diff --git a/components/style/gecko/non_ts_pseudo_class_list.rs b/components/style/gecko/non_ts_pseudo_class_list.rs
index b5c2c4cd5ba..0a5fe00be02 100644
--- a/components/style/gecko/non_ts_pseudo_class_list.rs
+++ b/components/style/gecko/non_ts_pseudo_class_list.rs
@@ -116,9 +116,6 @@ macro_rules! apply_non_ts_list {
             ],
             string: [
                 ("lang", Lang, lang, _, _),
-            ],
-            keyword: [
-                ("-moz-locale-dir", MozLocaleDir, mozLocaleDir, _, _),
             ]
         }
     }
diff --git a/components/style/gecko/selector_parser.rs b/components/style/gecko/selector_parser.rs
index 72da9346a36..b70054fe84a 100644
--- a/components/style/gecko/selector_parser.rs
+++ b/components/style/gecko/selector_parser.rs
@@ -36,9 +36,8 @@ pub type PseudoClassStringArg = Box<[u16]>;
 
 macro_rules! pseudo_class_name {
     (bare: [$(($css:expr, $name:ident, $gecko_type:tt, $state:tt, $flags:tt),)*],
-     string: [$(($s_css:expr, $s_name:ident, $s_gecko_type:tt, $s_state:tt, $s_flags:tt),)*],
-     keyword: [$(($k_css:expr, $k_name:ident, $k_gecko_type:tt, $k_state:tt, $k_flags:tt),)*]) => {
-        #[doc = "Our representation of a non tree-structural pseudo-class."]
+     string: [$(($s_css:expr, $s_name:ident, $s_gecko_type:tt, $s_state:tt, $s_flags:tt),)*]) => {
+        /// Our representation of a non tree-structural pseudo-class.
         #[derive(Clone, Debug, Eq, PartialEq)]
         pub enum NonTSPseudoClass {
             $(
@@ -49,10 +48,6 @@ macro_rules! pseudo_class_name {
                 #[doc = $s_css]
                 $s_name(PseudoClassStringArg),
             )*
-            $(
-                #[doc = $k_css]
-                $k_name(Box<[u16]>),
-            )*
             /// The `:dir` pseudo-class.
             Dir(Box<Direction>),
             /// The non-standard `:-moz-any` pseudo-class.
@@ -60,6 +55,8 @@ macro_rules! pseudo_class_name {
             /// TODO(emilio): We disallow combinators and pseudos here, so we
             /// should use SimpleSelector instead
             MozAny(Box<[Selector<SelectorImpl>]>),
+            /// The non-standard `:-moz-locale-dir` pseudo-class.
+            MozLocaleDir(Box<Direction>),
         }
     }
 }
@@ -71,8 +68,7 @@ impl ToCss for NonTSPseudoClass {
         use fmt::Write;
         macro_rules! pseudo_class_serialize {
             (bare: [$(($css:expr, $name:ident, $gecko_type:tt, $state:tt, $flags:tt),)*],
-             string: [$(($s_css:expr, $s_name:ident, $s_gecko_type:tt, $s_state:tt, $s_flags:tt),)*],
-             keyword: [$(($k_css:expr, $k_name:ident, $k_gecko_type:tt, $k_state:tt, $k_flags:tt),)*]) => {
+             string: [$(($s_css:expr, $s_name:ident, $s_gecko_type:tt, $s_state:tt, $s_flags:tt),)*]) => {
                 match *self {
                     $(NonTSPseudoClass::$name => concat!(":", $css),)*
                     $(NonTSPseudoClass::$s_name(ref s) => {
@@ -87,16 +83,14 @@ impl ToCss for NonTSPseudoClass {
                         }
                         return dest.write_str(")")
                     }, )*
-                    $(NonTSPseudoClass::$k_name(ref s) => {
-                        // Don't include the terminating nul.
-                        let value = String::from_utf16(&s[..s.len() - 1]).unwrap();
-                        dest.write_str(concat!(":", $k_css, "("))?;
-                        dest.write_str(&value)?;
+                    NonTSPseudoClass::MozLocaleDir(ref dir) => {
+                        dest.write_str(":-moz-locale-dir(")?;
+                        dir.to_css(dest)?;
                         return dest.write_char(')')
-                    }, )*
+                    },
                     NonTSPseudoClass::Dir(ref dir) => {
                         dest.write_str(":dir(")?;
-                        (**dir).to_css(dest)?;
+                        dir.to_css(dest)?;
                         return dest.write_char(')')
                     },
                     NonTSPseudoClass::MozAny(ref selectors) => {
@@ -146,13 +140,14 @@ impl NonTSPseudoClass {
         }
         macro_rules! pseudo_class_check_is_enabled_in {
             (bare: [$(($css:expr, $name:ident, $gecko_type:tt, $state:tt, $flags:tt),)*],
-            string: [$(($s_css:expr, $s_name:ident, $s_gecko_type:tt, $s_state:tt, $s_flags:tt),)*],
-            keyword: [$(($k_css:expr, $k_name:ident, $k_gecko_type:tt, $k_state:tt, $k_flags:tt),)*]) => {
+            string: [$(($s_css:expr, $s_name:ident, $s_gecko_type:tt, $s_state:tt, $s_flags:tt),)*]) => {
                 match *self {
                     $(NonTSPseudoClass::$name => check_flag!($flags),)*
                     $(NonTSPseudoClass::$s_name(..) => check_flag!($s_flags),)*
-                    $(NonTSPseudoClass::$k_name(..) => check_flag!($k_flags),)*
-                    NonTSPseudoClass::Dir(_) => false,
+                    // TODO(emilio): Maybe -moz-locale-dir shouldn't be
+                    // content-exposed.
+                    NonTSPseudoClass::MozLocaleDir(_) |
+                    NonTSPseudoClass::Dir(_) |
                     NonTSPseudoClass::MozAny(_) => false,
                 }
             }
@@ -191,13 +186,12 @@ impl NonTSPseudoClass {
         }
         macro_rules! pseudo_class_state {
             (bare: [$(($css:expr, $name:ident, $gecko_type:tt, $state:tt, $flags:tt),)*],
-             string: [$(($s_css:expr, $s_name:ident, $s_gecko_type:tt, $s_state:tt, $s_flags:tt),)*],
-             keyword: [$(($k_css:expr, $k_name:ident, $k_gecko_type:tt, $k_state:tt, $k_flags:tt),)*]) => {
+             string: [$(($s_css:expr, $s_name:ident, $s_gecko_type:tt, $s_state:tt, $s_flags:tt),)*]) => {
                 match *self {
                     $(NonTSPseudoClass::$name => flag!($state),)*
                     $(NonTSPseudoClass::$s_name(..) => flag!($s_state),)*
-                    $(NonTSPseudoClass::$k_name(..) => flag!($k_state),)*
-                    NonTSPseudoClass::Dir(..) => ElementState::empty(),
+                    NonTSPseudoClass::Dir(..) |
+                    NonTSPseudoClass::MozLocaleDir(..) |
                     NonTSPseudoClass::MozAny(..) => ElementState::empty(),
                 }
             }
@@ -256,12 +250,11 @@ impl NonTSPseudoClass {
         }
         macro_rules! pseudo_class_geckotype {
             (bare: [$(($css:expr, $name:ident, $gecko_type:tt, $state:tt, $flags:tt),)*],
-             string: [$(($s_css:expr, $s_name:ident, $s_gecko_type:tt, $s_state:tt, $s_flags:tt),)*],
-             keyword: [$(($k_css:expr, $k_name:ident, $k_gecko_type:tt, $k_state:tt, $k_flags:tt),)*]) => {
+             string: [$(($s_css:expr, $s_name:ident, $s_gecko_type:tt, $s_state:tt, $s_flags:tt),)*]) => {
                 match *self {
                     $(NonTSPseudoClass::$name => gecko_type!($gecko_type),)*
                     $(NonTSPseudoClass::$s_name(..) => gecko_type!($s_gecko_type),)*
-                    $(NonTSPseudoClass::$k_name(..) => gecko_type!($k_gecko_type),)*
+                    NonTSPseudoClass::MozLocaleDir(_) => gecko_type!(mozLocaleDir),
                     NonTSPseudoClass::Dir(_) => gecko_type!(dir),
                     NonTSPseudoClass::MozAny(_) => gecko_type!(any),
                 }
@@ -353,8 +346,7 @@ impl<'a, 'i> ::selectors::Parser<'i> for SelectorParser<'a> {
     ) -> Result<NonTSPseudoClass, ParseError<'i>> {
         macro_rules! pseudo_class_parse {
             (bare: [$(($css:expr, $name:ident, $gecko_type:tt, $state:tt, $flags:tt),)*],
-             string: [$(($s_css:expr, $s_name:ident, $s_gecko_type:tt, $s_state:tt, $s_flags:tt),)*],
-             keyword: [$(($k_css:expr, $k_name:ident, $k_gecko_type:tt, $k_state:tt, $k_flags:tt),)*]) => {
+             string: [$(($s_css:expr, $s_name:ident, $s_gecko_type:tt, $s_state:tt, $s_flags:tt),)*]) => {
                 match_ignore_ascii_case! { &name,
                     $($css => NonTSPseudoClass::$name,)*
                     _ => return Err(location.new_custom_error(
@@ -378,8 +370,7 @@ impl<'a, 'i> ::selectors::Parser<'i> for SelectorParser<'a> {
     ) -> Result<NonTSPseudoClass, ParseError<'i>> {
         macro_rules! pseudo_class_string_parse {
             (bare: [$(($css:expr, $name:ident, $gecko_type:tt, $state:tt, $flags:tt),)*],
-             string: [$(($s_css:expr, $s_name:ident, $s_gecko_type:tt, $s_state:tt, $s_flags:tt),)*],
-             keyword: [$(($k_css:expr, $k_name:ident, $k_gecko_type:tt, $k_state:tt, $k_flags:tt),)*]) => {
+             string: [$(($s_css:expr, $s_name:ident, $s_gecko_type:tt, $s_state:tt, $s_flags:tt),)*]) => {
                 match_ignore_ascii_case! { &name,
                     $($s_css => {
                         let name = parser.expect_ident_or_string()?;
@@ -388,23 +379,15 @@ impl<'a, 'i> ::selectors::Parser<'i> for SelectorParser<'a> {
                         let utf16: Vec<u16> = name.encode_utf16().chain(Some(0u16)).collect();
                         NonTSPseudoClass::$s_name(utf16.into_boxed_slice())
                     }, )*
-                    $($k_css => {
-                        let name = parser.expect_ident()?;
-                        // Convert to ASCII-lowercase nul-terminated UTF-16 string.
-                        let utf16: Vec<u16> = name.encode_utf16().map(utf16_to_ascii_lowercase)
-                            .chain(Some(0u16)).collect();
-                        NonTSPseudoClass::$k_name(utf16.into_boxed_slice())
-                    }, )*
+                    "-moz-locale-dir" => {
+                        NonTSPseudoClass::MozLocaleDir(
+                            Box::new(Direction::parse(parser)?)
+                        )
+                    },
                     "dir" => {
-                        let name: &str = parser.expect_ident()?;
-                        let direction = match_ignore_ascii_case! { name,
-                            "rtl" => Direction::Rtl,
-                            "ltr" => Direction::Ltr,
-                            _ => {
-                                Direction::Other(Box::from(name))
-                            },
-                        };
-                        NonTSPseudoClass::Dir(Box::new(direction))
+                        NonTSPseudoClass::Dir(
+                            Box::new(Direction::parse(parser)?)
+                        )
                     },
                     "-moz-any" => {
                         NonTSPseudoClass::MozAny(
@@ -496,13 +479,6 @@ impl SelectorImpl {
     }
 }
 
-fn utf16_to_ascii_lowercase(unit: u16) -> u16 {
-    match unit {
-        65...90 => unit + 32, // A-Z => a-z
-        _ => unit
-    }
-}
-
 unsafe impl HasFFI for SelectorList<SelectorImpl> {
     type FFIType = RawServoSelectorList;
 }
diff --git a/components/style/gecko/wrapper.rs b/components/style/gecko/wrapper.rs
index 687b95fde82..56ad17e6009 100644
--- a/components/style/gecko/wrapper.rs
+++ b/components/style/gecko/wrapper.rs
@@ -46,7 +46,6 @@ use gecko_bindings::bindings::Gecko_GetUnvisitedLinkAttrDeclarationBlock;
 use gecko_bindings::bindings::Gecko_GetVisitedLinkAttrDeclarationBlock;
 use gecko_bindings::bindings::Gecko_IsSignificantChild;
 use gecko_bindings::bindings::Gecko_MatchLang;
-use gecko_bindings::bindings::Gecko_MatchStringArgPseudo;
 use gecko_bindings::bindings::Gecko_UnsetDirtyStyleAttr;
 use gecko_bindings::bindings::Gecko_UpdateAnimations;
 use gecko_bindings::structs;
@@ -2111,7 +2110,8 @@ impl<'le> ::selectors::Element for GeckoElement<'le> {
                 self.get_document_theme() == DocumentTheme::Doc_Theme_Dark
             }
             NonTSPseudoClass::MozWindowInactive => {
-                self.document_state().contains(DocumentState::NS_DOCUMENT_STATE_WINDOW_INACTIVE)
+                self.document_state()
+                    .contains(DocumentState::NS_DOCUMENT_STATE_WINDOW_INACTIVE)
             }
             NonTSPseudoClass::MozPlaceholder => false,
             NonTSPseudoClass::MozAny(ref sels) => {
@@ -2125,13 +2125,15 @@ impl<'le> ::selectors::Element for GeckoElement<'le> {
             NonTSPseudoClass::Lang(ref lang_arg) => {
                 self.match_element_lang(None, lang_arg)
             }
-            NonTSPseudoClass::MozLocaleDir(ref s) => {
-                unsafe {
-                    Gecko_MatchStringArgPseudo(
-                        self.0,
-                        pseudo_class.to_gecko_pseudoclasstype().unwrap(),
-                        s.as_ptr(),
-                    )
+            NonTSPseudoClass::MozLocaleDir(ref dir) => {
+                let doc_is_rtl =
+                    self.document_state()
+                        .contains(DocumentState::NS_DOCUMENT_STATE_RTL_LOCALE);
+
+                match **dir {
+                    Direction::Ltr => !doc_is_rtl,
+                    Direction::Rtl => doc_is_rtl,
+                    Direction::Other(..) => false,
                 }
             }
             NonTSPseudoClass::Dir(ref dir) => {
diff --git a/components/style/selector_parser.rs b/components/style/selector_parser.rs
index b4870557cc2..54978d284b7 100644
--- a/components/style/selector_parser.rs
+++ b/components/style/selector_parser.rs
@@ -183,9 +183,23 @@ pub enum Direction {
     /// right-to-left semantic directionality
     Rtl,
     /// Some other provided directionality value
+    ///
+    /// TODO(emilio): If we atomize we can then unbox in NonTSPseudoClass.
     Other(Box<str>),
 }
 
+impl Direction {
+    /// Parse a direction value.
+    pub fn parse<'i, 't>(parser: &mut CssParser<'i, 't>) -> Result<Self, ParseError<'i>> {
+        let ident = parser.expect_ident()?;
+        Ok(match_ignore_ascii_case! { &ident,
+            "rtl" => Direction::Rtl,
+            "ltr" => Direction::Ltr,
+            _ => Direction::Other(Box::from(ident.as_ref())),
+        })
+    }
+}
+
 impl ToCss for Direction {
     fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: Write {
         let dir_str = match *self {