diff --git a/src/components/notification-i18n.en.json b/src/components/notification-i18n.en.json
index d0ae6e09..277d643a 100644
--- a/src/components/notification-i18n.en.json
+++ b/src/components/notification-i18n.en.json
@@ -13,6 +13,21 @@
             "action": "Reload"
         }
     },
+    "flashFirmware": {
+        "connectionFailed": "Could not connect to the hub. Restart the hub and try again.",
+        "timedOut": "The hub took too long to respond. Restart the hub and try again.",
+        "bleError": "There was a problem with Bluetooth.",
+        "disconnected": "The hub was disconnected before flashing was completed. Restart the hub and try again.",
+        "hubError": "The hub said something went wrong.",
+        "unsupportedDevice": "The connected hub is not supported.",
+        "deviceMismatch": "The firmware is for a different kind of hub from the connected hub.",
+        "failToFetch": "Failed to fetch firmware from the server: {status}",
+        "badZipFile": "The firmware.zip file is missing required files or is corrupt.",
+        "badMetadata": "The firmware.metadata.py file contains missing or invalid entries. Fix it then try again.",
+        "compileError": "The included main.py file could not be compiled. Fix it then try again.",
+        "sizeTooBig": "The combined firmware and main.py are too big to fit in the flash memory.",
+        "unexpectedError": "Unexpected error while trying to flash firmware: {errorMessage}"
+    },
     "mpy": {
         "error": "{errorMessage}"
     },
diff --git a/src/components/notification-i18n.ts b/src/components/notification-i18n.ts
index 48414268..c27294a6 100644
--- a/src/components/notification-i18n.ts
+++ b/src/components/notification-i18n.ts
@@ -10,6 +10,19 @@ export enum MessageId {
     BleGattPermission = 'ble.gattPermission',
     BleGattServiceNotFound = 'ble.gattServiceNotFound',
     BleNoWebBluetooth = 'ble.noWebBluetooth',
+    FlashFirmwareConnectionFailed = 'flashFirmware.connectionFailed',
+    FlashFirmwareTimedOut = 'flashFirmware.timedOut',
+    FlashFirmwareBleError = 'flashFirmware.bleError',
+    FlashFirmwareDisconnected = 'flashFirmware.disconnected',
+    FlashFirmwareHubError = 'flashFirmware.hubError',
+    FlashFirmwareUnsupportedDevice = 'flashFirmware.unsupportedDevice',
+    FlashFirmwareDeviceMismatch = 'flashFirmware.deviceMismatch',
+    FlashFirmwareFailToFetch = 'flashFirmware.failToFetch',
+    FlashFirmwareBadZipFile = 'flashFirmware.badZipFile',
+    FlashFirmwareBadMetadata = 'flashFirmware.badMetadata',
+    FlashFirmwareCompileError = 'flashFirmware.compileError',
+    FlashFirmwareSizeTooBig = 'flashFirmware.sizeTooBig',
+    FlashFirmwareUnexpectedError = 'flashFirmware.unexpectedError',
     ProgramChangedMessage = 'editor.programChanged.message',
     ProgramChangedAction = 'editor.programChanged.action',
     ServiceWorkerUpdateMessage = 'serviceWorker.update.message',
diff --git a/src/sagas/notification.test.ts b/src/sagas/notification.test.ts
index 28887502..0fa962a8 100644
--- a/src/sagas/notification.test.ts
+++ b/src/sagas/notification.test.ts
@@ -2,6 +2,7 @@
 // Copyright (c) 2021 The Pybricks Authors
 
 import { IToaster } from '@blueprintjs/core';
+import { FirmwareReaderError, FirmwareReaderErrorCode } from '@pybricks/firmware';
 import { AsyncSaga } from '../../test';
 import { Action } from '../actions';
 import {
@@ -9,6 +10,12 @@ import {
     didFailToConnect as bleDidFailToConnect,
 } from '../actions/ble';
 import { storageChanged } from '../actions/editor';
+import {
+    FailToFinishReasonType,
+    HubError,
+    MetadataProblem,
+    didFailToFinish,
+} from '../actions/flash-firmware';
 import {
     BootloaderConnectionFailureReason,
     didFailToConnect as bootloaderDidFailToConnect,
@@ -37,6 +44,32 @@ test.each([
     add('warning', 'message'),
     add('error', 'message', 'url'),
     didUpdate({} as ServiceWorkerRegistration),
+    didFailToFinish(FailToFinishReasonType.FailedToConnect),
+    didFailToFinish(FailToFinishReasonType.TimedOut),
+    didFailToFinish(
+        FailToFinishReasonType.BleError,
+        new DOMException('test error', 'NetworkError'),
+    ),
+    didFailToFinish(FailToFinishReasonType.Disconnected),
+    didFailToFinish(FailToFinishReasonType.HubError, HubError.UnknownCommand),
+    didFailToFinish(FailToFinishReasonType.NoFirmware),
+    didFailToFinish(FailToFinishReasonType.DeviceMismatch),
+    didFailToFinish(
+        FailToFinishReasonType.FailedToFetch,
+        new Response(undefined, { status: 404 }),
+    ),
+    didFailToFinish(
+        FailToFinishReasonType.ZipError,
+        new FirmwareReaderError(FirmwareReaderErrorCode.ZipError),
+    ),
+    didFailToFinish(
+        FailToFinishReasonType.BadMetadata,
+        'device-id',
+        MetadataProblem.NotSupported,
+    ),
+    didFailToFinish(FailToFinishReasonType.FailedToCompile),
+    didFailToFinish(FailToFinishReasonType.FirmwareSize),
+    didFailToFinish(FailToFinishReasonType.Unknown, new Error('test error')),
 ])('actions that should show notification: %o', async (action: Action) => {
     const getToasts = jest.fn().mockReturnValue([]);
     const show = jest.fn();
diff --git a/src/sagas/notification.ts b/src/sagas/notification.ts
index 687e0e59..1312f0a9 100644
--- a/src/sagas/notification.ts
+++ b/src/sagas/notification.ts
@@ -21,6 +21,11 @@ import {
     BleDeviceFailToConnectReasonType,
 } from '../actions/ble';
 import { EditorActionType, reloadProgram } from '../actions/editor';
+import {
+    FailToFinishReasonType,
+    FlashFirmwareActionType,
+    FlashFirmwareDidFailToFinishAction,
+} from '../actions/flash-firmware';
 import {
     BootloaderConnectionActionType,
     BootloaderConnectionDidFailToConnectAction,
@@ -226,6 +231,69 @@ function* showEditorStorageChanged(): Generator {
     yield put(reloadProgram());
 }
 
+function* showFlashFirmwareError(
+    action: FlashFirmwareDidFailToFinishAction,
+): Generator {
+    switch (action.reason.reason) {
+        case FailToFinishReasonType.FailedToConnect:
+            yield* showSingleton(Level.Error, MessageId.FlashFirmwareConnectionFailed);
+            break;
+        case FailToFinishReasonType.TimedOut:
+            yield* showSingleton(Level.Error, MessageId.FlashFirmwareTimedOut);
+            break;
+        case FailToFinishReasonType.BleError:
+            yield* showUnexpectedError(
+                MessageId.FlashFirmwareBleError,
+                action.reason.err,
+            );
+            break;
+        case FailToFinishReasonType.Disconnected:
+            yield* showSingleton(Level.Error, MessageId.FlashFirmwareDisconnected);
+            break;
+        case FailToFinishReasonType.HubError:
+            yield* showSingleton(Level.Error, MessageId.FlashFirmwareHubError);
+            if (process.env.NODE_ENV !== 'test') {
+                console.error(action.reason.hubError);
+            }
+            break;
+        case FailToFinishReasonType.NoFirmware:
+            yield* showSingleton(Level.Error, MessageId.FlashFirmwareUnsupportedDevice);
+            break;
+        case FailToFinishReasonType.DeviceMismatch:
+            yield* showSingleton(Level.Error, MessageId.FlashFirmwareDeviceMismatch);
+            break;
+        case FailToFinishReasonType.FailedToFetch:
+            yield* showSingleton(Level.Error, MessageId.FlashFirmwareFailToFetch, {
+                status: action.reason.response.statusText,
+            });
+            break;
+        case FailToFinishReasonType.ZipError:
+            yield* showSingleton(Level.Error, MessageId.FlashFirmwareBadZipFile);
+            if (process.env.NODE_ENV !== 'test') {
+                console.error(action.reason.err);
+            }
+            break;
+        case FailToFinishReasonType.BadMetadata:
+            yield* showSingleton(Level.Error, MessageId.FlashFirmwareBadMetadata);
+            if (process.env.NODE_ENV !== 'test') {
+                console.error(action.reason.property, action.reason.problem);
+            }
+            break;
+        case FailToFinishReasonType.FailedToCompile:
+            yield* showSingleton(Level.Error, MessageId.FlashFirmwareCompileError);
+            break;
+        case FailToFinishReasonType.FirmwareSize:
+            yield* showSingleton(Level.Error, MessageId.FlashFirmwareSizeTooBig);
+            break;
+        case FailToFinishReasonType.Unknown:
+            yield* showUnexpectedError(
+                MessageId.FlashFirmwareUnexpectedError,
+                action.reason.err,
+            );
+            break;
+    }
+}
+
 function* dismissCompilerError(): Generator {
     const { toaster } = (yield getContext('notification')) as NotificationContext;
     toaster.dismiss(MessageId.MpyError);
@@ -282,6 +350,7 @@ export default function* (): Generator {
         showBootloaderDidFailToConnectError,
     );
     yield takeEvery(EditorActionType.StorageChanged, showEditorStorageChanged);
+    yield takeEvery(FlashFirmwareActionType.DidFailToFinish, showFlashFirmwareError);
     yield takeEvery(MpyActionType.DidCompile, dismissCompilerError);
     yield takeEvery(MpyActionType.DidFailToCompile, showCompilerError);
     yield takeEvery(NotificationActionType.Add, addNotification);