diff --git a/testing/web-platform/meta/css/css-pseudo/idlharness.html.ini b/testing/web-platform/meta/css/css-pseudo/idlharness.html.ini
index 20c068d71ac1..f34d22de93c8 100644
--- a/testing/web-platform/meta/css/css-pseudo/idlharness.html.ini
+++ b/testing/web-platform/meta/css/css-pseudo/idlharness.html.ini
@@ -1,3 +1,5 @@
+prefs: [dom.animations-api.getAnimations.enabled:true]
+
 [idlharness.html]
   [CSSPseudoElementList interface: existence and properties of interface object]
     expected: FAIL