Firefox always accepts offline web content and user data, I never get any notification regardless of the "tell me when a website asks to store data for offline use" setting (found in Preferences > Advanced > network). I also completely cleared the about:permissions tab. Regardless of the "All sites > Offline storage" setting, offline storage is always allowed. Here is a step- by step guide to reproduce my issue. 1. Make sure about:permissions is clear 2. make sure the list at: preferences > Network > "The following websites are ...." is also clear 3. Close the preferences window 4. Go to go to http://appcachefacts.info/demo/ ... No notification regarding offline cache will be shown. 5. Open the preference window, the list at preferences > Network > "The following websites are ...." Will now be populated with http://appcachefacts.info (1.1MB) This list entry persists even after closing the browser window and re-opening it. This happens with complete disregard to the settings described in the first paragraph. I found a related issue, but it is old and archived: https://support.mozilla.org/he/questions/981189