role alert and Firefox

Alberto Buffolino

Hi all,
I have a problem with role="alert" and Firefox (80.0.1, on Windows 10).
Specifically, I have a button taht, when clicked, changes via JavaScript a div content and set its role to alert, so NVDA should read new content automatically. And in Chrome this happens correctly.
In Firefox, instead, I hear only "Alert" (or warning, I don't know, I'm translating from Italian), but nothing else.
This is the page, button is labelled "42":
Can you help?
I can provide also JavaScript code, if necessary.
Thanks in advance.