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Represents the local storage area. Items in local storage are local to the machine the add-on was installed on.

When the add-on is uninstalled, its associated local storage is cleared (note that in Firefox, this is only true from version 51 onwards).

Also in Firefox, you can prevent the browser from clearing local storage on uninstall by visiting "about:config" and setting the following two browser preferences to true: "keepUuidOnUninstall" and "keepStorageOnUninstall". This feature is provided to help developers test their add-on. WebExtensions themselves are not able to change these preferences.

Although this API is similar to Window.localStorage it is recommended that you don't use Window.localStorage in add-on code. Firefox will clear data stored by add-ons 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 local 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. When you set a value, the storage.onChanged event will fire.
Removes one or more items from the storage area.
Removes all items from the storage area.

Browser compatibility

ChromeEdgeFirefoxFirefox for AndroidOpera
Basic supportYesYes45 148Yes
1. The storage API is supported in content scripts from version 48.

Example Add-ons


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: wbamberg, iosart, chrisdavidmills
 Last updated by: wbamberg,