diff --git a/Libraries/LibWeb/HTML/Location.idl b/Libraries/LibWeb/HTML/Location.idl
index d79cb6eb70f..09d748f793f 100644
--- a/Libraries/LibWeb/HTML/Location.idl
+++ b/Libraries/LibWeb/HTML/Location.idl
@@ -15,5 +15,8 @@ interface Location { // but see also additional creation steps and overridden in
     [LegacyUnforgeable] undefined replace(USVString url);
     [LegacyUnforgeable] undefined reload();
 
-    [FIXME, LegacyUnforgeable, SameObject] readonly attribute DOMStringList ancestorOrigins;
+    // Intentionally not implemented at this stage due to https://github.com/whatwg/html/issues/1918
+    // This is not currently implemented by Firefox due to the above, and only seems to be used by
+    // ad tech on real sites.
+    // [LegacyUnforgeable, SameObject] readonly attribute DOMStringList ancestorOrigins;
 };