diff --git a/extension/extension-mpris.js b/extension/extension-mpris.js
--- a/extension/extension-mpris.js
+++ b/extension/extension-mpris.js
@@ -136,10 +136,11 @@
 
 // callbacks from a browser tab to our extension
 addRuntimeCallback("mpris", "playing", function (message, sender) {
-    // Before Firefox 67 it ran extensions in incognito mode by default
-    // so we disable media controls for them to prevent accidental private
+    // Before Firefox 67 it ran extensions in incognito mode by default.
+    // However, after the update the extension keeps running in incognito mode.
+    // So we keep disabling media controls for them to prevent accidental private
     // information leak on lock screen or now playing auto status in a messenger
-    if (!isNaN(firefoxVersion) && firefoxVersion < 67 && sender.tab.incognito) {
+    if (IS_FIREFOX && sender.tab.incognito) {
         return;
     }
 
diff --git a/extension/extension-tabsrunner.js b/extension/extension-tabsrunner.js
--- a/extension/extension-tabsrunner.js
+++ b/extension/extension-tabsrunner.js
@@ -50,8 +50,9 @@
         // remove incognito tabs and properties not in whitelist
         var filteredTabs = tabs;
 
-        // Firefox before 67 runs extensions in incognito by default, so exclude those tabs for it
-        if (!isNaN(firefoxVersion) && firefoxVersion < 67) {
+        // Firefox before 67 runs extensions in incognito by default
+        // but we keep running after an update, so exclude those tabs for it
+        if (IS_FIREFOX) {
             filteredTabs = filteredTabs.filter(function (tab) {
                 return !tab.incognito;
             });
diff --git a/extension/extension-utils.js b/extension/extension-utils.js
--- a/extension/extension-utils.js
+++ b/extension/extension-utils.js
@@ -25,9 +25,6 @@
 
 var storage = (IS_FIREFOX ? chrome.storage.local : chrome.storage.sync);
 
-let firefoxVersionMatch = navigator.userAgent.match(/Firefox\/(\d+)/)
-let firefoxVersion = firefoxVersionMatch ? Number(firefoxVersionMatch[1]) : NaN
-
 // Callback is called with following arguments (in that order);
 // - The actual message data/payload
 // - The name of the action triggered