add firefox extension template

externs/ts/AnyOf3.hx

@@ -0,0 +1,13 @@
+package ts;
+
+/**
+	AnyOf implementation generated by dts2hx
+**/
+@:transitive extern abstract AnyOf3<T0, T1, T2>(Dynamic) from T0 from T1 from T2 to T0 to T1 to T2 {
+	var asType0(get, never) : T0;
+	private inline function get_asType0():T0 return this;
+	var asType1(get, never) : T1;
+	private inline function get_asType1():T1 return this;
+	var asType2(get, never) : T2;
+	private inline function get_asType2():T2 return this;
+}