diff --git a/components/style/style_adjuster.rs b/components/style/style_adjuster.rs
index 6a3dc75f4d8..36463aad6fb 100644
--- a/components/style/style_adjuster.rs
+++ b/components/style/style_adjuster.rs
@@ -12,8 +12,6 @@ use crate::properties::longhands::float::computed_value::T as Float;
 use crate::properties::longhands::overflow_x::computed_value::T as Overflow;
 use crate::properties::longhands::position::computed_value::T as Position;
 use crate::properties::{self, ComputedValues, StyleBuilder};
-#[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
-use crate::values::specified::box_::DisplayInside;
 use app_units::Au;
 
 /// A struct that implements all the adjustment methods.
@@ -207,7 +205,7 @@ impl<'a, 'b: 'a> StyleAdjuster<'a, 'b> {
             self.style.pseudo.map_or(false, |p| p.is_marker()) &&
                 self.style.get_parent_list().clone_list_style_position() ==
                     ListStylePosition::Outside &&
-                layout_parent_style.get_box().clone_display().inside() != DisplayInside::Inline
+                !layout_parent_style.get_box().clone_display().is_inline_flow()
         );
 
         if !blockify {
diff --git a/components/style/values/specified/box.rs b/components/style/values/specified/box.rs
index ad8602ac431..1549f66e8e9 100644
--- a/components/style/values/specified/box.rs
+++ b/components/style/values/specified/box.rs
@@ -61,12 +61,9 @@ pub enum DisplayInside {
     None = 0,
     #[cfg(any(feature = "servo-layout-2020", feature = "gecko"))]
     Contents,
-    #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
-    Block,
+    Flow,
     FlowRoot,
     #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
-    Inline,
-    #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
     Flex,
     #[cfg(feature = "gecko")]
     Grid,
@@ -114,7 +111,6 @@ pub enum DisplayInside {
     MozGroupbox,
     #[cfg(feature = "gecko")]
     MozPopup,
-    Flow, // only used for parsing, not computed value
 }
 
 #[allow(missing_docs)]
@@ -147,14 +143,8 @@ impl Display {
     pub const None: Self = Self::new(DisplayOutside::None, DisplayInside::None);
     #[cfg(any(feature = "servo-layout-2020", feature = "gecko"))]
     pub const Contents: Self = Self::new(DisplayOutside::None, DisplayInside::Contents);
-    #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
-    pub const Inline: Self = Self::new(DisplayOutside::Inline, DisplayInside::Inline);
-    #[cfg(any(feature = "servo-layout-2020"))]
     pub const Inline: Self = Self::new(DisplayOutside::Inline, DisplayInside::Flow);
     pub const InlineBlock: Self = Self::new(DisplayOutside::Inline, DisplayInside::FlowRoot);
-    #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
-    pub const Block: Self = Self::new(DisplayOutside::Block, DisplayInside::Block);
-    #[cfg(any(feature = "servo-layout-2020"))]
     pub const Block: Self = Self::new(DisplayOutside::Block, DisplayInside::Flow);
     #[cfg(feature = "gecko")]
     pub const FlowRoot: Self = Self::new(DisplayOutside::Block, DisplayInside::FlowRoot);
@@ -171,7 +161,7 @@ impl Display {
     #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
     pub const InlineTable: Self = Self::new(DisplayOutside::Inline, DisplayInside::Table);
     #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
-    pub const TableCaption: Self = Self::new(DisplayOutside::TableCaption, DisplayInside::Block);
+    pub const TableCaption: Self = Self::new(DisplayOutside::TableCaption, DisplayInside::Flow);
     #[cfg(feature = "gecko")]
     pub const Ruby: Self = Self::new(DisplayOutside::Inline, DisplayInside::Ruby);
     #[cfg(feature = "gecko")]
@@ -256,18 +246,8 @@ impl Display {
     }
 
     /// Make a display enum value from <display-outside> and <display-inside> values.
-    /// We store `flow` as a synthetic `block` or `inline` inside-value to simplify
-    /// our layout code.
     #[inline]
     fn from3(outside: DisplayOutside, inside: DisplayInside, list_item: bool) -> Self {
-        let inside = match inside {
-            #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
-            DisplayInside::Flow => match outside {
-                DisplayOutside::Inline => DisplayInside::Inline,
-                _ => DisplayInside::Block,
-            },
-            _ => inside,
-        };
         let v = Self::new(outside, inside);
         if !list_item {
             return v;
@@ -290,6 +270,13 @@ impl Display {
         .unwrap()
     }
 
+    /// Whether this is `display: inline` (or `inline list-item`).
+    #[inline]
+    pub fn is_inline_flow(&self) -> bool {
+        self.outside() == DisplayOutside::Inline &&
+            self.inside() == DisplayInside::Flow
+    }
+
     /// Returns whether this `display` value is some kind of list-item.
     #[inline]
     pub const fn is_list_item(&self) -> bool {
@@ -381,9 +368,8 @@ impl Display {
         match self.outside() {
             DisplayOutside::Inline => {
                 let inside = match self.inside() {
-                    #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
-                    DisplayInside::Inline | DisplayInside::FlowRoot => DisplayInside::Block,
-                    #[cfg(feature = "servo-layout-2020")]
+                    // `inline-block` blockifies to `block` rather than
+                    // `flow-root`, for legacy reasons.
                     DisplayInside::FlowRoot => DisplayInside::Flow,
                     inside => inside,
                 };
@@ -407,7 +393,9 @@ impl Display {
         match self.outside() {
             DisplayOutside::Block => {
                 let inside = match self.inside() {
-                    DisplayInside::Block => DisplayInside::FlowRoot,
+                    // `display: block` inlinifies to `display: inline-block`,
+                    // rather than `inline`, for legacy reasons.
+                    DisplayInside::Flow => DisplayInside::FlowRoot,
                     inside => inside,
                 };
                 Display::from3(DisplayOutside::Inline, inside, self.is_list_item())
@@ -443,18 +431,8 @@ impl ToCss for Display {
     where
         W: fmt::Write,
     {
-        #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
-        debug_assert_ne!(
-            self.inside(),
-            DisplayInside::Flow,
-            "`flow` fears in `display` computed value"
-        );
         let outside = self.outside();
-        let inside = match self.inside() {
-            #[cfg(any(feature = "servo-layout-2013", feature = "gecko"))]
-            DisplayInside::Block | DisplayInside::Inline => DisplayInside::Flow,
-            inside => inside,
-        };
+        let inside = self.inside();
         match *self {
             Display::Block | Display::Inline => outside.to_css(dest),
             Display::InlineBlock => dest.write_str("inline-block"),