Comment # 3 on bug 1087741 from George Anchev

Further testing:

4. In System Settings -> Default Applications -> Web Browser set explicitly to
open http(s) URLs in application torbrowser.
5. Repeat step 3 

RESULT:

Now when I click a link (e.g. in claws-mail or in console) Tor Browser starts
(if it is not started) but does not open the URL. If it was already started I
simply get a message box:

"Tor Browser is already running, but is not responding. To open a new window,
you must first close the existing Tor Browser process, or restart your system."

and the URL still doesn't open in it.

Reported upstream:
https://trac.torproject.org/projects/tor/ticket/25806