diff --git a/js/src/tests/lib/manifest.py b/js/src/tests/lib/manifest.py
index f242e47c8a0..c6e2afdb4f6 100644
--- a/js/src/tests/lib/manifest.py
+++ b/js/src/tests/lib/manifest.py
@@ -344,7 +344,10 @@ def load(location, xul_tester, reldir = ''):
 
     # Any file whose basename matches something in this set is ignored.
     EXCLUDED = set(('browser.js', 'shell.js', 'jsref.js', 'template.js',
-                    'user.js', 'js-test-driver-begin.js', 'js-test-driver-end.js'))
+                    'user.js', 'test262-browser.js', 'test262-shell.js',
+                    'test402-browser.js', 'test402-shell.js',
+                    'testBuiltInObject.js', 'testIntl.js',
+                    'js-test-driver-begin.js', 'js-test-driver-end.js'))
 
     manifestFile = os.path.join(location, 'jstests.list')
     externalManifestEntries = _parse_external_manifest(manifestFile, '')
diff --git a/js/src/tests/supporting/test262-browser.js b/js/src/tests/supporting/test262-browser.js
new file mode 100644
index 00000000000..fb4c181069c
--- /dev/null
+++ b/js/src/tests/supporting/test262-browser.js
@@ -0,0 +1,11 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/*
+ * Test262 function $INCLUDE loads a file with support functions for the tests.
+ * Our initial import strategy will be to attempt to load all these files
+ * unconditionally (this may change at some point), so just ignore the call.
+ * This function replaces one in shell.js.
+ */
+function $INCLUDE(file) {}
diff --git a/js/src/tests/supporting/test262-shell.js b/js/src/tests/supporting/test262-shell.js
new file mode 100644
index 00000000000..4f1af7fb5d8
--- /dev/null
+++ b/js/src/tests/supporting/test262-shell.js
@@ -0,0 +1,39 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/*
+ * The current crop of Test262 test cases that we run are expected to pass
+ * unless they crash or throw.  (This isn't true for all Test262 test cases --
+ * for the ones marked @negative the logic is inverted.  We'll have to deal with
+ * that concern eventually, but for now we're punting so we can run subsets of
+ * Test262 tests.)
+ */
+testPassesUnlessItThrows();
+
+/*
+ * Test262 function $ERROR throws an error with the message provided. Test262
+ * test cases call it to indicate failure.
+ */
+function $ERROR(msg)
+{
+  throw new Error("Test262 error: " + msg);
+}
+
+/*
+ * Test262 function $INCLUDE loads a file with support functions for the tests.
+ * This function is replaced in browser.js.
+ */
+function $INCLUDE(file)
+{
+  load("supporting/" + file);
+}
+
+/*
+ * Test262 function fnGlobalObject returns the global object.
+ */
+var fnGlobalObject = (function()
+{
+  var global = Function("return this")();
+  return function fnGlobalObject() { return global; };
+})();
diff --git a/js/src/tests/supporting/test402-browser.js b/js/src/tests/supporting/test402-browser.js
new file mode 100644
index 00000000000..dae19cbd15d
--- /dev/null
+++ b/js/src/tests/supporting/test402-browser.js
@@ -0,0 +1,32 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/*
+ * Undo at least the damage done by taintArray so that the jstests
+ * harness won't die. The properties added to Object.prototype by the various
+ * tests have names that are less likely to cause trouble.
+ */
+setRestoreFunction((function () {
+    var Array_indexOf = Array.prototype.indexOf;
+    var Array_join = Array.prototype.join;
+    var Array_push = Array.prototype.push;
+    var Array_slice = Array.prototype.slice;
+    var Array_sort = Array.prototype.sort;
+    return function () {
+        delete Array.prototype["0"];
+        Array.prototype.indexOf = Array_indexOf;
+        Array.prototype.join = Array_join;
+        Array.prototype.push = Array_push;
+        Array.prototype.slice = Array_slice;
+        Array.prototype.sort = Array_sort;
+    };
+}()));
+
+/*
+ * Loading include files into the browser from a script so that they become
+ * synchronously available to that same script is difficult. Instead, request
+ * all of them to be loaded before we start.
+ */
+include("supporting/testBuiltInObject.js");
+include("supporting/testIntl.js");
diff --git a/js/src/tests/supporting/test402-shell.js b/js/src/tests/supporting/test402-shell.js
new file mode 100644
index 00000000000..2e6826e91f3
--- /dev/null
+++ b/js/src/tests/supporting/test402-shell.js
@@ -0,0 +1,10 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/*
+ * Test402 tests all pass unless they throw, and there are no @negative tests.
+ * Once Test262 includes @negative support, and this call in test262-shell.js is
+ * removed, this'll need to be uncommented.
+ */
+//testPassesUnlessItThrows();
diff --git a/js/src/tests/update-test262.sh b/js/src/tests/update-test262.sh
new file mode 100755
index 00000000000..23fa0af047a
--- /dev/null
+++ b/js/src/tests/update-test262.sh
@@ -0,0 +1,100 @@
+#!/bin/sh
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+# Abort when an error occurs.
+set -e
+
+# Updates the jstests copy of the test cases of Test262, the conformance test
+# suite for ECMA-262 and ECMA-402, ECMAScript and its Internationalization API.
+
+if [ $# -lt 1 ]; then
+  echo "Usage: update-test262.sh <URL of test262 hg, e.g. http://hg.ecmascript.org/tests/test262/ or a local clone>"
+  exit 1
+fi
+
+# Mercurial doesn't have a way to download just a part of a repository, or to
+# just get the working copy - we have to clone the entire thing. We use a
+# temporary test262 directory for that.
+unique_dir=`mktemp -d /tmp/test262.XXXX` || exit 1
+tmp_dir=${unique_dir}/test262
+
+# Remove the temporary test262 directory on exit.
+function cleanupTempFiles()
+{
+  rm -rf ${unique_dir}
+}
+trap cleanupTempFiles EXIT
+
+echo "Feel free to get some coffee - this could take a few minutes..."
+hg clone $1 ${tmp_dir}
+
+# Now to the actual test262 directory.
+js_src_tests_dir=`dirname $0`
+test262_dir=${js_src_tests_dir}/test262
+rm -rf ${test262_dir}
+mkdir ${test262_dir}
+
+# Copy over the test262 license.
+cp ${tmp_dir}/LICENSE ${test262_dir}
+
+# The test262 tests are in test/suite.  The "bestPractice" tests cover non-
+# standard extensions, or are not strictly required by specs, so we don't
+# include them.  The remaining tests are currently in "intl402" or "chNN"
+# directories (where NN is an ECMA-262 chapter number).  This may change at
+# some point, as there is some dissatisfaction on test262-discuss with using
+# impermanent section numbering (across ES5, ES6, etc.) to identify what's
+# tested.
+#
+# The large quantity of tests at issue here, and the variety of things being
+# tested, motivate importing portions of test262 incrementally.  So rather than
+# doing this:
+#
+#   cp -r ${tmp_dir}/test/suite/ch* ${test262_dir}
+#
+# ...we instead individually import folders whose tests we pass.  (Well, mostly
+# pass -- see the comment at the end of this script.)
+cp -r ${tmp_dir}/test/suite/ch06 ${test262_dir}/ch06
+
+# The test402 tests are in test/suite/intl402/.  For now there are no
+# "bestPractice" tests to omit.  The remaining tests are in chNN directories,
+# NN referring to chapters of ECMA-402.
+#
+# All intl402 tests are runnable, and only a few currently fail, so we import
+# them wildcard-style.
+mkdir ${test262_dir}/intl402
+cp -r ${tmp_dir}/test/suite/intl402/ch* ${test262_dir}/intl402
+
+# Copy over harness supporting files needed by the test402 tests.
+cp ${tmp_dir}/test/harness/testBuiltInObject.js ${js_src_tests_dir}/supporting/
+cp ${tmp_dir}/test/harness/testIntl.js ${js_src_tests_dir}/supporting/
+
+# Create empty browser.js and shell.js in all test directories to keep
+# jstests happy.
+for dir in `find ${test262_dir} ${test262_dir}/ch* ${test262_dir}/intl402/ch* -type d -print` ; do
+  touch $dir/browser.js
+  touch $dir/shell.js
+done
+
+# Restore the test262 tests' jstests adapter files.
+cp ${js_src_tests_dir}/supporting/test262-browser.js ${test262_dir}/browser.js
+cp ${js_src_tests_dir}/supporting/test262-shell.js ${test262_dir}/shell.js
+
+# Restore the Intl tests' jstests adapter files.
+cp ${js_src_tests_dir}/supporting/test402-browser.js ${test262_dir}/intl402/browser.js
+cp ${js_src_tests_dir}/supporting/test402-shell.js ${test262_dir}/intl402/shell.js
+
+# Keep a record of what we imported.
+echo "URL:         $1" > ${test262_dir}/HG-INFO
+hg -R ${tmp_dir} log -r. >> ${test262_dir}/HG-INFO
+
+# Update for the patch.
+hg addremove ${js_src_tests_dir}/supporting
+hg addremove ${test262_dir}
+
+# The alert reader may now be wondering: what about test262 tests that we don't
+# pass?  (And what about any test262 tests whose format we don't yet support?)
+# We explicitly disable all such tests in js/src/tests/jstests.list one by one.
+# This has the moderate benefit that if a bug is fixed, only that one file must
+# be updated, and we don't have to rerun this script.