add firefox extension template

externs/webextension_polyfill/tabs/OnUpdatedEvent.hx

@@ -0,0 +1,17 @@
+package webextension_polyfill.tabs;
+
+/**
+	Fired when a tab is updated.
+**/
+typedef OnUpdatedEvent = {
+	/**
+		Registers an event listener <em>callback</em> to an event.
+	**/
+	function addListener(callback:(tabId:Float, changeInfo:OnUpdatedChangeInfoType, tab:Tab) -> Void, ?filter:UpdateFilter):Void;
+	/**
+		Deregisters an event listener <em>callback</em> from an event.
+	**/
+	function removeListener(callback:(tabId:Float, changeInfo:OnUpdatedChangeInfoType, tab:Tab) -> Void):Void;
+	function hasListener(callback:(tabId:Float, changeInfo:OnUpdatedChangeInfoType, tab:Tab) -> Void):Bool;
+	function hasListeners():Bool;
+};