The icon is used from the Tango project under:
"All artwork is licensed under under the Creative Commons Attribution-Share Alike 3.0
United States License. To view a copy of this licence, visit
http://creativecommons.org/licenses/by-sa/3.0/ or send a letter to Creative
Commons, 171 Second Street, Suite 300, San Francisco, California 94105, USA.
Credit for icons imported from git://git.gnome.org/gnome-icon-theme or derivatives of these goes to the GNOME project (http://www.gnome.org)
The other icons were created by Alexander Wilms (email removed due to no filtering by addons.mozilla)"