GNOME Bugzilla – Bug 738998
Middle click does not work for closing tabs
Last modified: 2014-10-22 15:23:03 UTC
In every other browser I know the middle click on a tab closes it. IMO this is a very efficient thing, especially since this action is completely useless otherwise. See also bug #738997 if you're worried about users accidentally closing tabs and panicking.
*** This bug has been marked as a duplicate of bug 725123 ***