Bard toolbar behind set in Firefox

[AtmoFX]

Bug description

In a code block inside a set of a bard field, Firefox shows me a sticky toolbar behind the code block; as that code block has no background, it looks like the toolbar is transparent (but with a big zoom into the page, I can tell the toolbar's text is actually behind the code block's).

The issue may be linked to https://github.com/statamic/cms/pull/13429/changes and while the change introduced in that PR works in most case, it seems it won't for code blocks inside a set (possibly block types too).

Explanation: the CodeMirror-gutter-wrapper, CodeMirror-gutter-elt and possibly more classes have a z-index of 4, and they seem to somehow end up on top of the toolbar in the stacking context.
That places the div with class="bard-fixed-toolbar" behind them (due to --z-index-portal being set to 2).

As a quick test, if you force e.g. --z-index-portal: 5, the issue disappears (not that I am saying this is how the issue should be fixed nor that 5 is the correct value to set).

---

On an unrelated note, the gutter and the code overlap when code blocks are added into a Bard field, but it works well when added to the blueprint root directly.

How to reproduce

In Firefox:

1. Save the below blueprint
2. Create an entry.
3. Inside the bard field, add a Code set and edit something in it (Make it long enough that you can scroll down a little bit)
4. Click outside the set into the bard field
5. Scroll down

Logs

Environment

Environment
Application Name: All you need
Laravel Version: 12.49.0
PHP Version: 8.3.6
Composer Version: 2.9.2
Environment: local
Debug Mode: ENABLED
URL: allyouneed.local
Maintenance Mode: OFF
Timezone: UTC
Locale: en

Cache
Config: NOT CACHED
Events: NOT CACHED
Routes: NOT CACHED
Views: CACHED

Drivers
Broadcasting: log
Cache: file
Database: sqlite
Logs: stack / single
Mail: log
Queue: sync
Session: file

Storage
public/storage: NOT LINKED

Livewire
Livewire: v4.1.0

Statamic
Addons: 2
Sites: 1
Stache Watcher: Enabled (auto)
Static Caching: Disabled
Version: 6.3.3 PRO

Statamic Addons
allyouneed/seo: dev-main
allyouneed/statamic-forms: dev-main

Installation

Fresh statamic/statamic site via CLI

Additional details

Note that the issue seems absent from Chrome and I do not understand why (or rather, why it exists in Firefox as I would expected the stacking context to sort things out nicely).