update

frontend/public/sw.js

@@ -43,9 +43,14 @@ self.addEventListener('activate', (event) => {
 
 self.addEventListener('fetch', (event) => {
   const url = event.request.url;
-  if (url.includes('/api/') || url.includes('/socket.io/') || url.includes('/manifest.json')) {
-    return;
-  }
+
+  // Only intercept same-origin requests — never intercept cross-origin calls
+  // (Firebase API, Google CDN, socket.io CDN, etc.) or specific local paths.
+  // Intercepting cross-origin requests causes Firebase SDK calls to return
+  // cached HTML, producing "unsupported MIME type" errors and breaking FCM.
+  if (!url.startsWith(self.location.origin)) return;
+  if (url.includes('/api/') || url.includes('/socket.io/') || url.includes('/manifest.json')) return;
+
   event.respondWith(
     fetch(event.request).catch(() => caches.match(event.request))
   );