diff --git a/components/style/custom_properties.rs b/components/style/custom_properties.rs
index a6908bb4cfa..7e8a1e37f7f 100644
--- a/components/style/custom_properties.rs
+++ b/components/style/custom_properties.rs
@@ -71,7 +71,12 @@ static ENVIRONMENT_VARIABLES: [EnvironmentVariable; 4] = [
     make_variable!(atom!("safe-area-inset-right"), get_safearea_inset_right),
 ];
 
-static CHROME_ENVIRONMENT_VARIABLES: [EnvironmentVariable; 0] = [
+fn get_titlebar_radius(device: &Device) -> VariableValue {
+    VariableValue::pixel(device.titlebar_radius())
+}
+
+static CHROME_ENVIRONMENT_VARIABLES: [EnvironmentVariable; 1] = [
+    make_variable!(atom!("-moz-gtk-csd-titlebar-radius"), get_titlebar_radius),
 ];
 
 impl CssEnvironment {
diff --git a/components/style/gecko/media_queries.rs b/components/style/gecko/media_queries.rs
index 2966363a8eb..a560211d2f3 100644
--- a/components/style/gecko/media_queries.rs
+++ b/components/style/gecko/media_queries.rs
@@ -440,6 +440,13 @@ impl Device {
         }
     }
 
+    /// Returns the gtk titlebar radius in CSS pixels.
+    pub fn titlebar_radius(&self) -> f32 {
+        unsafe {
+            bindings::Gecko_GetLookAndFeelFloat(bindings::LookAndFeel_FloatID::TitlebarRadius as i32)
+        }
+    }
+
     /// Return whether the document is a chrome document.
     #[inline]
     pub fn is_chrome_document(&self) -> bool {