Firefox does support Passkeys - it’s just incomplete - specifically some of the major key storage locations aren’t supported yet (and it depends what operating system you’re running Firefox on, since every OS has different options for secure key storage).
For anyone else trying to get it to work on firefox, it doesn’t support passkeys yet but it’s on the roadmap. https://connect.mozilla.org/t5/ideas/support-webauthn-passkeys/idc-p/30123/highlight/true#M17028
Firefox does support Passkeys - it’s just incomplete - specifically some of the major key storage locations aren’t supported yet (and it depends what operating system you’re running Firefox on, since every OS has different options for secure key storage).