diff --git a/testing/web-platform/meta/serial/__dir__.ini b/testing/web-platform/meta/serial/__dir__.ini
new file mode 100644
index 000000000000..1701b2522d35
--- /dev/null
+++ b/testing/web-platform/meta/serial/__dir__.ini
@@ -0,0 +1 @@
+prefs: [dom.security.featurePolicy.enabled:true]