Regression test for blocking of Components.interfaces fails

The regression test for #2874 (closed) fails with

382 INFO TEST-UNEXPECTED-FAIL | 
js/xpconnect/tests/chrome/test_bug795275.xul | uncaught exception - 
TypeError: div.testMethod is not a function at 
http://mochi.test:8888/tests/js/xpconnect/tests/mochitest/file_bug795275.html:20