This appears to be either a long-running bug or an "unintended feature".

Certain websites store data for offline use. I don't know why, but I do know that this data is separate from cookies and cache.

In Firefox 57, under Site Data, one can see which websites have store how much data. However there is no option to prevent websites from storing said data in the first place.

Most online tutorials date from 2010 to 2014, and mention about:permissions, which no longer exists.

I have configured offline-apps.allow_by_default to false, and offline-apps.quota.warn to 0. Now all I get is a message of "[website] is now using more than 0MB of offline data storage". I am not getting a request for permission as I expected. I still cannot prevent websites from storing data.

How can I prevent websites from storing offline data in Firefox 57?


Open a new tab in Firefox and in the address bar type:


Press enter. Agree to the warning notice. In the search field, start typing:


Change its value to "false" to disable the offline cache.


  • This does not answer the question. The question refers to data independent of cookies and cache, e.g. localStorage and IndexedDB. The option you suggest only toggles the HTTP cache, which has little to nothing to do with websites intentionally storing offline data. – Bob Feb 25 '18 at 23:19
  • For example, a quick test shows that IndexedDB and localStorage persist even with your suggested option toggled. – Bob Feb 25 '18 at 23:20

While it should be possible to disable offline data entirely (mostly, localStorage and IndexedDB), this has the potential to break the websites that depend on it. If you still wish to do so, the relevant config entries are dom.storage.enabled/dom.storage.default_quota (quota to 0 shows the API as enabled but full, which could break either fewer or more sites depending on the site's error handling) and dom.indexedDB.enabled.

Generally, a better idea is to clear the data on browser exit. While this still allows tracking within the same session, it will reduce long-term tracking.

To do this, head to about:preferences (or menu => Options), Privacy & Security tab. Under History, select Use custom settings for history. Tick Clear history when Firefox closes, and head into its Settings to tick Offline Website Data. You might also want to untick browsing history, etc., if you want to keep those.

Gif video of the process

Another thing that some websites will use is a Service Worker. I believe the above delete-on-close should work to clear Service Worker caches, but it's rather more difficult to test. If you want, you can disable them entirely through about:config's dom.serviceWorkers.enabled option. Note that this runs into the same potential issues as disabling other storage methods entirely: some sites simply will not work without them.

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