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 storage.sync in Firefox relies on the Add-on ID. If you use storage.sync, you must set an ID for your extension using the browser_specific_settings 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

Update compatibility data on GitHub
ChromeEdgeFirefoxOperaSafariFirefox for Android
syncChrome Full support YesEdge Full support 15Firefox Full support 53Opera No support NoSafari Partial support 14
Partial support 14
Notes Safari does not sync items saved in the sync storage area, i.e. it behaves the same as the local storage area.
Firefox Android No support No


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

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.