Export modal elements are not read by screen readers on Firefox

Steps to reproduce

1. Start a screen reader application (e.g. NVDA)
2. Access the XWiki instance on Firefox (I've tested on FF 159)
3. Login and go to any page (e.g. Main.WebHome)
4. Click 'More Actions'> 'Export' to open the Export modal
5. Listen to the announcement
6. Press Tab through the modal
7. Listen to the announcement of the elements

Expected results

As the Tab key is pressed through the modal, all elements are announced by the screen reader: 

• Close button
• Filter edit: Type to filter... blank
• Options for exportFormat list  You can navigate through the options using arrow keys, the home and end keys. Select the currently highlighted option by pressing enter or space. Right and left arrows will move focus to the next possible option in the list. The Home key will bring focus to the start of the list and the END key to its end. Up and down arrows allow you to navigate quickly to the start of option categories. Office Formats (1)  grouping PDF 1 of 3
• Export dialog

Actual results

When clicking 'More Actions' > 'Export', the following is read:

link visited same page Edit link Toggle dropdown button collapsed subMenu Create visited link Followed button Current notification setting for this page: Followed - Click to change it More Actions.

However, nothing of the elements of the Export modal listed above are being read.

The issue couldn't be reproduced on Chrome (156) and Edge (156).