/usr/share/gconf/defaults/10_mumble is in mumble 1.2.8-2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 | /desktop/gnome/url-handlers/mumble/command "mumble %s"
/desktop/gnome/url-handlers/mumble/needs_terminal false
/desktop/gnome/url-handlers/mumble/enabled true
|