Weird vocal error message when trying to read mp3s on specific sites

I am using the site projet-voltaire.fr, it’s a grammar trainer for french.
When trying to read mp3s, like if it want to dictate a phrase that I would then write down, I get a vocal error message (like a text-to-speak audio). On windows 11 with the same firefox version (same pc, dual boot) it work fine.

The message tell me:

“this is the dummy output module, it seem your speach patcher is working, but none [incomprehensible] exept me. please check your logs to see what the problem is. You can find it in [list directories like /run/user/1000/log, /run/log]” (most of this listing is incomprehensible)

I can play mp3s on other websites like internet archive.
from the network dev tool, it look like the website is failing to load the file

I can not re-create this because your description is too scanty. I have no idea how to click through that websit to het to the same point as where you are.

the website need a subscription to access the training modules sadly. I was hoping it wasn’t a website-specific problem. for the detail of how the page work, you have to press a play button, it then try to load and play a mp3 file, but fail (the transfert size is 0 Gb) as shown in the screenshot, and instead play the error message I described.

Maybe a browser problem? Just downloading the file in the screenshot by:

wget https://particuliers.projet-voltaire.fr/services-pjv/rest/wol/lc/exercise/40917/resource/40917.mp3

works here (the file is some 10KB in length).
And plays in Firefox too, when pointed directly at that mp3 file.

It does work that way if I just past the link in the browser. Very weird. I had a similar but reversed problem where loging with a itch.io account to another specific site would fail on windows but work fine on linux. so yes, maybe a firefox problem