AppCache has been disabled starting with Firefox 81. AppCache was typically used for offline caching, is no longer supported by many web browsers because it has been removed from relevant web standards. To learn more about AppCache, see the Mozilla Developer Network (MDN)
If a web app you're visiting requires AppCache to function, we recommend contacting the Web developer to replace it with updated standards. Otherwise, you can re-enable AppCache manually (not recommended) until AppCache is completely removed in Firefox 84/85.
Re-enable AppCache (Advanced users only)
Note: This will no longer be an option starting with Firefox 84.
If you want to renable AppCache (not recommended), you can do so by flipping the browser.cache.offline.storage.enable pref in about:config to true.
