new file mode 100644
--- /dev/null
+++ b/toolkit/modules/IndexedDB.jsm
@@ -0,0 +1,353 @@
+/* -*- Mode: indent-tabs-mode: nil; js-indent-level: 2 -*- */
+/* vim: set sts=2 sw=2 et tw=80: */
+/* 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";
+
+/**
+ * @file
+ *
+ * This module provides Promise-based wrappers around ordinarily
+ * IDBRequest-based IndexedDB methods and classes.
+ */
+
+/* exported IndexedDB */
+var EXPORTED_SYMBOLS = ["IndexedDB"];
+
+const {classes: Cc, interfaces: Ci, utils: Cu, results: Cr} = Components;
+
+Cu.importGlobalProperties(["indexedDB"]);
+
+/**
+ * Wraps the given request object, and returns a Promise which resolves when
+ * the requests succeeds or rejects when it fails.
+ *
+ * @param {IDBRequest} request
+ *        An IndexedDB request object to wrap.
+ * @returns {Promise}
+ */
+function wrapRequest(request) {
+  return new Promise((resolve, reject) => {
+    request.onsuccess = () => {
+      resolve(request.result);
+    };
+    request.onerror = () => {
+      reject(request.error);
+    };
+  });
+}
+
+/**
+ * Forwards a set of getter properties from a wrapper class to the wrapped
+ * object.
+ *
+ * @param {function} cls
+ *        The class constructor for which to forward the getters.
+ * @param {string} target
+ *        The name of the property which contains the wrapped object to which
+ *        to forward the getters.
+ * @param {Array<string>} props
+ *        A list of property names to forward.
+ */
+function forwardGetters(cls, target, props) {
+  for (let prop of props) {
+    Object.defineProperty(cls.prototype, prop, {
+      get() {
+        return this[target][prop];
+      },
+    });
+  }
+}
+
+/**
+ * Forwards a set of getter and setter properties from a wrapper class to the
+ * wrapped object.
+ *
+ * @param {function} cls
+ *        The class constructor for which to forward the properties.
+ * @param {string} target
+ *        The name of the property which contains the wrapped object to which
+ *        to forward the properties.
+ * @param {Array<string>} props
+ *        A list of property names to forward.
+ */
+function forwardProps(cls, target, props) {
+  for (let prop of props) {
+    Object.defineProperty(cls.prototype, prop, {
+      get() {
+        return this[target][prop];
+      },
+      set(value) {
+        this[target][prop] = value;
+      },
+    });
+  }
+}
+
+/**
+ * Wraps a set of IDBRequest-based methods via {@link wrapRequest} and
+ * forwards them to the equivalent methods on the wrapped object.
+ *
+ * @param {function} cls
+ *        The class constructor for which to forward the methods.
+ * @param {string} target
+ *        The name of the property which contains the wrapped object to which
+ *        to forward the methods.
+ * @param {Array<string>} methods
+ *        A list of method names to forward.
+ */
+function wrapMethods(cls, target, methods) {
+  for (let method of methods) {
+    cls.prototype[method] = function(...args) {
+      return wrapRequest(this[target][method](...args));
+    };
+  }
+}
+
+/**
+ * Forwards a set of methods from a wrapper class to the wrapped object.
+ *
+ * @param {function} cls
+ *        The class constructor for which to forward the getters.
+ * @param {string} target
+ *        The name of the property which contains the wrapped object to which
+ *        to forward the methods.
+ * @param {Array<string>} methods
+ *        A list of method names to forward.
+ */
+function forwardMethods(cls, target, methods) {
+  for (let method of methods) {
+    cls.prototype[method] = function(...args) {
+      return this[target][method](...args);
+    };
+  }
+}
+
+class Cursor {
+  constructor(cursor, source) {
+    this.cursor = cursor;
+    this.source = source;
+  }
+}
+
+forwardGetters(Cursor, "cursor",
+               ["direction", "key", "primaryKey"]);
+
+wrapMethods(Cursor, "cursor", ["delete", "update"]);
+
+forwardMethods(Cursor, "cursor",
+               ["advance", "continue", "continuePrimaryKey"]);
+
+class CursorWithValue extends Cursor {}
+
+forwardGetters(CursorWithValue, "cursor", ["value"]);
+
+class Cursed {
+  constructor(cursed) {
+    this.cursed = cursed;
+  }
+
+  openCursor(...args) {
+    return wrapRequest(this.cursed.openCursor(...args)).then(cursor => {
+      return new CursorWithValue(cursor, this);
+    });
+  }
+
+  openKeyCursor(...args) {
+    return wrapRequest(this.cursed.openKeyCursor(...args)).then(cursor => {
+      return new Cursor(cursor, this);
+    });
+  }
+}
+
+wrapMethods(Cursed, "cursed",
+            ["count", "get", "getAll", "getAllKeys", "getKey"]);
+
+class Index extends Cursed {
+  constructor(index, objectStore) {
+    super(index);
+
+    this.objectStore = objectStore;
+    this.index = index;
+  }
+}
+
+forwardGetters(Index, "index",
+               ["isAutoLocale", "keyPath", "locale", "multiEntry", "name", "unique"]);
+
+class ObjectStore extends Cursed {
+  constructor(store) {
+    super(store);
+
+    this.store = store;
+  }
+
+  createIndex(...args) {
+    return new Index(this.store.createIndex(...args),
+                     this);
+  }
+
+  index(...args) {
+    return new Index(this.store.index(...args),
+                     this);
+  }
+}
+
+wrapMethods(ObjectStore, "store",
+            ["add", "clear", "delete", "put"]);
+
+forwardMethods(ObjectStore, "store", ["deleteIndex"]);
+
+class Transaction {
+  constructor(transaction) {
+    this.transaction = transaction;
+
+    this._completionPromise = new Promise((resolve, reject) => {
+      transaction.oncomplete = resolve;
+      transaction.onerror = () => {
+        reject(transaction.error);
+      };
+    });
+  }
+
+  objectStore(name) {
+    return new ObjectStore(this.transaction.objectStore(name));
+  }
+
+  /**
+   * Returns a Promise which resolves when the transaction completes, or
+   * rejects when a transaction error occurs.
+   *
+   * @returns {Promise}
+   */
+  promiseComplete() {
+    return this._completionPromise;
+  }
+}
+
+forwardGetters(Transaction, "transaction",
+               ["db", "mode", "error", "objectStoreNames"]);
+
+forwardMethods(Transaction, "transaction", ["abort"]);
+
+class IndexedDB {
+  /**
+   * Opens the database with the given name, and returns a Promise which
+   * resolves to an IndexedDB instance when the operation completes.
+   *
+   * @param {string} dbName
+   *        The name of the database to open.
+   * @param {object} options
+   *        The options with which to open the database.
+   * @param {integer} options.version
+   *        The schema version with which the database needs to be opened. If
+   *        the database does not exist, or its current schema version does
+   *        not match, the `onupgradeneeded` function will be called.
+   * @param {string} [options.storage]
+   *        The storage type of the database. If present, may be one of
+   *        "temporary" or "persistent".
+   * @param {function} [onupgradeneeded]
+   *        A function which will be called with an IndexedDB object as its
+   *        first parameter when the database needs to be created, or its
+   *        schema needs to be upgraded. If this function is not provided, the
+   *        {@link #onupgradeneeded} method will be called instead.
+   *
+   * @returns {Promise<IndexedDB>}
+   */
+  static open(dbName, options, onupgradeneeded = null) {
+    let request = indexedDB.open(dbName, options);
+
+    request.onupgradeneeded = event => {
+      let db = new this(request.result);
+      if (onupgradeneeded) {
+        onupgradeneeded(db, event);
+      } else {
+        db.onupgradeneeded(event);
+      }
+    };
+
+    return wrapRequest(request).then(db => new IndexedDB(db));
+  }
+
+  constructor(db) {
+    this.db = db;
+  }
+
+  onupgradeneeded() {}
+
+  /**
+   * Opens a transaction for the given object stores.
+   *
+   * @param {Array<string>} storeNames
+   *        The names of the object stores for which to open a transaction.
+   * @param {string} [mode = "readonly"]
+   *        The mode in which to open the transaction.
+   * @param {function} [callback]
+   *        An optional callback function. If provided, the function will be
+   *        called with the Transaction, and a Promise will be returned, which
+   *        will resolve to the callback's return value when the transaction
+   *        completes.
+   * @returns {Transaction|Promise}
+   */
+  transaction(storeNames, mode, callback = null) {
+    let transaction = new Transaction(this.db.transaction(storeNames, mode));
+
+    if (callback) {
+      let result = new Promise(resolve => {
+        resolve(callback(transaction));
+      });
+      return transaction.promiseComplete().then(() => result);
+    }
+
+    return transaction;
+  }
+
+  /**
+   * Opens a transaction for a single object store, and returns that object
+   * store.
+   *
+   * @param {string} storeName
+   *        The name of the object store to open.
+   * @param {string} [mode = "readonly"]
+   *        The mode in which to open the transaction.
+   * @param {function} [callback]
+   *        An optional callback function. If provided, the function will be
+   *        called with the ObjectStore, and a Promise will be returned, which
+   *        will resolve to the callback's return value when the transaction
+   *        completes.
+   * @returns {ObjectStore|Promise}
+   */
+  objectStore(storeName, mode, callback = null) {
+    let transaction = this.transaction([storeName], mode);
+    let objectStore = transaction.objectStore(storeName);
+
+    if (callback) {
+      let result = new Promise(resolve => {
+        resolve(callback(objectStore));
+      });
+      return transaction.promiseComplete().then(() => result);
+    }
+
+    return objectStore;
+  }
+
+  createObjectStore(...args) {
+    return new ObjectStore(this.db.createObjectStore(...args));
+  }
+}
+
+for (let method of ["cmp", "deleteDatabase"]) {
+  IndexedDB[method] = function(...args) {
+    return indexedDB[method](...args);
+  };
+}
+
+forwardMethods(IndexedDB, "db",
+               ["addEventListener", "close", "deleteObjectStore", "hasEventListener", "removeEventListener"]);
+
+forwardGetters(IndexedDB, "db",
+               ["name", "objectStoreNames", "version"]);
+
+forwardProps(IndexedDB, "db",
+             ["onabort", "onclose", "onerror", "onversionchange"]);

--- a/toolkit/modules/moz.build
+++ b/toolkit/modules/moz.build
@@ -43,16 +43,17 @@ EXTRA_JS_MODULES += [
     'Finder.jsm',
     'FinderHighlighter.jsm',
     'FinderIterator.jsm',
     'FormLikeFactory.jsm',
     'Geometry.jsm',
     'GMPInstallManager.jsm',
     'GMPUtils.jsm',
     'Http.jsm',
+    'IndexedDB.jsm',
     'InlineSpellChecker.jsm',
     'InlineSpellCheckerContent.jsm',
     'Integration.jsm',
     'JSONFile.jsm',
     'LoadContextInfo.jsm',
     'Locale.jsm',
     'Log.jsm',
     'Memory.jsm',