I've noticed in multiple instances while editing my preferences that some websites are "allowed to store data for offline use" (the blacked-out box in attachment "preferences->advanced->network" is how I've noticed this is happening) ... But my settings require that I am prompted before this can happen (see highlighted portions of attachments "preferences->advanced->network" and "about:permissions default permissions for all sites"), and I have never seen a prompt for offline storage. I then checked the individual domain's permissions and noticed that the permission to "Maintain Offline Storage" is set to "Use Default", but to the right of that it shows the default as "Allow" (see highlighted portions of attachment "permissions for specific domain") ... this inconsistency is apparently what is allowing any domain to use offline storage without prompting the user.

Mark, you recently worked on some permissions manager stuff, can you make sense of these prefs? I have to agree it's pretty confusing.

I've no insights here, but at face value, something sure looks either broken or terribly misleading. The "Advanced" pane for me does have the "tell me when a website asks to store data for offline use" option, but site-specific permissions seem to imply the default for "Maintain Offline Storage" is allow.

I can confirm this is happening exactly as described by William. In addition, I went to the about:permissions page and set the "Maintain Offline Storage" option to "Block". That had no effect. I went to the target website, right-clicked, then "View Page Info" -> "Permissions" tab, and blocked it from there. Still no effect.

Don't know if this can be the same in Firefox 57, here's the steps to reproduce the problem: 1) Open www.youtube.com 2) Display the Info page window and select the "Permissions" panel. 3) Scroll to "Maintain Offline Storage" and change "Use default" to "Block". 4) Delete content already saved locally. 5) Reload the page. Result: YouTube will continue to save local content. Expected result: YouTube should not save any local content if I have explicitly denied to do so.

Yes, we're about to remove it (see also bug 1405742 and bug 1354500).