diff --git a/testing/tps/tps/testrunner.py b/testing/tps/tps/testrunner.py
index fb59403aefbc..6b490b603aec 100644
--- a/testing/tps/tps/testrunner.py
+++ b/testing/tps/tps/testrunner.py
@@ -78,6 +78,7 @@ class TPSTestRunner(object):
         'xpinstall.signatures.required': False,
         'services.sync.testing.tps': True,
         'engine.bookmarks.repair.enabled': False,
+        'extensions.allow-non-mpc-extensions': True,
     }
 
     debug_preferences = {