diff --git a/docs/API-Reference/command/Commands.md b/docs/API-Reference/command/Commands.md
index 37a71de251..08e2feb9ff 100644
--- a/docs/API-Reference/command/Commands.md
+++ b/docs/API-Reference/command/Commands.md
@@ -854,6 +854,12 @@ Checks for updates
 ## HELP\_AUTO\_UPDATE
 Toggles auto update
 
+**Kind**: global variable  
+<a name="HELP_MIGRATE_DATA"></a>
+
+## HELP\_MIGRATE\_DATA
+Migrates browser data from the legacy web origin
+
 **Kind**: global variable  
 <a name="CMD_WORKINGSET_SORT_BY_ADDED"></a>
 
diff --git a/src/extensionsIntegrated/MigrateAssist/constants.js b/src/extensionsIntegrated/MigrateAssist/constants.js
index 1db7f0e090..ff366c1410 100644
--- a/src/extensionsIntegrated/MigrateAssist/constants.js
+++ b/src/extensionsIntegrated/MigrateAssist/constants.js
@@ -72,6 +72,15 @@ define(function (require, exports, module) {
      */
     const MIGRATION_DONE_KEY = "migrateAssist.v1.done";
 
+    /**
+     * PhStore key recording that the user has already been asked. The automatic path prompts at most
+     * once, whatever the outcome: declining, closing the tab, or a transfer that broke half way all
+     * count as having been asked. Re-prompting on every boot after any of those would be a nag, and
+     * the Help menu entry is always there for a deliberate retry.
+     * @type {string}
+     */
+    const MIGRATION_PROMPTED_KEY = "migrateAssist.v1.prompted";
+
     /**
      * Dev only override, so the whole cross origin flow can be exercised on one dev server.
      * http://localhost:8000 and http://127.0.0.1:8000 are different origins with separate IndexedDB
@@ -203,6 +212,7 @@ define(function (require, exports, module) {
     exports.SUNSET_DATE = SUNSET_DATE;
     exports.TWA_STORE_URL = TWA_STORE_URL;
     exports.MIGRATION_DONE_KEY = MIGRATION_DONE_KEY;
+    exports.MIGRATION_PROMPTED_KEY = MIGRATION_PROMPTED_KEY;
     exports.getLegacyOrigin = getLegacyOrigin;
     exports.getMigrateAssistURL = getMigrateAssistURL;
     exports.getLegacyDomainName = getLegacyDomainName;
diff --git a/src/extensionsIntegrated/MigrateAssist/migrator.js b/src/extensionsIntegrated/MigrateAssist/migrator.js
index b7276146bd..c7328cc36a 100644
--- a/src/extensionsIntegrated/MigrateAssist/migrator.js
+++ b/src/extensionsIntegrated/MigrateAssist/migrator.js
@@ -35,6 +35,7 @@
 define(function (require, exports, module) {
     const Dialogs = require("widgets/Dialogs"),
         DefaultDialogs = require("widgets/DefaultDialogs"),
+        NotificationUI = require("widgets/NotificationUI"),
         Strings = require("strings"),
         StringUtils = require("utils/StringUtils"),
         Metrics = require("utils/Metrics"),
@@ -51,6 +52,7 @@ define(function (require, exports, module) {
 
     const RESULT_MIGRATED = "migrated",
         RESULT_DECLINED = "declined",
+        RESULT_INTERRUPTED = "interrupted",
         RESULT_NOTHING = "nothing",
         RESULT_UNREACHABLE = "unreachable";
 
@@ -235,32 +237,39 @@ define(function (require, exports, module) {
         ).getPromise();
     }
 
+    /**
+     * Everything after the single up front question is reported at the bottom of the window rather
+     * than in another modal. The user opted in and went back to work; interrupting them again to say
+     * it finished would undo the point of moving progress out of a dialog in the first place.
+     */
+    function _toast(title, message, style, $extra) {
+        const $content = $("<div>").append($("<div>").text(message));
+        if ($extra) {
+            $content.append($extra);
+        }
+        return NotificationUI.createToastFromTemplate(title, $content, {
+            dismissOnClick: false, // there is a close button, and a stray click must not eat the action
+            toastStyle: style
+        });
+    }
+
     function _showCompletion(migratedFiles, failed) {
-        const message = failed.length
-            ? StringUtils.format(Strings.MIGRATE_DONE_MESSAGE, migratedFiles) + "<br><br>"
-                + StringUtils.format(Strings.MIGRATE_DONE_PARTIAL, failed.length)
-            : StringUtils.format(Strings.MIGRATE_DONE_MESSAGE, migratedFiles);
-        Dialogs.showModalDialog(
-            DefaultDialogs.DIALOG_ID_INFO,
-            Strings.MIGRATE_DONE_TITLE,
-            message,
-            [
-                {
-                    className: Dialogs.DIALOG_BTN_CLASS_NORMAL,
-                    id: Dialogs.DIALOG_BTN_CANCEL,
-                    text: Strings.MIGRATE_RELOAD_LATER
-                },
-                {
-                    className: Dialogs.DIALOG_BTN_CLASS_PRIMARY,
-                    id: Dialogs.DIALOG_BTN_OK,
-                    text: Strings.MIGRATE_RELOAD_NOW
-                }
-            ]
-        ).done(function (buttonId) {
-            if (buttonId === Dialogs.DIALOG_BTN_OK) {
-                CommandManager.execute(Commands.APP_RELOAD);
-            }
+        const $actions = $("<div>").addClass("migrate-assist-toast-actions");
+        const $reload = $("<button>").addClass("btn primary btn-mini")
+            .text(Strings.MIGRATE_RELOAD_NOW);
+        $reload.on("click", function () {
+            CommandManager.execute(Commands.APP_RELOAD);
         });
+        $actions.append($reload);
+        if (failed.length) {
+            $actions.prepend($("<div>").addClass("migrate-assist-toast-detail")
+                .text(StringUtils.format(Strings.MIGRATE_DONE_PARTIAL, failed.length)));
+        }
+        _toast(Strings.MIGRATE_DONE_TITLE,
+            StringUtils.format(Strings.MIGRATE_DONE_MESSAGE, migratedFiles),
+            failed.length ? NotificationUI.NOTIFICATION_STYLES_CSS_CLASS.WARNING
+                : NotificationUI.NOTIFICATION_STYLES_CSS_CLASS.SUCCESS,
+            $actions);
     }
 
     /**
@@ -306,6 +315,7 @@ define(function (require, exports, module) {
         migrationRunning = true;
         const bridge = _createBridge();
         let progress = null;
+        let userAccepted = false;
         try {
             const scan = await bridge.scan();
             if (!scan.hasData || !scan.files.length) {
@@ -314,12 +324,17 @@ define(function (require, exports, module) {
                 return RESULT_NOTHING;
             }
 
+            // Recorded before the dialog is even answered, so closing the tab on it counts as
+            // having been asked. The automatic path will not raise it again.
+            PhStore.setItem(Constants.MIGRATION_PROMPTED_KEY, { at: Date.now() });
+
             // Asked once, before anything is copied. After this the user is left alone.
             const choice = await _confirmStart(scan.files.length);
             if (choice !== Dialogs.DIALOG_BTN_OK) {
                 Metrics.countEvent(Metrics.EVENT_TYPE.PLATFORM, "migrateAssist", "declined");
                 return RESULT_DECLINED;
             }
+            userAccepted = true;
 
             Metrics.countEvent(Metrics.EVENT_TYPE.PLATFORM, "migrateAssist",
                 manual ? "manualStart" : "autoStart");
@@ -366,11 +381,21 @@ define(function (require, exports, module) {
             return RESULT_MIGRATED;
         } catch (err) {
             console.error("MigrateAssist: migration could not run", err);
-            Metrics.countEvent(Metrics.EVENT_TYPE.PLATFORM, "migrateAssist",
-                manual ? "manualUnreachable" : "autoUnreachable");
             if (progress) {
                 progress.fail();
             }
+            if (userAccepted) {
+                // They opted in and watched a task start, so a silent stop is not acceptable even on
+                // the automatic path. Whatever landed before the break stays; a retry overwrites it.
+                Metrics.countEvent(Metrics.EVENT_TYPE.PLATFORM, "migrateAssist", "interrupted");
+                _toast(Strings.MIGRATE_INTERRUPTED_TITLE,
+                    StringUtils.format(Strings.MIGRATE_INTERRUPTED_MESSAGE,
+                        Constants.getLegacyDomainName()),
+                    NotificationUI.NOTIFICATION_STYLES_CSS_CLASS.ERROR);
+                return RESULT_INTERRUPTED;
+            }
+            Metrics.countEvent(Metrics.EVENT_TYPE.PLATFORM, "migrateAssist",
+                manual ? "manualUnreachable" : "autoUnreachable");
             return RESULT_UNREACHABLE;
         } finally {
             migrationRunning = false;
@@ -392,6 +417,10 @@ define(function (require, exports, module) {
         if (PhStore.getItem(Constants.MIGRATION_DONE_KEY)) {
             return;
         }
+        // Already asked once. Anything further is on the user, from the Help menu.
+        if (PhStore.getItem(Constants.MIGRATION_PROMPTED_KEY)) {
+            return;
+        }
         // Once the legacy origin is gone there is nothing to probe, so the feature disables itself
         // rather than opening a doomed iframe on every boot forever.
         if (Constants.isPastSunset()) {
@@ -406,17 +435,18 @@ define(function (require, exports, module) {
      */
     async function runManually() {
         const result = await run(true);
-        if (result === RESULT_DECLINED) {
-            return; // the user said no, they do not need to be told what they just chose
+        if (result === RESULT_DECLINED || result === RESULT_INTERRUPTED) {
+            // Declining needs no confirmation, and an interrupted run has already said so itself.
+            return;
         }
         if (result === RESULT_NOTHING) {
-            Dialogs.showModalDialog(DefaultDialogs.DIALOG_ID_INFO,
-                Strings.MIGRATE_NOTHING_TITLE,
-                StringUtils.format(Strings.MIGRATE_NOTHING_MESSAGE, Constants.getLegacyDomainName()));
+            _toast(Strings.MIGRATE_NOTHING_TITLE,
+                StringUtils.format(Strings.MIGRATE_NOTHING_MESSAGE, Constants.getLegacyDomainName()),
+                NotificationUI.NOTIFICATION_STYLES_CSS_CLASS.INFO);
         } else if (result === RESULT_UNREACHABLE) {
-            Dialogs.showModalDialog(DefaultDialogs.DIALOG_ID_ERROR,
-                Strings.MIGRATE_UNREACHABLE_TITLE,
-                StringUtils.format(Strings.MIGRATE_UNREACHABLE_MESSAGE, Constants.getLegacyDomainName()));
+            _toast(Strings.MIGRATE_UNREACHABLE_TITLE,
+                StringUtils.format(Strings.MIGRATE_UNREACHABLE_MESSAGE, Constants.getLegacyDomainName()),
+                NotificationUI.NOTIFICATION_STYLES_CSS_CLASS.ERROR);
         }
     }
 
diff --git a/src/nls/root/strings.js b/src/nls/root/strings.js
index 4e11cbb6c4..3a4a35df17 100644
--- a/src/nls/root/strings.js
+++ b/src/nls/root/strings.js
@@ -2942,6 +2942,8 @@ define({
     "MIGRATE_RELOAD_NOW": "Reload",
     "MIGRATE_NOTHING_TITLE": "Nothing to bring over",
     "MIGRATE_NOTHING_MESSAGE": "We could not find any projects, settings or extensions on {0} that need copying.",
+    "MIGRATE_INTERRUPTED_TITLE": "Migration did not finish",
+    "MIGRATE_INTERRUPTED_MESSAGE": "The connection to {0} was lost part way through. Anything already copied has been kept. You can pick up where this left off any time from the Help menu.",
     "MIGRATE_UNREACHABLE_TITLE": "Could not reach the old site",
     "MIGRATE_UNREACHABLE_MESSAGE": "{APP_NAME} could not connect to {0} to check for your data. Please check your connection and try again.",
     "MIGRATE_START_MESSAGE": "Found {0} files on {1} to bring over. This runs in the background and you can keep working while it happens. It only needs to be done once.",
diff --git a/src/styles/Extn-MigrateAssist.less b/src/styles/Extn-MigrateAssist.less
index 33329e31d2..542318adbe 100644
--- a/src/styles/Extn-MigrateAssist.less
+++ b/src/styles/Extn-MigrateAssist.less
@@ -64,3 +64,18 @@
         background-position: -200% 0;
     }
 }
+
+// Completion toast: the reload action and the partial-failure note sit under the message.
+.migrate-assist-toast-actions {
+    margin-top: 10px;
+    display: flex;
+    align-items: center;
+    justify-content: flex-end;
+    gap: 8px;
+}
+
+.migrate-assist-toast-detail {
+    margin-right: auto;
+    font-size: 0.9em;
+    opacity: 0.8;
+}