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 (e.g. via Firefox sync, or a Google account), across different devices.

For Firefox a user must have Add-ons checked under the "Sync Settings" options in "about:preferences".

Note that the implementation of in Firefox relies on the Add-on ID. If you use, you must set an ID for your extension using the applications manifest.json key.

The main use case of this API is to store preferences about your extension and allow the user to sync them to different profiles. You can store up to 100KB of data using this API. If you try to store more than this, the call will fail with an error message. The API is provided without any guarantees about uptime or performance.


The sync object implements the methods defined on the storage.StorageArea type:

Retrieves one or more items from the storage area.
Gets the amount of storage space (in bytes) used one or more items being stored in the storage area.
Stores one or more items in the storage area. If the item already exists, its value will be updated.
Removes one or more items from the storage area.
Removes all items from the storage area.

Browser compatibility

ChromeEdgeFirefoxFirefox for AndroidOpera
Basic support Yes1553 No No

Example extensions


This API is based on Chromium's 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

 Contributors to this page: andymckay-github, andrewtruongmoz, wbamberg, chrisdavidmills
 Last updated by: andymckay-github,