Passkeys

Part 1.
I have a gmail account in a Firefox portable version. Accounts are synchronized. One of each is on a different Laptop.
How many Passkeys are needed?
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Part 2.
I have Google chrome installed on 2 Laptops. Both have the same gmail account but not the same one in FF portable. Accounts are synchronized.
I also use this one to log in to each Laptop.
How many Passkeys are needed?

It depends what you're using as your passkey. If it's the computer then 1 per device. If it's a physical passkey then it can be a single passkey or if it's your phone it can also be one passkey

Password managers like Bitwarden typically allow to use/save one passkey on multiple devices, not safe, but convenient.

I forgot to mention the passkeys were made bt Google.

You should be aware that there are device-bound passkeys and syncable passkeys.

Device-bound passkeys are those stored exclusively on the devices, like YubiKey or Windows Hello's passkeys. YubiKey is a portable authenticator, so you can use it anywhere that it is supported. Windows passkeys aren't portable, so you need to create a passkey for each computer you want to use as an authenticator.

Syncable passkeys are normally those stored in a password manager, like Bitwarden, 1Password, or Google Password Manager. Wherever you have the software installed and synced to the same account, the passkeys will be available on the platforms they support.

For each Google account:

• For maximum security (and accessibility), create a passkey for each YubiKey you have.
• Your Android phones (13+ ?), when logged into the Google account, will act as cross-device passkey authenticators for the account (Bluetooth needs to be on).
• For maximum convenience, create a passkey for each Windows computer you have (especially those you aren't likely to lose).

Sorry for the delay.
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Opening my Gmail accounts
on my main Laptop has:-
FF Portable = 4 passkeys
G Chrome = 4 passkeys
MS Edge = 4 passkeys
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Opening my Gmail accounts
on my other Laptop has:-
G Chrome = 4 passkeys
MS Edge = 4 passkeys
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