diff --git a/caps/moz.build b/caps/moz.build
index 978390671e0d..c50409655d50 100644
--- a/caps/moz.build
+++ b/caps/moz.build
@@ -6,6 +6,8 @@
 
 TEST_DIRS += ['tests/mochitest']
 
+XPCSHELL_TESTS_MANIFESTS += ['tests/unit/xpcshell.ini']
+
 XPIDL_SOURCES += [
     'nsIDomainPolicy.idl',
     'nsIPrincipal.idl',
diff --git a/caps/tests/unit/test_origin.js b/caps/tests/unit/test_origin.js
new file mode 100644
index 000000000000..666f84f3ed5f
--- /dev/null
+++ b/caps/tests/unit/test_origin.js
@@ -0,0 +1,14 @@
+var Cu = Components.utils;
+function run_test() {
+  do_check_eq(Cu.getObjectPrincipal({}).origin, '[System Principal]');
+  var exampleOrg = Cu.getObjectPrincipal(new Cu.Sandbox('http://example.org'));
+  do_check_eq(exampleOrg.origin, 'http://example.org');
+  var exampleCom = Cu.getObjectPrincipal(new Cu.Sandbox('https://www.example.com:123'));
+  do_check_eq(exampleCom.origin, 'https://www.example.com:123');
+  var nullPrin = Cu.getObjectPrincipal(new Cu.Sandbox(null));
+  do_check_true(/^moz-nullprincipal:\{([0-9]|[a-z]|\-){36}\}$/.test(nullPrin.origin));
+  var ep = Cu.getObjectPrincipal(new Cu.Sandbox([exampleCom, nullPrin, exampleOrg]));
+
+  // Origins should be in lexical order.
+  do_check_eq(ep.origin, `[Expanded Principal [${exampleOrg.origin}, ${exampleCom.origin}, ${nullPrin.origin}]]`);
+}
diff --git a/caps/tests/unit/xpcshell.ini b/caps/tests/unit/xpcshell.ini
new file mode 100644
index 000000000000..c06a6b4e92be
--- /dev/null
+++ b/caps/tests/unit/xpcshell.ini
@@ -0,0 +1,5 @@
+[DEFAULT]
+head =
+tail =
+
+[test_origin.js]