Alternative to Pop-Up window

Sorry that is not possible.
To change the width and height take a look at line 7 of email-js.js https://github.com/lesterchan/wp-email/blob/master/email-js.js#L7
width=500,height=500

Ok. But the window seems to be re-sizing with a smaller width than 500.

Delete Line 30-42 of email-popup.php

https://github.com/lesterchan/wp-email/blob/master/email-popup.php#L30-L42