While setting up your username be careful because you can create this username only once.
=>Trick to Get @facebook.com Email Address :- To set up a @facebook.com address, go to your Messages view and click the Claim your Facebook email link.
Now you will also be able to login into your Facebook Account with @facebook.com rather than any other Email Address. At the Facebook login Page enter your facebook username along with @facebook.com. i.e. firstname.lastname@example.org and enter your password. Your Facebook homepage will be open.