add firefox extension template

externs/webextension_polyfill/runtime/Port.hx

@@ -0,0 +1,30 @@
+package webextension_polyfill.runtime;
+
+/**
+	An object which allows two way communication with other pages.
+**/
+typedef Port = {
+	var name : String;
+	function disconnect():Void;
+	var onDisconnect : webextension_polyfill.events.Event<(port:Port) -> Void>;
+	var onMessage : webextension_polyfill.events.Event<(message:Dynamic, port:Port) -> Void>;
+	/**
+		Send a message to the other end. This takes one argument, which is a JSON object representing the message to send.
+		It will be delivered to any script listening to the port's onMessage event, or to the native application if this port
+		is connected to a native application.
+	**/
+	function postMessage(message:Dynamic):Void;
+	/**
+		This property will <b>only</b> be present on ports passed to onConnect/onConnectExternal listeners.
+		Optional.
+	**/
+	@:optional
+	var sender : MessageSender;
+	/**
+		If the port was disconnected due to an error, this will be set to an object with a string property message,
+		giving you more information about the error. See onDisconnect.
+		Optional.
+	**/
+	@:optional
+	var error : PortErrorType;
+};