bug 622507 - snap popup menu's view position to device pixels. r+a=roc

layout/xul/base/src/nsMenuPopupFrame.cpp

@@ -1281,6 +1281,11 @@ nsMenuPopupFrame::SetPopupPosition(nsIFrame* aAnchorFrame, PRBool aIsMove)
   // determine the x and y position of the view by subtracting the desired
   // screen position from the screen position of the root frame.
   nsPoint viewPoint = screenPoint - rootScreenRect.TopLeft();
+
+  // snap the view's position to device pixels, see bug 622507
+  viewPoint.x = presContext->RoundAppUnitsToNearestDevPixels(viewPoint.x);
+  viewPoint.y = presContext->RoundAppUnitsToNearestDevPixels(viewPoint.y);
+
   nsIView* view = GetView();
   NS_ASSERTION(view, "popup with no view");
   presContext->GetPresShell()->GetViewManager()->