diff -r 000000000000 -r 6474c204b198 dom/base/IndexedDBHelper.jsm
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/dom/base/IndexedDBHelper.jsm	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,168 @@
+/* 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";
+
+let DEBUG = 0;
+let debug;
+if (DEBUG) {
+  debug = function (s) { dump("-*- IndexedDBHelper: " + s + "\n"); }
+} else {
+  debug = function (s) {}
+}
+
+const Cu = Components.utils;
+const Cc = Components.classes;
+const Ci = Components.interfaces;
+
+this.EXPORTED_SYMBOLS = ["IndexedDBHelper"];
+
+Cu.import("resource://gre/modules/XPCOMUtils.jsm");
+Cu.import("resource://gre/modules/Services.jsm");
+Cu.importGlobalProperties(["indexedDB"]);
+
+this.IndexedDBHelper = function IndexedDBHelper() {}
+
+IndexedDBHelper.prototype = {
+
+  // Cache the database
+  _db: null,
+
+  // Close the database
+  close: function close() {
+    if (this._db) {
+      this._db.close();
+      this._db = null;
+    }
+  },
+
+  /**
+   * Open a new database.
+   * User has to provide upgradeSchema.
+   *
+   * @param successCb
+   *        Success callback to call once database is open.
+   * @param failureCb
+   *        Error callback to call when an error is encountered.
+   */
+  open: function open(aSuccessCb, aFailureCb) {
+    let self = this;
+    if (DEBUG) debug("Try to open database:" + self.dbName + " " + self.dbVersion);
+    let req = indexedDB.open(this.dbName, this.dbVersion);
+    req.onsuccess = function (event) {
+      if (DEBUG) debug("Opened database:" + self.dbName + " " + self.dbVersion);
+      self._db = event.target.result;
+      self._db.onversionchange = function(event) {
+        if (DEBUG) debug("WARNING: DB modified from a different window.");
+      }
+      aSuccessCb && aSuccessCb();
+    };
+
+    req.onupgradeneeded = function (aEvent) {
+      if (DEBUG) {
+        debug("Database needs upgrade:" + self.dbName + aEvent.oldVersion + aEvent.newVersion);
+        debug("Correct new database version:" + (aEvent.newVersion == this.dbVersion));
+      }
+
+      let _db = aEvent.target.result;
+      self.upgradeSchema(req.transaction, _db, aEvent.oldVersion, aEvent.newVersion);
+    };
+    req.onerror = function (aEvent) {
+      if (DEBUG) debug("Failed to open database: " + self.dbName);
+      aFailureCb && aFailureCb(aEvent.target.error.name);
+    };
+    req.onblocked = function (aEvent) {
+      if (DEBUG) debug("Opening database request is blocked.");
+    };
+  },
+
+  /**
+   * Use the cached DB or open a new one.
+   *
+   * @param successCb
+   *        Success callback to call.
+   * @param failureCb
+   *        Error callback to call when an error is encountered.
+   */
+  ensureDB: function ensureDB(aSuccessCb, aFailureCb) {
+    if (this._db) {
+      if (DEBUG) debug("ensureDB: already have a database, returning early.");
+      aSuccessCb && aSuccessCb();
+      return;
+    }
+    this.open(aSuccessCb, aFailureCb);
+  },
+
+  /**
+   * Start a new transaction.
+   *
+   * @param txn_type
+   *        Type of transaction (e.g. "readwrite")
+   * @param store_name
+   *        The object store you want to be passed to the callback
+   * @param callback
+   *        Function to call when the transaction is available. It will
+   *        be invoked with the transaction and the `store' object store.
+   * @param successCb
+   *        Success callback to call on a successful transaction commit.
+   *        The result is stored in txn.result.
+   * @param failureCb
+   *        Error callback to call when an error is encountered.
+   */
+  newTxn: function newTxn(txn_type, store_name, callback, successCb, failureCb) {
+    this.ensureDB(function () {
+      if (DEBUG) debug("Starting new transaction" + txn_type);
+      let txn = this._db.transaction(Array.isArray(store_name) ? store_name : this.dbStoreNames, txn_type);
+      if (DEBUG) debug("Retrieving object store", this.dbName);
+      let stores;
+      if (Array.isArray(store_name)) {
+        stores = [];
+        for (let i = 0; i < store_name.length; ++i) {
+          stores.push(txn.objectStore(store_name[i]));
+        }
+      } else {
+        stores = txn.objectStore(store_name);
+      }
+
+      txn.oncomplete = function (event) {
+        if (DEBUG) debug("Transaction complete. Returning to callback.");
+        if (successCb) {
+          successCb(txn.result);
+        }
+      };
+
+      txn.onabort = function (event) {
+        if (DEBUG) debug("Caught error on transaction");
+        /*
+         * event.target.error may be null
+         * if txn was aborted by calling txn.abort()
+         */
+        if (failureCb) {
+          if (event.target.error) {
+            failureCb(event.target.error.name);
+          } else {
+            failureCb("UnknownError");
+          }
+        }
+      };
+      callback(txn, stores);
+    }.bind(this), failureCb);
+  },
+
+  /**
+   * Initialize the DB. Does not call open.
+   *
+   * @param aDBName
+   *        DB name for the open call.
+   * @param aDBVersion
+   *        Current DB version. User has to implement upgradeSchema.
+   * @param aDBStoreName
+   *        ObjectStore that is used.
+   */
+  initDBHelper: function initDBHelper(aDBName, aDBVersion, aDBStoreNames) {
+    this.dbName = aDBName;
+    this.dbVersion = aDBVersion;
+    this.dbStoreNames = aDBStoreNames;
+  }
+}