add firefox extension template

externs/webextension_polyfill/windows/GetInfo.hx

@@ -0,0 +1,15 @@
+package webextension_polyfill.windows;
+
+/**
+	Specifies whether the $(ref:windows.Window) returned should contain a list of the $(ref:tabs.Tab) objects.
+**/
+typedef GetInfo = {
+	/**
+		If true, the $(ref:windows.Window) returned will have a <var>tabs</var> property that contains a list of the $(ref:tabs.
+		Tab) objects. The <code>Tab</code> objects only contain the <code>url</code>, <code>title</code> and <code>
+		favIconUrl</code> properties if the extension's manifest file includes the <code>"tabs"</code> permission.
+		Optional.
+	**/
+	@:optional
+	var populate : Bool;
+};