--- a/testing/tps/tps/testrunner.py
+++ b/testing/tps/tps/testrunner.py
@@ -73,16 +73,17 @@ class TPSTestRunner(object):
         'extensions.update.notifyUser': False,
         'services.sync.firstSync': 'notReady',
         'services.sync.lastversion': '1.0',
         'toolkit.startup.max_resumed_crashes': -1,
         # hrm - not sure what the release/beta channels will do?
         'xpinstall.signatures.required': False,
         'services.sync.testing.tps': True,
         'engine.bookmarks.repair.enabled': False,
+        'extensions.allow-non-mpc-extensions': True,
     }
 
     debug_preferences = {
         'services.sync.log.appender.console': 'Trace',
         'services.sync.log.appender.dump': 'Trace',
         'services.sync.log.appender.file.level': 'Trace',
         'services.sync.log.appender.file.logOnSuccess': True,
         'services.sync.log.rootLogger': 'Trace',