--- a/browser/components/customizableui/test/browser.ini
+++ b/browser/components/customizableui/test/browser.ini
@@ -9,29 +9,27 @@ support-files =
 [browser_873501_handle_specials.js]
 [browser_876926_customize_mode_wrapping.js]
 [browser_876944_customize_mode_create_destroy.js]
 [browser_877006_missing_view.js]
 [browser_877178_unregisterArea.js]
 [browser_877447_skip_missing_ids.js]
 [browser_878452_drag_to_panel.js]
 [browser_880164_customization_context_menus.js]
-[browser_880382_drag_wide_widgets_in_panel.js]
 [browser_884402_customize_from_overflow.js]
 skip-if = os == "linux"
 [browser_885052_customize_mode_observers_disabed.js]
 tags = fullscreen
 # Bug 951403 - Disabled on OSX for frequent failures
 skip-if = os == "mac"
 
 [browser_885530_showInPrivateBrowsing.js]
 [browser_886323_buildArea_removable_nodes.js]
 [browser_887438_currentset_shim.js]
 [browser_888817_currentset_updating.js]
-[browser_890140_orphaned_placeholders.js]
 [browser_890262_destroyWidget_after_add_to_panel.js]
 [browser_892955_isWidgetRemovable_for_removed_widgets.js]
 [browser_892956_destroyWidget_defaultPlacements.js]
 [browser_909779_overflow_toolbars_new_window.js]
 skip-if = os == "linux"
 
 [browser_901207_searchbar_in_panel.js]
 [browser_913972_currentset_overflow.js]

--- a/browser/components/customizableui/test/browser_876926_customize_mode_wrapping.js
+++ b/browser/components/customizableui/test/browser_876926_customize_mode_wrapping.js
@@ -1,17 +1,17 @@
 /* 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";
 
 const kXULWidgetId = "a-test-button"; // we'll create a button with this ID.
 const kAPIWidgetId = "feed-button";
-const kPanel = CustomizableUI.AREA_PANEL;
+const kPanel = CustomizableUI.AREA_FIXED_OVERFLOW_PANEL;
 const kToolbar = CustomizableUI.AREA_NAVBAR;
 const kVisiblePalette = "customization-palette";
 const kPlaceholderClass = "panel-customization-placeholder";
 
 function checkWrapper(id) {
   is(document.querySelectorAll("#wrapper-" + id).length, 1, "There should be exactly 1 wrapper for " + id + " in the customizing window.");
 }
 
@@ -150,37 +150,48 @@ function createXULButtonForWindow(win) {
 function removeXULButtonForWindow(win) {
   win.gNavToolbox.palette.querySelector(`#${kXULWidgetId}`).remove();
 }
 
 var otherWin;
 
 // Moving widgets in two windows, one with customize mode and one without, should work.
 add_task(async function MoveWidgetsInTwoWindows() {
-  await SpecialPowers.pushPrefEnv({set: [["browser.photon.structure.enabled", false]]});
+  CustomizableUI.createWidget({
+    id: "cui-mode-wrapping-some-panel-item",
+    label: "Test panel wrapping",
+  });
   await startCustomizing();
   otherWin = await openAndLoadWindow(null, true);
   await otherWin.PanelUI.ensureReady();
   // Create the XUL button to use in the test in both windows.
   createXULButtonForWindow(window);
   createXULButtonForWindow(otherWin);
   ok(CustomizableUI.inDefaultState, "Should start in default state");
 
   for (let widgetId of [kXULWidgetId, kAPIWidgetId]) {
     for (let method of ["API", "drag", "dragToItem"]) {
       info("Moving widget " + widgetId + " using " + method);
       checkToolbar(widgetId, method);
+      // We add an item to the panel because otherwise we can't test dragging
+      // to items that are already there. We remove it because
+      // 'checkPalette' checks that we leave the browser in the default state.
+      CustomizableUI.addWidgetToArea("cui-mode-wrapping-some-panel-item", CustomizableUI.AREA_FIXED_OVERFLOW_PANEL);
       checkPanel(widgetId, method);
+      CustomizableUI.removeWidgetFromArea("cui-mode-wrapping-some-panel-item");
       checkPalette(widgetId, method);
+      CustomizableUI.addWidgetToArea("cui-mode-wrapping-some-panel-item", CustomizableUI.AREA_FIXED_OVERFLOW_PANEL);
       checkPanel(widgetId, method);
       checkToolbar(widgetId, method);
+      CustomizableUI.removeWidgetFromArea("cui-mode-wrapping-some-panel-item");
       checkPalette(widgetId, method);
     }
   }
   await promiseWindowClosed(otherWin);
   otherWin = null;
   await endCustomizing();
   removeXULButtonForWindow(window);
 });
 
 add_task(async function asyncCleanup() {
+  CustomizableUI.destroyWidget("cui-mode-wrapping-some-panel-item");
   await resetCustomization();
 });

--- a/browser/components/customizableui/test/browser_876944_customize_mode_create_destroy.js
+++ b/browser/components/customizableui/test/browser_876944_customize_mode_create_destroy.js
@@ -1,65 +1,32 @@
 /* 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";
 
 const kTestWidget1 = "test-customize-mode-create-destroy1";
-const kTestWidget2 = "test-customize-mode-create-destroy2";
 
 // Creating and destroying a widget should correctly wrap/unwrap stuff
 add_task(async function testWrapUnwrap() {
-  await SpecialPowers.pushPrefEnv({set: [["browser.photon.structure.enabled", false]]});
   await startCustomizing();
   CustomizableUI.createWidget({id: kTestWidget1, label: "Pretty label", tooltiptext: "Pretty tooltip"});
   let elem = document.getElementById(kTestWidget1);
   let wrapper = document.getElementById("wrapper-" + kTestWidget1);
   ok(elem, "There should be an item");
   ok(wrapper, "There should be a wrapper");
   is(wrapper.firstChild.id, kTestWidget1, "Wrapper should have test widget");
   is(wrapper.parentNode.id, "customization-palette", "Wrapper should be in palette");
   CustomizableUI.destroyWidget(kTestWidget1);
   wrapper = document.getElementById("wrapper-" + kTestWidget1);
   ok(!wrapper, "There should be a wrapper");
   let item = document.getElementById(kTestWidget1);
   ok(!item, "There should no longer be an item");
 });
 
-// Creating and destroying a widget should correctly deal with panel placeholders
-add_task(async function testPanelPlaceholders() {
-  let panel = document.getElementById(CustomizableUI.AREA_PANEL);
-  // The value of expectedPlaceholders depends on the default palette layout.
-  // Bug 1229236 is for these tests to be smarter so the test doesn't need to
-  // change when the default placements change.
-  let expectedPlaceholders = 1;
-  if (isInNightly()) {
-    expectedPlaceholders += 2;
-  }
-  is(panel.querySelectorAll(".panel-customization-placeholder").length, expectedPlaceholders, "The number of placeholders should be correct.");
-  CustomizableUI.createWidget({id: kTestWidget2, label: "Pretty label", tooltiptext: "Pretty tooltip", defaultArea: CustomizableUI.AREA_PANEL});
-  let elem = document.getElementById(kTestWidget2);
-  let wrapper = document.getElementById("wrapper-" + kTestWidget2);
-  ok(elem, "There should be an item");
-  ok(wrapper, "There should be a wrapper");
-  is(wrapper.firstChild.id, kTestWidget2, "Wrapper should have test widget");
-  is(wrapper.parentNode, panel, "Wrapper should be in panel");
-  expectedPlaceholders = (expectedPlaceholders - 1) || 3;
-  is(panel.querySelectorAll(".panel-customization-placeholder").length, expectedPlaceholders, "The number of placeholders should be correct.");
-  CustomizableUI.destroyWidget(kTestWidget2);
-  wrapper = document.getElementById("wrapper-" + kTestWidget2);
-  ok(!wrapper, "There should be a wrapper");
-  let item = document.getElementById(kTestWidget2);
-  ok(!item, "There should no longer be an item");
-  await endCustomizing();
-});
-
 add_task(async function asyncCleanup() {
   await endCustomizing();
   try {
     CustomizableUI.destroyWidget(kTestWidget1);
   } catch (ex) {}
-  try {
-    CustomizableUI.destroyWidget(kTestWidget2);
-  } catch (ex) {}
   await resetCustomization();
 });

--- a/browser/components/customizableui/test/browser_878452_drag_to_panel.js
+++ b/browser/components/customizableui/test/browser_878452_drag_to_panel.js
@@ -1,64 +1,67 @@
 /* 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";
+CustomizableUI.createWidget({id: "cui-panel-item-to-drag-to", defaultArea: CustomizableUI.AREA_FIXED_OVERFLOW_PANEL, label: "Item in panel to drag to"});
 
 // Dragging an item from the palette to another button in the panel should work.
 add_task(async function() {
-  await SpecialPowers.pushPrefEnv({set: [["browser.photon.structure.enabled", false]]});
   await startCustomizing();
   let btn = document.getElementById("feed-button");
-  let placements = getAreaWidgetIds(CustomizableUI.AREA_PANEL);
+  let placements = getAreaWidgetIds(CustomizableUI.AREA_FIXED_OVERFLOW_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);
+  assertAreaPlacements(CustomizableUI.AREA_FIXED_OVERFLOW_PANEL, placementsAfterInsert);
   ok(!CustomizableUI.inDefaultState, "Should no longer be in default state.");
   let palette = document.getElementById("customization-palette");
   simulateItemDrag(btn, palette);
+  CustomizableUI.removeWidgetFromArea("cui-panel-item-to-drag-to");
   ok(CustomizableUI.inDefaultState, "Should be in default state again.");
 });
 
 // Dragging an item from the palette to the panel itself should also work.
 add_task(async function() {
+  CustomizableUI.addWidgetToArea("cui-panel-item-to-drag-to", CustomizableUI.AREA_FIXED_OVERFLOW_PANEL);
   await startCustomizing();
   let btn = document.getElementById("feed-button");
-  let panel = document.getElementById(CustomizableUI.AREA_PANEL);
-  let placements = getAreaWidgetIds(CustomizableUI.AREA_PANEL);
+  let panel = document.getElementById(CustomizableUI.AREA_FIXED_OVERFLOW_PANEL);
+  let placements = getAreaWidgetIds(CustomizableUI.AREA_FIXED_OVERFLOW_PANEL);
 
   let placementsAfterAppend = placements.concat(["feed-button"]);
   simulateItemDrag(btn, panel);
-  assertAreaPlacements(CustomizableUI.AREA_PANEL, placementsAfterAppend);
+  assertAreaPlacements(CustomizableUI.AREA_FIXED_OVERFLOW_PANEL, placementsAfterAppend);
   ok(!CustomizableUI.inDefaultState, "Should no longer be in default state.");
   let palette = document.getElementById("customization-palette");
   simulateItemDrag(btn, palette);
+  CustomizableUI.removeWidgetFromArea("cui-panel-item-to-drag-to");
   ok(CustomizableUI.inDefaultState, "Should be in default state again.");
 });
 
 // Dragging an item from the palette to an empty panel should also work.
 add_task(async function() {
-  let widgetIds = getAreaWidgetIds(CustomizableUI.AREA_PANEL);
+  let widgetIds = getAreaWidgetIds(CustomizableUI.AREA_FIXED_OVERFLOW_PANEL);
   while (widgetIds.length) {
     CustomizableUI.removeWidgetFromArea(widgetIds.shift());
   }
   await startCustomizing();
   let btn = document.getElementById("feed-button");
-  let panel = document.getElementById(CustomizableUI.AREA_PANEL);
+  let panel = document.getElementById(CustomizableUI.AREA_FIXED_OVERFLOW_PANEL);
 
   assertAreaPlacements(panel.id, []);
 
   let placementsAfterAppend = ["feed-button"];
   simulateItemDrag(btn, panel);
-  assertAreaPlacements(CustomizableUI.AREA_PANEL, placementsAfterAppend);
+  assertAreaPlacements(CustomizableUI.AREA_FIXED_OVERFLOW_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(async function asyncCleanup() {
   await endCustomizing();

deleted file mode 100644
--- a/browser/components/customizableui/test/browser_880382_drag_wide_widgets_in_panel.js
+++ /dev/null
@@ -1,520 +0,0 @@
-/* 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";
-
-requestLongerTimeout(5);
-
-// Dragging the zoom controls to be before the print button should not move any controls.
-add_task(async function() {
-  await SpecialPowers.pushPrefEnv({set: [["browser.photon.structure.enabled", false]]});
-  await startCustomizing();
-  let zoomControls = document.getElementById("zoom-controls");
-  let printButton = document.getElementById("print-button");
-  let placementsAfterMove = ["edit-controls",
-                             "new-window-button",
-                             "privatebrowsing-button",
-                             "save-page-button",
-                             "zoom-controls",
-                             "print-button",
-                             "history-panelmenu",
-                             "fullscreen-button",
-                             "find-button",
-                             "preferences-button",
-                             "add-ons-button",
-                             "developer-button",
-                             "sync-button",
-                             "webcompat-reporter-button"
-                            ];
-  removeNonReleaseButtons(placementsAfterMove);
-  simulateItemDrag(zoomControls, printButton);
-  assertAreaPlacements(CustomizableUI.AREA_PANEL, placementsAfterMove);
-  ok(!CustomizableUI.inDefaultState, "Should no longer be in default state.");
-  let newWindowButton = document.getElementById("new-window-button");
-  simulateItemDrag(zoomControls, newWindowButton);
-  ok(CustomizableUI.inDefaultState, "Should be in default state again.");
-});
-
-// Dragging the zoom controls to be before the save button should not move any controls.
-add_task(async function() {
-  await startCustomizing();
-  let zoomControls = document.getElementById("zoom-controls");
-  let savePageButton = document.getElementById("save-page-button");
-  let placementsAfterMove = ["edit-controls",
-                             "zoom-controls",
-                             "new-window-button",
-                             "privatebrowsing-button",
-                             "save-page-button",
-                             "print-button",
-                             "history-panelmenu",
-                             "fullscreen-button",
-                             "find-button",
-                             "preferences-button",
-                             "add-ons-button",
-                             "developer-button",
-                             "sync-button",
-                             "webcompat-reporter-button"
-                            ];
-  removeNonReleaseButtons(placementsAfterMove);
-  simulateItemDrag(zoomControls, savePageButton);
-  assertAreaPlacements(CustomizableUI.AREA_PANEL, placementsAfterMove);
-  ok(CustomizableUI.inDefaultState, "Should be in default state.");
-});
-
-
-// Dragging the zoom controls to be before the new-window button should not move any widgets.
-add_task(async function() {
-  await startCustomizing();
-  let zoomControls = document.getElementById("zoom-controls");
-  let newWindowButton = document.getElementById("new-window-button");
-  let placementsAfterMove = ["edit-controls",
-                             "zoom-controls",
-                             "new-window-button",
-                             "privatebrowsing-button",
-                             "save-page-button",
-                             "print-button",
-                             "history-panelmenu",
-                             "fullscreen-button",
-                             "find-button",
-                             "preferences-button",
-                             "add-ons-button",
-                             "developer-button",
-                             "sync-button",
-                             "webcompat-reporter-button"
-                            ];
-  removeNonReleaseButtons(placementsAfterMove);
-  simulateItemDrag(zoomControls, newWindowButton);
-  assertAreaPlacements(CustomizableUI.AREA_PANEL, placementsAfterMove);
-  ok(CustomizableUI.inDefaultState, "Should still be in default state.");
-});
-
-// Dragging the zoom controls to be before the history-panelmenu should move the zoom-controls in to the row higher than the history-panelmenu.
-add_task(async function() {
-  await startCustomizing();
-  let zoomControls = document.getElementById("zoom-controls");
-  let historyPanelMenu = document.getElementById("history-panelmenu");
-  let placementsAfterMove = ["edit-controls",
-                             "new-window-button",
-                             "privatebrowsing-button",
-                             "save-page-button",
-                             "zoom-controls",
-                             "print-button",
-                             "history-panelmenu",
-                             "fullscreen-button",
-                             "find-button",
-                             "preferences-button",
-                             "add-ons-button",
-                             "developer-button",
-                             "sync-button",
-                             "webcompat-reporter-button"
-                            ];
-  removeNonReleaseButtons(placementsAfterMove);
-  simulateItemDrag(zoomControls, historyPanelMenu);
-  assertAreaPlacements(CustomizableUI.AREA_PANEL, placementsAfterMove);
-  ok(!CustomizableUI.inDefaultState, "Should no longer be in default state.");
-  let newWindowButton = document.getElementById("new-window-button");
-  simulateItemDrag(zoomControls, newWindowButton);
-  ok(CustomizableUI.inDefaultState, "Should be in default state again.");
-});
-
-// Dragging the zoom controls to be before the preferences-button should move the zoom-controls
-// in to the row higher than the preferences-button.
-add_task(async function() {
-  await startCustomizing();
-  let zoomControls = document.getElementById("zoom-controls");
-  let preferencesButton = document.getElementById("preferences-button");
-  let placementsAfterMove = ["edit-controls",
-                             "new-window-button",
-                             "privatebrowsing-button",
-                             "save-page-button",
-                             "print-button",
-                             "history-panelmenu",
-                             "fullscreen-button",
-                             "zoom-controls",
-                             "find-button",
-                             "preferences-button",
-                             "add-ons-button",
-                             "developer-button",
-                             "sync-button",
-                             "webcompat-reporter-button"
-                            ];
-  removeNonReleaseButtons(placementsAfterMove);
-  simulateItemDrag(zoomControls, preferencesButton);
-  assertAreaPlacements(CustomizableUI.AREA_PANEL, placementsAfterMove);
-  ok(!CustomizableUI.inDefaultState, "Should no longer be in default state.");
-  let newWindowButton = document.getElementById("new-window-button");
-  simulateItemDrag(zoomControls, newWindowButton);
-  ok(CustomizableUI.inDefaultState, "Should be in default state again.");
-});
-
-// Dragging an item from the palette to before the zoom-controls should move it and two other buttons before the zoom controls.
-add_task(async function() {
-  await startCustomizing();
-  let openFileButton = document.getElementById("open-file-button");
-  let zoomControls = document.getElementById("zoom-controls");
-  let placementsAfterInsert = ["edit-controls",
-                               "open-file-button",
-                               "new-window-button",
-                               "privatebrowsing-button",
-                               "zoom-controls",
-                               "save-page-button",
-                               "print-button",
-                               "history-panelmenu",
-                               "fullscreen-button",
-                               "find-button",
-                               "preferences-button",
-                               "add-ons-button",
-                               "developer-button",
-                               "sync-button",
-                               "webcompat-reporter-button"
-                              ];
-  removeNonReleaseButtons(placementsAfterInsert);
-  simulateItemDrag(openFileButton, zoomControls);
-  assertAreaPlacements(CustomizableUI.AREA_PANEL, placementsAfterInsert);
-  ok(!CustomizableUI.inDefaultState, "Should no longer be in default state.");
-  let palette = document.getElementById("customization-palette");
-  // Check that the palette items are re-wrapped correctly.
-  let feedWrapper = document.getElementById("wrapper-feed-button");
-  let feedButton = document.getElementById("feed-button");
-  is(feedButton.parentNode, feedWrapper,
-     "feed-button should be a child of wrapper-feed-button");
-  is(feedWrapper.getAttribute("place"), "palette",
-     "The feed-button wrapper should have it's place set to 'palette'");
-  simulateItemDrag(openFileButton, palette);
-  is(openFileButton.parentNode.tagName, "toolbarpaletteitem",
-     "The open-file-button should be wrapped by a toolbarpaletteitem");
-  let newWindowButton = document.getElementById("new-window-button");
-  simulateItemDrag(zoomControls, newWindowButton);
-  ok(CustomizableUI.inDefaultState, "Should be in default state again.");
-});
-
-// Dragging an item from the palette to before the edit-controls
-// should move it and two other buttons before the edit and zoom controls.
-add_task(async function() {
-  await startCustomizing();
-  let openFileButton = document.getElementById("open-file-button");
-  let editControls = document.getElementById("edit-controls");
-  let placementsAfterInsert = ["open-file-button",
-                               "new-window-button",
-                               "privatebrowsing-button",
-                               "edit-controls",
-                               "zoom-controls",
-                               "save-page-button",
-                               "print-button",
-                               "history-panelmenu",
-                               "fullscreen-button",
-                               "find-button",
-                               "preferences-button",
-                               "add-ons-button",
-                               "developer-button",
-                               "sync-button",
-                               "webcompat-reporter-button"
-                              ];
-  removeNonReleaseButtons(placementsAfterInsert);
-  simulateItemDrag(openFileButton, editControls);
-  assertAreaPlacements(CustomizableUI.AREA_PANEL, placementsAfterInsert);
-  ok(!CustomizableUI.inDefaultState, "Should no longer be in default state.");
-  let palette = document.getElementById("customization-palette");
-  // Check that the palette items are re-wrapped correctly.
-  let feedWrapper = document.getElementById("wrapper-feed-button");
-  let feedButton = document.getElementById("feed-button");
-  is(feedButton.parentNode, feedWrapper,
-     "feed-button should be a child of wrapper-feed-button");
-  is(feedWrapper.getAttribute("place"), "palette",
-     "The feed-button wrapper should have it's place set to 'palette'");
-  simulateItemDrag(openFileButton, palette);
-  is(openFileButton.parentNode.tagName, "toolbarpaletteitem",
-     "The open-file-button should be wrapped by a toolbarpaletteitem");
-  ok(CustomizableUI.inDefaultState, "Should be in default state again.");
-});
-
-// Dragging the edit-controls to be before the zoom-controls button
-// should not move any widgets.
-add_task(async function() {
-  await startCustomizing();
-  let editControls = document.getElementById("edit-controls");
-  let zoomControls = document.getElementById("zoom-controls");
-  let placementsAfterMove = ["edit-controls",
-                             "zoom-controls",
-                             "new-window-button",
-                             "privatebrowsing-button",
-                             "save-page-button",
-                             "print-button",
-                             "history-panelmenu",
-                             "fullscreen-button",
-                             "find-button",
-                             "preferences-button",
-                             "add-ons-button",
-                             "developer-button",
-                             "sync-button",
-                             "webcompat-reporter-button"
-                            ];
-  removeNonReleaseButtons(placementsAfterMove);
-  simulateItemDrag(editControls, zoomControls);
-  assertAreaPlacements(CustomizableUI.AREA_PANEL, placementsAfterMove);
-  ok(CustomizableUI.inDefaultState, "Should still be in default state.");
-});
-
-// Dragging the edit-controls to be before the new-window-button should
-// move the zoom-controls before the edit-controls.
-add_task(async function() {
-  await startCustomizing();
-  let editControls = document.getElementById("edit-controls");
-  let newWindowButton = document.getElementById("new-window-button");
-  let placementsAfterMove = ["zoom-controls",
-                             "edit-controls",
-                             "new-window-button",
-                             "privatebrowsing-button",
-                             "save-page-button",
-                             "print-button",
-                             "history-panelmenu",
-                             "fullscreen-button",
-                             "find-button",
-                             "preferences-button",
-                             "add-ons-button",
-                             "developer-button",
-                             "sync-button",
-                             "webcompat-reporter-button"
-                            ];
-  removeNonReleaseButtons(placementsAfterMove);
-  simulateItemDrag(editControls, newWindowButton);
-  assertAreaPlacements(CustomizableUI.AREA_PANEL, placementsAfterMove);
-  let zoomControls = document.getElementById("zoom-controls");
-  simulateItemDrag(editControls, zoomControls);
-  ok(CustomizableUI.inDefaultState, "Should still be in default state.");
-});
-
-// Dragging the edit-controls to be before the privatebrowsing-button
-// should move the edit-controls in to the row higher than the
-// privatebrowsing-button.
-add_task(async function() {
-  await startCustomizing();
-  let editControls = document.getElementById("edit-controls");
-  let privateBrowsingButton = document.getElementById("privatebrowsing-button");
-  let placementsAfterMove = ["zoom-controls",
-                             "edit-controls",
-                             "new-window-button",
-                             "privatebrowsing-button",
-                             "save-page-button",
-                             "print-button",
-                             "history-panelmenu",
-                             "fullscreen-button",
-                             "find-button",
-                             "preferences-button",
-                             "add-ons-button",
-                             "developer-button",
-                             "sync-button",
-                             "webcompat-reporter-button"
-                            ];
-  removeNonReleaseButtons(placementsAfterMove);
-  simulateItemDrag(editControls, privateBrowsingButton);
-  assertAreaPlacements(CustomizableUI.AREA_PANEL, placementsAfterMove);
-  let zoomControls = document.getElementById("zoom-controls");
-  simulateItemDrag(editControls, zoomControls);
-  ok(CustomizableUI.inDefaultState, "Should still be in default state.");
-});
-
-// Dragging the edit-controls to be before the save-page-button
-// should move the edit-controls in to the row higher than the
-// save-page-button.
-add_task(async function() {
-  await startCustomizing();
-  let editControls = document.getElementById("edit-controls");
-  let savePageButton = document.getElementById("save-page-button");
-  let placementsAfterMove = ["zoom-controls",
-                             "edit-controls",
-                             "new-window-button",
-                             "privatebrowsing-button",
-                             "save-page-button",
-                             "print-button",
-                             "history-panelmenu",
-                             "fullscreen-button",
-                             "find-button",
-                             "preferences-button",
-                             "add-ons-button",
-                             "developer-button",
-                             "sync-button",
-                             "webcompat-reporter-button"
-                            ];
-  removeNonReleaseButtons(placementsAfterMove);
-  simulateItemDrag(editControls, savePageButton);
-  assertAreaPlacements(CustomizableUI.AREA_PANEL, placementsAfterMove);
-  let zoomControls = document.getElementById("zoom-controls");
-  simulateItemDrag(editControls, zoomControls);
-  ok(CustomizableUI.inDefaultState, "Should still be in default state.");
-});
-
-// Dragging the edit-controls to the panel itself should append
-// the edit controls to the bottom of the panel.
-add_task(async function editControlsToPanelEmptySpace() {
-  await startCustomizing();
-  let editControls = document.getElementById("edit-controls");
-  let panel = document.getElementById(CustomizableUI.AREA_PANEL);
-  let placementsAfterMove = ["zoom-controls",
-                             "new-window-button",
-                             "privatebrowsing-button",
-                             "save-page-button",
-                             "print-button",
-                             "history-panelmenu",
-                             "fullscreen-button",
-                             "find-button",
-                             "preferences-button",
-                             "add-ons-button",
-                             "edit-controls",
-                             "developer-button",
-                             "sync-button",
-                            ];
-  removeNonReleaseButtons(placementsAfterMove);
-  if (isNotReleaseOrBeta()) {
-    CustomizableUI.removeWidgetFromArea("webcompat-reporter-button");
-  }
-  simulateItemDrag(editControls, panel);
-  assertAreaPlacements(CustomizableUI.AREA_PANEL, placementsAfterMove);
-  let zoomControls = document.getElementById("zoom-controls");
-  simulateItemDrag(editControls, zoomControls);
-  if (isNotReleaseOrBeta()) {
-    CustomizableUI.addWidgetToArea("webcompat-reporter-button", CustomizableUI.AREA_PANEL);
-  }
-  ok(CustomizableUI.inDefaultState, "Should still be in default state.");
-});
-
-// Dragging the edit-controls to the customization-palette and
-// back should work.
-add_task(async function() {
-  await startCustomizing();
-  let editControls = document.getElementById("edit-controls");
-  let palette = document.getElementById("customization-palette");
-  let placementsAfterMove = ["zoom-controls",
-                             "new-window-button",
-                             "privatebrowsing-button",
-                             "save-page-button",
-                             "print-button",
-                             "history-panelmenu",
-                             "fullscreen-button",
-                             "find-button",
-                             "preferences-button",
-                             "add-ons-button",
-                             "developer-button",
-                             "sync-button",
-                             "webcompat-reporter-button",
-                            ];
-  removeNonReleaseButtons(placementsAfterMove);
-  let paletteChildElementCount = palette.childElementCount;
-  simulateItemDrag(editControls, palette);
-  assertAreaPlacements(CustomizableUI.AREA_PANEL, placementsAfterMove);
-  is(paletteChildElementCount + 1, palette.childElementCount,
-     "The palette should have a new child, congratulations!");
-  is(editControls.parentNode.id, "wrapper-edit-controls",
-     "The edit-controls should be properly wrapped.");
-  is(editControls.parentNode.getAttribute("place"), "palette",
-     "The edit-controls should have the place of 'palette'.");
-  let zoomControls = document.getElementById("zoom-controls");
-  simulateItemDrag(editControls, zoomControls);
-  is(paletteChildElementCount, palette.childElementCount,
-     "The palette child count should have returned to its prior value.");
-  ok(CustomizableUI.inDefaultState, "Should still be in default state.");
-});
-
-// Dragging the edit-controls to each of the panel placeholders
-// should append the edit-controls to the bottom of the panel.
-add_task(async function editControlsToPanelPlaceholders() {
-  await startCustomizing();
-  let editControls = document.getElementById("edit-controls");
-  let panel = document.getElementById(CustomizableUI.AREA_PANEL);
-  let numPlaceholders = 2;
-  for (let i = 0; i < numPlaceholders; i++) {
-    // This test relies on there being a specific number of widgets in the
-    // panel. The addition of sync-button and webcompat-reporter-button screwed
-    // this up, so we remove them here. We should either fix the tests to not
-    // rely on the specific layout, or fix bug 1007910 which would change the
-    // placeholder logic in different ways. Bug 1229236 is for these tests to
-    // be smarter.
-    removeNonOriginalButtons();
-    // NB: We can't just iterate over all of the placeholders
-    // because each drag-drop action recreates them.
-    let placeholder = panel.getElementsByClassName("panel-customization-placeholder")[i];
-    let placementsAfterMove = ["zoom-controls",
-                               "new-window-button",
-                               "privatebrowsing-button",
-                               "save-page-button",
-                               "print-button",
-                               "history-panelmenu",
-                               "fullscreen-button",
-                               "find-button",
-                               "preferences-button",
-                               "add-ons-button",
-                               "edit-controls",
-                               "developer-button",
-                              ];
-    removeNonReleaseButtons(placementsAfterMove);
-    simulateItemDrag(editControls, placeholder);
-    assertAreaPlacements(CustomizableUI.AREA_PANEL, placementsAfterMove);
-    let zoomControls = document.getElementById("zoom-controls");
-    simulateItemDrag(editControls, zoomControls);
-    restoreNonOriginalButtons();
-    ok(CustomizableUI.inDefaultState, "Should still be in default state.");
-  }
-});
-
-// Dragging the open-file-button back on to itself should work.
-add_task(async function() {
-  await startCustomizing();
-  let openFileButton = document.getElementById("open-file-button");
-  is(openFileButton.parentNode.tagName, "toolbarpaletteitem",
-     "open-file-button should be wrapped by a toolbarpaletteitem");
-  simulateItemDrag(openFileButton, openFileButton);
-  is(openFileButton.parentNode.tagName, "toolbarpaletteitem",
-     "open-file-button should be wrapped by a toolbarpaletteitem");
-  let editControls = document.getElementById("edit-controls");
-  is(editControls.parentNode.tagName, "toolbarpaletteitem",
-     "edit-controls should be wrapped by a toolbarpaletteitem");
-  ok(CustomizableUI.inDefaultState, "Should still be in default state.");
-});
-
-// Dragging a small button onto the last big button should work.
-add_task(async function() {
-  // Bug 1007910 requires there be a placeholder on the final row for this
-  // test to work as written. The addition of sync-button and
-  // webcompat-reporter-button meant that's not true so we remove them from
-  // here. Bug 1229236 is for these tests to be smarter.
-  removeNonOriginalButtons();
-  await startCustomizing();
-  let editControls = document.getElementById("edit-controls");
-  let panel = document.getElementById(CustomizableUI.AREA_PANEL);
-  let target = panel.getElementsByClassName("panel-customization-placeholder")[0];
-  let placementsAfterMove = ["zoom-controls",
-                             "new-window-button",
-                             "privatebrowsing-button",
-                             "save-page-button",
-                             "print-button",
-                             "history-panelmenu",
-                             "fullscreen-button",
-                             "find-button",
-                             "preferences-button",
-                             "add-ons-button",
-                             "edit-controls",
-                             "developer-button",
-                            ];
-  removeNonReleaseButtons(placementsAfterMove);
-  simulateItemDrag(editControls, target);
-  assertAreaPlacements(CustomizableUI.AREA_PANEL, placementsAfterMove);
-  let itemToDrag = "email-link-button"; // any button in the palette by default.
-  let button = document.getElementById(itemToDrag);
-  placementsAfterMove.splice(11, 0, itemToDrag);
-  simulateItemDrag(button, editControls);
-  assertAreaPlacements(CustomizableUI.AREA_PANEL, placementsAfterMove);
-
-  // Put stuff back:
-  let palette = document.getElementById("customization-palette");
-  let zoomControls = document.getElementById("zoom-controls");
-  simulateItemDrag(button, palette);
-  simulateItemDrag(editControls, zoomControls);
-  restoreNonOriginalButtons();
-  ok(CustomizableUI.inDefaultState, "Should be in default state again.");
-});
-
-add_task(async function asyncCleanup() {
-  await endCustomizing();
-  await resetCustomization();
-});

deleted file mode 100644
--- a/browser/components/customizableui/test/browser_890140_orphaned_placeholders.js
+++ /dev/null
@@ -1,211 +0,0 @@
-/* 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";
-
-requestLongerTimeout(2);
-
-// One orphaned item should have two placeholders next to it.
-add_task(async function() {
-  await SpecialPowers.pushPrefEnv({set: [["browser.photon.structure.enabled", false]]});
-  await startCustomizing();
-
-  if (isInDevEdition()) {
-    CustomizableUI.addWidgetToArea("developer-button", CustomizableUI.AREA_PANEL);
-    ok(!CustomizableUI.inDefaultState, "Should no longer be in default state.");
-  }
-  if (!isInDevEdition()) {
-    ok(CustomizableUI.inDefaultState, "Should be in default state.");
-  } else {
-    ok(!CustomizableUI.inDefaultState, "Should not be in default state if on DevEdition.");
-  }
-
-  // This test relies on an exact number of widgets being in the panel.
-  // Remove the buttons to satisfy that. (bug 1229236)
-  removeNonOriginalButtons();
-  let panel = document.getElementById(CustomizableUI.AREA_PANEL);
-  let placements = getAreaWidgetIds(CustomizableUI.AREA_PANEL);
-
-  assertAreaPlacements(CustomizableUI.AREA_PANEL, placements);
-  is(getVisiblePlaceholderCount(panel), 2, "Should only have 2 visible placeholders before exiting");
-
-  await endCustomizing();
-  await startCustomizing();
-  is(getVisiblePlaceholderCount(panel), 2, "Should only have 2 visible placeholders after re-entering");
-
-  if (isInDevEdition()) {
-    CustomizableUI.addWidgetToArea("developer-button", CustomizableUI.AREA_NAVBAR, 2);
-  }
-
-  restoreNonOriginalButtons();
-  ok(CustomizableUI.inDefaultState, "Should be in default state again.");
-});
-
-// Two orphaned items should have one placeholder next to them (case 1).
-add_task(async function() {
-  await startCustomizing();
-
-  if (isInDevEdition()) {
-    CustomizableUI.addWidgetToArea("developer-button", CustomizableUI.AREA_PANEL);
-  }
-
-  // This test relies on an exact number of widgets being in the panel.
-  // Remove the button to satisfy that. (bug 1229236)
-  removeNonOriginalButtons()
-
-  let btn = document.getElementById("open-file-button");
-  let panel = document.getElementById(CustomizableUI.AREA_PANEL);
-  let placements = getAreaWidgetIds(CustomizableUI.AREA_PANEL);
-  let placementsAfterAppend = placements;
-
-  placementsAfterAppend = placements.concat(["open-file-button"]);
-  simulateItemDrag(btn, panel);
-
-  assertAreaPlacements(CustomizableUI.AREA_PANEL, placementsAfterAppend);
-
-  ok(!CustomizableUI.inDefaultState, "Should not be in default state.");
-
-  is(getVisiblePlaceholderCount(panel), 1, "Should only have 1 visible placeholder before exiting");
-
-  await endCustomizing();
-  await startCustomizing();
-  is(getVisiblePlaceholderCount(panel), 1, "Should only have 1 visible placeholder after re-entering");
-
-  let palette = document.getElementById("customization-palette");
-  simulateItemDrag(btn, palette);
-
-  btn = document.getElementById("open-file-button");
-  simulateItemDrag(btn, palette);
-
-  if (isInDevEdition()) {
-    CustomizableUI.addWidgetToArea("developer-button", CustomizableUI.AREA_NAVBAR, 2);
-  }
-
-  restoreNonOriginalButtons();
-  ok(CustomizableUI.inDefaultState, "Should be in default state again.");
-});
-
-// Two orphaned items should have one placeholder next to them (case 2).
-add_task(async function() {
-  await startCustomizing();
-
-  if (isInDevEdition()) {
-    CustomizableUI.addWidgetToArea("developer-button", CustomizableUI.AREA_PANEL);
-  }
-  // This test relies on an exact number of widgets being in the panel.
-  // Remove the buttons to satisfy that. (bug 1229236)
-  removeNonOriginalButtons();
-
-  let btn = document.getElementById("add-ons-button");
-  let btn2 = document.getElementById("developer-button");
-  let panel = document.getElementById(CustomizableUI.AREA_PANEL);
-  let palette = document.getElementById("customization-palette");
-  let placements = getAreaWidgetIds(CustomizableUI.AREA_PANEL);
-
-  let placementsAfterAppend = placements.filter(p => p != btn.id && p != btn2.id);
-  simulateItemDrag(btn, palette);
-  simulateItemDrag(btn2, palette);
-
-  assertAreaPlacements(CustomizableUI.AREA_PANEL, placementsAfterAppend);
-  ok(!CustomizableUI.inDefaultState, "Should no longer be in default state.");
-  is(getVisiblePlaceholderCount(panel), 1, "Should only have 1 visible placeholder before exiting");
-
-  await endCustomizing();
-  await startCustomizing();
-  is(getVisiblePlaceholderCount(panel), 1, "Should only have 1 visible placeholder after re-entering");
-
-  simulateItemDrag(btn, panel);
-  simulateItemDrag(btn2, panel);
-
-  assertAreaPlacements(CustomizableUI.AREA_PANEL, placements);
-
-  if (isInDevEdition()) {
-    CustomizableUI.addWidgetToArea("developer-button", CustomizableUI.AREA_NAVBAR, 2);
-  }
-
-  restoreNonOriginalButtons();
-  ok(CustomizableUI.inDefaultState, "Should be in default state again.");
-});
-
-// A wide widget at the bottom of the panel should have three placeholders after it.
-add_task(async function() {
-  await startCustomizing();
-
-  if (isInDevEdition()) {
-    CustomizableUI.addWidgetToArea("developer-button", CustomizableUI.AREA_PANEL);
-  }
-
-  // This test relies on an exact number of widgets being in the panel.
-  // Remove the buttons to satisfy that. (bug 1229236)
-  removeNonOriginalButtons();
-
-  let btn = document.getElementById("edit-controls");
-  let btn2 = document.getElementById("developer-button");
-  let panel = document.getElementById(CustomizableUI.AREA_PANEL);
-  let palette = document.getElementById("customization-palette");
-  let placements = getAreaWidgetIds(CustomizableUI.AREA_PANEL);
-
-  placements.pop();
-  simulateItemDrag(btn2, palette);
-
-  let placementsAfterAppend = placements.concat([placements.shift()]);
-  simulateItemDrag(btn, panel);
-  assertAreaPlacements(CustomizableUI.AREA_PANEL, placementsAfterAppend);
-  ok(!CustomizableUI.inDefaultState, "Should no longer be in default state.");
-  is(getVisiblePlaceholderCount(panel), 3, "Should have 3 visible placeholders before exiting");
-
-  await endCustomizing();
-  await startCustomizing();
-  is(getVisiblePlaceholderCount(panel), 3, "Should have 3 visible placeholders after re-entering");
-
-  simulateItemDrag(btn2, panel);
-
-  let zoomControls = document.getElementById("zoom-controls");
-  simulateItemDrag(btn, zoomControls);
-
-  if (isInDevEdition()) {
-    CustomizableUI.addWidgetToArea("developer-button", CustomizableUI.AREA_NAVBAR, 2);
-  }
-
-  restoreNonOriginalButtons();
-  ok(CustomizableUI.inDefaultState, "Should be in default state again.");
-});
-
-// The default placements should have two placeholders at the bottom (or 1 in win8).
-add_task(async function() {
-  await startCustomizing();
-  let numPlaceholders = -1;
-
-  if (isInDevEdition()) {
-    numPlaceholders = 3;
-  } else {
-    numPlaceholders = 2;
-  }
-
-  let panel = document.getElementById(CustomizableUI.AREA_PANEL);
-  ok(CustomizableUI.inDefaultState, "Should be in default state.");
-
-  // This test relies on an exact number of widgets being in the panel.
-  // Remove the buttons to satisfy that. (bug 1229236)
-  removeNonOriginalButtons();
-
-  is(getVisiblePlaceholderCount(panel), numPlaceholders, "Should have " + numPlaceholders + " visible placeholders before exiting");
-
-  await endCustomizing();
-  await startCustomizing();
-  is(getVisiblePlaceholderCount(panel), numPlaceholders, "Should have " + numPlaceholders + " visible placeholders after re-entering");
-
-  restoreNonOriginalButtons();
-  ok(CustomizableUI.inDefaultState, "Should still be in default state.");
-});
-
-add_task(async function asyncCleanup() {
-  await endCustomizing();
-  await resetCustomization();
-});
-
-function getVisiblePlaceholderCount(aPanel) {
-  let visiblePlaceholders = aPanel.querySelectorAll(".panel-customization-placeholder:not([hidden=true])");
-  return visiblePlaceholders.length;
-}