add firefox extension template

externs/webextension_polyfill/history/HistoryItem.hx

@@ -0,0 +1,41 @@
+package webextension_polyfill.history;
+
+/**
+	An object encapsulating one result of a history query.
+**/
+typedef HistoryItem = {
+	/**
+		The unique identifier for the item.
+	**/
+	var id : String;
+	/**
+		The URL navigated to by a user.
+		Optional.
+	**/
+	@:optional
+	var url : String;
+	/**
+		The title of the page when it was last loaded.
+		Optional.
+	**/
+	@:optional
+	var title : String;
+	/**
+		When this page was last loaded, represented in milliseconds since the epoch.
+		Optional.
+	**/
+	@:optional
+	var lastVisitTime : Float;
+	/**
+		The number of times the user has navigated to this page.
+		Optional.
+	**/
+	@:optional
+	var visitCount : Float;
+	/**
+		The number of times the user has navigated to this page by typing in the address.
+		Optional.
+	**/
+	@:optional
+	var typedCount : Float;
+};