diff --git a/layout/xul/nsSliderFrame.cpp b/layout/xul/nsSliderFrame.cpp
index d430272f8c1..90ac5e88f94 100644
--- a/layout/xul/nsSliderFrame.cpp
+++ b/layout/xul/nsSliderFrame.cpp
@@ -690,7 +690,15 @@ nsSliderFrame::CurrentPositionChanged()
 
   // avoid putting the scroll thumb at subpixel positions which cause needless invalidations
   nscoord appUnitsPerPixel = PresContext()->AppUnitsPerDevPixel();
-  newThumbRect = newThumbRect.ToNearestPixels(appUnitsPerPixel).ToAppUnits(appUnitsPerPixel);
+  nsRect snappedThumbRect = newThumbRect.ToNearestPixels(appUnitsPerPixel).ToAppUnits(appUnitsPerPixel);
+  if (IsHorizontal()) {
+    newThumbRect.x = snappedThumbRect.x;
+    newThumbRect.width = snappedThumbRect.width;
+  } else {
+    newThumbRect.y = snappedThumbRect.y;
+    newThumbRect.height = snappedThumbRect.height;
+  }
+  newThumbRect = newThumbRect.Intersect(clientRect);
 
   // set the rect
   thumbFrame->SetRect(newThumbRect);