diff --git a/components/selectors/parser.rs b/components/selectors/parser.rs
index 6be95b5d018..ff9f45eac85 100644
--- a/components/selectors/parser.rs
+++ b/components/selectors/parser.rs
@@ -127,7 +127,7 @@ pub trait Parser<'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 is_pseudo_element_allows_single_colon(name: &CowRcStr<'i>) -> bool {
+    fn pseudo_element_allows_single_colon(name: &str) -> bool {
         is_css2_pseudo_element(name)
     }
 
@@ -1701,7 +1701,7 @@ 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<'i>(name: &CowRcStr<'i>) -> bool {
+pub 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,
@@ -1760,7 +1760,7 @@ where
                 )),
             };
             let is_pseudo_element = !is_single_colon ||
-                P::is_pseudo_element_allows_single_colon(&name);
+                P::pseudo_element_allows_single_colon(&name);
             if is_pseudo_element {
                 let pseudo_element = if is_functional {
                     input.parse_nested_block(|input| {
diff --git a/components/style/gecko/selector_parser.rs b/components/style/gecko/selector_parser.rs
index 827e832ebcd..0c8e189faa3 100644
--- a/components/style/gecko/selector_parser.rs
+++ b/components/style/gecko/selector_parser.rs
@@ -333,9 +333,10 @@ impl<'a, 'i> ::selectors::Parser<'i> for SelectorParser<'a> {
     type Impl = SelectorImpl;
     type Error = StyleParseErrorKind<'i>;
 
-    fn is_pseudo_element_allows_single_colon(name: &CowRcStr<'i>) -> bool {
+    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-") // tree pseudo-elements
+            name.starts_with("-moz-tree-")
     }
 
     fn parse_non_ts_pseudo_class(
@@ -431,6 +432,8 @@ impl<'a, 'i> ::selectors::Parser<'i> for SelectorParser<'a> {
     ) -> Result<PseudoElement, ParseError<'i>> {
         PseudoElement::from_slice(&name, self.in_user_agent_stylesheet())
             .or_else(|| {
+                // FIXME: -moz-tree check should probably be
+                // ascii-case-insensitive.
                 if name.starts_with("-moz-tree-") {
                     PseudoElement::tree_pseudo_element(&name, Box::new([]))
                 } else {
@@ -445,9 +448,10 @@ impl<'a, 'i> ::selectors::Parser<'i> for SelectorParser<'a> {
         name: CowRcStr<'i>,
         parser: &mut Parser<'i, 't>,
     ) -> Result<PseudoElement, ParseError<'i>> {
+        // FIXME: -moz-tree check should probably be ascii-case-insensitive.
         if name.starts_with("-moz-tree-") {
-            // Tree pseudo-elements can have zero or more arguments,
-            // separated by either comma or space.
+            // Tree pseudo-elements can have zero or more arguments, separated
+            // by either comma or space.
             let mut args = Vec::new();
             loop {
                 let location = parser.current_source_location();