For anyone else like me using a #Yubikey or other #webauthn #2FA in #Firefox who just had it recently start prompting for a PIN when it shouldn't be, apparently the is a bug, and the workaround here helped me:
https://support.nitrokey.com/t/fido2-firefox-asks-for-a-device-pin-that-i-never-set/4927

I'm not sure if this is an issue with the most recent Firefox version for #Linux or just the current #linuxMint package.