Passwords are also a standard supported by pretty much everyone, and password managers (including those built into browsers) already generate long, unique, phishing resistant (it only prompts on the matching domain) passwords.
The main difference I see with passkeys from a usability standpoint is that Firefox doesn't have built-in support for a software implementation, making them literally unusable for me.
Firefox does support passkeys but their native implementation is behind a feature flag. Beyond that Firefox add-ons (such as those for password managers) can enable support for their own purposes.
For example 1Password can be used for passkeys in Firefox.
I can't find that option's documentation. Do you have a link? The only documentation I've seen indicates that they only support hardware devices, and I don't own one.
The main difference I see with passkeys from a usability standpoint is that Firefox doesn't have built-in support for a software implementation, making them literally unusable for me.