Implement Zen UI migration functionality and initialize on startup

src/browser/base/zen-components/ZenUIMigration.mjs

@@ -0,0 +1,61 @@
+
+{
+  const PREF_NAME = "zen.migration.version";
+  const MIGRATION_VERSION = 1;
+
+  class ZenUIMigration {
+    init() {
+      if (Services.prefs.prefHasUserValue(PREF_NAME)) {
+        this._migrate();
+      }
+      this.clearVariables();
+    }
+
+    get _migrationVersion() {
+      return Services.prefs.getIntPref(PREF_NAME, 0);
+    }
+
+    set _migrationVersion(value) {
+      Services.prefs.setIntPref(PREF_NAME, value);
+    }
+
+    _migrate() {
+      if (this._migrationVersion < 1) {
+        this._migrateV1();
+      }
+    }
+
+    clearVariables() {
+      this._migrationVersion = MIGRATION_VERSION;
+      window.gZenUIMigration = null;
+    }
+
+    async _migrateV1() {
+      // Introduction of the new URL bar, show a message to the user
+      const notification = gNotificationBox.appendNotification(
+        'zen-new-urlbar-notification',
+        {
+          label: { 'l10n-id': 'zen-new-urlbar-notification' },
+          image: 'chrome://browser/skin/notification-icons/persistent-storage-blocked.svg',
+          priority: gNotificationBox.PRIORITY_WARNING_HIGH,
+        },
+        [
+          {
+            'l10n-id': 'zen-disable',
+            accessKey: 'D',
+            callback: () => {
+              Services.prefs.setBoolPref('zen.urlbar.replace-newtab', false);
+            },
+          },
+          {
+            link: "https://docs.zen-browser.app/user-manual/urlbar/",
+            'l10n-id': "zen-learn-more-text",
+          }
+        ],
+      );
+      notification.persistence = -1;
+    }
+  }
+
+  window.gZenUIMigration = new ZenUIMigration();
+}