diff --git a/crates/web-sys/webidls/enabled/nsISupports.webidl b/crates/web-sys/webidls/enabled/nsISupports.webidl
new file mode 100644
index 000000000..7578b9d5c
--- /dev/null
+++ b/crates/web-sys/webidls/enabled/nsISupports.webidl
@@ -0,0 +1,4 @@
+// `nsISupports` is a Gecko thing that can be queried if it implements some
+// interface. We can query anything via `JsCast`, so it is good enough to just
+// call it an Object.
+typedef Object nsISupports;