diff --git a/testing/web-platform/tests/css/css-grid/__dir__.ini b/testing/web-platform/tests/css/css-grid/__dir__.ini
new file mode 100644
index 000000000000..11fce723ba85
--- /dev/null
+++ b/testing/web-platform/tests/css/css-grid/__dir__.ini
@@ -0,0 +1 @@
+prefs: [layout.css.serialize-grid-implicit-tracks:false]