diff --git a/js/sudoku.js b/js/sudoku.js
index 809ba1d..0f58aec 100755
--- a/js/sudoku.js
+++ b/js/sudoku.js
@@ -70,8 +70,8 @@ window.onload = function() {
         label.control.label = label
     }
 
-    if (/Win/.test(navigator.platform) || /Linux/.test(navigator.platform)) accessKeyModifiers = "Alt+Maj+"
-    else if (/Mac/.test(navigator.platform)) accessKeyModifiers = "⌃⌥"
+    if (/Win/.test(navigator.userAgent) || /Linux/.test(navigator.userAgent)) accessKeyModifiers = "Alt+Maj+"
+    else if (/Mac/.test(navigator.userAgent)) accessKeyModifiers = "⌃⌥"
     for (node of document.querySelectorAll("*[accesskey]")) {
         shortcut = ` [${node.accessKeyLabel||(accessKeyModifiers+node.accessKey)}]`
         if (node.title) node.title += shortcut
@@ -83,7 +83,7 @@ window.onload = function() {
     colorPickerInput.value = window.getComputedStyle(grid).getPropertyValue("--bs-body-color")
 
     if ("serviceWorker" in navigator) {
-        navigator.serviceWorker.register(`service-worker.php?location=${location.pathname}`)
+        navigator.serviceWorker.register(`service-worker.js`)
     }
 }
 
diff --git a/service-worker.php b/service-worker.js
similarity index 92%
rename from service-worker.php
rename to service-worker.js
index 779d131..5b1e5ce 100644
--- a/service-worker.php
+++ b/service-worker.js
@@ -1,11 +1,3 @@
-<?php
-    session_start();
-    if (isset($_SESSION["currentGrid"]))
-        $currentGrid = $_SESSION["currentGrid"];
-    else
-        $currentGrid = ".";
-    header ("Content-type: application/javascript");
-?>
 /*
 Copyright 2015, 2019, 2020 Google LLC. All Rights Reserved.
  Licensed under the Apache License, Version 2.0 (the "License");
@@ -24,7 +16,7 @@ Copyright 2015, 2019, 2020 Google LLC. All Rights Reserved.
 const OFFLINE_VERSION = 1;
 const CACHE_NAME = "offline";
 // Customize this with a different URL if needed.
-const OFFLINE_URL = "<?=$currentGrid?>";
+const OFFLINE_URL = ".";
 
 self.addEventListener("install", (event) => {
   event.waitUntil(