--- a/testing/marionette/harness/marionette_harness/tests/unit/test_navigation.py
+++ b/testing/marionette/harness/marionette_harness/tests/unit/test_navigation.py
@@ -197,25 +197,27 @@ class TestTLSNavigation(MarionetteTestCa
             pass
         MarionetteTestCase.tearDown(self)
 
     @contextlib.contextmanager
     def safe_session(self):
         try:
             self.capabilities = self.marionette.start_session(
                 desired_capabilities=self.secure_tls)
+            self.assertFalse(self.capabilities["acceptInsecureCerts"])
             yield self.marionette
         finally:
             self.marionette.delete_session()
 
     @contextlib.contextmanager
     def unsafe_session(self):
         try:
             self.capabilities = self.marionette.start_session(
                 desired_capabilities=self.insecure_tls)
+            self.assertTrue(self.capabilities["acceptInsecureCerts"])
             yield self.marionette
         finally:
             self.marionette.delete_session()
 
     def test_navigate_by_command(self):
         self.marionette.navigate(
             self.fixtures.where_is("/test.html", on="https"))
         self.assertIn("https", self.marionette.get_url())