Of course there is, it can be on the same page (even hidden) up until the point it recognises a different mechanism is needed. Then browser autofill still works if the password is used.
I also have the opposite problem - sometimes I want Firefox to remember my username but not password; the only way seems to be to have it remember a dummy password (1 char so I recognise it as such) and then decline to 'update password' every time I change it in order to login.
It recognizes that when the user confirms they've finished entering their username by clicking some kind of button.
At which point either a password box is shown or the alternative mechanism is shown.
There's no way to know in advance. And it's a UX problem if a password box is shown by default, because then users who don't have passwords think there's a bug in accessing the resource (because they don't have a password).
If your password manager has a problem with filling in the username, then the problem is with your password manager, not with the login flow. Starting with username-only is an industry standard for any product used in enterprises.
> And it's a UX problem if a password box is shown by default, because then users who don't have passwords think there's a bug in accessing the resource (because they don't have a password).
Hence why I said it can be hidden.
> If your password manager has a problem with filling in the username, then the problem is with your password manager
For sure not filling username only is a problem/missing feature with Firefox, I didn't claim otherwise. My main use for this feature is not dealing with what I consider to be bad UX, but logging in to sites that for security I don't want FF remembering my password.
> Starting with username-only is an industry standard for any product used in enterprises.
I also have the opposite problem - sometimes I want Firefox to remember my username but not password; the only way seems to be to have it remember a dummy password (1 char so I recognise it as such) and then decline to 'update password' every time I change it in order to login.