diff --git a/webapp/src/dl/index.ts b/webapp/src/dl/index.ts
index 7582163..8b68834 100644
--- a/webapp/src/dl/index.ts
+++ b/webapp/src/dl/index.ts
@@ -26,6 +26,12 @@ function cleanupKey(key: string) {
 async function run() {
   const loc = window.location;
   const rootUrl = loc.origin + loc.pathname.replace("/dl","/");
+
+  if (navigator.serviceWorker == null) {
+    alert('No serviceWorker available ! Please note the feature may not be available in private mode in Firefox');
+    loc.replace(rootUrl);
+    return;
+  }
   try {
     await navigator.serviceWorker.register('./sw.js', {'scope': '/v1/download/'});
   }
diff --git a/webapp/src/gui/index.ts b/webapp/src/gui/index.ts
index 0ead45d..e0f170a 100644
--- a/webapp/src/gui/index.ts
+++ b/webapp/src/gui/index.ts
@@ -33,8 +33,14 @@ app.route('/', uploadView);
 
 const mountProm = app.mount('body');
 
-// Register service worker
-navigator.serviceWorker.register('./sw.js', {'scope': '/v1/download/'});
+// Test if serviceWorker is available, the feature may not be available in private mode in FF
+// see https://developer.mozilla.org/en-US/docs/Web/API/Navigator/serviceWorker
+if (navigator.serviceWorker == null) {
+  console.log('[**] No serviceWorker available, maybe due to FF in private mode ?');
+} else {
+  // Register service worker
+  navigator.serviceWorker.register('./sw.js', {'scope': '/v1/download/'});
+}
 
 export default async () => {
   await mountProm;