Hi Bernd, I believe that the problem is due to torbrowser-launcher not only launching the browser, like when you launch Firefox, but also launching it's own instance of tor. When this instance is already running under your current user, you won't be able to launch a second instance using the same SOCKS port.
Holger Levsen has created a how to run torbrowser-launcher as another user in another X environment: https://anonscm.debian.org/git/pkg-privacy/packages/torbrowser-launcher.git/tree/debian/examples?h=debian/sid It's also possible to run a second TorBrowser configured to use system tor, which might be a workaround for the tor instance problem. Some other ideas: https://tor.stackexchange.com/questions/2006/how-to-run-multiple-tor-browsers-with-different-ips I've not tested any of these myself. If you do, please report back. Although I find this very interesting, I'd like to close this bug, as I believe that it exceeds the intended usage of this package and is not a bug in the packaging itself. This should either be reported upstream or documented on the Debian wiki. What do you think? Cheers! u.