This feature is non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future.

This feature is obsolete. Although it may still work in some browsers, its use is discouraged since it could be removed at any time. Try to avoid using it.

The Navigator.mozIsLocallyAvailable() method allows add-ons to determine whether or not a given resource is available.

Note: Security exceptions can occur if the requested URI is not from the same origin.


navigator.mozIsLocallyAvailable(uri, ifOffline);


The URI of the resource whose availability is to be checked, as a string.

Allows you to specify whether or not the offline resources cache should be checked; specify true to consider the offline resources cache.


var available = navigator.mozIsLocallyAvailable("my-image-file.png", true);
if (available) {
  /* the offline resource is present */
} else {
  console.log("Certain needed resources are not available offline");


Not part of any specifications.

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support No support (Yes)
Removed in 35 (35)
No support No support No support
Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
Basic support No support No support (Yes)
Removed in 35.0 (35)
No support No support No support

Document Tags and Contributors

 Last updated by: Sebastianz,