diff -r 000000000000 -r 6474c204b198 browser/base/content/test/newtab/browser_newtab_drop_preview.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/base/content/test/newtab/browser_newtab_drop_preview.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,22 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+/*
+ * These tests ensure that the drop preview correctly arranges sites when
+ * dragging them around.
+ */
+function runTests() {
+  // the first three sites are pinned - make sure they're re-arranged correctly
+  yield setLinks("0,1,2,3,4,5,6,7,8");
+  setPinnedLinks("0,1,2,,,5");
+
+  yield addNewTabPageTab();
+  checkGrid("0p,1p,2p,3,4,5p,6,7,8");
+
+  let cw = getContentWindow();
+  cw.gDrag._draggedSite = getCell(0).site;
+  let sites = cw.gDropPreview.rearrange(getCell(4));
+  cw.gDrag._draggedSite = null;
+
+  checkGrid("3,1p,2p,4,0p,5p,6,7,8", sites);
+}