NavigatorStorage.storage read-only property returns the singleton
StorageManager object used to access the overall storage capabilities of the browser for the current site or app. The returned object lets you examine and configure persistence of data stores and learn approximately how much more space your browser has available for local storage use.
var storageManager = navigator.storage;
StorageManager object you can use to maintain persistence for stored data, as well as to determine roughly how much room there is for data to be stored.
The definition of 'navigator.storage' in that specification.
|Living Standard||Initial definition.|
|Feature||Chrome||Firefox (Gecko)||Internet Explorer||Microsoft Edge||Opera||Safari (WebKit)|
|Basic support||55||51 (51)
|Feature||Android Webview||Chrome for Android||Firefox Mobile (Gecko)||IE Mobile||Opera Mobile||Safari Mobile|
|Basic support||?||55||51.0 (51)||?||42||?|
 Firefox 51 introduced
Navigator.storage, and the
StorageManager.estimate() method. These are enabled by default in nightly builds but disabled by default in all other builds. You can enable these features by setting the
preference dom.storageManager.enabled to
 The Storage API is implemented and enabled by default in Firefox 57 Desktop.