Facebook password not syncing to iCloud keychain on iPad and iMac

My iPad recently decided not to recognise my Facebook password ('Old Password') even though I was entering it correctly and it had worked fine for the last three years. On my iMac I changed the Facebook password ('New Password'). However, this was not saved to keychain (nor to Firefox saved Passwords) which still had 'Old Password'. On the iPad I entered the new password and gain access just fine. However, on the iPad I checked Settings, Passwords and that is still showing 'Old Password'.

Am I missing something?

How can I force new passwords to be saved to iCloud Keychain from the iMac and iPad (not just Facebook but more generally).

[Re-Titled by Moderator]