diff --git a/components/style/gecko/wrapper.rs b/components/style/gecko/wrapper.rs
index 0666338058e..12a4c884336 100644
--- a/components/style/gecko/wrapper.rs
+++ b/components/style/gecko/wrapper.rs
@@ -51,7 +51,7 @@ use gecko_bindings::structs::NODE_IS_NATIVE_ANONYMOUS;
 use gecko_bindings::sugar::ownership::HasArcFFI;
 use parking_lot::RwLock;
 use properties::{ComputedValues, parse_style_attribute};
-use properties::PropertyDeclarationBlock;
+use properties::{Importance, PropertyDeclaration, PropertyDeclarationBlock};
 use properties::animated_properties::AnimationValueMap;
 use rule_tree::CascadeLevel as ServoCascadeLevel;
 use selector_parser::{ElementExt, Snapshot};
@@ -624,6 +624,24 @@ impl<'le> PresentationalHintsSynthetizer for GeckoElement<'le> {
     fn synthesize_presentational_hints_for_legacy_attributes<V>(&self, hints: &mut V)
         where V: Push<ApplicableDeclarationBlock>,
     {
+        use properties::longhands::text_align::SpecifiedValue;
+        lazy_static! {
+            static ref TH_RULE: ApplicableDeclarationBlock = {
+                let global_style_data = &*GLOBAL_STYLE_DATA;
+                let pdb = PropertyDeclarationBlock::with_one(
+                    PropertyDeclaration::TextAlign(SpecifiedValue::MozCenterOrInherit),
+                    Importance::Normal
+                );
+                let arc = Arc::new(global_style_data.shared_lock.wrap(pdb));
+                ApplicableDeclarationBlock::from_declarations(arc, ServoCascadeLevel::PresHints)
+            };
+        };
+
+        // <th> elements get a default MozCenterOrInherit which may get overridden
+        if self.get_namespace() == &*Namespace(atom!("http://www.w3.org/1999/xhtml")) &&
+          self.get_local_name().as_ptr() == atom!("th").as_ptr() {
+            hints.push(TH_RULE.clone());
+        }
         let declarations = unsafe { Gecko_GetHTMLPresentationAttrDeclarationBlock(self.0) };
         let declarations = declarations.and_then(|s| s.as_arc_opt());
         if let Some(decl) = declarations {
diff --git a/components/style/properties/gecko.mako.rs b/components/style/properties/gecko.mako.rs
index 78db1f0bd62..bc6d5471b0d 100644
--- a/components/style/properties/gecko.mako.rs
+++ b/components/style/properties/gecko.mako.rs
@@ -2797,8 +2797,12 @@ fn static_assert() {
                                   -webkit-text-stroke-width text-emphasis-position -moz-tab-size -moz-text-size-adjust">
 
     <% text_align_keyword = Keyword("text-align", "start end left right center justify -moz-center -moz-left " +
-                                                  "-moz-right match-parent char") %>
+                                                  "-moz-right char") %>
+    <% text_align_reachable_keyword = Keyword("text-align", "start end left right center justify char") %>
     ${impl_keyword('text_align', 'mTextAlign', text_align_keyword, need_clone=False)}
+    // Stable rust errors on unreachable patterns, and there is overlap, so we run with the overlapping
+    // constants removed
+    ${impl_keyword_clone('text_align', 'mTextAlign', text_align_reachable_keyword)}
 
     pub fn set_text_shadow(&mut self, v: longhands::text_shadow::computed_value::T) {
         self.gecko.mTextShadow.replace_with_new(v.0.len() as u32);
diff --git a/components/style/properties/longhand/inherited_text.mako.rs b/components/style/properties/longhand/inherited_text.mako.rs
index b24cdbbcacf..37d58b07386 100644
--- a/components/style/properties/longhand/inherited_text.mako.rs
+++ b/components/style/properties/longhand/inherited_text.mako.rs
@@ -250,11 +250,10 @@ ${helpers.single_keyword("text-align-last",
                          spec="https://drafts.csswg.org/css-text/#propdef-text-align-last")}
 
 // TODO make this a shorthand and implement text-align-last/text-align-all
-<%helpers:longhand name="text-align" animatable="False" spec="https://drafts.csswg.org/css-text/#propdef-text-align">
-    pub use self::computed_value::T as SpecifiedValue;
+<%helpers:longhand name="text-align" animatable="False" need_clone="True"
+                   spec="https://drafts.csswg.org/css-text/#propdef-text-align">
     use values::computed::ComputedValueAsSpecified;
     use values::HasViewportPercentage;
-    impl ComputedValueAsSpecified for SpecifiedValue {}
     no_viewport_percentage!(SpecifiedValue);
     pub mod computed_value {
         use style_traits::ToCss;
@@ -299,21 +298,110 @@ ${helpers.single_keyword("text-align-last",
             _moz_center("-moz-center") => 6,
             _moz_left("-moz-left") => 7,
             _moz_right("-moz-right") => 8,
-            match_parent("match-parent") => 9,
             char("char") => 10,
             % endif
         }
+
+        ${helpers.gecko_keyword_conversion(Keyword('text-align',
+                                                   """left right center justify -moz-left -moz-right
+                                                    -moz-center char end""",
+                                                    gecko_strip_moz_prefix=False), type="T")}
     }
+
     #[inline] pub fn get_initial_value() -> computed_value::T {
         computed_value::T::start
     }
-    pub fn parse(_context: &ParserContext, input: &mut Parser) -> Result<SpecifiedValue, ()> {
-        computed_value::T::parse(input)
-    }
-    ${helpers.gecko_keyword_conversion(Keyword('text-align',
-                                               """left right center justify -moz-left -moz-right
-                                                -moz-center char end match-parent""",
-                                                gecko_strip_moz_prefix=False))}
+
+
+    % if product == "gecko":
+        use std::fmt;
+        use style_traits::ToCss;
+
+        #[derive(Copy, Clone, Eq, PartialEq, Debug, Hash)]
+        pub enum SpecifiedValue {
+            Keyword(computed_value::T),
+            MatchParent,
+            MozCenterOrInherit,
+        }
+        pub fn parse(_context: &ParserContext, input: &mut Parser) -> Result<SpecifiedValue, ()> {
+            // MozCenterOrInherit cannot be parsed, only set directly on th elements
+            if let Ok(key) = input.try(computed_value::T::parse) {
+                Ok(SpecifiedValue::Keyword(key))
+            } else {
+                input.expect_ident_matching("match-parent")?;
+                Ok(SpecifiedValue::MatchParent)
+            }
+        }
+        impl ToCss for SpecifiedValue {
+            fn to_css<W>(&self, dest: &mut W) -> fmt::Result where W: fmt::Write {
+                match *self {
+                    SpecifiedValue::Keyword(key) => key.to_css(dest),
+                    SpecifiedValue::MatchParent => dest.write_str("match-parent"),
+                    SpecifiedValue::MozCenterOrInherit => Ok(()),
+                }
+            }
+        }
+
+        impl SpecifiedValue {
+            pub fn from_gecko_keyword(kw: u32) -> Self {
+                use gecko_bindings::structs::NS_STYLE_TEXT_ALIGN_MATCH_PARENT;
+                if kw == NS_STYLE_TEXT_ALIGN_MATCH_PARENT {
+                    SpecifiedValue::MatchParent
+                } else {
+                    SpecifiedValue::Keyword(computed_value::T::from_gecko_keyword(kw))
+                }
+            }
+        }
+        impl ToComputedValue for SpecifiedValue {
+            type ComputedValue = computed_value::T;
+
+            #[inline]
+            fn to_computed_value(&self, context: &Context) -> computed_value::T {
+                match *self {
+                    SpecifiedValue::Keyword(key) => key,
+                    SpecifiedValue::MatchParent => {
+                        // on the root <html> element we should still respect the dir
+                        // but the parent dir of that element is LTR even if it's <html dir=rtl>
+                        // and will only be RTL if certain prefs have been set.
+                        // In that case, the default behavior here will set it to left,
+                        // but we want to set it to right -- instead set it to the default (`start`),
+                        // which will do the right thing in this case (but not the general case)
+                        if context.is_root_element {
+                            return get_initial_value();
+                        }
+                        let parent = context.inherited_style().get_inheritedtext().clone_text_align();
+                        let ltr = context.inherited_style().writing_mode.is_bidi_ltr();
+                        match (parent, ltr) {
+                            (computed_value::T::start, true) => computed_value::T::left,
+                            (computed_value::T::start, false) => computed_value::T::right,
+                            (computed_value::T::end, true) => computed_value::T::right,
+                            (computed_value::T::end, false) => computed_value::T::left,
+                            _ => parent
+                        }
+                    }
+                    SpecifiedValue::MozCenterOrInherit => {
+                        let parent = context.inherited_style().get_inheritedtext().clone_text_align();
+                        if parent == computed_value::T::start {
+                            computed_value::T::center
+                        } else {
+                            parent
+                        }
+                    }
+                }
+            }
+
+            #[inline]
+            fn from_computed_value(computed: &computed_value::T) -> Self {
+                SpecifiedValue::Keyword(*computed)
+            }
+        }
+    % else:
+        impl ComputedValueAsSpecified for SpecifiedValue {}
+        pub use self::computed_value::T as SpecifiedValue;
+        pub fn parse(_context: &ParserContext, input: &mut Parser) -> Result<SpecifiedValue, ()> {
+            computed_value::T::parse(input)
+        }
+    % endif
 </%helpers:longhand>
 
 // FIXME: This prop should be animatable.