Referring to the Firefox snap from Mozilla.
Chromium was granted this auto-connection: Auto-connecting the u2f-devices interface for the chromium snap.
I submitted a ticket to Firefox regarding this here.
Apparently, Firefox has already requested this feature here:
https://forum.snapcraft.io/t/auto-connecting-the-u2f-devices-interface-for-the-firefox-snap/14330
but it never went anywhere. Sorry, new users can only post 2 links so I had to disguise the link in a block…
This default behavior is expected by the end user and render’s using FIDO security keys in Firefox effectively impossible for the average user who probably won’t be able to figure out how to make a manual connection.