add firefox extension template

externs/webextension_polyfill/tabs/ZoomSettings.hx

@@ -0,0 +1,27 @@
+package webextension_polyfill.tabs;
+
+/**
+	Defines how zoom changes in a tab are handled and at what scope.
+**/
+typedef ZoomSettings = {
+	/**
+		Defines how zoom changes are handled, i.e. which entity is responsible for the actual scaling of the page; defaults to
+		<code>automatic</code>.
+		Optional.
+	**/
+	@:optional
+	var mode : ZoomSettingsMode;
+	/**
+		Defines whether zoom changes will persist for the page's origin, or only take effect in this tab; defaults to <code>
+		per-origin</code> when in <code>automatic</code> mode, and <code>per-tab</code> otherwise.
+		Optional.
+	**/
+	@:optional
+	var scope : ZoomSettingsScope;
+	/**
+		Used to return the default zoom level for the current tab in calls to tabs.getZoomSettings.
+		Optional.
+	**/
+	@:optional
+	var defaultZoomFactor : Float;
+};