--- a/layout/tools/reftest/runreftest.py
+++ b/layout/tools/reftest/runreftest.py
@@ -326,22 +326,22 @@ class RefTest(object):
 
         # Bug 1300355: Disable canvas cache for win7 as it uses
         # too much memory and causes OOMs.
         if platform.system() in ("Windows", "Microsoft") and \
            '6.1' in platform.version():
             prefs['reftest.nocache'] = True
 
         if options.marionette:
-            port = options.marionette.split(':')[1]
-            prefs['marionette.defaultPrefs.port'] = int(port)
+            port = options.marionette.split(":")[1]
+            prefs["marionette.port"] = int(port)
 
             # Enable tracing output for detailed failures in case of
             # failing connection attempts, and hangs (bug 1397201)
-            prefs['marionette.logging'] = "TRACE"
+            prefs["marionette.log.level"] = "TRACE"
 
         preference_file = os.path.join(here, 'reftest-preferences.js')
         prefs.update(mozprofile.Preferences.read_prefs(preference_file))
 
         for v in options.extraPrefs:
             thispref = v.split('=')
             if len(thispref) < 2:
                 print "Error: syntax error in --setpref=" + v