diff --git a/inline-script.js b/inline-script.js
index 6dc37c7..6b7c1b4 100644
--- a/inline-script.js
+++ b/inline-script.js
@@ -3,7 +3,17 @@
 // the build process and write it to inline-script-checksum.json.
 window.__themeColors = process.env.THEME_COLORS
 
-if (localStorage.store_currentInstance && localStorage.store_instanceThemes) {
+const hasLocalStorage = (() => {
+  try {
+    // iOS safari throws here if cookies are disabled
+    let unused = localStorage.length // eslint-disable-line
+    return true
+  } catch (e) {
+    return false
+  }
+})()
+
+if (hasLocalStorage && localStorage.store_currentInstance && localStorage.store_instanceThemes) {
   let safeParse = (str) => str === 'undefined' ? undefined : JSON.parse(str)
   let theme = safeParse(localStorage.store_instanceThemes)[safeParse(localStorage.store_currentInstance)]
   if (theme && theme !== 'default') {
@@ -18,14 +28,14 @@ if (localStorage.store_currentInstance && localStorage.store_instanceThemes) {
   }
 }
 
-if (!localStorage.store_currentInstance) {
+if (!hasLocalStorage || !localStorage.store_currentInstance) {
   // if not logged in, show all these 'hidden-from-ssr' elements
   let style = document.createElement('style')
   style.textContent = '.hidden-from-ssr { opacity: 1 !important; }'
   document.head.appendChild(style)
 }
 
-if (localStorage.store_disableCustomScrollbars === 'true') {
+if (hasLocalStorage && localStorage.store_disableCustomScrollbars === 'true') {
   // if user has disabled custom scrollbars, remove this style
   let theScrollbarStyle = document.getElementById('theScrollbarStyle')
   theScrollbarStyle.setAttribute('media', 'only x') // disables the style
diff --git a/package-lock.json b/package-lock.json
index a550c43..d138ef9 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -6003,6 +6003,11 @@
         "json5": "^0.5.0"
       }
     },
+    "localstorage-memory": {
+      "version": "1.0.3",
+      "resolved": "https://registry.npmjs.org/localstorage-memory/-/localstorage-memory-1.0.3.tgz",
+      "integrity": "sha512-t9P8WB6DcVttbw/W4PIE8HOqum8Qlvx5SjR6oInwR9Uia0EEmyUeBh7S+weKByW+l/f45Bj4L/dgZikGFDM6ng=="
+    },
     "locate-path": {
       "version": "2.0.0",
       "resolved": "https://registry.npmjs.org/locate-path/-/locate-path-2.0.0.tgz",
diff --git a/package.json b/package.json
index 008181a..980e1cd 100644
--- a/package.json
+++ b/package.json
@@ -72,6 +72,7 @@
     "idb-keyval": "^3.1.0",
     "indexeddb-getall-shim": "^1.3.5",
     "intersection-observer": "^0.5.1",
+    "localstorage-memory": "^1.0.3",
     "lodash-es": "^4.17.11",
     "lodash-webpack-plugin": "^0.11.5",
     "mini-css-extract-plugin": "^0.4.5",
diff --git a/routes/_pages/settings/instances/add.html b/routes/_pages/settings/instances/add.html
index a36e7c3..15a063e 100644
--- a/routes/_pages/settings/instances/add.html
+++ b/routes/_pages/settings/instances/add.html
@@ -3,10 +3,18 @@
 
   <form class="add-new-instance" on:submit='onSubmit(event)' aria-labelledby="add-an-instance-h1">
 
+    {#if !hasIndexedDB}
+      <div class="form-error form-error-user-error" role="alert">
+        Your browser doesn't support IndexedDB, possibly because it's in private browsing mode
+        or blocking cookies. Pinafore stores all data locally, and requires IndexedDB to work
+        correctly.
+      </div>
+    {/if}
+
     {#if $logInToInstanceError && $logInToInstanceErrorForText === $instanceNameInSearch}
-    <div class="form-error form-error-user-error" role="alert">
-      Error: {$logInToInstanceError}
-    </div>
+      <div class="form-error form-error-user-error" role="alert">
+        Error: {$logInToInstanceError}
+      </div>
     {/if}
 
     <noscript>
@@ -69,19 +77,25 @@
   import { store } from '../../../_store/store'
   import { logInToInstance, handleOauthCode } from '../../../_actions/addInstance'
   import ExternalLink from '../../../_components/ExternalLink.html'
+  import { testHasIndexedDB } from '../../../_utils/testStorage'
 
   export default {
     async oncreate () {
       let codeMatch = location.search.match(/code=([^&]+)/)
       if (codeMatch) {
-        handleOauthCode(codeMatch[1])
+        return handleOauthCode(codeMatch[1])
       }
+      let hasIndexedDB = await testHasIndexedDB()
+      this.set({ hasIndexedDB })
     },
     components: {
       SettingsLayout,
       ExternalLink
     },
     store: () => store,
+    data: () => ({
+      hasIndexedDB: true
+    }),
     methods: {
       onSubmit (event) {
         event.preventDefault()
diff --git a/routes/_store/LocalStorageStore.js b/routes/_store/LocalStorageStore.js
index f9a98cc..6bb33ba 100644
--- a/routes/_store/LocalStorageStore.js
+++ b/routes/_store/LocalStorageStore.js
@@ -1,11 +1,11 @@
 import { Store } from 'svelte/store'
+import { safeLocalStorage as LS } from '../_utils/safeLocalStorage'
+
 let lifecycle
 if (process.browser) {
   lifecycle = require('page-lifecycle/dist/lifecycle.mjs').default
 }
 
-const LS = process.browser && localStorage
-
 function safeParse (str) {
   return !str ? undefined : (str === 'undefined' ? undefined : JSON.parse(str))
 }
diff --git a/routes/_utils/safeLocalStorage.js b/routes/_utils/safeLocalStorage.js
new file mode 100644
index 0000000..8cf57e5
--- /dev/null
+++ b/routes/_utils/safeLocalStorage.js
@@ -0,0 +1,6 @@
+import localStorageMemory from 'localstorage-memory'
+import { testHasLocalStorage } from './testStorage'
+
+const safeLocalStorage = testHasLocalStorage() ? localStorage : localStorageMemory
+
+export { safeLocalStorage }
diff --git a/routes/_utils/testStorage.js b/routes/_utils/testStorage.js
new file mode 100644
index 0000000..acce697
--- /dev/null
+++ b/routes/_utils/testStorage.js
@@ -0,0 +1,42 @@
+// LocalStorage and IDB may be disabled in private mode, when "blocking cookies" in Safari,
+// or other cases
+
+import { thunk } from './thunk'
+
+const testKey = '__test__'
+
+export const testHasLocalStorage = thunk(() => {
+  try {
+    localStorage.setItem(testKey, testKey)
+    if (!localStorage.length || localStorage.getItem(testKey) !== testKey) {
+      return false
+    }
+    localStorage.removeItem(testKey)
+  } catch (e) {
+    return false
+  }
+  return true
+})
+
+export const testHasIndexedDB = thunk(async () => {
+  if (typeof indexedDB === 'undefined') {
+    return false
+  }
+
+  try {
+    let idbFailed = await new Promise(resolve => {
+      let db = indexedDB.open(testKey)
+      db.onerror = () => resolve(true)
+      db.onsuccess = () => {
+        indexedDB.deleteDatabase(testKey)
+        resolve(false)
+      }
+    })
+    if (idbFailed) {
+      return false
+    }
+  } catch (e) {
+    return false
+  }
+  return true
+})
diff --git a/routes/_utils/thunk.js b/routes/_utils/thunk.js
new file mode 100644
index 0000000..7418206
--- /dev/null
+++ b/routes/_utils/thunk.js
@@ -0,0 +1,11 @@
+export function thunk (func) {
+  let cached
+  let runOnce
+  return () => {
+    if (!runOnce) {
+      cached = func()
+      runOnce = true
+    }
+    return cached
+  }
+}
diff --git a/templates/2xx.html b/templates/2xx.html
index c361930..c493b9a 100644
--- a/templates/2xx.html
+++ b/templates/2xx.html
@@ -52,7 +52,17 @@ html{scrollbar-face-color:var(--scrollbar-face-color);scrollbar-track-color:var(
 // the build process and write it to inline-script-checksum.json.
 window.__themeColors = {"default":"royalblue","scarlet":"#e04e41","seafoam":"#177380","hotpants":"hotpink","oaken":"saddlebrown","majesty":"blueviolet","gecko":"#4ab92f","ozark":"#5263af","cobalt":"#08439b","sorcery":"#ae91e8","punk":"#e04e41","riot":"hotpink","hacker":"#4ab92f","pitchblack":"#000"}
 
-if (localStorage.store_currentInstance && localStorage.store_instanceThemes) {
+const hasLocalStorage = (() => {
+  try {
+    // iOS safari throws here if cookies are disabled
+    let unused = localStorage.length // eslint-disable-line
+    return true
+  } catch (e) {
+    return false
+  }
+})()
+
+if (hasLocalStorage && localStorage.store_currentInstance && localStorage.store_instanceThemes) {
   let safeParse = (str) => str === 'undefined' ? undefined : JSON.parse(str)
   let theme = safeParse(localStorage.store_instanceThemes)[safeParse(localStorage.store_currentInstance)]
   if (theme && theme !== 'default') {
@@ -67,14 +77,14 @@ if (localStorage.store_currentInstance && localStorage.store_instanceThemes) {
   }
 }
 
-if (!localStorage.store_currentInstance) {
+if (!hasLocalStorage || !localStorage.store_currentInstance) {
   // if not logged in, show all these 'hidden-from-ssr' elements
   let style = document.createElement('style')
   style.textContent = '.hidden-from-ssr { opacity: 1 !important; }'
   document.head.appendChild(style)
 }
 
-if (localStorage.store_disableCustomScrollbars === 'true') {
+if (hasLocalStorage && localStorage.store_disableCustomScrollbars === 'true') {
   // if user has disabled custom scrollbars, remove this style
   let theScrollbarStyle = document.getElementById('theScrollbarStyle')
   theScrollbarStyle.setAttribute('media', 'only x') // disables the style