Firefox supports WebAuthn, but as far as I could tell only with hardware tokens. I could not find a word about Firefoxs support of Passkeys (like Apple announced recently) anywhere
Personally I don't know why passkeys werent adopted much sooner, it seems such a long hanging fruit to just store the key in the FF password manager.
I use FF to support a web where there is not only one option, like Chrome, but FF keeps falling behind and behind instead of being at the forefront. This should be a top priority.