add polyfill

src/ui/pages/panel.html

@@ -19,6 +19,7 @@
 	<main>
 		<iframe id="view-panel" src="options.html#side-panel"></iframe>
 	</main>
+	<script src="/lib/chrome-browser-polyfill.js"></script>
 	<script type="module" src="../bg/ui-panel.js"></script>
 </body>