diff --git a/browser/themes/shared/places/tree-icons.css b/browser/themes/shared/places/tree-icons.css
index 80f42a7e82e7..645f930bf53b 100644
--- a/browser/themes/shared/places/tree-icons.css
+++ b/browser/themes/shared/places/tree-icons.css
@@ -2,7 +2,7 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-treechildren:-moz-tree-image {
+treechildren::-moz-tree-image {
   -moz-context-properties: fill, fill-opacity;
   fill-opacity: 0.7;
 }
diff --git a/layout/style/test/test_selectors.html b/layout/style/test/test_selectors.html
index 7eabcb6d1d0a..23fbf9006b73 100644
--- a/layout/style/test/test_selectors.html
+++ b/layout/style/test/test_selectors.html
@@ -1102,15 +1102,15 @@ function runTests() {
     test_parseable(":-moz-lwtheme-brighttext");
     test_parseable(":-moz-lwtheme-darktext");
 
-    test_parseable(":-moz-tree-row(selected)");
+    test_balanced_unparseable(":-moz-tree-row(selected)");
     test_parseable("::-moz-tree-row(selected)");
     test_parseable("::-MoZ-trEE-RoW(sElEcTeD)");
-    test_parseable(":-moz-tree-row(selected focus)");
-    test_parseable(":-moz-tree-row(selected , focus)");
+    test_balanced_unparseable(":-moz-tree-row(selected focus)");
+    test_balanced_unparseable(":-moz-tree-row(selected , focus)");
     test_parseable("::-moz-tree-row(selected ,focus)");
-    test_parseable(":-moz-tree-row(selected, focus)");
+    test_balanced_unparseable(":-moz-tree-row(selected, focus)");
     test_parseable("::-moz-tree-row(selected,focus)");
-    test_parseable(":-moz-tree-row(selected     focus)");
+    test_balanced_unparseable(":-moz-tree-row(selected     focus)");
     test_parseable("::-moz-tree-row(selected    ,   focus)");
     test_parseable("::-moz-tree-twisty(  hover open  )");
     test_balanced_unparseable("::-moz-tree-row(selected {[]} )");
diff --git a/modules/libpref/init/StaticPrefList.h b/modules/libpref/init/StaticPrefList.h
index 79e2a5c587de..6943771ec35d 100644
--- a/modules/libpref/init/StaticPrefList.h
+++ b/modules/libpref/init/StaticPrefList.h
@@ -1007,7 +1007,7 @@ VARCACHE_PREF(
   bool, false
 )
 
-// Pref to control whether ::xul-tree-* pseudo-elements are parsed in content
+// Pref to control whether XUL ::-tree-* pseudo-elements are parsed in content
 // pages.
 VARCACHE_PREF(
   "layout.css.xul-tree-pseudos.content.enabled",
diff --git a/servo/components/selectors/parser.rs b/servo/components/selectors/parser.rs
index afb7280508df..e3afab57e169 100644
--- a/servo/components/selectors/parser.rs
+++ b/servo/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/servo/components/style/gecko/selector_parser.rs b/servo/components/style/gecko/selector_parser.rs
index 36558b9f5dbe..ec0db9286ec8 100644
--- a/servo/components/style/gecko/selector_parser.rs
+++ b/servo/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,