Xero prevents web browsers from remembering your username and password. While stopping them remember the password is (arguably) a great security measure, stopping it remembering the email address on your own computer servers no real purpose other than to waste your time.
This extension simply allows Chrome's autocomplete to work on the Xero login email address field.
Just drop the .crx file into Chrome for automatic installation. To build the extension yourself clone this repository and use the Developer Tools within the Chrome Extensions control panel.