According to a demonstration by a Finnish web developer, Chrome and Safari have autofill capability to enter data into a web form. Phishers could hide the fields on the web form and fool the user into autofilling sensitive data, such as address, date-of-birth, etc.
Apparently LastPass also autofills hidden registration fields.
Users who type the start of their names will generate a prompt that when selected will throw an option to fill out their complete details. If clicked on a phishing site Kuosmanen describes, a user's sensitive information will be entered into boxes the user cannot see. Browser Autocomplete Phishing for Chrome and Safari [theregister.co.uk]
Mozilla says Firefox is not vulnerable as it does not autocomplete forms.