--- a/servo/components/style/properties/gecko.mako.rs
+++ b/servo/components/style/properties/gecko.mako.rs
@@ -2114,16 +2114,69 @@ fn static_assert() {
         use gecko_bindings::bindings::Gecko_CopyAlternateValuesFrom;
 
         self.gecko.mFont.variantAlternates = other.gecko.mFont.variantAlternates;
         unsafe {
             Gecko_CopyAlternateValuesFrom(&mut self.gecko.mFont, &other.gecko.mFont);
         }
     }
 
+    pub fn clone_font_variant_alternates(&self) -> longhands::font_variant_alternates::computed_value::T {
+        use Atom;
+        % for value in "normal swash stylistic ornaments annotation styleset character_variant historical".split():
+            use gecko_bindings::structs::NS_FONT_VARIANT_ALTERNATES_${value.upper()};
+        % endfor
+        use properties::longhands::font_variant_alternates::VariantAlternates;
+        use properties::longhands::font_variant_alternates::VariantAlternatesList;
+        use values::CustomIdent;
+
+        if self.gecko.mFont.variantAlternates == NS_FONT_VARIANT_ALTERNATES_NORMAL as u16 {
+            return VariantAlternatesList(vec![].into_boxed_slice());
+        }
+
+        let mut alternates = Vec::with_capacity(self.gecko.mFont.alternateValues.len());
+        if self.gecko.mFont.variantAlternates & (NS_FONT_VARIANT_ALTERNATES_HISTORICAL as u16) != 0 {
+            alternates.push(VariantAlternates::HistoricalForms);
+        }
+
+        <%
+            property_need_ident_list = "styleset character_variant".split()
+        %>
+        % for value in property_need_ident_list:
+            let mut ${value}_list = Vec::new();
+        % endfor
+
+        for gecko_alternate_value in self.gecko.mFont.alternateValues.iter() {
+            let ident = Atom::from(gecko_alternate_value.value.to_string());
+            match gecko_alternate_value.alternate {
+                % for value in "Swash Stylistic Ornaments Annotation".split():
+                    NS_FONT_VARIANT_ALTERNATES_${value.upper()} => {
+                        alternates.push(VariantAlternates::${value}(CustomIdent(ident)));
+                    },
+                % endfor
+                % for value in property_need_ident_list:
+                    NS_FONT_VARIANT_ALTERNATES_${value.upper()} => {
+                        ${value}_list.push(CustomIdent(ident));
+                    },
+                % endfor
+                x => {
+                    panic!("Found unexpected value for font-variant-alternates: {:?}", x);
+                }
+            }
+        }
+
+        % for value in property_need_ident_list:
+            if !${value}_list.is_empty() {
+                alternates.push(VariantAlternates::${to_camel_case(value)}(${value}_list.into_boxed_slice()));
+            }
+        % endfor
+
+        VariantAlternatesList(alternates.into_boxed_slice())
+    }
+
     ${impl_simple_type_with_conversion("font_variant_ligatures", "mFont.variantLigatures")}
     ${impl_simple_type_with_conversion("font_variant_east_asian", "mFont.variantEastAsian")}
     ${impl_simple_type_with_conversion("font_variant_numeric", "mFont.variantNumeric")}
 
     #[allow(non_snake_case)]
     pub fn set__moz_min_font_size_ratio(&mut self, v: longhands::_moz_min_font_size_ratio::computed_value::T) {
         let percentage = if v.0 > 255. {
             255.

--- a/servo/components/style/properties/longhand/font.mako.rs
+++ b/servo/components/style/properties/longhand/font.mako.rs
@@ -1257,17 +1257,17 @@ macro_rules! impl_gecko_keyword_conversi
                                 "auto none normal",
                                 products="gecko",
                                 gecko_ffi_name="mFont.kerning",
                                 gecko_constant_prefix="NS_FONT_KERNING",
                                 spec="https://drafts.csswg.org/css-fonts/#propdef-font-kerning",
                                 flags="APPLIES_TO_FIRST_LETTER APPLIES_TO_FIRST_LINE APPLIES_TO_PLACEHOLDER",
                                 animation_value_type="discrete")}
 
-<%helpers:longhand name="font-variant-alternates" products="gecko" animation_value_type="none"
+<%helpers:longhand name="font-variant-alternates" products="gecko" animation_value_type="discrete"
                    flags="APPLIES_TO_FIRST_LETTER APPLIES_TO_FIRST_LINE APPLIES_TO_PLACEHOLDER"
                    spec="https://drafts.csswg.org/css-fonts/#propdef-font-variant-alternates">
     use properties::longhands::system_font::SystemFont;
     use std::fmt;
     use style_traits::ToCss;
     use values::CustomIdent;
 
     no_viewport_percentage!(SpecifiedValue);