diff --git a/app/scripts/background.js b/app/scripts/background.js
index c3b8a0c..e2a0e50 100644
--- a/app/scripts/background.js
+++ b/app/scripts/background.js
@@ -205,14 +205,14 @@ browser.runtime.onInstalled.addListener(function () {
 
 // create the offscreen document if it doesn't already exist
 async function createOffscreen() {
-  if (await chrome.offscreen.hasDocument?.()) return;
-  await chrome.offscreen.createDocument({
+  if (await browser.offscreen === undefined || await browser.offscreen.hasDocument?.()) return;
+  await browser.offscreen.createDocument({
     url: 'pages/offscreen.html',
     reasons: ['BLOBS'],
     justification: 'keep service worker running',
   });
 }
 // a message from an offscreen document every 20 second resets the inactivity timer
-chrome.runtime.onMessage.addListener((msg) => {
+browser.runtime.onMessage.addListener((msg) => {
   if (msg.keepAlive) console.log('keepAlive');
 });
diff --git a/app/scripts/offscreen.js b/app/scripts/offscreen.js
index 92dce9d..70ceaba 100644
--- a/app/scripts/offscreen.js
+++ b/app/scripts/offscreen.js
@@ -1,4 +1,6 @@
+import * as browser from 'webextension-polyfill';
+
 // send a message every 20 sec to service worker
 setInterval(() => {
-  chrome.runtime.sendMessage({ keepAlive: true });
+  browser.runtime.sendMessage({ keepAlive: true });
 }, 20000);