diff -r 000000000000 -r 6474c204b198 browser/components/tabview/groupitems.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/components/tabview/groupitems.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,2668 @@
+/* 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/. */
+
+// **********
+// Title: groupItems.js
+
+// ##########
+// Class: GroupItem
+// A single groupItem in the TabView window. Descended from <Item>.
+// Note that it implements the <Subscribable> interface.
+//
+// ----------
+// Constructor: GroupItem
+//
+// Parameters:
+//   listOfEls - an array of DOM elements for tabs to be added to this groupItem
+//   options - various options for this groupItem (see below). In addition, gets passed
+//     to <add> along with the elements provided.
+//
+// Possible options:
+//   id - specifies the groupItem's id; otherwise automatically generated
+//   userSize - see <Item.userSize>; default is null
+//   bounds - a <Rect>; otherwise based on the locations of the provided elements
+//   container - a DOM element to use as the container for this groupItem; otherwise will create
+//   title - the title for the groupItem; otherwise blank
+//   focusTitle - focus the title's input field after creation
+//   dontPush - true if this groupItem shouldn't push away or snap on creation; default is false
+//   immediately - true if we want all placement immediately, not with animation
+function GroupItem(listOfEls, options) {
+  if (!options)
+    options = {};
+
+  this._inited = false;
+  this._uninited = false;
+  this._children = []; // an array of Items
+  this.isAGroupItem = true;
+  this.id = options.id || GroupItems.getNextID();
+  this._isStacked = false;
+  this.expanded = null;
+  this.hidden = false;
+  this.fadeAwayUndoButtonDelay = 15000;
+  this.fadeAwayUndoButtonDuration = 300;
+
+  this.keepProportional = false;
+  this._frozenItemSizeData = {};
+
+  this._onChildClose = this._onChildClose.bind(this);
+
+  // Variable: _activeTab
+  // The <TabItem> for the groupItem's active tab.
+  this._activeTab = null;
+
+  if (Utils.isPoint(options.userSize))
+    this.userSize = new Point(options.userSize);
+
+  var self = this;
+
+  var rectToBe;
+  if (options.bounds) {
+    Utils.assert(Utils.isRect(options.bounds), "options.bounds must be a Rect");
+    rectToBe = new Rect(options.bounds);
+  }
+
+  if (!rectToBe) {
+    rectToBe = GroupItems.getBoundingBox(listOfEls);
+    rectToBe.inset(-42, -42);
+  }
+
+  var $container = options.container;
+  let immediately = options.immediately || $container ? true : false;
+  if (!$container) {
+    $container = iQ('<div>')
+      .addClass('groupItem')
+      .css({position: 'absolute'})
+      .css(rectToBe);
+  }
+
+  this.bounds = $container.bounds();
+
+  this.isDragging = false;
+  $container
+    .css({zIndex: -100})
+    .attr("data-id", this.id)
+    .appendTo("body");
+
+  // ___ Resizer
+  this.$resizer = iQ("<div>")
+    .addClass('resizer')
+    .appendTo($container)
+    .hide();
+
+  // ___ Titlebar
+  var html =
+    "<div class='title-container'>" +
+      "<input class='name' />" +
+      "<div class='title-shield' />" +
+    "</div>";
+
+  this.$titlebar = iQ('<div>')
+    .addClass('titlebar')
+    .html(html)
+    .appendTo($container);
+
+  this.$closeButton = iQ('<div>')
+    .addClass('close')
+    .click(function() {
+      self.closeAll();
+    })
+    .attr("title", tabviewString("groupItem.closeGroup"))
+    .appendTo($container);
+
+  // ___ Title
+  this.$titleContainer = iQ('.title-container', this.$titlebar);
+  this.$title = iQ('.name', this.$titlebar).attr('placeholder', this.defaultName);
+  this.$titleShield = iQ('.title-shield', this.$titlebar);
+  this.setTitle(options.title);
+
+  var handleKeyPress = function (e) {
+    if (e.keyCode == KeyEvent.DOM_VK_ESCAPE ||
+        e.keyCode == KeyEvent.DOM_VK_RETURN) {
+      (self.$title)[0].blur();
+      self.$title
+        .addClass("transparentBorder")
+        .one("mouseout", function() {
+          self.$title.removeClass("transparentBorder");
+        });
+      e.stopPropagation();
+      e.preventDefault();
+    }
+  };
+
+  var handleKeyUp = function(e) {
+    // NOTE: When user commits or cancels IME composition, the last key
+    //       event fires only a keyup event.  Then, we shouldn't take any
+    //       reactions but we should update our status.
+    self.save();
+  };
+
+  this.$title
+    .blur(function() {
+      self._titleFocused = false;
+      self.$title[0].setSelectionRange(0, 0);
+      self.$titleShield.show();
+      if (self.getTitle())
+        gTabView.firstUseExperienced = true;
+      self.save();
+    })
+    .focus(function() {
+      self._unfreezeItemSize();
+      if (!self._titleFocused) {
+        (self.$title)[0].select();
+        self._titleFocused = true;
+      }
+    })
+    .mousedown(function(e) {
+      e.stopPropagation();
+    })
+    .keypress(handleKeyPress)
+    .keyup(handleKeyUp)
+    .attr("title", tabviewString("groupItem.defaultName"));
+
+  this.$titleShield
+    .mousedown(function(e) {
+      self.lastMouseDownTarget = (Utils.isLeftClick(e) ? e.target : null);
+    })
+    .mouseup(function(e) {
+      var same = (e.target == self.lastMouseDownTarget);
+      self.lastMouseDownTarget = null;
+      if (!same)
+        return;
+
+      if (!self.isDragging)
+        self.focusTitle();
+    })
+    .attr("title", tabviewString("groupItem.defaultName"));
+
+  if (options.focusTitle)
+    this.focusTitle();
+
+  // ___ Stack Expander
+  this.$expander = iQ("<div/>")
+    .addClass("stackExpander")
+    .appendTo($container)
+    .hide();
+
+  // ___ app tabs: create app tab tray and populate it
+  let appTabTrayContainer = iQ("<div/>")
+    .addClass("appTabTrayContainer")
+    .appendTo($container);
+  this.$appTabTray = iQ("<div/>")
+    .addClass("appTabTray")
+    .appendTo(appTabTrayContainer);
+
+  let pinnedTabCount = gBrowser._numPinnedTabs;
+  AllTabs.tabs.forEach(function (xulTab, index) {
+    // only adjust tray when it's the last app tab.
+    if (xulTab.pinned)
+      this.addAppTab(xulTab, {dontAdjustTray: index + 1 < pinnedTabCount});
+  }, this);
+
+  // ___ Undo Close
+  this.$undoContainer = null;
+  this._undoButtonTimeoutId = null;
+
+  // ___ Superclass initialization
+  this._init($container[0]);
+
+  // ___ Children
+  // We explicitly set dontArrange=true to prevent the groupItem from
+  // re-arranging its children after a tabItem has been added. This saves us a
+  // group.arrange() call per child and therefore some tab.setBounds() calls.
+  options.dontArrange = true;
+  listOfEls.forEach(function (el) {
+    self.add(el, options);
+  });
+
+  // ___ Finish Up
+  this._addHandlers($container);
+
+  this.setResizable(true, immediately);
+
+  GroupItems.register(this);
+
+  // ___ Position
+  this.setBounds(rectToBe, immediately);
+  if (options.dontPush) {
+    this.setZ(drag.zIndex);
+    drag.zIndex++; 
+  } else {
+    // Calling snap will also trigger pushAway
+    this.snap(immediately);
+  }
+
+  if (!options.immediately && listOfEls.length > 0)
+    $container.hide().fadeIn();
+
+  this._inited = true;
+  this.save();
+
+  GroupItems.updateGroupCloseButtons();
+};
+
+// ----------
+GroupItem.prototype = Utils.extend(new Item(), new Subscribable(), {
+  // ----------
+  // Function: toString
+  // Prints [GroupItem id=id] for debug use
+  toString: function GroupItem_toString() {
+    return "[GroupItem id=" + this.id + "]";
+  },
+
+  // ----------
+  // Variable: defaultName
+  // The prompt text for the title field.
+  defaultName: tabviewString('groupItem.defaultName'),
+
+  // -----------
+  // Function: setActiveTab
+  // Sets the active <TabItem> for this groupItem; can be null, but only
+  // if there are no children.
+  setActiveTab: function GroupItem_setActiveTab(tab) {
+    Utils.assertThrow((!tab && this._children.length == 0) || tab.isATabItem,
+        "tab must be null (if no children) or a TabItem");
+
+    this._activeTab = tab;
+
+    if (this.isStacked())
+      this.arrange({immediately: true});
+  },
+
+  // -----------
+  // Function: getActiveTab
+  // Gets the active <TabItem> for this groupItem; can be null, but only
+  // if there are no children.
+  getActiveTab: function GroupItem_getActiveTab() {
+    return this._activeTab;
+  },
+
+  // ----------
+  // Function: getStorageData
+  // Returns all of the info worth storing about this groupItem.
+  getStorageData: function GroupItem_getStorageData() {
+    var data = {
+      bounds: this.getBounds(),
+      userSize: null,
+      title: this.getTitle(),
+      id: this.id
+    };
+
+    if (Utils.isPoint(this.userSize))
+      data.userSize = new Point(this.userSize);
+
+    return data;
+  },
+
+  // ----------
+  // Function: isEmpty
+  // Returns true if the tab groupItem is empty and unnamed.
+  isEmpty: function GroupItem_isEmpty() {
+    return !this._children.length && !this.getTitle();
+  },
+
+  // ----------
+  // Function: isStacked
+  // Returns true if this item is in a stacked groupItem.
+  isStacked: function GroupItem_isStacked() {
+    return this._isStacked;
+  },
+
+  // ----------
+  // Function: isTopOfStack
+  // Returns true if the item is showing on top of this group's stack,
+  // determined by whether the tab is this group's topChild, or
+  // if it doesn't have one, its first child.
+  isTopOfStack: function GroupItem_isTopOfStack(item) {
+    return this.isStacked() && item == this.getTopChild();
+  },
+
+  // ----------
+  // Function: save
+  // Saves this groupItem to persistent storage.
+  save: function GroupItem_save() {
+    if (!this._inited || this._uninited) // too soon/late to save
+      return;
+
+    var data = this.getStorageData();
+    if (GroupItems.groupItemStorageSanity(data))
+      Storage.saveGroupItem(gWindow, data);
+  },
+
+  // ----------
+  // Function: deleteData
+  // Deletes the groupItem in the persistent storage.
+  deleteData: function GroupItem_deleteData() {
+    this._uninited = true;
+    Storage.deleteGroupItem(gWindow, this.id);
+  },
+
+  // ----------
+  // Function: getTitle
+  // Returns the title of this groupItem as a string.
+  getTitle: function GroupItem_getTitle() {
+    return this.$title ? this.$title.val() : '';
+  },
+
+  // ----------
+  // Function: setTitle
+  // Sets the title of this groupItem with the given string
+  setTitle: function GroupItem_setTitle(value) {
+    this.$title.val(value);
+    this.save();
+  },
+
+  // ----------
+  // Function: focusTitle
+  // Hide the title's shield and focus the underlying input field.
+  focusTitle: function GroupItem_focusTitle() {
+    this.$titleShield.hide();
+    this.$title[0].focus();
+  },
+
+  // ----------
+  // Function: adjustAppTabTray
+  // Used to adjust the appTabTray size, to split the appTabIcons across
+  // multiple columns when needed - if the groupItem size is too small.
+  //
+  // Parameters:
+  //   arrangeGroup - rearrange the groupItem if the number of appTab columns
+  //   changes. If true, then this.arrange() is called, otherwise not.
+  adjustAppTabTray: function GroupItem_adjustAppTabTray(arrangeGroup) {
+    let icons = iQ(".appTabIcon", this.$appTabTray);
+    let container = iQ(this.$appTabTray[0].parentNode);
+    if (!icons.length) {
+      // There are no icons, so hide the appTabTray if needed.
+      if (parseInt(container.css("width")) != 0) {
+        this.$appTabTray.css("-moz-column-count", "auto");
+        this.$appTabTray.css("height", 0);
+        container.css("width", 0);
+        container.css("height", 0);
+
+        if (container.hasClass("appTabTrayContainerTruncated"))
+          container.removeClass("appTabTrayContainerTruncated");
+
+        if (arrangeGroup)
+          this.arrange();
+      }
+      return;
+    }
+
+    let iconBounds = iQ(icons[0]).bounds();
+    let boxBounds = this.getBounds();
+    let contentHeight = boxBounds.height -
+                        parseInt(container.css("top")) -
+                        this.$resizer.height();
+    let rows = Math.floor(contentHeight / iconBounds.height);
+    let columns = Math.ceil(icons.length / rows);
+    let columnsGap = parseInt(this.$appTabTray.css("-moz-column-gap"));
+    let iconWidth = iconBounds.width + columnsGap;
+    let maxColumns = Math.floor((boxBounds.width * 0.20) / iconWidth);
+
+    Utils.assert(rows > 0 && columns > 0 && maxColumns > 0,
+      "make sure the calculated rows, columns and maxColumns are correct");
+
+    if (columns > maxColumns)
+      container.addClass("appTabTrayContainerTruncated");
+    else if (container.hasClass("appTabTrayContainerTruncated"))
+      container.removeClass("appTabTrayContainerTruncated");
+
+    // Need to drop the -moz- prefix when Gecko makes it obsolete.
+    // See bug 629452.
+    if (parseInt(this.$appTabTray.css("-moz-column-count")) != columns)
+      this.$appTabTray.css("-moz-column-count", columns);
+
+    if (parseInt(this.$appTabTray.css("height")) != contentHeight) {
+      this.$appTabTray.css("height", contentHeight + "px");
+      container.css("height", contentHeight + "px");
+    }
+
+    let fullTrayWidth = iconWidth * columns - columnsGap;
+    if (parseInt(this.$appTabTray.css("width")) != fullTrayWidth)
+      this.$appTabTray.css("width", fullTrayWidth + "px");
+
+    let trayWidth = iconWidth * Math.min(columns, maxColumns) - columnsGap;
+    if (parseInt(container.css("width")) != trayWidth) {
+      container.css("width", trayWidth + "px");
+
+      // Rearrange the groupItem if the width changed.
+      if (arrangeGroup)
+        this.arrange();
+    }
+  },
+
+  // ----------
+  // Function: getContentBounds
+  // Returns a <Rect> for the groupItem's content area (which doesn't include the title, etc).
+  //
+  // Parameters:
+  //   options - an object with additional parameters, see below
+  //
+  // Possible options:
+  //   stacked - true to get content bounds for stacked mode
+  getContentBounds: function GroupItem_getContentBounds(options) {
+    let box = this.getBounds();
+    let titleHeight = this.$titlebar.height();
+    box.top += titleHeight;
+    box.height -= titleHeight;
+
+    let appTabTrayContainer = iQ(this.$appTabTray[0].parentNode);
+    let appTabTrayWidth = appTabTrayContainer.width();
+    if (appTabTrayWidth)
+      appTabTrayWidth += parseInt(appTabTrayContainer.css(UI.rtl ? "left" : "right"));
+
+    box.width -= appTabTrayWidth;
+    if (UI.rtl) {
+      box.left += appTabTrayWidth;
+    }
+
+    // Make the computed bounds' "padding" and expand button margin actually be
+    // themeable --OR-- compute this from actual bounds. Bug 586546
+    box.inset(6, 6);
+
+    // make some room for the expand button in stacked mode
+    if (options && options.stacked)
+      box.height -= this.$expander.height() + 9; // the button height plus padding
+
+    return box;
+  },
+
+  // ----------
+  // Function: setBounds
+  // Sets the bounds with the given <Rect>, animating unless "immediately" is false.
+  //
+  // Parameters:
+  //   inRect - a <Rect> giving the new bounds
+  //   immediately - true if it should not animate; default false
+  //   options - an object with additional parameters, see below
+  //
+  // Possible options:
+  //   force - true to always update the DOM even if the bounds haven't changed; default false
+  setBounds: function GroupItem_setBounds(inRect, immediately, options) {
+      Utils.assert(Utils.isRect(inRect), 'GroupItem.setBounds: rect is not a real rectangle!');
+
+    // Validate and conform passed in size
+    let validSize = GroupItems.calcValidSize(
+      new Point(inRect.width, inRect.height));
+    let rect = new Rect(inRect.left, inRect.top, validSize.x, validSize.y);
+
+    if (!options)
+      options = {};
+
+    var titleHeight = this.$titlebar.height();
+
+    // ___ Determine what has changed
+    var css = {};
+    var titlebarCSS = {};
+    var contentCSS = {};
+
+    if (rect.left != this.bounds.left || options.force)
+      css.left = rect.left;
+
+    if (rect.top != this.bounds.top || options.force)
+      css.top = rect.top;
+
+    if (rect.width != this.bounds.width || options.force) {
+      css.width = rect.width;
+      titlebarCSS.width = rect.width;
+      contentCSS.width = rect.width;
+    }
+
+    if (rect.height != this.bounds.height || options.force) {
+      css.height = rect.height;
+      contentCSS.height = rect.height - titleHeight;
+    }
+
+    if (Utils.isEmptyObject(css))
+      return;
+
+    var offset = new Point(rect.left - this.bounds.left, rect.top - this.bounds.top);
+    this.bounds = new Rect(rect);
+
+    // Make sure the AppTab icons fit the new groupItem size.
+    if (css.width || css.height)
+      this.adjustAppTabTray();
+
+    // ___ Deal with children
+    if (css.width || css.height) {
+      this.arrange({animate: !immediately}); //(immediately ? 'sometimes' : true)});
+    } else if (css.left || css.top) {
+      this._children.forEach(function(child) {
+        if (!child.getHidden()) {
+          var box = child.getBounds();
+          child.setPosition(box.left + offset.x, box.top + offset.y, immediately);
+        }
+      });
+    }
+
+    // ___ Update our representation
+    if (immediately) {
+      iQ(this.container).css(css);
+      this.$titlebar.css(titlebarCSS);
+    } else {
+      TabItems.pausePainting();
+      iQ(this.container).animate(css, {
+        duration: 350,
+        easing: "tabviewBounce",
+        complete: function() {
+          TabItems.resumePainting();
+        }
+      });
+
+      this.$titlebar.animate(titlebarCSS, {
+        duration: 350
+      });
+    }
+
+    UI.clearShouldResizeItems();
+    this.setTrenches(rect);
+    this.save();
+  },
+
+  // ----------
+  // Function: setZ
+  // Set the Z order for the groupItem's container, as well as its children.
+  setZ: function GroupItem_setZ(value) {
+    this.zIndex = value;
+
+    iQ(this.container).css({zIndex: value});
+
+    var count = this._children.length;
+    if (count) {
+      var topZIndex = value + count + 1;
+      var zIndex = topZIndex;
+      var self = this;
+      this._children.forEach(function(child) {
+        if (child == self.getTopChild())
+          child.setZ(topZIndex + 1);
+        else {
+          child.setZ(zIndex);
+          zIndex--;
+        }
+      });
+    }
+  },
+
+  // ----------
+  // Function: close
+  // Closes the groupItem, removing (but not closing) all of its children.
+  //
+  // Parameters:
+  //   options - An object with optional settings for this call.
+  //
+  // Options:
+  //   immediately - (bool) if true, no animation will be used
+  close: function GroupItem_close(options) {
+    this.removeAll({dontClose: true});
+    GroupItems.unregister(this);
+
+    // remove unfreeze event handlers, if item size is frozen
+    this._unfreezeItemSize({dontArrange: true});
+
+    let self = this;
+    let destroyGroup = function () {
+      iQ(self.container).remove();
+      if (self.$undoContainer) {
+        self.$undoContainer.remove();
+        self.$undoContainer = null;
+      }
+      self.removeTrenches();
+      Items.unsquish();
+      self._sendToSubscribers("close");
+      GroupItems.updateGroupCloseButtons();
+    }
+
+    if (this.hidden || (options && options.immediately)) {
+      destroyGroup();
+    } else {
+      iQ(this.container).animate({
+        opacity: 0,
+        "transform": "scale(.3)",
+      }, {
+        duration: 170,
+        complete: destroyGroup
+      });
+    }
+
+    this.deleteData();
+  },
+
+  // ----------
+  // Function: closeAll
+  // Closes the groupItem and all of its children.
+  closeAll: function GroupItem_closeAll() {
+    if (this._children.length > 0) {
+      this._unfreezeItemSize();
+      this._children.forEach(function(child) {
+        iQ(child.container).hide();
+      });
+
+      iQ(this.container).animate({
+         opacity: 0,
+         "transform": "scale(.3)",
+      }, {
+        duration: 170,
+        complete: function() {
+          iQ(this).hide();
+        }
+      });
+
+      this.droppable(false);
+      this.removeTrenches();
+      this._createUndoButton();
+    } else
+      this.close();
+
+    this._makeLastActiveGroupItemActive();
+  },
+  
+  // ----------
+  // Function: _makeClosestTabActive
+  // Make the closest tab external to this group active.
+  // Used when closing the group.
+  _makeClosestTabActive: function GroupItem__makeClosestTabActive() {
+    let closeCenter = this.getBounds().center();
+    // Find closest tab to make active
+    let closestTabItem = UI.getClosestTab(closeCenter);
+    if (closestTabItem)
+      UI.setActive(closestTabItem);
+  },
+
+  // ----------
+  // Function: _makeLastActiveGroupItemActive
+  // Makes the last active group item active.
+  _makeLastActiveGroupItemActive: function GroupItem__makeLastActiveGroupItemActive() {
+    let groupItem = GroupItems.getLastActiveGroupItem();
+    if (groupItem)
+      UI.setActive(groupItem);
+    else
+      this._makeClosestTabActive();
+  },
+
+  // ----------
+  // Function: closeIfEmpty
+  // Closes the group if it's empty, is closable, and autoclose is enabled
+  // (see pauseAutoclose()). Returns true if the close occurred and false
+  // otherwise.
+  closeIfEmpty: function GroupItem_closeIfEmpty() {
+    if (this.isEmpty() && !UI._closedLastVisibleTab &&
+        !GroupItems.getUnclosableGroupItemId() && !GroupItems._autoclosePaused) {
+      this.close();
+      return true;
+    }
+    return false;
+  },
+
+  // ----------
+  // Function: _unhide
+  // Shows the hidden group.
+  //
+  // Parameters:
+  //   options - various options (see below)
+  //
+  // Possible options:
+  //   immediately - true when no animations should be used
+  _unhide: function GroupItem__unhide(options) {
+    this._cancelFadeAwayUndoButtonTimer();
+    this.hidden = false;
+    this.$undoContainer.remove();
+    this.$undoContainer = null;
+    this.droppable(true);
+    this.setTrenches(this.bounds);
+
+    let self = this;
+
+    let finalize = function () {
+      self._children.forEach(function(child) {
+        iQ(child.container).show();
+      });
+
+      UI.setActive(self);
+      self._sendToSubscribers("groupShown");
+    };
+
+    let $container = iQ(this.container).show();
+
+    if (!options || !options.immediately) {
+      $container.animate({
+        "transform": "scale(1)",
+        "opacity": 1
+      }, {
+        duration: 170,
+        complete: finalize
+      });
+    } else {
+      $container.css({"transform": "none", opacity: 1});
+      finalize();
+    }
+
+    GroupItems.updateGroupCloseButtons();
+  },
+
+  // ----------
+  // Function: closeHidden
+  // Removes the group item, its children and its container.
+  closeHidden: function GroupItem_closeHidden() {
+    let self = this;
+
+    this._cancelFadeAwayUndoButtonTimer();
+
+    // When the last non-empty groupItem is closed and there are no
+    // pinned tabs then create a new group with a blank tab.
+    let remainingGroups = GroupItems.groupItems.filter(function (groupItem) {
+      return (groupItem != self && groupItem.getChildren().length);
+    });
+
+    let tab = null;
+
+    if (!gBrowser._numPinnedTabs && !remainingGroups.length) {
+      let emptyGroups = GroupItems.groupItems.filter(function (groupItem) {
+        return (groupItem != self && !groupItem.getChildren().length);
+      });
+      let group = (emptyGroups.length ? emptyGroups[0] : GroupItems.newGroup());
+      tab = group.newTab(null, {dontZoomIn: true});
+    }
+
+    let closed = this.destroy();
+
+    if (!tab)
+      return;
+
+    if (closed) {
+      // Let's make the new tab the selected tab.
+      UI.goToTab(tab);
+    } else {
+      // Remove the new tab and group, if this group is no longer closed.
+      tab._tabViewTabItem.parent.destroy({immediately: true});
+    }
+  },
+
+  // ----------
+  // Function: destroy
+  // Close all tabs linked to children (tabItems), removes all children and 
+  // close the groupItem.
+  //
+  // Parameters:
+  //   options - An object with optional settings for this call.
+  //
+  // Options:
+  //   immediately - (bool) if true, no animation will be used
+  //
+  // Returns true if the groupItem has been closed, or false otherwise. A group
+  // could not have been closed due to a tab with an onUnload handler (that
+  // waits for user interaction).
+  destroy: function GroupItem_destroy(options) {
+    let self = this;
+
+    // when "TabClose" event is fired, the browser tab is about to close and our 
+    // item "close" event is fired.  And then, the browser tab gets closed. 
+    // In other words, the group "close" event is fired before all browser
+    // tabs in the group are closed.  The below code would fire the group "close"
+    // event only after all browser tabs in that group are closed.
+    this._children.concat().forEach(function(child) {
+      child.removeSubscriber("close", self._onChildClose);
+
+      if (child.close(true)) {
+        self.remove(child, { dontArrange: true });
+      } else {
+        // child.removeSubscriber() must be called before child.close(), 
+        // therefore we call child.addSubscriber() if the tab is not removed.
+        child.addSubscriber("close", self._onChildClose);
+      }
+    });
+
+    if (this._children.length) {
+      if (this.hidden)
+        this.$undoContainer.fadeOut(function() { self._unhide() });
+
+      return false;
+    } else {
+      this.close(options);
+      return true;
+    }
+  },
+
+  // ----------
+  // Function: _fadeAwayUndoButton
+  // Fades away the undo button
+  _fadeAwayUndoButton: function GroupItem__fadeAwayUndoButton() {
+    let self = this;
+
+    if (this.$undoContainer) {
+      // if there is more than one group and other groups are not empty,
+      // fade away the undo button.
+      let shouldFadeAway = false;
+
+      if (GroupItems.groupItems.length > 1) {
+        shouldFadeAway = 
+          GroupItems.groupItems.some(function(groupItem) {
+            return (groupItem != self && groupItem.getChildren().length > 0);
+          });
+      }
+
+      if (shouldFadeAway) {
+        self.$undoContainer.animate({
+          color: "transparent",
+          opacity: 0
+        }, {
+          duration: this._fadeAwayUndoButtonDuration,
+          complete: function() { self.closeHidden(); }
+        });
+      }
+    }
+  },
+
+  // ----------
+  // Function: _createUndoButton
+  // Makes the affordance for undo a close group action
+  _createUndoButton: function GroupItem__createUndoButton() {
+    let self = this;
+    this.$undoContainer = iQ("<div/>")
+      .addClass("undo")
+      .attr("type", "button")
+      .attr("data-group-id", this.id)
+      .appendTo("body");
+    iQ("<span/>")
+      .text(tabviewString("groupItem.undoCloseGroup"))
+      .appendTo(this.$undoContainer);
+    let undoClose = iQ("<span/>")
+      .addClass("close")
+      .attr("title", tabviewString("groupItem.discardClosedGroup"))
+      .appendTo(this.$undoContainer);
+
+    this.$undoContainer.css({
+      left: this.bounds.left + this.bounds.width/2 - iQ(self.$undoContainer).width()/2,
+      top:  this.bounds.top + this.bounds.height/2 - iQ(self.$undoContainer).height()/2,
+      "transform": "scale(.1)",
+      opacity: 0
+    });
+    this.hidden = true;
+
+    // hide group item and show undo container.
+    setTimeout(function() {
+      self.$undoContainer.animate({
+        "transform": "scale(1)",
+        "opacity": 1
+      }, {
+        easing: "tabviewBounce",
+        duration: 170,
+        complete: function() {
+          self._sendToSubscribers("groupHidden");
+        }
+      });
+    }, 50);
+
+    // add click handlers
+    this.$undoContainer.click(function(e) {
+      // don't do anything if the close button is clicked.
+      if (e.target == undoClose[0])
+        return;
+
+      self.$undoContainer.fadeOut(function() { self._unhide(); });
+    });
+
+    undoClose.click(function() {
+      self.$undoContainer.fadeOut(function() { self.closeHidden(); });
+    });
+
+    this.setupFadeAwayUndoButtonTimer();
+    // Cancel the fadeaway if you move the mouse over the undo
+    // button, and restart the countdown once you move out of it.
+    this.$undoContainer.mouseover(function() { 
+      self._cancelFadeAwayUndoButtonTimer();
+    });
+    this.$undoContainer.mouseout(function() {
+      self.setupFadeAwayUndoButtonTimer();
+    });
+
+    GroupItems.updateGroupCloseButtons();
+  },
+
+  // ----------
+  // Sets up fade away undo button timeout. 
+  setupFadeAwayUndoButtonTimer: function GroupItem_setupFadeAwayUndoButtonTimer() {
+    let self = this;
+
+    if (!this._undoButtonTimeoutId) {
+      this._undoButtonTimeoutId = setTimeout(function() { 
+        self._fadeAwayUndoButton(); 
+      }, this.fadeAwayUndoButtonDelay);
+    }
+  },
+  
+  // ----------
+  // Cancels the fade away undo button timeout. 
+  _cancelFadeAwayUndoButtonTimer: function GroupItem__cancelFadeAwayUndoButtonTimer() {
+    clearTimeout(this._undoButtonTimeoutId);
+    this._undoButtonTimeoutId = null;
+  }, 
+
+  // ----------
+  // Function: add
+  // Adds an item to the groupItem.
+  // Parameters:
+  //
+  //   a - The item to add. Can be an <Item>, a DOM element or an iQ object.
+  //       The latter two must refer to the container of an <Item>.
+  //   options - An object with optional settings for this call.
+  //
+  // Options:
+  //
+  //   index - (int) if set, add this tab at this index
+  //   immediately - (bool) if true, no animation will be used
+  //   dontArrange - (bool) if true, will not trigger an arrange on the group
+  add: function GroupItem_add(a, options) {
+    try {
+      var item;
+      var $el;
+      if (a.isAnItem) {
+        item = a;
+        $el = iQ(a.container);
+      } else {
+        $el = iQ(a);
+        item = Items.item($el);
+      }
+
+      // safeguard to remove the item from its previous group
+      if (item.parent && item.parent !== this)
+        item.parent.remove(item);
+
+      item.removeTrenches();
+
+      if (!options)
+        options = {};
+
+      var self = this;
+
+      var wasAlreadyInThisGroupItem = false;
+      var oldIndex = this._children.indexOf(item);
+      if (oldIndex != -1) {
+        this._children.splice(oldIndex, 1);
+        wasAlreadyInThisGroupItem = true;
+      }
+
+      // Insert the tab into the right position.
+      var index = ("index" in options) ? options.index : this._children.length;
+      this._children.splice(index, 0, item);
+
+      item.setZ(this.getZ() + 1);
+
+      if (!wasAlreadyInThisGroupItem) {
+        item.droppable(false);
+        item.groupItemData = {};
+
+        item.addSubscriber("close", this._onChildClose);
+        item.setParent(this);
+        $el.attr("data-group-id", this.id);
+
+        if (typeof item.setResizable == 'function')
+          item.setResizable(false, options.immediately);
+
+        if (item == UI.getActiveTab() || !this._activeTab)
+          this.setActiveTab(item);
+
+        // if it matches the selected tab or no active tab and the browser
+        // tab is hidden, the active group item would be set.
+        if (item.tab.selected ||
+            (!GroupItems.getActiveGroupItem() && !item.tab.hidden))
+          UI.setActive(this);
+      }
+
+      if (!options.dontArrange)
+        this.arrange({animate: !options.immediately});
+
+      this._unfreezeItemSize({dontArrange: true});
+      this._sendToSubscribers("childAdded", { item: item });
+
+      UI.setReorderTabsOnHide(this);
+    } catch(e) {
+      Utils.log('GroupItem.add error', e);
+    }
+  },
+
+  // ----------
+  // Function: _onChildClose
+  // Handles "close" events from the group's children.
+  //
+  // Parameters:
+  //   tabItem - The tabItem that is closed.
+  _onChildClose: function GroupItem__onChildClose(tabItem) {
+    let count = this._children.length;
+    let dontArrange = tabItem.closedManually &&
+                      (this.expanded || !this.shouldStack(count));
+    let dontClose = !tabItem.closedManually && gBrowser._numPinnedTabs > 0;
+    this.remove(tabItem, {dontArrange: dontArrange, dontClose: dontClose});
+
+    if (dontArrange)
+      this._freezeItemSize(count);
+
+    if (this._children.length > 0 && this._activeTab && tabItem.closedManually)
+      UI.setActive(this);
+  },
+
+  // ----------
+  // Function: remove
+  // Removes an item from the groupItem.
+  // Parameters:
+  //
+  //   a - The item to remove. Can be an <Item>, a DOM element or an iQ object.
+  //       The latter two must refer to the container of an <Item>.
+  //   options - An optional object with settings for this call. See below.
+  //
+  // Possible options: 
+  //   dontArrange - don't rearrange the remaining items
+  //   dontClose - don't close the group even if it normally would
+  //   immediately - don't animate
+  remove: function GroupItem_remove(a, options) {
+    try {
+      let $el;
+      let item;
+
+      if (a.isAnItem) {
+        item = a;
+        $el = iQ(item.container);
+      } else {
+        $el = iQ(a);
+        item = Items.item($el);
+      }
+
+      if (!options)
+        options = {};
+
+      let index = this._children.indexOf(item);
+      if (index != -1)
+        this._children.splice(index, 1);
+
+      if (item == this._activeTab || !this._activeTab) {
+        if (this._children.length > 0)
+          this._activeTab = this._children[0];
+        else
+          this._activeTab = null;
+      }
+
+      $el[0].removeAttribute("data-group-id");
+      item.setParent(null);
+      item.removeClass("stacked");
+      item.isStacked = false;
+      item.setHidden(false);
+      item.removeClass("stack-trayed");
+      item.setRotation(0);
+
+      // Force tabItem resize if it's dragged out of a stacked groupItem.
+      // The tabItems's title will be visible and that's why we need to
+      // recalculate its height.
+      if (item.isDragging && this.isStacked())
+        item.setBounds(item.getBounds(), true, {force: true});
+
+      item.droppable(true);
+      item.removeSubscriber("close", this._onChildClose);
+
+      if (typeof item.setResizable == 'function')
+        item.setResizable(true, options.immediately);
+
+      // if a blank tab is selected while restoring a tab the blank tab gets
+      // removed. we need to keep the group alive for the restored tab.
+      if (item.isRemovedAfterRestore)
+        options.dontClose = true;
+
+      let closed = options.dontClose ? false : this.closeIfEmpty();
+      if (closed ||
+          (this._children.length == 0 && !gBrowser._numPinnedTabs &&
+           !item.isDragging)) {
+        this._makeLastActiveGroupItemActive();
+      } else if (!options.dontArrange) {
+        this.arrange({animate: !options.immediately});
+        this._unfreezeItemSize({dontArrange: true});
+      }
+
+      this._sendToSubscribers("childRemoved", { item: item });
+    } catch(e) {
+      Utils.log(e);
+    }
+  },
+
+  // ----------
+  // Function: removeAll
+  // Removes all of the groupItem's children.
+  // The optional "options" param is passed to each remove call. 
+  removeAll: function GroupItem_removeAll(options) {
+    let self = this;
+    let newOptions = {dontArrange: true};
+    if (options)
+      Utils.extend(newOptions, options);
+      
+    let toRemove = this._children.concat();
+    toRemove.forEach(function(child) {
+      self.remove(child, newOptions);
+    });
+  },
+
+  // ----------
+  // Adds the given xul:tab as an app tab in this group's apptab tray
+  //
+  // Parameters:
+  //   xulTab - the xul:tab.
+  //   options - change how the app tab is added.
+  //
+  // Options:
+  //   position - the position of the app tab should be added to.
+  //   dontAdjustTray - (boolean) if true, do not adjust the tray.
+  addAppTab: function GroupItem_addAppTab(xulTab, options) {
+    GroupItems.getAppTabFavIconUrl(xulTab, function(iconUrl) {
+      // The tab might have been removed or unpinned while waiting.
+      if (!Utils.isValidXULTab(xulTab) || !xulTab.pinned)
+        return;
+
+      let self = this;
+      let $appTab = iQ("<img>")
+        .addClass("appTabIcon")
+        .attr("src", iconUrl)
+        .data("xulTab", xulTab)
+        .mousedown(function GroupItem_addAppTab_onAppTabMousedown(event) {
+          // stop mousedown propagation to disable group dragging on app tabs
+          event.stopPropagation();
+        })
+        .click(function GroupItem_addAppTab_onAppTabClick(event) {
+          if (!Utils.isLeftClick(event))
+            return;
+
+          UI.setActive(self, { dontSetActiveTabInGroup: true });
+          UI.goToTab(iQ(this).data("xulTab"));
+        });
+
+      if (options && "position" in options) {
+        let children = this.$appTabTray[0].childNodes;
+
+        if (options.position >= children.length)
+          $appTab.appendTo(this.$appTabTray);
+        else
+          this.$appTabTray[0].insertBefore($appTab[0], children[options.position]);
+      } else {
+        $appTab.appendTo(this.$appTabTray);
+      }
+      if (!options || !options.dontAdjustTray)
+        this.adjustAppTabTray(true);
+
+      this._sendToSubscribers("appTabIconAdded", { item: $appTab });
+    }.bind(this));
+  },
+
+  // ----------
+  // Removes the given xul:tab as an app tab in this group's apptab tray
+  removeAppTab: function GroupItem_removeAppTab(xulTab) {
+    // remove the icon
+    iQ(".appTabIcon", this.$appTabTray).each(function(icon) {
+      let $icon = iQ(icon);
+      if ($icon.data("xulTab") != xulTab)
+        return true;
+        
+      $icon.remove();
+      return false;
+    });
+    
+    // adjust the tray
+    this.adjustAppTabTray(true);
+  },
+
+  // ----------
+  // Arranges the given xul:tab as an app tab in the group's apptab tray
+  arrangeAppTab: function GroupItem_arrangeAppTab(xulTab) {
+    let self = this;
+
+    let elements = iQ(".appTabIcon", this.$appTabTray);
+    let length = elements.length;
+
+    elements.each(function(icon) {
+      let $icon = iQ(icon);
+      if ($icon.data("xulTab") != xulTab)
+        return true;
+
+      let targetIndex = xulTab._tPos;
+
+      $icon.remove({ preserveEventHandlers: true });
+      if (targetIndex < (length - 1))
+        self.$appTabTray[0].insertBefore(
+          icon,
+          iQ(".appTabIcon:nth-child(" + (targetIndex + 1) + ")", self.$appTabTray)[0]);
+      else
+        $icon.appendTo(self.$appTabTray);
+      return false;
+    });
+  },
+
+  // ----------
+  // Function: hideExpandControl
+  // Hide the control which expands a stacked groupItem into a quick-look view.
+  hideExpandControl: function GroupItem_hideExpandControl() {
+    this.$expander.hide();
+  },
+
+  // ----------
+  // Function: showExpandControl
+  // Show the control which expands a stacked groupItem into a quick-look view.
+  showExpandControl: function GroupItem_showExpandControl() {
+    let parentBB = this.getBounds();
+    let childBB = this.getChild(0).getBounds();
+    this.$expander
+        .show()
+        .css({
+          left: parentBB.width/2 - this.$expander.width()/2
+        });
+  },
+
+  // ----------
+  // Function: shouldStack
+  // Returns true if the groupItem, given "count", should stack (instead of 
+  // grid).
+  shouldStack: function GroupItem_shouldStack(count) {
+    let bb = this.getContentBounds();
+    let options = {
+      return: 'widthAndColumns',
+      count: count || this._children.length,
+      hideTitle: false
+    };
+    let arrObj = Items.arrange(this._children, bb, options);
+
+    let shouldStack = arrObj.childWidth < TabItems.minTabWidth * 1.35;
+    this._columns = shouldStack ? null : arrObj.columns;
+
+    return shouldStack;
+  },
+
+  // ----------
+  // Function: _freezeItemSize
+  // Freezes current item size (when removing a child).
+  //
+  // Parameters:
+  //   itemCount - the number of children before the last one was removed
+  _freezeItemSize: function GroupItem__freezeItemSize(itemCount) {
+    let data = this._frozenItemSizeData;
+
+    if (!data.lastItemCount) {
+      let self = this;
+      data.lastItemCount = itemCount;
+
+      // unfreeze item size when tabview is hidden
+      data.onTabViewHidden = function () self._unfreezeItemSize();
+      window.addEventListener('tabviewhidden', data.onTabViewHidden, false);
+
+      // we don't need to observe mouse movement when expanded because the
+      // tray is closed when we leave it and collapse causes unfreezing
+      if (!self.expanded) {
+        // unfreeze item size when cursor is moved out of group bounds
+        data.onMouseMove = function (e) {
+          let cursor = new Point(e.pageX, e.pageY);
+          if (!self.bounds.contains(cursor))
+            self._unfreezeItemSize();
+        }
+        iQ(window).mousemove(data.onMouseMove);
+      }
+    }
+
+    this.arrange({animate: true, count: data.lastItemCount});
+  },
+
+  // ----------
+  // Function: _unfreezeItemSize
+  // Unfreezes and updates item size.
+  //
+  // Parameters:
+  //   options - various options (see below)
+  //
+  // Possible options:
+  //   dontArrange - do not arrange items when unfreezing
+  _unfreezeItemSize: function GroupItem__unfreezeItemSize(options) {
+    let data = this._frozenItemSizeData;
+    if (!data.lastItemCount)
+      return;
+
+    if (!options || !options.dontArrange)
+      this.arrange({animate: true});
+
+    // unbind event listeners
+    window.removeEventListener('tabviewhidden', data.onTabViewHidden, false);
+    if (data.onMouseMove)
+      iQ(window).unbind('mousemove', data.onMouseMove);
+
+    // reset freeze status
+    this._frozenItemSizeData = {};
+  },
+
+  // ----------
+  // Function: arrange
+  // Lays out all of the children.
+  //
+  // Parameters:
+  //   options - passed to <Items.arrange> or <_stackArrange>, except those below
+  //
+  // Options:
+  //   addTab - (boolean) if true, we add one to the child count
+  //   oldDropIndex - if set, we will only set any bounds if the dropIndex has
+  //                  changed
+  //   dropPos - (<Point>) a position where a tab is currently positioned, above
+  //             this group.
+  //   animate - (boolean) if true, movement of children will be animated.
+  //
+  // Returns:
+  //   dropIndex - an index value for where an item would be dropped, if 
+  //               options.dropPos is given.
+  arrange: function GroupItem_arrange(options) {
+    if (!options)
+      options = {};
+
+    let childrenToArrange = [];
+    this._children.forEach(function(child) {
+      if (child.isDragging)
+        options.addTab = true;
+      else
+        childrenToArrange.push(child);
+    });
+
+    if (GroupItems._arrangePaused) {
+      GroupItems.pushArrange(this, options);
+      return false;
+    }
+
+    let shouldStack = this.shouldStack(childrenToArrange.length + (options.addTab ? 1 : 0));
+    let shouldStackArrange = (shouldStack && !this.expanded);
+    let box;
+
+    // if we should stack and we're not expanded
+    if (shouldStackArrange) {
+      this.showExpandControl();
+      box = this.getContentBounds({stacked: true});
+      this._stackArrange(childrenToArrange, box, options);
+      return false;
+    } else {
+      this.hideExpandControl();
+      box = this.getContentBounds();
+      // a dropIndex is returned
+      return this._gridArrange(childrenToArrange, box, options);
+    }
+  },
+
+  // ----------
+  // Function: _stackArrange
+  // Arranges the children in a stack.
+  //
+  // Parameters:
+  //   childrenToArrange - array of <TabItem> children
+  //   bb - <Rect> to arrange within
+  //   options - see below
+  //
+  // Possible "options" properties:
+  //   animate - whether to animate; default: true.
+  _stackArrange: function GroupItem__stackArrange(childrenToArrange, bb, options) {
+    if (!options)
+      options = {};
+    var animate = "animate" in options ? options.animate : true;
+
+    var count = childrenToArrange.length;
+    if (!count)
+      return;
+
+    let itemAspect = TabItems.tabHeight / TabItems.tabWidth;
+    let zIndex = this.getZ() + count + 1;
+    let maxRotation = 35; // degress
+    let scale = 0.7;
+    let newTabsPad = 10;
+    let bbAspect = bb.height / bb.width;
+    let numInPile = 6;
+    let angleDelta = 3.5; // degrees
+
+    // compute size of the entire stack, modulo rotation.
+    let size;
+    if (bbAspect > itemAspect) { // Tall, thin groupItem
+      size = TabItems.calcValidSize(new Point(bb.width * scale, -1),
+        {hideTitle:true});
+     } else { // Short, wide groupItem
+      size = TabItems.calcValidSize(new Point(-1, bb.height * scale),
+        {hideTitle:true});
+     }
+
+    // x is the left margin that the stack will have, within the content area (bb)
+    // y is the vertical margin
+    var x = (bb.width - size.x) / 2;
+    var y = Math.min(size.x, (bb.height - size.y) / 2);
+    var box = new Rect(bb.left + x, bb.top + y, size.x, size.y);
+
+    var self = this;
+    var children = [];
+
+    // ensure topChild is the first item in childrenToArrange
+    let topChild = this.getTopChild();
+    let topChildPos = childrenToArrange.indexOf(topChild);
+    if (topChildPos > 0) {
+      childrenToArrange.splice(topChildPos, 1);
+      childrenToArrange.unshift(topChild);
+    }
+
+    childrenToArrange.forEach(function GroupItem__stackArrange_order(child) {
+      // Children are still considered stacked even if they're hidden later.
+      child.addClass("stacked");
+      child.isStacked = true;
+      if (numInPile-- > 0) {
+        children.push(child);
+      } else {
+        child.setHidden(true);
+      }
+    });
+
+    self._isStacked = true;
+
+    let angleAccum = 0;
+    children.forEach(function GroupItem__stackArrange_apply(child, index) {
+      child.setZ(zIndex);
+      zIndex--;
+
+      // Force a recalculation of height because we've changed how the title
+      // is shown.
+      child.setBounds(box, !animate || child.getHidden(), {force:true});
+      child.setRotation((UI.rtl ? -1 : 1) * angleAccum);
+      child.setHidden(false);
+      angleAccum += angleDelta;
+    });
+  },
+  
+  // ----------
+  // Function: _gridArrange
+  // Arranges the children into a grid.
+  //
+  // Parameters:
+  //   childrenToArrange - array of <TabItem> children
+  //   box - <Rect> to arrange within
+  //   options - see below
+  //
+  // Possible "options" properties:
+  //   animate - whether to animate; default: true.
+  //   z - (int) a z-index to assign the children
+  //   columns - the number of columns to use in the layout, if known in advance
+  //
+  // Returns:
+  //   dropIndex - (int) the index at which a dragged item (if there is one) should be added
+  //               if it is dropped. Otherwise (boolean) false.
+  _gridArrange: function GroupItem__gridArrange(childrenToArrange, box, options) {
+    let arrangeOptions;
+    if (this.expanded) {
+      // if we're expanded, we actually want to use the expanded tray's bounds.
+      box = new Rect(this.expanded.bounds);
+      box.inset(8, 8);
+      arrangeOptions = Utils.extend({}, options, {z: 99999});
+    } else {
+      this._isStacked = false;
+      arrangeOptions = Utils.extend({}, options, {
+        columns: this._columns
+      });
+
+      childrenToArrange.forEach(function(child) {
+        child.removeClass("stacked");
+        child.isStacked = false;
+        child.setHidden(false);
+      });
+    }
+  
+    if (!childrenToArrange.length)
+      return false;
+
+    // Items.arrange will determine where/how the child items should be
+    // placed, but will *not* actually move them for us. This is our job.
+    let result = Items.arrange(childrenToArrange, box, arrangeOptions);
+    let {dropIndex, rects, columns} = result;
+    if ("oldDropIndex" in options && options.oldDropIndex === dropIndex)
+      return dropIndex;
+
+    this._columns = columns;
+    let index = 0;
+    let self = this;
+    childrenToArrange.forEach(function GroupItem_arrange_children_each(child, i) {
+      // If dropIndex spacing is active and this is a child after index,
+      // bump it up one so we actually use the correct rect
+      // (and skip one for the dropPos)
+      if (self._dropSpaceActive && index === dropIndex)
+        index++;
+      child.setBounds(rects[index], !options.animate);
+      child.setRotation(0);
+      if (arrangeOptions.z)
+        child.setZ(arrangeOptions.z);
+      index++;
+    });
+
+    return dropIndex;
+  },
+
+  expand: function GroupItem_expand() {
+    var self = this;
+    // ___ we're stacked, and command is held down so expand
+    UI.setActive(this.getTopChild());
+    
+    var startBounds = this.getChild(0).getBounds();
+    var $tray = iQ("<div>").css({
+      top: startBounds.top,
+      left: startBounds.left,
+      width: startBounds.width,
+      height: startBounds.height,
+      position: "absolute",
+      zIndex: 99998
+    }).appendTo("body");
+    $tray[0].id = "expandedTray";
+
+    var w = 180;
+    var h = w * (TabItems.tabHeight / TabItems.tabWidth) * 1.1;
+    var padding = 20;
+    var col = Math.ceil(Math.sqrt(this._children.length));
+    var row = Math.ceil(this._children.length/col);
+
+    var overlayWidth = Math.min(window.innerWidth - (padding * 2), w*col + padding*(col+1));
+    var overlayHeight = Math.min(window.innerHeight - (padding * 2), h*row + padding*(row+1));
+
+    var pos = {left: startBounds.left, top: startBounds.top};
+    pos.left -= overlayWidth / 3;
+    pos.top  -= overlayHeight / 3;
+
+    if (pos.top < 0)
+      pos.top = 20;
+    if (pos.left < 0)
+      pos.left = 20;
+    if (pos.top + overlayHeight > window.innerHeight)
+      pos.top = window.innerHeight - overlayHeight - 20;
+    if (pos.left + overlayWidth > window.innerWidth)
+      pos.left = window.innerWidth - overlayWidth - 20;
+
+    $tray
+      .animate({
+        width:  overlayWidth,
+        height: overlayHeight,
+        top: pos.top,
+        left: pos.left
+      }, {
+        duration: 200,
+        easing: "tabviewBounce",
+        complete: function GroupItem_expand_animate_complete() {
+          self._sendToSubscribers("expanded");
+        }
+      })
+      .addClass("overlay");
+
+    this._children.forEach(function(child) {
+      child.addClass("stack-trayed");
+      child.setHidden(false);
+    });
+
+    var $shield = iQ('<div>')
+      .addClass('shield')
+      .css({
+        zIndex: 99997
+      })
+      .appendTo('body')
+      .click(function() { // just in case
+        self.collapse();
+      });
+
+    // There is a race-condition here. If there is
+    // a mouse-move while the shield is coming up
+    // it will collapse, which we don't want. Thus,
+    // we wait a little bit before adding this event
+    // handler.
+    setTimeout(function() {
+      $shield.mouseover(function() {
+        self.collapse();
+      });
+    }, 200);
+
+    this.expanded = {
+      $tray: $tray,
+      $shield: $shield,
+      bounds: new Rect(pos.left, pos.top, overlayWidth, overlayHeight)
+    };
+
+    this.arrange();
+  },
+
+  // ----------
+  // Function: collapse
+  // Collapses the groupItem from the expanded "tray" mode.
+  collapse: function GroupItem_collapse() {
+    if (this.expanded) {
+      var z = this.getZ();
+      var box = this.getBounds();
+      let self = this;
+      this.expanded.$tray
+        .css({
+          zIndex: z + 1
+        })
+        .animate({
+          width:  box.width,
+          height: box.height,
+          top: box.top,
+          left: box.left,
+          opacity: 0
+        }, {
+          duration: 350,
+          easing: "tabviewBounce",
+          complete: function GroupItem_collapse_animate_complete() {
+            iQ(this).remove();
+            self._sendToSubscribers("collapsed");
+          }
+        });
+
+      this.expanded.$shield.remove();
+      this.expanded = null;
+
+      this._children.forEach(function(child) {
+        child.removeClass("stack-trayed");
+      });
+
+      this.arrange({z: z + 2});
+      this._unfreezeItemSize({dontArrange: true});
+    }
+  },
+
+  // ----------
+  // Function: _addHandlers
+  // Helper routine for the constructor; adds various event handlers to the container.
+  _addHandlers: function GroupItem__addHandlers(container) {
+    let self = this;
+    let lastMouseDownTarget;
+
+    container.mousedown(function(e) {
+      let target = e.target;
+      // only set the last mouse down target if it is a left click, not on the
+      // close button, not on the expand button, not on the title bar and its
+      // elements
+      if (Utils.isLeftClick(e) &&
+          self.$closeButton[0] != target &&
+          self.$titlebar[0] != target &&
+          self.$expander[0] != target &&
+          !self.$titlebar.contains(target) &&
+          !self.$appTabTray.contains(target)) {
+        lastMouseDownTarget = target;
+      } else {
+        lastMouseDownTarget = null;
+      }
+    });
+    container.mouseup(function(e) {
+      let same = (e.target == lastMouseDownTarget);
+      lastMouseDownTarget = null;
+
+      if (same && !self.isDragging) {
+        if (gBrowser.selectedTab.pinned &&
+            UI.getActiveTab() != self.getActiveTab() &&
+            self.getChildren().length > 0) {
+          UI.setActive(self, { dontSetActiveTabInGroup: true });
+          UI.goToTab(gBrowser.selectedTab);
+        } else {
+          let tabItem = self.getTopChild();
+          if (tabItem)
+            tabItem.zoomIn();
+          else
+            self.newTab();
+        }
+      }
+    });
+
+    let dropIndex = false;
+    let dropSpaceTimer = null;
+
+    // When the _dropSpaceActive flag is turned on on a group, and a tab is
+    // dragged on top, a space will open up.
+    this._dropSpaceActive = false;
+
+    this.dropOptions.over = function GroupItem_dropOptions_over(event) {
+      iQ(this.container).addClass("acceptsDrop");
+    };
+    this.dropOptions.move = function GroupItem_dropOptions_move(event) {
+      let oldDropIndex = dropIndex;
+      let dropPos = drag.info.item.getBounds().center();
+      let options = {dropPos: dropPos,
+                     addTab: self._dropSpaceActive && drag.info.item.parent != self,
+                     oldDropIndex: oldDropIndex};
+      let newDropIndex = self.arrange(options);
+      // If this is a new drop index, start a timer!
+      if (newDropIndex !== oldDropIndex) {
+        dropIndex = newDropIndex;
+        if (this._dropSpaceActive)
+          return;
+          
+        if (dropSpaceTimer) {
+          clearTimeout(dropSpaceTimer);
+          dropSpaceTimer = null;
+        }
+
+        dropSpaceTimer = setTimeout(function GroupItem_arrange_evaluateDropSpace() {
+          // Note that dropIndex's scope is GroupItem__addHandlers, but
+          // newDropIndex's scope is GroupItem_dropOptions_move. Thus,
+          // dropIndex may change with other movement events before we come
+          // back and check this. If it's still the same dropIndex, activate
+          // drop space display!
+          if (dropIndex === newDropIndex) {
+            self._dropSpaceActive = true;
+            dropIndex = self.arrange({dropPos: dropPos,
+                                      addTab: drag.info.item.parent != self,
+                                      animate: true});
+          }
+          dropSpaceTimer = null;
+        }, 250);
+      }
+    };
+    this.dropOptions.drop = function GroupItem_dropOptions_drop(event) {
+      iQ(this.container).removeClass("acceptsDrop");
+      let options = {};
+      if (this._dropSpaceActive)
+        this._dropSpaceActive = false;
+
+      if (dropSpaceTimer) {
+        clearTimeout(dropSpaceTimer);
+        dropSpaceTimer = null;
+        // If we drop this item before the timed rearrange was executed,
+        // we won't have an accurate dropIndex value. Get that now.
+        let dropPos = drag.info.item.getBounds().center();
+        dropIndex = self.arrange({dropPos: dropPos,
+                                  addTab: drag.info.item.parent != self,
+                                  animate: true});
+      }
+
+      if (dropIndex !== false)
+        options = {index: dropIndex};
+      this.add(drag.info.$el, options);
+      UI.setActive(this);
+      dropIndex = false;
+    };
+    this.dropOptions.out = function GroupItem_dropOptions_out(event) {
+      dropIndex = false;
+      if (this._dropSpaceActive)
+        this._dropSpaceActive = false;
+
+      if (dropSpaceTimer) {
+        clearTimeout(dropSpaceTimer);
+        dropSpaceTimer = null;
+      }
+      self.arrange();
+      var groupItem = drag.info.item.parent;
+      if (groupItem)
+        groupItem.remove(drag.info.$el, {dontClose: true});
+      iQ(this.container).removeClass("acceptsDrop");
+    }
+
+    this.draggable();
+    this.droppable(true);
+
+    this.$expander.click(function() {
+      self.expand();
+    });
+  },
+
+  // ----------
+  // Function: setResizable
+  // Sets whether the groupItem is resizable and updates the UI accordingly.
+  setResizable: function GroupItem_setResizable(value, immediately) {
+    var self = this;
+
+    this.resizeOptions.minWidth = GroupItems.minGroupWidth;
+    this.resizeOptions.minHeight = GroupItems.minGroupHeight;
+
+    let start = this.resizeOptions.start;
+    this.resizeOptions.start = function (event) {
+      start.call(self, event);
+      self._unfreezeItemSize();
+    }
+
+    if (value) {
+      immediately ? this.$resizer.show() : this.$resizer.fadeIn();
+      this.resizable(true);
+    } else {
+      immediately ? this.$resizer.hide() : this.$resizer.fadeOut();
+      this.resizable(false);
+    }
+  },
+
+  // ----------
+  // Function: newTab
+  // Creates a new tab within this groupItem.
+  // Parameters:
+  //  url - the new tab should open this url as well
+  //  options - the options object
+  //    dontZoomIn - set to true to not zoom into the newly created tab
+  //    closedLastTab - boolean indicates the last tab has just been closed
+  newTab: function GroupItem_newTab(url, options) {
+    if (options && options.closedLastTab)
+      UI.closedLastTabInTabView = true;
+
+    UI.setActive(this, { dontSetActiveTabInGroup: true });
+
+    let dontZoomIn = !!(options && options.dontZoomIn);
+    return gBrowser.loadOneTab(url || gWindow.BROWSER_NEW_TAB_URL, { inBackground: dontZoomIn });
+  },
+
+  // ----------
+  // Function: reorderTabItemsBasedOnTabOrder
+  // Reorders the tabs in a groupItem based on the arrangment of the tabs
+  // shown in the tab bar. It does it by sorting the children
+  // of the groupItem by the positions of their respective tabs in the
+  // tab bar.
+  reorderTabItemsBasedOnTabOrder: function GroupItem_reorderTabItemsBasedOnTabOrder() {
+    this._children.sort(function(a,b) a.tab._tPos - b.tab._tPos);
+
+    this.arrange({animate: false});
+    // this.arrange calls this.save for us
+  },
+
+  // Function: reorderTabsBasedOnTabItemOrder
+  // Reorders the tabs in the tab bar based on the arrangment of the tabs
+  // shown in the groupItem.
+  reorderTabsBasedOnTabItemOrder: function GroupItem_reorderTabsBasedOnTabItemOrder() {
+    let indices;
+    let tabs = this._children.map(function (tabItem) tabItem.tab);
+
+    tabs.forEach(function (tab, index) {
+      if (!indices)
+        indices = tabs.map(function (tab) tab._tPos);
+
+      let start = index ? indices[index - 1] + 1 : 0;
+      let end = index + 1 < indices.length ? indices[index + 1] - 1 : Infinity;
+      let targetRange = new Range(start, end);
+
+      if (!targetRange.contains(tab._tPos)) {
+        gBrowser.moveTabTo(tab, start);
+        indices = null;
+      }
+    });
+  },
+
+  // ----------
+  // Function: getTopChild
+  // Gets the <Item> that should be displayed on top when in stack mode.
+  getTopChild: function GroupItem_getTopChild() {
+    if (!this.getChildren().length) {
+      return null;
+    }
+
+    return this.getActiveTab() || this.getChild(0);
+  },
+
+  // ----------
+  // Function: getChild
+  // Returns the nth child tab or null if index is out of range.
+  //
+  // Parameters:
+  //  index - the index of the child tab to return, use negative
+  //          numbers to index from the end (-1 is the last child)
+  getChild: function GroupItem_getChild(index) {
+    if (index < 0)
+      index = this._children.length + index;
+    if (index >= this._children.length || index < 0)
+      return null;
+    return this._children[index];
+  },
+
+  // ----------
+  // Function: getChildren
+  // Returns all children.
+  getChildren: function GroupItem_getChildren() {
+    return this._children;
+  }
+});
+
+// ##########
+// Class: GroupItems
+// Singleton for managing all <GroupItem>s.
+let GroupItems = {
+  groupItems: [],
+  nextID: 1,
+  _inited: false,
+  _activeGroupItem: null,
+  _cleanupFunctions: [],
+  _arrangePaused: false,
+  _arrangesPending: [],
+  _removingHiddenGroups: false,
+  _delayedModUpdates: [],
+  _autoclosePaused: false,
+  minGroupHeight: 110,
+  minGroupWidth: 125,
+  _lastActiveList: null,
+
+  // ----------
+  // Function: toString
+  // Prints [GroupItems] for debug use
+  toString: function GroupItems_toString() {
+    return "[GroupItems count=" + this.groupItems.length + "]";
+  },
+
+  // ----------
+  // Function: init
+  init: function GroupItems_init() {
+    let self = this;
+
+    // setup attr modified handler, and prepare for its uninit
+    function handleAttrModified(event) {
+      self._handleAttrModified(event.target);
+    }
+
+    // make sure any closed tabs are removed from the delay update list
+    function handleClose(event) {
+      let idx = self._delayedModUpdates.indexOf(event.target);
+      if (idx != -1)
+        self._delayedModUpdates.splice(idx, 1);
+    }
+
+    this._lastActiveList = new MRUList();
+
+    AllTabs.register("attrModified", handleAttrModified);
+    AllTabs.register("close", handleClose);
+    this._cleanupFunctions.push(function() {
+      AllTabs.unregister("attrModified", handleAttrModified);
+      AllTabs.unregister("close", handleClose);
+    });
+  },
+
+  // ----------
+  // Function: uninit
+  uninit: function GroupItems_uninit() {
+    // call our cleanup functions
+    this._cleanupFunctions.forEach(function(func) {
+      func();
+    });
+
+    this._cleanupFunctions = [];
+
+    // additional clean up
+    this.groupItems = null;
+  },
+
+  // ----------
+  // Function: newGroup
+  // Creates a new empty group.
+  newGroup: function GroupItems_newGroup() {
+    let bounds = new Rect(20, 20, 250, 200);
+    return new GroupItem([], {bounds: bounds, immediately: true});
+  },
+
+  // ----------
+  // Function: pauseArrange
+  // Bypass arrange() calls and collect for resolution in
+  // resumeArrange()
+  pauseArrange: function GroupItems_pauseArrange() {
+    Utils.assert(this._arrangePaused == false, 
+      "pauseArrange has been called while already paused");
+    Utils.assert(this._arrangesPending.length == 0, 
+      "There are bypassed arrange() calls that haven't been resolved");
+    this._arrangePaused = true;
+  },
+
+  // ----------
+  // Function: pushArrange
+  // Push an arrange() call and its arguments onto an array
+  // to be resolved in resumeArrange()
+  pushArrange: function GroupItems_pushArrange(groupItem, options) {
+    Utils.assert(this._arrangePaused, 
+      "Ensure pushArrange() called while arrange()s aren't paused"); 
+    let i;
+    for (i = 0; i < this._arrangesPending.length; i++)
+      if (this._arrangesPending[i].groupItem === groupItem)
+        break;
+    let arrangeInfo = {
+      groupItem: groupItem,
+      options: options
+    };
+    if (i < this._arrangesPending.length)
+      this._arrangesPending[i] = arrangeInfo;
+    else
+      this._arrangesPending.push(arrangeInfo);
+  },
+
+  // ----------
+  // Function: resumeArrange
+  // Resolve bypassed and collected arrange() calls
+  resumeArrange: function GroupItems_resumeArrange() {
+    this._arrangePaused = false;
+    for (let i = 0; i < this._arrangesPending.length; i++) {
+      let g = this._arrangesPending[i];
+      g.groupItem.arrange(g.options);
+    }
+    this._arrangesPending = [];
+  },
+
+  // ----------
+  // Function: _handleAttrModified
+  // watch for icon changes on app tabs
+  _handleAttrModified: function GroupItems__handleAttrModified(xulTab) {
+    if (!UI.isTabViewVisible()) {
+      if (this._delayedModUpdates.indexOf(xulTab) == -1) {
+        this._delayedModUpdates.push(xulTab);
+      }
+    } else
+      this._updateAppTabIcons(xulTab); 
+  },
+
+  // ----------
+  // Function: flushTabUpdates
+  // Update apptab icons based on xulTabs which have been updated
+  // while the TabView hasn't been visible 
+  flushAppTabUpdates: function GroupItems_flushAppTabUpdates() {
+    let self = this;
+    this._delayedModUpdates.forEach(function(xulTab) {
+      self._updateAppTabIcons(xulTab);
+    });
+    this._delayedModUpdates = [];
+  },
+
+  // ----------
+  // Function: _updateAppTabIcons
+  // Update images of any apptab icons that point to passed in xultab 
+  _updateAppTabIcons: function GroupItems__updateAppTabIcons(xulTab) {
+    if (!xulTab.pinned)
+      return;
+
+    this.getAppTabFavIconUrl(xulTab, function(iconUrl) {
+      iQ(".appTabIcon").each(function GroupItems__updateAppTabIcons_forEach(icon) {
+         let $icon = iQ(icon);
+         if ($icon.data("xulTab") == xulTab && iconUrl != $icon.attr("src"))
+           $icon.attr("src", iconUrl);
+      });
+    });
+  },
+
+  // ----------
+  // Function: getAppTabFavIconUrl
+  // Gets the fav icon url for app tab.
+  getAppTabFavIconUrl: function GroupItems_getAppTabFavIconUrl(xulTab, callback) {
+    FavIcons.getFavIconUrlForTab(xulTab, function GroupItems_getAppTabFavIconUrl_getFavIconUrlForTab(iconUrl) {
+      callback(iconUrl || FavIcons.defaultFavicon);
+    });
+  },
+
+  // ----------
+  // Function: addAppTab
+  // Adds the given xul:tab to the app tab tray in all groups
+  addAppTab: function GroupItems_addAppTab(xulTab) {
+    this.groupItems.forEach(function(groupItem) {
+      groupItem.addAppTab(xulTab);
+    });
+    this.updateGroupCloseButtons();
+  },
+
+  // ----------
+  // Function: removeAppTab
+  // Removes the given xul:tab from the app tab tray in all groups
+  removeAppTab: function GroupItems_removeAppTab(xulTab) {
+    this.groupItems.forEach(function(groupItem) {
+      groupItem.removeAppTab(xulTab);
+    });
+    this.updateGroupCloseButtons();
+  },
+
+  // ----------
+  // Function: arrangeAppTab
+  // Arranges the given xul:tab as an app tab from app tab tray in all groups
+  arrangeAppTab: function GroupItems_arrangeAppTab(xulTab) {
+    this.groupItems.forEach(function(groupItem) {
+      groupItem.arrangeAppTab(xulTab);
+    });
+  },
+
+  // ----------
+  // Function: getNextID
+  // Returns the next unused groupItem ID.
+  getNextID: function GroupItems_getNextID() {
+    var result = this.nextID;
+    this.nextID++;
+    this._save();
+    return result;
+  },
+
+  // ----------
+  // Function: saveAll
+  // Saves GroupItems state, as well as the state of all of the groupItems.
+  saveAll: function GroupItems_saveAll() {
+    this._save();
+    this.groupItems.forEach(function(groupItem) {
+      groupItem.save();
+    });
+  },
+
+  // ----------
+  // Function: _save
+  // Saves GroupItems state.
+  _save: function GroupItems__save() {
+    if (!this._inited) // too soon to save now
+      return;
+
+    let activeGroupId = this._activeGroupItem ? this._activeGroupItem.id : null;
+    Storage.saveGroupItemsData(
+      gWindow,
+      { nextID: this.nextID, activeGroupId: activeGroupId,
+        totalNumber: this.groupItems.length });
+  },
+
+  // ----------
+  // Function: getBoundingBox
+  // Given an array of DOM elements, returns a <Rect> with (roughly) the union of their locations.
+  getBoundingBox: function GroupItems_getBoundingBox(els) {
+    var bounds = [iQ(el).bounds() for each (el in els)];
+    var left   = Math.min.apply({},[ b.left   for each (b in bounds) ]);
+    var top    = Math.min.apply({},[ b.top    for each (b in bounds) ]);
+    var right  = Math.max.apply({},[ b.right  for each (b in bounds) ]);
+    var bottom = Math.max.apply({},[ b.bottom for each (b in bounds) ]);
+
+    return new Rect(left, top, right-left, bottom-top);
+  },
+
+  // ----------
+  // Function: reconstitute
+  // Restores to stored state, creating groupItems as needed.
+  reconstitute: function GroupItems_reconstitute(groupItemsData, groupItemData) {
+    try {
+      let activeGroupId;
+
+      if (groupItemsData) {
+        if (groupItemsData.nextID)
+          this.nextID = Math.max(this.nextID, groupItemsData.nextID);
+        if (groupItemsData.activeGroupId)
+          activeGroupId = groupItemsData.activeGroupId;
+      }
+
+      if (groupItemData) {
+        var toClose = this.groupItems.concat();
+        for (var id in groupItemData) {
+          let data = groupItemData[id];
+          if (this.groupItemStorageSanity(data)) {
+            let groupItem = this.groupItem(data.id); 
+            if (groupItem && !groupItem.hidden) {
+              groupItem.userSize = data.userSize;
+              groupItem.setTitle(data.title);
+              groupItem.setBounds(data.bounds, true);
+              
+              let index = toClose.indexOf(groupItem);
+              if (index != -1)
+                toClose.splice(index, 1);
+            } else {
+              var options = {
+                dontPush: true,
+                immediately: true
+              };
+  
+              new GroupItem([], Utils.extend({}, data, options));
+            }
+          }
+        }
+
+        toClose.forEach(function(groupItem) {
+          // all tabs still existing in closed groups will be moved to new
+          // groups. prepare them to be reconnected later.
+          groupItem.getChildren().forEach(function (tabItem) {
+            if (tabItem.parent.hidden)
+              iQ(tabItem.container).show();
+
+            tabItem._reconnected = false;
+
+            // sanity check the tab's groupID
+            let tabData = Storage.getTabData(tabItem.tab);
+
+            if (tabData) {
+              let parentGroup = GroupItems.groupItem(tabData.groupID);
+
+              // the tab's group id could be invalid or point to a non-existing
+              // group. correct it by assigning the active group id or the first
+              // group of the just restored session.
+              if (!parentGroup || -1 < toClose.indexOf(parentGroup)) {
+                tabData.groupID = activeGroupId || Object.keys(groupItemData)[0];
+                Storage.saveTab(tabItem.tab, tabData);
+              }
+            }
+          });
+
+          // this closes the group but not its children
+          groupItem.close({immediately: true});
+        });
+      }
+
+      // set active group item
+      if (activeGroupId) {
+        let activeGroupItem = this.groupItem(activeGroupId);
+        if (activeGroupItem)
+          UI.setActive(activeGroupItem);
+      }
+
+      this._inited = true;
+      this._save(); // for nextID
+    } catch(e) {
+      Utils.log("error in recons: "+e);
+    }
+  },
+
+  // ----------
+  // Function: load
+  // Loads the storage data for groups. 
+  // Returns true if there was global group data.
+  load: function GroupItems_load() {
+    let groupItemsData = Storage.readGroupItemsData(gWindow);
+    let groupItemData = Storage.readGroupItemData(gWindow);
+    this.reconstitute(groupItemsData, groupItemData);
+    
+    return (groupItemsData && !Utils.isEmptyObject(groupItemsData));
+  },
+
+  // ----------
+  // Function: groupItemStorageSanity
+  // Given persistent storage data for a groupItem, returns true if it appears to not be damaged.
+  groupItemStorageSanity: function GroupItems_groupItemStorageSanity(groupItemData) {
+    let sane = true;
+    if (!groupItemData.bounds || !Utils.isRect(groupItemData.bounds)) {
+      Utils.log('GroupItems.groupItemStorageSanity: bad bounds', groupItemData.bounds);
+      sane = false;
+    } else if ((groupItemData.userSize && 
+               !Utils.isPoint(groupItemData.userSize)) ||
+               !groupItemData.id) {
+      sane = false;
+    }
+
+    return sane;
+  },
+
+  // ----------
+  // Function: register
+  // Adds the given <GroupItem> to the list of groupItems we're tracking.
+  register: function GroupItems_register(groupItem) {
+    Utils.assert(groupItem, 'groupItem');
+    Utils.assert(this.groupItems.indexOf(groupItem) == -1, 'only register once per groupItem');
+    this.groupItems.push(groupItem);
+    UI.updateTabButton();
+  },
+
+  // ----------
+  // Function: unregister
+  // Removes the given <GroupItem> from the list of groupItems we're tracking.
+  unregister: function GroupItems_unregister(groupItem) {
+    var index = this.groupItems.indexOf(groupItem);
+    if (index != -1)
+      this.groupItems.splice(index, 1);
+
+    if (groupItem == this._activeGroupItem)
+      this._activeGroupItem = null;
+
+    this._arrangesPending = this._arrangesPending.filter(function (pending) {
+      return groupItem != pending.groupItem;
+    });
+
+    this._lastActiveList.remove(groupItem);
+    UI.updateTabButton();
+  },
+
+  // ----------
+  // Function: groupItem
+  // Given some sort of identifier, returns the appropriate groupItem.
+  // Currently only supports groupItem ids.
+  groupItem: function GroupItems_groupItem(a) {
+    if (!this.groupItems) {
+      // uninit has been called
+      return null;
+    }
+    var result = null;
+    this.groupItems.forEach(function(candidate) {
+      if (candidate.id == a)
+        result = candidate;
+    });
+
+    return result;
+  },
+
+  // ----------
+  // Function: removeAll
+  // Removes all tabs from all groupItems (which automatically closes all unnamed groupItems).
+  removeAll: function GroupItems_removeAll() {
+    var toRemove = this.groupItems.concat();
+    toRemove.forEach(function(groupItem) {
+      groupItem.removeAll();
+    });
+  },
+
+  // ----------
+  // Function: newTab
+  // Given a <TabItem>, files it in the appropriate groupItem.
+  newTab: function GroupItems_newTab(tabItem, options) {
+    let activeGroupItem = this.getActiveGroupItem();
+
+    // 1. Active group
+    // 2. First visible non-app tab (that's not the tab in question)
+    // 3. First group
+    // 4. At this point there should be no groups or tabs (except for app tabs and the
+    // tab in question): make a new group
+
+    if (activeGroupItem && !activeGroupItem.hidden) {
+      activeGroupItem.add(tabItem, options);
+      return;
+    }
+
+    let targetGroupItem;
+    // find first non-app visible tab belongs a group, and add the new tabItem
+    // to that group
+    gBrowser.visibleTabs.some(function(tab) {
+      if (!tab.pinned && tab != tabItem.tab) {
+        if (tab._tabViewTabItem && tab._tabViewTabItem.parent &&
+            !tab._tabViewTabItem.parent.hidden) {
+          targetGroupItem = tab._tabViewTabItem.parent;
+        }
+        return true;
+      }
+      return false;
+    });
+
+    let visibleGroupItems;
+    if (targetGroupItem) {
+      // add the new tabItem to the first group item
+      targetGroupItem.add(tabItem);
+      UI.setActive(targetGroupItem);
+      return;
+    } else {
+      // find the first visible group item
+      visibleGroupItems = this.groupItems.filter(function(groupItem) {
+        return (!groupItem.hidden);
+      });
+      if (visibleGroupItems.length > 0) {
+        visibleGroupItems[0].add(tabItem);
+        UI.setActive(visibleGroupItems[0]);
+        return;
+      }
+    }
+
+    // create new group for the new tabItem
+    tabItem.setPosition(60, 60, true);
+    let newGroupItemBounds = tabItem.getBounds();
+
+    newGroupItemBounds.inset(-40,-40);
+    let newGroupItem = new GroupItem([tabItem], { bounds: newGroupItemBounds });
+    newGroupItem.snap();
+    UI.setActive(newGroupItem);
+  },
+
+  // ----------
+  // Function: getActiveGroupItem
+  // Returns the active groupItem. Active means its tabs are
+  // shown in the tab bar when not in the TabView interface.
+  getActiveGroupItem: function GroupItems_getActiveGroupItem() {
+    return this._activeGroupItem;
+  },
+
+  // ----------
+  // Function: setActiveGroupItem
+  // Sets the active groupItem, thereby showing only the relevant tabs and
+  // setting the groupItem which will receive new tabs.
+  //
+  // Paramaters:
+  //  groupItem - the active <GroupItem>
+  setActiveGroupItem: function GroupItems_setActiveGroupItem(groupItem) {
+    Utils.assert(groupItem, "groupItem must be given");
+
+    if (this._activeGroupItem)
+      iQ(this._activeGroupItem.container).removeClass('activeGroupItem');
+
+    iQ(groupItem.container).addClass('activeGroupItem');
+
+    this._lastActiveList.update(groupItem);
+    this._activeGroupItem = groupItem;
+    this._save();
+  },
+
+  // ----------
+  // Function: getLastActiveGroupItem
+  // Gets last active group item.
+  // Returns the <groupItem>. If nothing is found, return null.
+  getLastActiveGroupItem: function GroupItem_getLastActiveGroupItem() {
+    return this._lastActiveList.peek(function(groupItem) {
+      return (groupItem && !groupItem.hidden && groupItem.getChildren().length > 0)
+    });
+  },
+
+  // ----------
+  // Function: _updateTabBar
+  // Hides and shows tabs in the tab bar based on the active groupItem
+  _updateTabBar: function GroupItems__updateTabBar() {
+    if (!window.UI)
+      return; // called too soon
+
+    Utils.assert(this._activeGroupItem, "There must be something to show in the tab bar!");
+
+    let tabItems = this._activeGroupItem._children;
+    gBrowser.showOnlyTheseTabs(tabItems.map(function(item) item.tab));
+  },
+
+  // ----------
+  // Function: updateActiveGroupItemAndTabBar
+  // Sets active TabItem and GroupItem, and updates tab bar appropriately.
+  // Parameters:
+  // tabItem - the tab item
+  // options - is passed to UI.setActive() directly
+  updateActiveGroupItemAndTabBar: 
+    function GroupItems_updateActiveGroupItemAndTabBar(tabItem, options) {
+    Utils.assertThrow(tabItem && tabItem.isATabItem, "tabItem must be a TabItem");
+
+    UI.setActive(tabItem, options);
+    this._updateTabBar();
+  },
+
+  // ----------
+  // Function: getNextGroupItemTab
+  // Paramaters:
+  //  reverse - the boolean indicates the direction to look for the next groupItem.
+  // Returns the <tabItem>. If nothing is found, return null.
+  getNextGroupItemTab: function GroupItems_getNextGroupItemTab(reverse) {
+    var groupItems = Utils.copy(GroupItems.groupItems);
+    var activeGroupItem = GroupItems.getActiveGroupItem();
+    var tabItem = null;
+
+    if (reverse)
+      groupItems = groupItems.reverse();
+
+    if (!activeGroupItem) {
+      if (groupItems.length > 0) {
+        groupItems.some(function(groupItem) {
+          if (!groupItem.hidden) {
+            // restore the last active tab in the group
+            let activeTab = groupItem.getActiveTab();
+            if (activeTab) {
+              tabItem = activeTab;
+              return true;
+            }
+            // if no tab is active, use the first one
+            var child = groupItem.getChild(0);
+            if (child) {
+              tabItem = child;
+              return true;
+            }
+          }
+          return false;
+        });
+      }
+    } else {
+      var currentIndex;
+      groupItems.some(function(groupItem, index) {
+        if (!groupItem.hidden && groupItem == activeGroupItem) {
+          currentIndex = index;
+          return true;
+        }
+        return false;
+      });
+      var firstGroupItems = groupItems.slice(currentIndex + 1);
+      firstGroupItems.some(function(groupItem) {
+        if (!groupItem.hidden) {
+          // restore the last active tab in the group
+          let activeTab = groupItem.getActiveTab();
+          if (activeTab) {
+            tabItem = activeTab;
+            return true;
+          }
+          // if no tab is active, use the first one
+          var child = groupItem.getChild(0);
+          if (child) {
+            tabItem = child;
+            return true;
+          }
+        }
+        return false;
+      });
+      if (!tabItem) {
+        var secondGroupItems = groupItems.slice(0, currentIndex);
+        secondGroupItems.some(function(groupItem) {
+          if (!groupItem.hidden) {
+            // restore the last active tab in the group
+            let activeTab = groupItem.getActiveTab();
+            if (activeTab) {
+              tabItem = activeTab;
+              return true;
+            }
+            // if no tab is active, use the first one
+            var child = groupItem.getChild(0);
+            if (child) {
+              tabItem = child;
+              return true;
+            }
+          }
+          return false;
+        });
+      }
+    }
+    return tabItem;
+  },
+
+  // ----------
+  // Function: moveTabToGroupItem
+  // Used for the right click menu in the tab strip; moves the given tab
+  // into the given group. Does nothing if the tab is an app tab.
+  // Paramaters:
+  //  tab - the <xul:tab>.
+  //  groupItemId - the <groupItem>'s id.  If nothing, create a new <groupItem>.
+  moveTabToGroupItem : function GroupItems_moveTabToGroupItem(tab, groupItemId) {
+    if (tab.pinned)
+      return;
+
+    Utils.assertThrow(tab._tabViewTabItem, "tab must be linked to a TabItem");
+
+    // given tab is already contained in target group
+    if (tab._tabViewTabItem.parent && tab._tabViewTabItem.parent.id == groupItemId)
+      return;
+
+    let shouldUpdateTabBar = false;
+    let shouldShowTabView = false;
+    let groupItem;
+
+    // switch to the appropriate tab first.
+    if (tab.selected) {
+      if (gBrowser.visibleTabs.length > 1) {
+        gBrowser._blurTab(tab);
+        shouldUpdateTabBar = true;
+      } else {
+        shouldShowTabView = true;
+      }
+    } else {
+      shouldUpdateTabBar = true
+    }
+
+    // remove tab item from a groupItem
+    if (tab._tabViewTabItem.parent)
+      tab._tabViewTabItem.parent.remove(tab._tabViewTabItem);
+
+    // add tab item to a groupItem
+    if (groupItemId) {
+      groupItem = GroupItems.groupItem(groupItemId);
+      groupItem.add(tab._tabViewTabItem);
+      groupItem.reorderTabsBasedOnTabItemOrder()
+    } else {
+      let pageBounds = Items.getPageBounds();
+      pageBounds.inset(20, 20);
+
+      let box = new Rect(pageBounds);
+      box.width = 250;
+      box.height = 200;
+
+      new GroupItem([ tab._tabViewTabItem ], { bounds: box, immediately: true });
+    }
+
+    if (shouldUpdateTabBar)
+      this._updateTabBar();
+    else if (shouldShowTabView)
+      UI.showTabView();
+  },
+
+  // ----------
+  // Function: removeHiddenGroups
+  // Removes all hidden groups' data and its browser tabs.
+  removeHiddenGroups: function GroupItems_removeHiddenGroups() {
+    if (this._removingHiddenGroups)
+      return;
+    this._removingHiddenGroups = true;
+
+    let groupItems = this.groupItems.concat();
+    groupItems.forEach(function(groupItem) {
+      if (groupItem.hidden)
+        groupItem.closeHidden();
+     });
+
+    this._removingHiddenGroups = false;
+  },
+
+  // ----------
+  // Function: getUnclosableGroupItemId
+  // If there's only one (non-hidden) group, and there are app tabs present, 
+  // returns that group.
+  // Return the <GroupItem>'s Id
+  getUnclosableGroupItemId: function GroupItems_getUnclosableGroupItemId() {
+    let unclosableGroupItemId = null;
+
+    if (gBrowser._numPinnedTabs > 0) {
+      let hiddenGroupItems = 
+        this.groupItems.concat().filter(function(groupItem) {
+          return !groupItem.hidden;
+        });
+      if (hiddenGroupItems.length == 1)
+        unclosableGroupItemId = hiddenGroupItems[0].id;
+    }
+
+    return unclosableGroupItemId;
+  },
+
+  // ----------
+  // Function: updateGroupCloseButtons
+  // Updates group close buttons.
+  updateGroupCloseButtons: function GroupItems_updateGroupCloseButtons() {
+    let unclosableGroupItemId = this.getUnclosableGroupItemId();
+
+    if (unclosableGroupItemId) {
+      let groupItem = this.groupItem(unclosableGroupItemId);
+
+      if (groupItem) {
+        groupItem.$closeButton.hide();
+      }
+    } else {
+      this.groupItems.forEach(function(groupItem) {
+        groupItem.$closeButton.show();
+      });
+    }
+  },
+  
+  // ----------
+  // Function: calcValidSize
+  // Basic measure rules. Assures that item is a minimum size.
+  calcValidSize: function GroupItems_calcValidSize(size, options) {
+    Utils.assert(Utils.isPoint(size), 'input is a Point');
+    Utils.assert((size.x>0 || size.y>0) && (size.x!=0 && size.y!=0), 
+      "dimensions are valid:"+size.x+","+size.y);
+    return new Point(
+      Math.max(size.x, GroupItems.minGroupWidth),
+      Math.max(size.y, GroupItems.minGroupHeight));
+  },
+
+  // ----------
+  // Function: pauseAutoclose()
+  // Temporarily disable the behavior that closes groups when they become
+  // empty. This is used when entering private browsing, to avoid trashing the
+  // user's groups while private browsing is shuffling things around.
+  pauseAutoclose: function GroupItems_pauseAutoclose() {
+    this._autoclosePaused = true;
+  },
+
+  // ----------
+  // Function: unpauseAutoclose()
+  // Re-enables the auto-close behavior.
+  resumeAutoclose: function GroupItems_resumeAutoclose() {
+    this._autoclosePaused = false;
+  }
+};