diff --git a/components/style/gecko/non_ts_pseudo_class_list.rs b/components/style/gecko/non_ts_pseudo_class_list.rs
index f6551ce90d4..524ecb2e655 100644
--- a/components/style/gecko/non_ts_pseudo_class_list.rs
+++ b/components/style/gecko/non_ts_pseudo_class_list.rs
@@ -107,6 +107,7 @@ macro_rules! apply_non_ts_list {
                 ("-moz-only-whitespace", MozOnlyWhitespace, mozOnlyWhitespace, _, _),
                 ("-moz-native-anonymous", MozNativeAnonymous, mozNativeAnonymous, _, PSEUDO_CLASS_INTERNAL),
                 ("-moz-is-html", MozIsHTML, mozIsHTML, _, _),
+                ("-moz-placeholder", MozPlaceholder, mozPlaceholder, _, _),
             ],
             string: [
                 ("-moz-system-metric", MozSystemMetric, mozSystemMetric, _, PSEUDO_CLASS_INTERNAL),
diff --git a/components/style/gecko/selector_parser.rs b/components/style/gecko/selector_parser.rs
index 787ecd5b2cb..30242dc9bcb 100644
--- a/components/style/gecko/selector_parser.rs
+++ b/components/style/gecko/selector_parser.rs
@@ -166,7 +166,8 @@ impl NonTSPseudoClass {
         !matches!(*self,
                   NonTSPseudoClass::MozAny(_) |
                   NonTSPseudoClass::Dir(_) |
-                  NonTSPseudoClass::MozIsHTML)
+                  NonTSPseudoClass::MozIsHTML |
+                  NonTSPseudoClass::MozPlaceholder)
     }
 
     /// Convert NonTSPseudoClass to Gecko's CSSPseudoClassType.
diff --git a/components/style/gecko/wrapper.rs b/components/style/gecko/wrapper.rs
index e043ff57223..3732ea40051 100644
--- a/components/style/gecko/wrapper.rs
+++ b/components/style/gecko/wrapper.rs
@@ -1335,6 +1335,7 @@ impl<'le> ::selectors::Element for GeckoElement<'le> {
             NonTSPseudoClass::MozIsHTML => {
                 self.is_html_element_in_html_document()
             }
+            NonTSPseudoClass::MozPlaceholder => false,
             NonTSPseudoClass::MozAny(ref sels) => {
                 sels.iter().any(|s| {
                     matches_complex_selector(s, self, context, flags_setter)