The Tor Browser / file revision

 // Set methods throw when passed a this-value that isn't a Set.

 load(libdir + "asserts.js");

 function testcase(obj, fn) {

     assertEq(typeof fn, "function");

     var args = Array.slice(arguments, 2);

     assertThrowsInstanceOf(function () { fn.apply(obj, args); }, TypeError);

 }

 var Set_size_getter = Object.getOwnPropertyDescriptor(Set.prototype, "size").get;

 function test(obj) {

     testcase(obj, Set.prototype.has, 12);

     testcase(obj, Set.prototype.add, 12);

     testcase(obj, Set.prototype.delete, 12);

     testcase(obj, Set.prototype.clear);

     testcase(obj, Set.prototype.keys);

     testcase(obj, Set.prototype.values);

     testcase(obj, Set.prototype.entries);

     testcase(obj, Set_size_getter);

 }

 test(Set.prototype);

 test(Object.create(new Set));

 test(new Map());

 test({});

 test(null);

 test(undefined);