to make safe and
    // easy to implement "Undo" an unknown number of transactions (including 0),
    // "above" beginBatch and endBatch. Otherwise,implementing Undo that way
    // head to dataloss: for example, if no changes were done in the
    // edit-item panel, the last transaction on the undo stack would be the
    // initial createItem transaction, or even worse, the batched editing of
    // some other item.
    // DO NOT MOVE this to the window scope, that would leak (bug 490068)! 
    this.doTransaction({ doTransaction: function() { },
                         undoTransaction: function() { },
                         redoTransaction: function() { },
                         isTransient: false,
                         merge: function() { return false; } });
  },

  endBatch: function() this.mTransactionManager.endBatch(),

  doTransaction: function placesTxn_doTransaction(txn) {
    this.mTransactionManager.doTransaction(txn);
    this._updateCommands();
  },

  undoTransaction: function placesTxn_undoTransaction() {
    this.mTransactionManager.undoTransaction();
    this._updateCommands();
  },

  redoTransaction: function placesTxn_redoTransaction() {
    this.mTransactionManager.redoTransaction();
    this._updateCommands();
  },

  clear: function() this.mTransactionManager.clear(),

  get numberOfUndoItems() {
    return this.mTransactionManager.numberOfUndoItems;
  },

  get numberOfRedoItems() {
    return this.mTransactionManager.numberOfRedoItems;
  },

  get maxTransactionCount() {
    return this.mTransactionManager.maxTransactionCount;
  },
  set maxTransactionCount(val) {
    return this.mTransactionManager.maxTransactionCount = val;
  },

  peekUndoStack: function() this.mTransactionManager.peekUndoStack(),
  peekRedoStack: function() this.mTransactionManager.peekRedoStack(),
  getUndoStack: function() this.mTransactionManager.getUndoStack(),
  getRedoStack: function() this.mTransactionManager.getRedoStack(),
  AddListener: function(l) this.mTransactionManager.AddListener(l),
  RemoveListener: function(l) this.mTransactionManager.RemoveListener(l)
};

/**
 * Method and utility stubs for Places Edit Transactions
 */
function placesBaseTransaction() {
}

placesBaseTransaction.prototype = {
  // for child-transactions
  get wrappedJSObject() {
    return this;
  },

  // nsITransaction
  redoTransaction: function PBT_redoTransaction() {
    throw Cr.NS_ERROR_NOT_IMPLEMENTED;
  },

  get isTransient() {
    return false;
  },

  merge: function mergeFunc(transaction) {
    return false;
  },

  // nsISupports
  QueryInterface: XPCOMUtils.generateQI([Ci.nsITransaction]),
};

function placesAggregateTransactions(name, transactions) {
  this._transactions = transactions;
  this._name = name;
  this.container = -1;
  this.redoTransaction = this.doTransaction;

  // Check child transactions number.  We will batch if we have more than
  // MIN_TRANSACTIONS_FOR_BATCH total number of transactions.
  var countTransactions = function(aTransactions, aTxnCount) {
    for (let i = 0;
         i < aTransacti