diff --git a/components/style/values/specified/box.rs b/components/style/values/specified/box.rs
index 0bcc5876beb..f62d3c15101 100644
--- a/components/style/values/specified/box.rs
+++ b/components/style/values/specified/box.rs
@@ -93,8 +93,6 @@ pub enum DisplayInside {
     WebkitBox,
     #[cfg(feature = "gecko")]
     MozBox,
-    #[cfg(feature = "gecko")]
-    MozPopup,
 }
 
 #[allow(missing_docs)]
@@ -194,8 +192,6 @@ impl Display {
     pub const MozBox: Self = Self::new(DisplayOutside::Block, DisplayInside::MozBox);
     #[cfg(feature = "gecko")]
     pub const MozInlineBox: Self = Self::new(DisplayOutside::Inline, DisplayInside::MozBox);
-    #[cfg(feature = "gecko")]
-    pub const MozPopup: Self = Self::new(DisplayOutside::XUL, DisplayInside::MozPopup);
 
     /// Make a raw display value from <display-outside> and <display-inside> values.
     #[inline]
@@ -558,8 +554,6 @@ impl Parse for Display {
             "-moz-box" if moz_display_values_enabled(context) => Display::MozBox,
             #[cfg(feature = "gecko")]
             "-moz-inline-box" if moz_display_values_enabled(context) => Display::MozInlineBox,
-            #[cfg(feature = "gecko")]
-            "-moz-popup" if moz_display_values_enabled(context) => Display::MozPopup,
         })
     }
 }