diff --git a/components/style/properties/gecko.mako.rs b/components/style/properties/gecko.mako.rs
index fe8b2de3499..18f2e3fa27e 100644
--- a/components/style/properties/gecko.mako.rs
+++ b/components/style/properties/gecko.mako.rs
@@ -3333,6 +3333,38 @@ fn static_assert() {
         }
     }
 
+    #[allow(non_snake_case)]
+    pub fn clone__moz_image_region(&self) -> longhands::_moz_image_region::computed_value::T {
+        use values::{Auto, Either};
+        use values::computed::ClipRect;
+
+        // There is no ideal way to detect auto type for structs::nsRect and its components, so
+        // if all components are zero, we use Auto.
+        if self.gecko.mImageRegion.x == 0 &&
+           self.gecko.mImageRegion.y == 0 &&
+           self.gecko.mImageRegion.width == 0 &&
+           self.gecko.mImageRegion.height == 0 {
+           return Either::Second(Auto);
+        }
+
+        let get_clip_rect_component = |value: structs::nscoord| -> Option<Au> {
+            if value == 0 {
+                None
+            } else {
+                Some(Au(value))
+            }
+        };
+
+        Either::First(ClipRect {
+            top: get_clip_rect_component(self.gecko.mImageRegion.y),
+            right: get_clip_rect_component(self.gecko.mImageRegion.width).map(
+                |v| v + Au(self.gecko.mImageRegion.x)),
+            bottom: get_clip_rect_component(self.gecko.mImageRegion.height).map(
+                |v| v + Au(self.gecko.mImageRegion.y)),
+            left: get_clip_rect_component(self.gecko.mImageRegion.x),
+        })
+    }
+
     ${impl_simple_copy('_moz_image_region', 'mImageRegion')}
 
 </%self:impl_trait>
diff --git a/components/style/properties/longhand/list.mako.rs b/components/style/properties/longhand/list.mako.rs
index 34f51b97b9d..620695f3eba 100644
--- a/components/style/properties/longhand/list.mako.rs
+++ b/components/style/properties/longhand/list.mako.rs
@@ -228,7 +228,7 @@ ${helpers.single_keyword("list-style-position", "outside inside", animation_valu
 ${helpers.predefined_type("-moz-image-region",
                           "ClipRectOrAuto",
                           "computed::ClipRectOrAuto::auto()",
-                          animation_value_type="none",
+                          animation_value_type="ComputedValue",
                           products="gecko",
                           boxed="True",
                           spec="Nonstandard (https://developer.mozilla.org/en-US/docs/Web/CSS/-moz-image-region)")}