support multi-frame following

src/content/index.js

@@ -10,5 +10,20 @@ let rootComponent = window.self === window.top
   ? new TopContentComponent(window, store)
   : new FrameContentComponent(window, store);
 
+store.subscribe(() => {
+  rootComponent.update();
+});
+
 browser.runtime.onMessage.addListener(msg => rootComponent.onMessage(msg));
 rootComponent.update();
+
+window.addEventListener('message', (event) => {
+  let message = null;
+  try {
+    message = JSON.parse(event.data);
+  } catch (e) {
+    // ignore unexpected message
+    return;
+  }
+  rootComponent.onMessage(message, event.source);
+});