add firefox extension template

externs/webextension_polyfill/theme/Static.hx

@@ -0,0 +1,23 @@
+package webextension_polyfill.theme;
+
+typedef Static = {
+	/**
+		Returns the current theme for the specified window or the last focused window.
+	**/
+	function getCurrent(?windowId:Float):js.lib.Promise<Dynamic>;
+	/**
+		Make complete updates to the theme. Resolves when the update has completed.
+		
+		Make complete updates to the theme. Resolves when the update has completed.
+	**/
+	@:overload(function(details:webextension_polyfill.manifest.ThemeType):js.lib.Promise<ts.Undefined> { })
+	function update(windowId:Null<Float>, details:webextension_polyfill.manifest.ThemeType):js.lib.Promise<ts.Undefined>;
+	/**
+		Removes the updates made to the theme.
+	**/
+	function reset(?windowId:Float):js.lib.Promise<ts.Undefined>;
+	/**
+		Fired when a new theme has been applied
+	**/
+	var onUpdated : webextension_polyfill.events.Event<(updateInfo:ThemeUpdateInfo) -> Void>;
+};