Utilities for implementing APIs
===============================
This page covers some utility classes that are useful for
implementing WebExtension APIs:

WindowManager
-------------
This class manages the mapping between the opaque window identifiers used
in the `browser.windows <https://developer.mozilla.org/en-US/Add-ons/WebExtensions/API/windows>`_ API.
See the reference docs `here <reference.html#windowmanager-class>`_.

TabManager
----------
This class manages the mapping between the opaque tab identifiers used
in the `browser.tabs <https://developer.mozilla.org/en-US/Add-ons/WebExtensions/API/tabs>`_ API.
See the reference docs `here <reference.html#tabmanager-class>`_.

ExtensionSettingsStore
----------------------
*XXX describe*

ExtensionPreferencesManager
---------------------------
*XXX describe*
