With no extensions installed, Firefox adds folders and files to [profile folder]->storage->persistent For example, if a user visits http://html5test.com/ a folder named "http+++html5test.com" gets added with stuff in it (I don't know what the stuff is). With Firefox set to clear history on shutdown, that folder doesn't get removed. If I clear recent history manually, the folder doesn't get removed. I can find no way to automatically remove these folders. This is a privacy concern because the folder names themselves are a partial representation of my browsing history.

It seems that the location has changed to [profile folder]->storage->default The same problem remains.

I have been able to determine that these are from IndexedDB (https://developer.mozilla.org/en-US/docs/Web/API/IndexedDB_API) ... Try IndexedDB demos from the following URL: https://developer.mozilla.org/en-US/demos/tag/tech:indexeddb You can see folders and sqlite databases getting added within the above mentioned folder, and there's no way to clear them through Firefox.

Thanks for the report! This is a known issue.