Enables extensions to store and retrieve data, and listen for changes to stored items.

The storage system is based on the Web Storage API, with a few differences. Among other differences, these include:

  • It's asynchronous.
  • Values are scoped to the extension, not to a specific domain (i.e. the same set of key/value pairs are available to all scripts in the background context and content scripts).
  • The values stored can be any JSON-ifiable value, not just String. Among other things, this includes: Array and Object, but only when their contents can can be represented as JSON, which does not include DOM nodes. You don't need to convert your values to JSON Strings prior to storing them, but they are represented as JSON internally, thus the requirement that they be JSON-ifiable.
  • Multiple key/value pairs can be set or retrieved in the same API call.

To use this API you need to include the "storage" permission in your manifest.json file.

Each extension has its own storage area, which can be split into different types of storage.

Although this API is similar to Window.localStorage it is recommended that you don't use Window.localStorage in the extension code to store extension-related data. Firefox will clear data stored by extensions using the localStorage API in various scenarios where users clear their browsing history and data for privacy reasons, while data saved using the storage.local API will be correctly persisted in these scenarios.

The storage area is not encrypted and shouldn't be used for storing confidential user information.

Types

storage.StorageArea
An object representing a storage area.
storage.StorageChange
An object representing a change to a storage area.

Properties

storage has three properties, which represent the different types of available storage area.

storage.sync
Represents the sync storage area. Items in sync storage are synced by the browser, and are available across all instances of that browser that the user is logged into, across different devices.
storage.local
Represents the local storage area. Items in local storage are local to the machine the extension was installed on.
storage.managed
Represents the managed storage area. Items in managed storage are set by the domain administrator and are read-only for the extension. Trying to modify this namespace results in an error.

Events

storage.onChanged
Fired when one or more items change in a storage area.

Browser compatibility

Update compatibility data on GitHub
DesktopMobile
ChromeEdgeFirefoxOperaFirefox for Android
StorageAreaChrome Full support YesEdge Full support 14Firefox Full support 45Opera Full support YesFirefox Android Full support 48
StorageChangeChrome Full support YesEdge Full support 14Firefox Full support 45Opera Full support YesFirefox Android Full support 48
localChrome Full support YesEdge Full support 14Firefox Full support 45
Notes
Full support 45
Notes
Notes The storage API is supported in content scripts from version 48.
Opera Full support YesFirefox Android Full support 48
managedChrome Full support YesEdge No support NoFirefox Full support 57
Notes
Full support 57
Notes
Notes Platform-specific storage backends, such as Windows registry keys, are not supported.
Notes Enforcement of extension-provided storage schemas is not supported.
Notes The onChanged event is not supported.
Opera No support NoFirefox Android No support No
onChangedChrome Full support YesEdge Full support 14Firefox Full support 45Opera Full support YesFirefox Android Full support 48
syncChrome Full support YesEdge Full support 15Firefox Full support 53Opera No support NoFirefox Android No support No

Legend

Full support  
Full support
No support  
No support
See implementation notes.
See implementation notes.

Example extensions

Acknowledgements

This API is based on Chromium's chrome.storage API. This documentation is derived from storage.json in the Chromium code.

Microsoft Edge compatibility data is supplied by Microsoft Corporation and is included here under the Creative Commons Attribution 3.0 United States License.

Document Tags and Contributors

Last updated by: wbamberg,