diff --git a/src/js/background.js b/src/js/background.js
index c6c1ebb..93f07d2 100644
--- a/src/js/background.js
+++ b/src/js/background.js
@@ -21,8 +21,10 @@ const subtome = {
     browser.browserAction.setTitle({ tabId : tabId, title : browser.i18n.getMessage('page_has_no_feed') });
   },
 
-  hasFeeds () {
-    browser.tabs.executeScript(null, { file : 'js/hasfeeds.js', runAt : 'document_end' });
+  hasFeeds (tabId, changeInfo) {
+    if (changeInfo.url) {
+      browser.tabs.executeScript(tabId, { file : 'js/hasfeeds.js', runAt : 'document_end' });
+    }
   },
 
   handleResponse (response) {
diff --git a/src/js/hasfeeds.js b/src/js/hasfeeds.js
index 5ad96dd..2bfffaa 100644
--- a/src/js/hasfeeds.js
+++ b/src/js/hasfeeds.js
@@ -1,23 +1,27 @@
 'use strict';
 
-const feeds = [];
-const links = document.getElementsByTagName('link');
-const linksLength = links.length;
+// use IIFE to avoid redeclaration of const/let
+(() => {
+  const links = document.getElementsByTagName('link');
+  const linksLength = links.length;
+  let hasFeeds = false;
 
-for (let i = 0; i < linksLength; i++) {
-  const link = links[i];
-  if (link.type && link.rel && link.rel.split(' ').indexOf('alternate') >= 0) {
-    if (link.type.indexOf('rss') >= 0 || link.type.indexOf('atom') >= 0) {
-      if (link.href && link.href.length > 0) {
-        feeds.push(encodeURIComponent(link.href));
+  for (let i = 0; i < linksLength; i++) {
+    const link = links[i];
+    if (link.type && link.rel && link.rel.split(' ').indexOf('alternate') >= 0) {
+      if (link.type.indexOf('rss') >= 0 || link.type.indexOf('atom') >= 0) {
+        if (link.href && link.href.length > 0) {
+          hasFeeds = true;
+          break;
+        }
       }
     }
   }
-}
 
-if (feeds.length > 0) {
-  browser.runtime.sendMessage({ message : 'has_feed' });
-}
-else {
-  browser.runtime.sendMessage({ message : 'has_no_feed' });
-}
+  if (hasFeeds) {
+    browser.runtime.sendMessage({ message : 'has_feed' });
+  }
+  else {
+    browser.runtime.sendMessage({ message : 'has_no_feed' });
+  }
+})();
diff --git a/src/js/subtome.js b/src/js/subtome.js
index 0625ffe..e623c4b 100644
--- a/src/js/subtome.js
+++ b/src/js/subtome.js
@@ -1,20 +1,35 @@
 'use strict';
 
-/* global feeds */
+// use IIFE to avoid redeclaration of const/let
+(() => {
+  const feeds = [];
+  const links = document.getElementsByTagName('link');
+  const linksLength = links.length;
+  const iframe = document.createElement('iframe');
+  const resource = window.location.toString();
+  let loaded = false;
 
-const iframe = document.createElement('iframe');
-const resource = window.location.toString();
-let loaded = false;
+  for (let i = 0; i < linksLength; i++) {
+    const link = links[i];
+    if (link.type && link.rel && link.rel.split(' ').indexOf('alternate') >= 0) {
+      if (link.type.indexOf('rss') >= 0 || link.type.indexOf('atom') >= 0) {
+        if (link.href && link.href.length > 0) {
+          feeds.push(encodeURIComponent(link.href));
+        }
+      }
+    }
+  }
 
-iframe.setAttribute('style', 'display:block; position:fixed; top:0px; left:0px; width:100%; height:100%; border:0px; background: transparent; z-index: 2147483647');
-iframe.setAttribute('src', 'https://www.subtome.com/?subs/#/subscribe?resource=' + encodeURIComponent(resource) + '&feeds=' + encodeURIComponent(feeds.join(',')));
+  iframe.setAttribute('style', 'display:block; position:fixed; top:0px; left:0px; width:100%; height:100%; border:0px; background: transparent; z-index: 2147483647');
+  iframe.setAttribute('src', 'https://www.subtome.com/?subs/#/subscribe?resource=' + encodeURIComponent(resource) + '&feeds=' + encodeURIComponent(feeds.join(',')));
 
-iframe.onload = function () {
-  if (loaded) {
-    document.getElementsByTagName('body')[0].removeChild(iframe);
-  }
+  iframe.onload = function () {
+    if (loaded) {
+      document.getElementsByTagName('body')[0].removeChild(iframe);
+    }
 
-  loaded = true;
-};
+    loaded = true;
+  };
 
-document.getElementsByTagName('body')[0].appendChild(iframe);
+  document.getElementsByTagName('body')[0].appendChild(iframe);
+})();