The lines shouldBeTrue("canCall('targetWindow.history.back')"); shouldBeTrue("canCall('targetWindow.history.forward')"); shouldBeTrue("canCall('targetWindow.history.go', '-1')"); in http/tests/security/cross-frame-access-history.html causes http/tests/security/cross-frame-access-location.html, the test run after it to intermittently fail with the dump of cross-frame-access-history.html's render tree.