diff --git a/components/selectors/parser.rs b/components/selectors/parser.rs
index afb7280508d..e3afab57e16 100644
--- a/components/selectors/parser.rs
+++ b/components/selectors/parser.rs
@@ -191,12 +191,6 @@ pub trait Parser<'i> {
     type Impl: SelectorImpl;
     type Error: 'i + From<SelectorParseErrorKind<'i>>;
 
-    /// Whether the name is a pseudo-element that can be specified with
-    /// the single colon syntax in addition to the double-colon syntax.
-    fn pseudo_element_allows_single_colon(name: &str) -> bool {
-        is_css2_pseudo_element(name)
-    }
-
     /// Whether to parse the `::slotted()` pseudo-element.
     fn parse_slotted(&self) -> bool {
         false
@@ -2038,7 +2032,7 @@ where
 /// Returns whether the name corresponds to a CSS2 pseudo-element that
 /// can be specified with the single colon syntax (in addition to the
 /// double-colon syntax, which can be used for all pseudo-elements).
-pub fn is_css2_pseudo_element(name: &str) -> bool {
+fn is_css2_pseudo_element(name: &str) -> bool {
     // ** Do not add to this list! **
     match_ignore_ascii_case! { name,
         "before" | "after" | "first-line" | "first-letter" => true,
@@ -2114,7 +2108,7 @@ where
                 },
             };
             let is_pseudo_element =
-                !is_single_colon || P::pseudo_element_allows_single_colon(&name);
+                !is_single_colon || is_css2_pseudo_element(&name);
             if is_pseudo_element {
                 if state.intersects(SelectorParsingState::AFTER_PSEUDO_ELEMENT) {
                     return Err(input.new_custom_error(SelectorParseErrorKind::InvalidState));
diff --git a/components/style/gecko/selector_parser.rs b/components/style/gecko/selector_parser.rs
index 36558b9f5db..ec0db9286ec 100644
--- a/components/style/gecko/selector_parser.rs
+++ b/components/style/gecko/selector_parser.rs
@@ -351,11 +351,6 @@ impl<'a, 'i> ::selectors::Parser<'i> for SelectorParser<'a> {
         self.parse_slotted()
     }
 
-    fn pseudo_element_allows_single_colon(name: &str) -> bool {
-        // FIXME: -moz-tree check should probably be ascii-case-insensitive.
-        ::selectors::parser::is_css2_pseudo_element(name) || name.starts_with("-moz-tree-")
-    }
-
     fn parse_non_ts_pseudo_class(
         &self,
         location: SourceLocation,