diff --git a/components/style/properties/gecko.mako.rs b/components/style/properties/gecko.mako.rs
index 967ffa21972..5d3ebaae4e8 100644
--- a/components/style/properties/gecko.mako.rs
+++ b/components/style/properties/gecko.mako.rs
@@ -2204,7 +2204,7 @@ fn static_assert() {
 
 <%self:impl_trait style_struct_name="InheritedText"
                   skip_longhands="text-align text-emphasis-style text-shadow line-height letter-spacing word-spacing
-                                  -webkit-text-stroke-width text-emphasis-position">
+                                  -webkit-text-stroke-width text-emphasis-position -moz-tab-size">
 
     <% text_align_keyword = Keyword("text-align", "start end left right center justify -moz-center -moz-left " +
                                                   "-moz-right match-parent") %>
@@ -2373,6 +2373,22 @@ fn static_assert() {
 
     <%call expr="impl_app_units('_webkit_text_stroke_width', 'mWebkitTextStrokeWidth', need_clone=False)"></%call>
 
+    #[allow(non_snake_case)]
+    pub fn set__moz_tab_size(&mut self, v: longhands::_moz_tab_size::computed_value::T) {
+        use values::Either;
+
+        match v {
+            Either::Second(number) => {
+                self.gecko.mTabSize.set_value(CoordDataValue::Factor(number));
+            }
+            Either::First(au) => {
+                self.gecko.mTabSize.set(au);
+            }
+        }
+    }
+
+    <%call expr="impl_coord_copy('_moz_tab_size', 'mTabSize')"></%call>
+
 </%self:impl_trait>
 
 <%self:impl_trait style_struct_name="Text"
diff --git a/components/style/properties/longhand/border.mako.rs b/components/style/properties/longhand/border.mako.rs
index 624e8ac7926..8a85377febb 100644
--- a/components/style/properties/longhand/border.mako.rs
+++ b/components/style/properties/longhand/border.mako.rs
@@ -257,10 +257,10 @@ ${helpers.single_keyword("-moz-float-edge", "content-box margin-box",
         }
     }
 
-    pub fn parse(_context: &ParserContext, input: &mut Parser) -> Result<SpecifiedValue, ()> {
+    pub fn parse(context: &ParserContext, input: &mut Parser) -> Result<SpecifiedValue, ()> {
         let mut values = vec![];
         for _ in 0..4 {
-            let value = input.try(|input| LengthOrNumber::parse_non_negative(input));
+            let value = input.try(|input| LengthOrNumber::parse_non_negative(context, input));
             match value {
                 Ok(val) => values.push(val),
                 Err(_) => break,
diff --git a/components/style/properties/longhand/inherited_text.mako.rs b/components/style/properties/longhand/inherited_text.mako.rs
index 0a4d7a90632..dc3e32f99b3 100644
--- a/components/style/properties/longhand/inherited_text.mako.rs
+++ b/components/style/properties/longhand/inherited_text.mako.rs
@@ -1030,6 +1030,15 @@ ${helpers.predefined_type("text-emphasis-color", "CSSColor",
                           boxed=True,
                           spec="https://drafts.csswg.org/css-text-decor/#propdef-text-emphasis-color")}
 
+
+${helpers.predefined_type(
+    "-moz-tab-size", "LengthOrNumber",
+    "::values::Either::Second(8.0)",
+    "parse_non_negative",
+    products="gecko", animatable=False,
+    spec="https://drafts.csswg.org/css-text-3/#tab-size-property")}
+
+
 // CSS Compatibility
 // https://compat.spec.whatwg.org
 ${helpers.predefined_type(
diff --git a/components/style/values/specified/length.rs b/components/style/values/specified/length.rs
index 99c4a09abf1..fb4ac9c0b60 100644
--- a/components/style/values/specified/length.rs
+++ b/components/style/values/specified/length.rs
@@ -1215,7 +1215,7 @@ pub type LengthOrNumber = Either<Length, Number>;
 
 impl LengthOrNumber {
     /// Parse a non-negative LengthOrNumber.
-    pub fn parse_non_negative(input: &mut Parser) -> Result<Self, ()> {
+    pub fn parse_non_negative(_context: &ParserContext, input: &mut Parser) -> Result<Self, ()> {
         // We try to parse as a Number first because, for cases like LengthOrNumber,
         // we want "0" to be parsed as a plain Number rather than a Length (0px); this
         // matches the behaviour of all major browsers