🐞 ActiveAdmin 4.0.0.beta15 not working on Firefox 138.0.1 due to import map issues

✅ Expected behavior

Basic UI interactions in ActiveAdmin should work in all modern browsers, including Firefox. Specifically:

• Clicking “Add new” in has_many nested forms should dynamically add a new input block.
• Clicking the delete link in index tables (e.g. to destroy a resource) should trigger the delete confirmation and perform the request.

These interactions should work without JavaScript errors in the browser console.

❌ Actual behavior

On Firefox 138.0.1, the following interactions do not work:

• The "Add new" link in has_many fields does nothing.
• The delete link in resource index tables does not trigger any action or confirmation.

The browser console reports:

Import maps are not allowed after a module load or preload has started. Uncaught TypeError: The specifier “active_admin” was a bare specifier, but was not remapped to anything. Relative module specifiers must start with “./“, “../” or “/”.

This makes ActiveAdmin unusable in Firefox out of the box when both Vite and Importmap are present.

🧪 How to reproduce

1. Use activeadmin (4.0.0.beta15) in a Rails app with importmap-rails and vite_rails.
2. In your app/views/active_admin/_html_head.html.erb, include the following:

<meta name="viewport" content="width=device-width,initial-scale=1">
<%= csrf_meta_tags %>
<%= csp_meta_tag %>
<% # On page load or when changing themes, best to add inline in `head` to avoid FOUC %>
<%= javascript_tag nonce: true do %>
  if (localStorage.theme === 'dark' || (!('theme' in localStorage) && window.matchMedia('(prefers-color-scheme: dark)').matches)) {
    document.documentElement.classList.add('dark')
  } else {
    document.documentElement.classList.remove('dark')
  }
<% end %>

<%= javascript_importmap_tags "active_admin", importmap: ActiveAdmin.importmap %>
<%= vite_typescript_tag 'active_admin' %>

3. Open any ActiveAdmin form with has_many fields in Firefox 138.0.1.
4. Click “Add new” or the delete link.
5. Observe that nothing happens.
6. Check the browser console for the above-mentioned error.

💻 System configuration
• activeadmin (4.0.0.beta15)
• Firefox version: 138.0.1
• Using both importmap-rails and vite_rails
• Rails 8.0.2