add firefox extension template

externs/webextension_polyfill/networkstatus/NetworkLinkInfo.hx

@@ -0,0 +1,18 @@
+package webextension_polyfill.networkstatus;
+
+typedef NetworkLinkInfo = {
+	/**
+		Status of the network link, if "unknown" then link is usually assumed to be "up"
+	**/
+	var status : NetworkLinkInfoStatusEnum;
+	/**
+		If known, the type of network connection that is avialable.
+	**/
+	var type : NetworkLinkInfoTypeEnum;
+	/**
+		If known, the network id or name.
+		Optional.
+	**/
+	@:optional
+	var id : String;
+};