amp-story-page-outlink button not appearing or delayed in Firefox

### Description

**Description**
We are encountering an issue with the `amp-story-page-outlink` component in Web Stories. When stories are opened in modal view, the outlink button:

- Sometimes **does not appear at all**, or
- **Appears with a significant delay**

This issue is specific to **Firefox (latest version)** and does **not occur in Google Chrome**, where the button renders consistently and immediately.

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**Expected Behavior**
The `amp-story-page-outlink` button should appear immediately and reliably across all supported browsers, including Firefox.

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**Actual Behavior**
In Firefox:
- The button is often missing, or
- Appears only after a delay

In Chrome:
- The button appears immediately and as expected.

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**Browsers Affected**
- ✅ **Google Chrome** – Working as expected
- ✅ **Safari** – Working as expected
- ❌ **Firefox (latest version)** – Issue present

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**Environment**
- **macOS Sequoia 15.3.2**
- **Chip**: Apple M4 Pro
- **Memory**: 24 GB RAM
- **Browser**: Firefox (latest), Chrome (latest), Safari (latest)
- **Component**: `amp-story-page-outlink`
- Context: Web Stories rendered in modal view
- Story content is automatically generated from a feed (no manual editing)

### Reproduction Steps

**Steps to Reproduce**
1. Open a Web Story in modal view.
2. Navigate to a page that includes the `amp-story-page-outlink` component.
3. Observe the behavior of the outlink button.

### Relevant Logs

```shell

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### Browser(s) Affected

_No response_

### OS(s) Affected

_No response_

### Device(s) Affected

_No response_

### AMP Version Affected

_No response_