tor-browser mozilla_user0 directory often appear in /tmp

tor-browser-linux64-6.0.5_en-US

sometimes a this directory appear: /tmp/mozilla_user0 Modification time is updated every now and then. I think is used to store temporary data ( user data ? ).

That doesn't happen often. For example it happen sometimes watching youtube ( maybe some advertisement or script ?) and when a download is finished to save to disk in mega, the site.

This happen when I run Tor Browser. It happen every now and then, frequently. My privacy settings are at default ( low ). If I delete that directory, sometimes it is recreated. If I close Tor-Browser, the directory stay there.

Which conditions let the directory mozilla_user0 appear in /tmp ? What about linux x86 (32bit), Windows and macOS versions ? That could be privacy related or worse?

Happy to contribute

Trac:
Username: anon