sanity check potential move coordinates
 //
 //-------------------------------------------------------------------------
-NS_METHOD nsWindow::ConstrainPosition(PRInt32 *aX, PRInt32 *aY)
+NS_METHOD nsWindow::ConstrainPosition(PRBool aAllowSlop, PRInt32 *aX, PRInt32 *aY)
 {
 	NS_WARNING("nsWindow::ConstrainPosition - not implemented");
 	return NS_OK;
diff --git a/widget/src/beos/nsWindow.h b/widget/src/beos/nsWindow.h
index 320490e26e7b..45d50833c21d 100644
--- a/widget/src/beos/nsWindow.h
+++ b/widget/src/beos/nsWindow.h
@@ -113,7 +113,8 @@ public:
 	NS_IMETHOD				CaptureRollupEvents(nsIRollupListener *aListener, PRBool aDoCapture, PRBool aConsumeRollupEvent);
     NS_IMETHOD              IsVisible(PRBool & aState);
 
-    NS_IMETHOD              ConstrainPosition(PRInt32 *aX, PRInt32 *aY);
+    NS_IMETHOD              ConstrainPosition(PRBool aAllowSlop,
+                                              PRInt32 *aX, PRInt32 *aY);
     NS_IMETHOD              Move(PRInt32 aX, PRInt32 aY);
     NS_IMETHOD              Resize(PRInt32 aWidth,
                                    PRInt32 aHeight,
diff --git a/widget/src/cocoa/nsChildView.h b/widget/src/cocoa/nsChildView.h
index 569849396f34..c38b59644bb8 100644
--- a/widget/src/cocoa/nsChildView.h
+++ b/widget/src/cocoa/nsChildView.h
@@ -150,7 +150,8 @@ public:
   NS_IMETHOD              ModalEventFilter(PRBool aRealEvent, void *aEvent,
                                            PRBool *aForWindow);
 
-  NS_IMETHOD                  ConstrainPosition(PRInt32 *aX, PRInt32 *aY);
+  NS_IMETHOD              ConstrainPosition(PRBool aAllowSlop,
+                                            PRInt32 *aX, PRInt32 *aY);
   NS_IMETHOD              Move(PRInt32 aX, PRInt32 aY);
   NS_IMETHOD              Resize(PRInt32 aWidth,PRInt32 aHeight, PRBool aRepaint);
   NS_IMETHOD              Resize(PRInt32 aX, PRInt32 aY,PRInt32 aWidth,PRInt32 aHeight, PRBool aRepaint);
diff --git a/widget/src/cocoa/nsChildView.mm b/widget/src/cocoa/nsChildView.mm
index 8aa55abab61f..4c301444346f 100644
--- a/widget/src/cocoa/nsChildView.mm
+++ b/widget/src/cocoa/nsChildView.mm
@@ -799,7 +799,8 @@ NS_METHOD nsChildView::SetBounds(const nsRect &aRect)
 }
 
 
-NS_IMETHODIMP nsChildView::ConstrainPosition(PRInt32 *aX, PRInt32 *aY)
+NS_IMETHODIMP nsChildView::ConstrainPosition(PRBool aAllowSlop,
+                                             PRInt32 *aX, PRInt32 *aY)
 {
   return NS_OK;
 }
diff --git a/widget/src/cocoa/nsCocoaWindow.h b/widget/src/cocoa/nsCocoaWindow.h
index 8f54904e934f..c1fb6f92fd7b 100644
--- a/widget/src/cocoa/nsCocoaWindow.h
+++ b/widget/src/cocoa/nsCocoaWindow.h
@@ -125,7 +125,8 @@ public:
     
     virtual void* GetNativeData(PRUint32 aDataType) ;
 
-    NS_IMETHOD              ConstrainPosition(PRInt32 *aX, PRInt32 *aY);
+    NS_IMETHOD              ConstrainPosition(PRBool aAllowSlop,
+                                              PRInt32 *aX, PRInt32 *aY);
     NS_IMETHOD              Move(PRInt32 aX, PRInt32 aY);
     NS_IMETHOD              PlaceBehind(nsIWidget *aWidget, PRBool aActivate);
     NS_IMETHOD              SetSizeMode(PRInt32 aMode);
diff --git a/widget/src/cocoa/nsCocoaWindow.mm b/widget/src/cocoa/nsCocoaWindow.mm
index 5f6bf5e8534b..6b41ea10c6b6 100644
--- a/widget/src/cocoa/nsCocoaWindow.mm
+++ b/widget/src/cocoa/nsCocoaWindow.mm
@@ -920,7 +920,8 @@ NS_METHOD nsWindow::Restore(void)
 }
 */
 
-NS_IMETHODIMP nsCocoaWindow::ConstrainPosition(PRInt32 *aX, PRInt32 *aY)
+NS_IMETHODIMP nsCocoaWindow::ConstrainPosition(PRBool aAllowSlop,
+                                               PRInt32 *aX, PRInt32 *aY)
 {
 #if 0
   if (eWindowType_popup == mWindowType || !mWindowMadeHere)
@@ -1737,4 +1738,4 @@ void StopResizing ( )
   printf("did move\n");
 }
 
-@end
\ No newline at end of file
+@end
diff --git a/widget/src/gtk/nsWidget.cpp b/widget/src/gtk/nsWidget.cpp
index 930e8998caf8..702e463bd9f0 100644
--- a/widget/src/gtk/nsWidget.cpp
+++ b/widget/src/gtk/nsWidget.cpp
@@ -480,7 +480,8 @@ NS_IMETHODIMP nsWidget::IsVisible(PRBool &aState)
 //
 //-------------------------------------------------------------------------
 
-NS_IMETHODIMP nsWidget::ConstrainPosition(PRInt32 *aX, PRInt32 *aY)
+NS_IMETHODIMP nsWidget::ConstrainPosition(PRBool aAllowSlop,
+                                          PRInt32 *aX, PRInt32 *aY)
 {
   return NS_OK;
 }
diff --git a/widget/src/gtk/nsWidget.h b/widget/src/gtk/nsWidget.h
index e5d4f83ea36f..9654220a6f01 100644
--- a/widget/src/gtk/nsWidget.h
+++ b/widget/src/gtk/nsWidget.h
@@ -113,7 +113,7 @@ public:
   NS_IMETHOD CaptureRollupEvents(nsIRollupListener *aListener, PRBool aDoCapture, PRBool aConsumeRollupEvent);
   NS_IMETHOD IsVisible(PRBool &aState);
 
-  NS_IMETHOD ConstrainPosition(PRInt32 *aX, PRInt32 *aY);
+  NS_IMETHOD ConstrainPosition(PRBool aAllowSlop, PRInt32 *aX, PRInt32 *aY);
   NS_IMETHOD Move(PRInt32 aX, PRInt32 aY);
   NS_IMETHOD Resize(PRInt32 aWidth, PRInt32 aHeight, PRBool aRepaint);
   NS_IMETHOD Resize(PRInt32 aX, PRInt32 aY, PRInt32 aWidth,
diff --git a/widget/src/gtk/nsWindow.h b/widget/src/gtk/nsWindow.h
index 100a28d2a6ea..d9064e529da9 100644
--- a/widget/src/gtk/nsWindow.h
+++ b/widget/src/gtk/nsWindow.h
@@ -86,7 +86,8 @@ public:
   NS_IMETHOD           Show(PRBool aShow);
   NS_IMETHOD           CaptureMouse(PRBool aCapture);
 
-  NS_IMETHOD           ConstrainPosition(PRInt32 *aX, PRInt32 *aY);
+  NS_IMETHOD           ConstrainPosition(PRBool aAllowSlop,
+                                         PRInt32 *aX, PRInt32 *aY);
   NS_IMETHOD           Move(PRInt32 aX, PRInt32 aY);
 
   NS_IMETHOD           Resize(PRInt32 aWidth, PRInt32 aHeight, PRBool aRepaint);
diff --git a/widget/src/gtk2/nsScrollbar.cpp b/widget/src/gtk2/nsScrollbar.cpp
index 7b5c7ac8969d..0485f8f6f85a 100644
--- a/widget/src/gtk2/nsScrollbar.cpp
+++ b/widget/src/gtk2/nsScrollbar.cpp
@@ -119,7 +119,7 @@ nsScrollbar::IsVisible(PRBool & aState)
 }
 
 NS_IMETHODIMP
-nsScrollbar::ConstrainPosition(PRInt32 *aX, PRInt32 *aY)
+nsScrollbar::ConstrainPosition(PRBool aAllowSlop, PRInt32 *aX, PRInt32 *aY)
 {
   return NS_ERROR_NOT_IMPLEMENTED;
 }
diff --git a/widget/src/gtk2/nsScrollbar.h b/widget/src/gtk2/nsScrollbar.h
index 8529beb3beb5..936c7123d900 100644
--- a/widget/src/gtk2/nsScrollbar.h
+++ b/widget/src/gtk2/nsScrollbar.h
@@ -65,7 +65,7 @@ class nsScrollbar : public nsCommonWidget,
                     nsWidgetInitData *aInitData = nsnull);
   NS_IMETHOD Destroy(void);
   NS_IMETHOD IsVisible(PRBool & aState);
-  NS_IMETHOD ConstrainPosition(PRInt32 *aX, PRInt32 *aY);
+  NS_IMETHOD ConstrainPosition(PRBool aAllowSlop, PRInt32 *aX, PRInt32 *aY);
   NS_IMETHOD Move(PRInt32 aX, PRInt32 aY);
   NS_IMETHOD Enable(PRBool aState);
   NS_IMETHOD SetFocus(PRBool aRaise = PR_FALSE);
diff --git a/widget/src/gtk2/nsWindow.cpp b/widget/src/gtk2/nsWindow.cpp
index b68447f988f3..b08c0d50c3b9 100644
--- a/widget/src/gtk2/nsWindow.cpp
+++ b/widget/src/gtk2/nsWindow.cpp
@@ -194,7 +194,7 @@ nsWindow::IsVisible(PRBool & aState)
 }
 
 NS_IMETHODIMP
-nsWindow::ConstrainPosition(PRInt32 *aX, PRInt32 *aY)
+nsWindow::ConstrainPosition(PRBool aAllowSlop, PRInt32 *aX, PRInt32 *aY)
 {
   return NS_ERROR_NOT_IMPLEMENTED; 
 }
diff --git a/widget/src/gtk2/nsWindow.h b/widget/src/gtk2/nsWindow.h
index a7abed783013..427c8ef08b8b 100644
--- a/widget/src/gtk2/nsWindow.h
+++ b/widget/src/gtk2/nsWindow.h
@@ -63,7 +63,8 @@ class nsWindow : public nsCommonWidget {
   NS_IMETHOD         Destroy(void);
   NS_IMETHOD         SetModal(PRBool aModal);
   NS_IMETHOD         IsVisible(PRBool & aState);
-  NS_IMETHOD         ConstrainPosition(PRInt32 *aX,
+  NS_IMETHOD         ConstrainPosition(PRBool aAllowSlop,
+                                       PRInt32 *aX,
 				       PRInt32 *aY);
   NS_IMETHOD         Move(PRInt32 aX,
 			   PRInt32 aY);
diff --git a/widget/src/mac/nsMacWindow.h b/widget/src/mac/nsMacWindow.h
index f5b06cbb4dc5..481baf7c113a 100644
--- a/widget/src/mac/nsMacWindow.h
+++ b/widget/src/mac/nsMacWindow.h
@@ -107,7 +107,8 @@ public:
 				                            nsNativeWidget aNativeParent = nsnull);
 
     NS_IMETHOD              Show(PRBool aState);
-    NS_IMETHOD              ConstrainPosition(PRInt32 *aX, PRInt32 *aY);
+    NS_IMETHOD              ConstrainPosition(PRBool aAllowSlop,
+                                              PRInt32 *aX, PRInt32 *aY);
     NS_IMETHOD              Move(PRInt32 aX, PRInt32 aY);
     NS_IMETHOD              PlaceBehind(nsIWidget *aWidget, PRBool aActivate);
     NS_IMETHOD              SetSizeMode(PRInt32 aMode);
diff --git a/widget/src/mac/nsWindow.cpp b/widget/src/mac/nsWindow.cpp
index 1014a6b1398c..8acc2dbbb522 100644
--- a/widget/src/mac/nsWindow.cpp
+++ b/widget/src/mac/nsWindow.cpp
@@ -782,7 +782,8 @@ NS_METHOD nsWindow::SetBounds(const nsRect &aRect)
 }
 
 
-NS_IMETHODIMP nsWindow::ConstrainPosition(PRInt32 *aX, PRInt32 *aY)
+NS_IMETHODIMP nsWindow::ConstrainPosition(PRBool aAllowSlop,
+                                          PRInt32 *aX, PRInt32 *aY)
 {
 	return NS_OK;
 }
diff --git a/widget/src/mac/nsWindow.h b/widget/src/mac/nsWindow.h
index 5f21e013f9d8..75e889b76484 100644
--- a/widget/src/mac/nsWindow.h
+++ b/widget/src/mac/nsWindow.h
@@ -128,7 +128,8 @@ public:
     NS_IMETHOD              ModalEventFilter(PRBool aRealEvent, void *aEvent,
                                              PRBool *aForWindow);
 
-    NS_IMETHOD                  ConstrainPosition(PRInt32 *aX, PRInt32 *aY);
+    NS_IMETHOD                  ConstrainPosition(PRBool aAllowSlop,
+                                                  PRInt32 *aX, PRInt32 *aY);
     NS_IMETHOD            	Move(PRInt32 aX, PRInt32 aY);
     NS_IMETHOD            	Resize(PRInt32 aWidth,PRInt32 aHeight, PRBool aRepaint);
     NS_IMETHOD            	Resize(PRInt32 aX, PRInt32 aY,PRInt32 aWidth,PRInt32 aHeight, PRBool aRepaint);
diff --git a/widget/src/os2/nsWindow.cpp b/widget/src/os2/nsWindow.cpp
index e0bc1be30c1b..46d0e589aa0a 100644
--- a/widget/src/os2/nsWindow.cpp
+++ b/widget/src/os2/nsWindow.cpp
@@ -1189,7 +1189,8 @@ NS_METHOD nsWindow::ModalEventFilter(PRBool aRealEvent, void *aEvent,
 // Constrain a potential move to fit onscreen
 //
 //-------------------------------------------------------------------------
-NS_METHOD nsWindow::ConstrainPosition(PRInt32 *aX, PRInt32 *aY)
+NS_METHOD nsWindow::ConstrainPosition(PRBool aAllowSlop,
+                                      PRInt32 *aX, PRInt32 *aY)
 {
     return NS_OK;
 }
diff --git a/widget/src/os2/nsWindow.h b/widget/src/os2/nsWindow.h
index 365a193ec6dc..3613ca845c0e 100644
--- a/widget/src/os2/nsWindow.h
+++ b/widget/src/os2/nsWindow.h
@@ -104,7 +104,7 @@ class nsWindow : public nsBaseWidget,
 
    // Physical properties
    NS_IMETHOD Show( PRBool bState);
-   NS_IMETHOD ConstrainPosition(PRInt32 *aX, PRInt32 *aY);
+   NS_IMETHOD ConstrainPosition(PRBool aAllowSlop, PRInt32 *aX, PRInt32 *aY);
    NS_IMETHOD Move( PRInt32 aX, PRInt32 aY);
    NS_IMETHOD Resize( PRInt32 aWidth,
                       PRInt32 aHeight,
diff --git a/widget/src/photon/nsWidget.cpp b/widget/src/photon/nsWidget.cpp
index fedc8c2ba5a0..1ba113709734 100644
--- a/widget/src/photon/nsWidget.cpp
+++ b/widget/src/photon/nsWidget.cpp
@@ -371,9 +371,10 @@ NS_METHOD nsWidget::IsVisible( PRBool &aState ) {
 // Constrain a potential move to see if it fits onscreen
 //
 //-------------------------------------------------------------------------
-NS_METHOD nsWidget::ConstrainPosition( PRInt32 *aX, PRInt32 *aY ) {
+NS_METHOD nsWidget::ConstrainPosition( PRBool aAllowSlop,
+                                       PRInt32 *aX, PRInt32 *aY ) {
   return NS_OK;
-	}
+}
 
 //-------------------------------------------------------------------------
 //
diff --git a/widget/src/photon/nsWidget.h b/widget/src/photon/nsWidget.h
index 6bf96b4049f2..04751f04ec6c 100644
--- a/widget/src/photon/nsWidget.h
+++ b/widget/src/photon/nsWidget.h
@@ -99,7 +99,7 @@ public:
   NS_IMETHOD CaptureRollupEvents(nsIRollupListener *aListener, PRBool aDoCapture, PRBool aConsumeRollupEvent);
   NS_IMETHOD IsVisible(PRBool &aState);
 
-  NS_IMETHOD ConstrainPosition(PRInt32 *aX, PRInt32 *aY);
+  NS_IMETHOD ConstrainPosition(PRBool aAllowSlop, PRInt32 *aX, PRInt32 *aY);
   NS_IMETHOD Move(PRInt32 aX, PRInt32 aY);
   NS_IMETHOD Resize(PRInt32 aWidth, PRInt32 aHeight, PRBool aRepaint);
   NS_IMETHOD Resize(PRInt32 aX, PRInt32 aY, PRInt32 aWidth,
diff --git a/widget/src/photon/nsWindow.cpp b/widget/src/photon/nsWindow.cpp
index e007bbd77d42..d68fa45f74b5 100644
--- a/widget/src/photon/nsWindow.cpp
+++ b/widget/src/photon/nsWindow.cpp
@@ -1107,9 +1107,10 @@ NS_IMETHODIMP nsWindow::CaptureMouse( PRBool aCapture ) {
   return NS_OK;
 	}
 
-NS_METHOD nsWindow::ConstrainPosition( PRInt32 *aX, PRInt32 *aY ) {
+NS_METHOD nsWindow::ConstrainPosition( PRBool aAllowSlop,
+                                       PRInt32 *aX, PRInt32 *aY ) {
   return NS_OK;
-	}
+}
 
 //-------------------------------------------------------------------------
 //
diff --git a/widget/src/photon/nsWindow.h b/widget/src/photon/nsWindow.h
index 4fd864047b13..a5ddd890ac49 100644
--- a/widget/src/photon/nsWindow.h
+++ b/widget/src/photon/nsWindow.h
@@ -80,7 +80,8 @@ public:
   NS_IMETHOD           SetTitle(const nsString& aTitle);
   NS_IMETHOD           CaptureMouse(PRBool aCapture);
  
-  NS_IMETHOD           ConstrainPosition(PRInt32 *aX, PRInt32 *aY);
+  NS_IMETHOD           ConstrainPosition(PRBool aAllowSlop,
+                                         PRInt32 *aX, PRInt32 *aY);
   NS_IMETHOD           Move(PRInt32 aX, PRInt32 aY);
 
   NS_IMETHOD           Resize(PRInt32 aWidth, PRInt32 aHeight, PRBool aRepaint);
diff --git a/widget/src/qt/nsWidget.cpp b/widget/src/qt/nsWidget.cpp
index 6c9727fe8a98..5fc7da7cc813 100644
--- a/widget/src/qt/nsWidget.cpp
+++ b/widget/src/qt/nsWidget.cpp
@@ -244,7 +244,8 @@ NS_METHOD nsWidget::IsVisible(PRBool &aState)
 //-------------------------------------------------------------------------
 // Constrain a potential move so that it remains onscreen
 //-------------------------------------------------------------------------
-NS_METHOD nsWidget::ConstrainPosition(PRInt32 *aX, PRInt32 *aY)
+NS_METHOD nsWidget::ConstrainPosition(PRBool aAllowSlop,
+                                      PRInt32 *aX, PRInt32 *aY)
 {
   return NS_OK;
 }
diff --git a/widget/src/qt/nsWidget.h b/widget/src/qt/nsWidget.h
index c832e13d6bde..9d50d184b797 100644
--- a/widget/src/qt/nsWidget.h
+++ b/widget/src/qt/nsWidget.h
@@ -84,7 +84,7 @@ public:
                                    PRBool aConsumeRollupEvent);
     NS_IMETHOD IsVisible(PRBool &aState);
 
-    NS_IMETHOD ConstrainPosition(PRInt32 *aX, PRInt32 *aY);
+    NS_IMETHOD ConstrainPosition(PRBool aAllowSlop, PRInt32 *aX, PRInt32 *aY);
     NS_IMETHOD Move(PRInt32 aX, PRInt32 aY);
     NS_IMETHOD Resize(PRInt32 aWidth, PRInt32 aHeight, PRBool aRepaint);
     NS_IMETHOD Resize(PRInt32 aX, PRInt32 aY, PRInt32 aWidth, PRInt32 aHeight, 
diff --git a/widget/src/qt/nsWindow.cpp b/widget/src/qt/nsWindow.cpp
index 58efa2c20d54..54fcdbb6690f 100644
--- a/widget/src/qt/nsWindow.cpp
+++ b/widget/src/qt/nsWindow.cpp
@@ -458,7 +458,8 @@ PRBool nsWindow::OnScroll(nsScrollbarEvent &aEvent, PRUint32 cPos)
   return PR_FALSE;
 }
 
-NS_METHOD nsWindow::ConstrainPosition(PRInt32 *aX, PRInt32 *aY)
+NS_METHOD nsWindow::ConstrainPosition(PRBool aAllowSlop,
+                                      PRInt32 *aX, PRInt32 *aY)
 {
   return NS_OK;
 }
diff --git a/widget/src/qt/nsWindow.h b/widget/src/qt/nsWindow.h
index 78889c2ec8e8..82e270b6ddce 100644
--- a/widget/src/qt/nsWindow.h
+++ b/widget/src/qt/nsWindow.h
@@ -58,7 +58,7 @@ public:
     NS_IMETHOD SetColorMap(nsColorMap *aColorMap);
     NS_IMETHOD Scroll(PRInt32 aDx,PRInt32 aDy,nsRect *aClipRect);
 
-    NS_IMETHOD ConstrainPosition(PRInt32 *aX,PRInt32 *aY);
+    NS_IMETHOD ConstrainPosition(PRBool aAllowSlop, PRInt32 *aX,PRInt32 *aY);
     NS_IMETHOD Move(PRInt32 aX,PRInt32 aY);
 
     NS_IMETHOD CaptureRollupEvents(nsIRollupListener *aListener,
diff --git a/widget/src/windows/nsWindow.h b/widget/src/windows/nsWindow.h
index 5d15b0dff458..176bf1e9b0dc 100644
--- a/widget/src/windows/nsWindow.h
+++ b/widget/src/windows/nsWindow.h
@@ -247,7 +247,8 @@ public:
                                              PRBool *aForWindow);
 
     NS_IMETHOD              CaptureMouse(PRBool aCapture);
-    NS_IMETHOD              ConstrainPosition(PRInt32 *aX, PRInt32 *aY);
+    NS_IMETHOD              ConstrainPosition(PRBool aAllowSlop,
+                                              PRInt32 *aX, PRInt32 *aY);
     NS_IMETHOD              Move(PRInt32 aX, PRInt32 aY);
     NS_IMETHOD              Resize(PRInt32 aWidth,
                                    PRInt32 aHeight,
diff --git a/widget/src/xlib/nsWidget.cpp b/widget/src/xlib/nsWidget.cpp
index 64e507529673..78e363bb60e0 100644
--- a/widget/src/xlib/nsWidget.cpp
+++ b/widget/src/xlib/nsWidget.cpp
@@ -385,7 +385,8 @@ NS_IMETHODIMP nsWidget::Destroy()
 
 }
 
-NS_IMETHODIMP nsWidget::ConstrainPosition(PRInt32 *aX, PRInt32 *aY)
+NS_IMETHODIMP nsWidget::ConstrainPosition(PRBool aAllowSlop,
+                                          PRInt32 *aX, PRInt32 *aY)
 {
   return NS_OK;
 }
diff --git a/widget/src/xlib/nsWidget.h b/widget/src/xlib/nsWidget.h
index 6f43b0160780..9a8cfacb89dc 100644
--- a/widget/src/xlib/nsWidget.h
+++ b/widget/src/xlib/nsWidget.h
@@ -91,7 +91,7 @@ public:
   NS_IMETHOD Show(PRBool bState);
   NS_IMETHOD IsVisible(PRBool &aState);
 
-  NS_IMETHOD ConstrainPosition(PRInt32 *aX, PRInt32 *aY);
+  NS_IMETHOD ConstrainPosition(PRBool aAllowSlop, PRInt32 *aX, PRInt32 *aY);
   NS_IMETHOD Move(PRInt32 aX, PRInt32 aY);
   NS_IMETHOD Resize(PRInt32 aWidth,
                     PRInt32 aHeight,