add firefox extension template

externs/webextension_polyfill/bookmarks/CreateDetails.hx

@@ -0,0 +1,34 @@
+package webextension_polyfill.bookmarks;
+
+/**
+	Object passed to the create() function.
+**/
+typedef CreateDetails = {
+	/**
+		Defaults to the Other Bookmarks folder.
+		Optional.
+	**/
+	@:optional
+	var parentId : String;
+	/**
+		Optional.
+	**/
+	@:optional
+	var index : Float;
+	/**
+		Optional.
+	**/
+	@:optional
+	var title : String;
+	/**
+		Optional.
+	**/
+	@:optional
+	var url : String;
+	/**
+		Indicates the type of BookmarkTreeNode to create, which can be one of bookmark, folder or separator.
+		Optional.
+	**/
+	@:optional
+	var type : BookmarkTreeNodeType;
+};