diff -r 000000000000 -r 6474c204b198 browser/components/customizableui/test/browser_884402_customize_from_overflow.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/components/customizableui/test/browser_884402_customize_from_overflow.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,82 @@
+"use strict";
+
+let overflowPanel = document.getElementById("widget-overflow");
+
+const isOSX = (Services.appinfo.OS === "Darwin");
+
+let originalWindowWidth;
+registerCleanupFunction(function() {
+  overflowPanel.removeAttribute("animate");
+  window.resizeTo(originalWindowWidth, window.outerHeight);
+});
+
+// Right-click on an item within the overflow panel should
+// show a context menu with options to move it.
+add_task(function() {
+
+  overflowPanel.setAttribute("animate", "false");
+
+  originalWindowWidth = window.outerWidth;
+  let navbar = document.getElementById(CustomizableUI.AREA_NAVBAR);
+  ok(!navbar.hasAttribute("overflowing"), "Should start with a non-overflowing toolbar.");
+  let oldChildCount = navbar.customizationTarget.childElementCount;
+  window.resizeTo(400, window.outerHeight);
+
+  yield waitForCondition(() => navbar.hasAttribute("overflowing"));
+  ok(navbar.hasAttribute("overflowing"), "Should have an overflowing toolbar.");
+
+  let chevron = document.getElementById("nav-bar-overflow-button");
+  let shownPanelPromise = promisePanelElementShown(window, overflowPanel);
+  chevron.click();
+  yield shownPanelPromise;
+
+  let contextMenu = document.getElementById("toolbar-context-menu");
+  let shownContextPromise = popupShown(contextMenu);
+  let homeButton = document.getElementById("home-button");
+  ok(homeButton, "home-button was found");
+  is(homeButton.getAttribute("overflowedItem"), "true", "Home button is overflowing");
+  EventUtils.synthesizeMouse(homeButton, 2, 2, {type: "contextmenu", button: 2});
+  yield shownContextPromise;
+
+  is(overflowPanel.state, "open", "The widget overflow panel should still be open.");
+
+  let expectedEntries = [
+    [".customize-context-moveToPanel", true],
+    [".customize-context-removeFromToolbar", true],
+    ["---"]
+  ];
+  if (!isOSX) {
+    expectedEntries.push(["#toggle_toolbar-menubar", true]);
+  }
+  expectedEntries.push(
+    ["#toggle_PersonalToolbar", true],
+    ["---"],
+    [".viewCustomizeToolbar", true]
+  );
+  checkContextMenu(contextMenu, expectedEntries);
+
+  let hiddenContextPromise = popupHidden(contextMenu);
+  let hiddenPromise = promisePanelElementHidden(window, overflowPanel);
+  let moveToPanel = contextMenu.querySelector(".customize-context-moveToPanel");
+  if (moveToPanel) {
+    moveToPanel.click();
+  }
+  contextMenu.hidePopup();
+  yield hiddenContextPromise;
+  yield hiddenPromise;
+
+  let homeButtonPlacement = CustomizableUI.getPlacementOfWidget("home-button");
+  ok(homeButtonPlacement, "Home button should still have a placement");
+  is(homeButtonPlacement && homeButtonPlacement.area, "PanelUI-contents", "Home button should be in the panel now");
+  CustomizableUI.reset();
+
+  // In some cases, it can take a tick for the navbar to overflow again. Wait for it:
+  yield waitForCondition(() => navbar.hasAttribute("overflowing"));
+  ok(navbar.hasAttribute("overflowing"), "Should have an overflowing toolbar.");
+
+  let homeButtonPlacement = CustomizableUI.getPlacementOfWidget("home-button");
+  ok(homeButtonPlacement, "Home button should still have a placement");
+  is(homeButtonPlacement && homeButtonPlacement.area, "nav-bar", "Home button should be back in the navbar now");
+
+  is(homeButton.getAttribute("overflowedItem"), "true", "Home button should still be overflowed");
+});