simplified app/main.js a bit

app/main.js

@@ -27,6 +27,9 @@ if (process.env.NODE_ENV === 'production') {
 
 (async function start() {
   const capabilities = await getCapabilities();
+  if (!capabilities.crypto) {
+    return window.location.assign('/unsupported/crypto');
+  }
   if (capabilities.serviceWorker) {
     await navigator.serviceWorker.register('/serviceWorker.js');
     await navigator.serviceWorker.ready;
@@ -44,29 +47,6 @@ if (process.env.NODE_ENV === 'production') {
   };
 
   const app = routes(choo());
-  app.use((state, emitter) => {
-    window.appState = state;
-    window.appEmit = emitter.emit.bind(emitter);
-    let unsupportedReason = null;
-
-    if (
-      // Firefox < 50
-      /firefox/i.test(navigator.userAgent) &&
-      parseInt(navigator.userAgent.match(/firefox\/*([^\n\r]*)\./i)[1], 10) < 50
-    ) {
-      unsupportedReason = 'outdated';
-    }
-    if (!state.capabilities.crypto) {
-      unsupportedReason = /firefox/i.test(navigator.userAgent)
-        ? 'outdated'
-        : 'gcm';
-    }
-    if (unsupportedReason) {
-      setTimeout(() =>
-        emitter.emit('replaceState', `/unsupported/${unsupportedReason}`)
-      );
-    }
-  });
   app.use(metrics);
   app.use(controller);
   app.use(dragManager);

server/initScript.js

@@ -39,8 +39,16 @@ module.exports = function(state) {
   var isIE = /trident\\\/7\.|msie/i.test(navigator.userAgent);
   var isUnsupportedPage = /\\\/unsupported/.test(location.pathname);
   if (isIE && !isUnsupportedPage) {
-    window.location.replace('/unsupported/ie');
+    window.location.assign('/unsupported/ie');
   }
+  if (
+    // Firefox < 50
+    /firefox/i.test(navigator.userAgent) &&
+    parseInt(navigator.userAgent.match(/firefox\\/*([^\\n\\r]*)\./i)[1], 10) < 50
+  ) {
+    window.location.assign('/unsupported/outdated');
+  }
+
   var LIMITS = {
     ANON: {
       MAX_FILE_SIZE: ${config.anon_max_file_size},