diff --git a/hermes_cli/main.py b/hermes_cli/main.py
index 41c4a23f932..a893ee85846 100644
--- a/hermes_cli/main.py
+++ b/hermes_cli/main.py
@@ -7226,17 +7226,24 @@ def _update_node_dependencies() -> None:
         if not (path / "package.json").exists():
             continue
 
+        # Stream npm output (no `--silent`, no `capture_output`) so any
+        # optional dependency postinstall scripts (e.g. `agent-browser`'s
+        # Chromium fetch on first install) print progress instead of
+        # appearing to hang silently for minutes (#18840).  The
+        # `_UpdateOutputStream` wrapper installed by the updater mirrors
+        # streamed output to ``~/.hermes/logs/update.log`` so nothing is lost.
         result = _run_npm_install_deterministic(
             npm,
             path,
-            extra_args=("--silent", "--no-fund", "--no-audit", "--progress=false"),
+            extra_args=("--no-fund", "--no-audit", "--progress=false"),
+            capture_output=False,
         )
         if result.returncode == 0:
             print(f"  ✓ {label}")
             continue
 
         print(f"  ⚠ npm install failed in {label}")
-        stderr = (result.stderr or "").strip()
+        stderr = (result.stderr or "").strip() if result.stderr else ""
         if stderr:
             print(f"    {stderr.splitlines()[-1]}")
 
diff --git a/tests/hermes_cli/test_cmd_update.py b/tests/hermes_cli/test_cmd_update.py
index f059e54ac05..2f4b836286b 100644
--- a/tests/hermes_cli/test_cmd_update.py
+++ b/tests/hermes_cli/test_cmd_update.py
@@ -130,17 +130,22 @@ class TestCmdUpdateBranchFallback:
         #   1. repo root  — slash-command / TUI bridge deps
         #   2. ui-tui/    — Ink TUI deps
         #   3. web/       — install + "npm run build" for the web frontend
-        full_flags = [
+        #
+        # Repo-root and ui-tui installs intentionally omit `--silent` and run
+        # without `capture_output` so optional postinstall scripts (e.g.
+        # `@askjo/camofox-browser`'s browser-binary fetch) print progress —
+        # otherwise long downloads look like a hang (#18840).  The web/ install
+        # keeps `--silent` because its build step is short and noisy.
+        update_flags = [
             "/usr/bin/npm",
             "ci",
-            "--silent",
             "--no-fund",
             "--no-audit",
             "--progress=false",
         ]
         assert npm_calls[:2] == [
-            (full_flags, PROJECT_ROOT),
-            (full_flags, PROJECT_ROOT / "ui-tui"),
+            (update_flags, PROJECT_ROOT),
+            (update_flags, PROJECT_ROOT / "ui-tui"),
         ]
         if len(npm_calls) > 2:
             assert npm_calls[2:] == [
@@ -148,6 +153,24 @@ class TestCmdUpdateBranchFallback:
                 (["/usr/bin/npm", "run", "build"], PROJECT_ROOT / "web"),
             ]
 
+        # Regression for #18840: repo root + ui-tui installs must stream
+        # output (capture_output=False) so postinstall progress is visible
+        # to the user.
+        repo_and_tui_calls = [
+            call
+            for call in mock_run.call_args_list
+            if call.args
+            and call.args[0][0] == "/usr/bin/npm"
+            and call.args[0][1] == "ci"
+            and call.kwargs.get("cwd") in (PROJECT_ROOT, PROJECT_ROOT / "ui-tui")
+        ]
+        assert len(repo_and_tui_calls) == 2
+        for call in repo_and_tui_calls:
+            assert call.kwargs.get("capture_output") is False, (
+                "repo-root / ui-tui npm install must stream output "
+                "(no capture_output) so postinstall progress is visible"
+            )
+
     def test_update_non_interactive_runs_safe_config_migrations(self, mock_args, capsys):
         """Dashboard/web updates apply non-interactive migrations before restart."""
         with patch("shutil.which", return_value=None), patch(