diff -r 000000000000 -r 6474c204b198 browser/components/customizableui/test/browser_878452_drag_to_panel.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/components/customizableui/test/browser_878452_drag_to_panel.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,66 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+// Dragging an item from the palette to another button in the panel should work.
+add_task(function() {
+  yield startCustomizing();
+  let btn = document.getElementById("feed-button");
+  let panel = document.getElementById(CustomizableUI.AREA_PANEL);
+  let placements = getAreaWidgetIds(CustomizableUI.AREA_PANEL);
+
+  let lastButtonIndex = placements.length - 1;
+  let lastButton = placements[lastButtonIndex];
+  let placementsAfterInsert = placements.slice(0, lastButtonIndex).concat(["feed-button", lastButton]);
+  let lastButtonNode = document.getElementById(lastButton);
+  simulateItemDrag(btn, lastButtonNode);
+  assertAreaPlacements(CustomizableUI.AREA_PANEL, placementsAfterInsert);
+  ok(!CustomizableUI.inDefaultState, "Should no longer be in default state.");
+  let palette = document.getElementById("customization-palette");
+  simulateItemDrag(btn, palette);
+  ok(CustomizableUI.inDefaultState, "Should be in default state again.");
+});
+
+// Dragging an item from the palette to the panel itself should also work.
+add_task(function() {
+  yield startCustomizing();
+  let btn = document.getElementById("feed-button");
+  let panel = document.getElementById(CustomizableUI.AREA_PANEL);
+  let placements = getAreaWidgetIds(CustomizableUI.AREA_PANEL);
+
+  let placementsAfterAppend = placements.concat(["feed-button"]);
+  simulateItemDrag(btn, panel);
+  assertAreaPlacements(CustomizableUI.AREA_PANEL, placementsAfterAppend);
+  ok(!CustomizableUI.inDefaultState, "Should no longer be in default state.");
+  let palette = document.getElementById("customization-palette");
+  simulateItemDrag(btn, palette);
+  ok(CustomizableUI.inDefaultState, "Should be in default state again.");
+});
+
+// Dragging an item from the palette to an empty panel should also work.
+add_task(function() {
+  let widgetIds = getAreaWidgetIds(CustomizableUI.AREA_PANEL);
+  while (widgetIds.length) {
+    CustomizableUI.removeWidgetFromArea(widgetIds.shift());
+  }
+  yield startCustomizing();
+  let btn = document.getElementById("feed-button");
+  let panel = document.getElementById(CustomizableUI.AREA_PANEL);
+
+  assertAreaPlacements(panel.id, []);
+
+  let placementsAfterAppend = ["feed-button"];
+  simulateItemDrag(btn, panel);
+  assertAreaPlacements(CustomizableUI.AREA_PANEL, placementsAfterAppend);
+  ok(!CustomizableUI.inDefaultState, "Should no longer be in default state.");
+  let palette = document.getElementById("customization-palette");
+  simulateItemDrag(btn, palette);
+  assertAreaPlacements(panel.id, []);
+});
+
+add_task(function asyncCleanup() {
+  yield endCustomizing();
+  yield resetCustomization();
+});