diff --git a/components/style/gecko/media_features.rs b/components/style/gecko/media_features.rs
index 65faf300396..a0cd1329135 100644
--- a/components/style/gecko/media_features.rs
+++ b/components/style/gecko/media_features.rs
@@ -576,7 +576,7 @@ macro_rules! bool_pref_feature {
 /// to support new types in these entries and (2) ensuring that either
 /// nsPresContext::MediaFeatureValuesChanged is called when the value that
 /// would be returned by the evaluator function could change.
-pub static MEDIA_FEATURES: [QueryFeatureDescription; 60] = [
+pub static MEDIA_FEATURES: [QueryFeatureDescription; 61] = [
     feature!(
         atom!("width"),
         AllowsRanges::Yes,
@@ -868,4 +868,6 @@ pub static MEDIA_FEATURES: [QueryFeatureDescription; 60] = [
     ),
     lnf_int_feature!(atom!("-moz-system-dark-theme"), SystemUsesDarkTheme),
     bool_pref_feature!(atom!("-moz-box-flexbox-emulation"), "layout.css.moz-box-flexbox-emulation.enabled"),
+    // media query for MathML Core's implementation of maction/semantics
+    bool_pref_feature!(atom!("-moz-mathml-core-maction-and-semantics"), "mathml.legacy_maction_and_semantics_implementations.disabled"),
 ];