diff --git a/components/style/gecko/non_ts_pseudo_class_list.rs b/components/style/gecko/non_ts_pseudo_class_list.rs
index f18bbf839748..fce2c2968290 100644
--- a/components/style/gecko/non_ts_pseudo_class_list.rs
+++ b/components/style/gecko/non_ts_pseudo_class_list.rs
@@ -67,6 +67,11 @@ macro_rules! apply_non_ts_list {
             ],
             string: [
                 ("-moz-system-metric", MozSystemMetric, mozSystemMetric, _, PSEUDO_CLASS_INTERNAL),
+                ("-moz-locale-dir", MozLocaleDir, mozLocaleDir, _, PSEUDO_CLASS_INTERNAL),
+                ("-moz-empty-except-children-with-localname", MozEmptyExceptChildrenWithLocalname,
+                 mozEmptyExceptChildrenWithLocalname, _, PSEUDO_CLASS_INTERNAL),
+                ("dir", Dir, dir, _, _),
+                ("lang", Lang, lang, _, _),
             ]
         }
     }
diff --git a/components/style/gecko/selector_parser.rs b/components/style/gecko/selector_parser.rs
index 25785beee023..3eccac4443c6 100644
--- a/components/style/gecko/selector_parser.rs
+++ b/components/style/gecko/selector_parser.rs
@@ -151,7 +151,7 @@ macro_rules! pseudo_class_name {
             )*
             $(
                 #[doc = $s_css]
-                $s_name(Box<str>),
+                $s_name(Box<[u16]>),
             )*
             /// The non-standard `:-moz-any` pseudo-class.
             MozAny(Vec<ComplexSelector<SelectorImpl>>),
@@ -162,13 +162,20 @@ apply_non_ts_list!(pseudo_class_name);
 
 impl ToCss for NonTSPseudoClass {
     fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
+        use cssparser::CssStringWriter;
+        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),)*]) => {
                 match *self {
                     $(NonTSPseudoClass::$name => concat!(":", $css),)*
                     $(NonTSPseudoClass::$s_name(ref s) => {
-                        return dest.write_str(&format!(":{}({})", $s_css, s))
+                        write!(dest, ":{}(", $s_css)?;
+                        {
+                            let mut css = CssStringWriter::new(dest);
+                            css.write_str(&String::from_utf16(&s).unwrap())?;
+                        }
+                        return dest.write_str(")")
                     }, )*
                     NonTSPseudoClass::MozAny(ref selectors) => {
                         dest.write_str(":-moz-any(")?;
@@ -334,8 +341,11 @@ impl<'a> ::selectors::Parser for SelectorParser<'a> {
              string: [$(($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 = String::from(parser.expect_ident_or_string()?).into_boxed_str();
-                        NonTSPseudoClass::$s_name(name)
+                        let name = parser.expect_ident_or_string()?;
+                        // convert to null terminated utf16 string
+                        // since that's what Gecko deals with
+                        let utf16: Vec<u16> = name.encode_utf16().chain(Some(0u16)).collect();
+                        NonTSPseudoClass::$s_name(utf16.into_boxed_slice())
                     }, )*
                     "-moz-any" => {
                         let selectors = parser.parse_comma_separated(|input| {
diff --git a/components/style/gecko/wrapper.rs b/components/style/gecko/wrapper.rs
index b9cab601f2c4..d98546734b36 100644
--- a/components/style/gecko/wrapper.rs
+++ b/components/style/gecko/wrapper.rs
@@ -35,6 +35,7 @@ use gecko_bindings::bindings::Gecko_GetAnimationRule;
 use gecko_bindings::bindings::Gecko_GetHTMLPresentationAttrDeclarationBlock;
 use gecko_bindings::bindings::Gecko_GetStyleAttrDeclarationBlock;
 use gecko_bindings::bindings::Gecko_GetStyleContext;
+use gecko_bindings::bindings::Gecko_MatchStringArgPseudo;
 use gecko_bindings::bindings::Gecko_UpdateAnimations;
 use gecko_bindings::structs;
 use gecko_bindings::structs::{RawGeckoElement, RawGeckoNode};
@@ -702,10 +703,26 @@ impl<'le> ::selectors::Element for GeckoElement<'le> {
             NonTSPseudoClass::MozBrowserFrame => unsafe {
                 Gecko_MatchesElement(pseudo_class.to_gecko_pseudoclasstype().unwrap(), self.0)
             },
-            NonTSPseudoClass::MozSystemMetric(_) => false,
             NonTSPseudoClass::MozAny(ref sels) => {
                 sels.iter().any(|s| matches_complex_selector(s, self, None, relations, flags))
             }
+            NonTSPseudoClass::MozSystemMetric(ref s) |
+            NonTSPseudoClass::MozLocaleDir(ref s) |
+            NonTSPseudoClass::MozEmptyExceptChildrenWithLocalname(ref s) |
+            NonTSPseudoClass::Dir(ref s) |
+            NonTSPseudoClass::Lang(ref s) => {
+                use selectors::matching::HAS_SLOW_SELECTOR;
+                unsafe {
+                    let mut set_slow_selector = false;
+                    let matches = Gecko_MatchStringArgPseudo(self.0,
+                                       pseudo_class.to_gecko_pseudoclasstype().unwrap(),
+                                       s.as_ptr(), &mut set_slow_selector);
+                    if set_slow_selector {
+                        *flags |= HAS_SLOW_SELECTOR;
+                    }
+                    matches
+                }
+            }
         }
     }
 
diff --git a/components/style/gecko_bindings/bindings.rs b/components/style/gecko_bindings/bindings.rs
index b28183c6ab38..7c2ccb6450c4 100644
--- a/components/style/gecko_bindings/bindings.rs
+++ b/components/style/gecko_bindings/bindings.rs
@@ -1003,6 +1003,12 @@ extern "C" {
                                                RawGeckoPresContextBorrowed)
      -> nscolor;
 }
+extern "C" {
+    pub fn Gecko_MatchStringArgPseudo(element: RawGeckoElementBorrowed,
+                                      type_: CSSPseudoClassType,
+                                      ident: *const u16,
+                                      set_slow_selector: *mut bool) -> bool;
+}
 extern "C" {
     pub fn Gecko_Construct_Default_nsStyleFont(ptr: *mut nsStyleFont,
                                                pres_context: