Instructions
Turn on your Xbox and log in to your Xbox Live profile.
Press the Xbox logo button and press "Y" to access the dashboard menu.
Scroll up to the "My Community" section.
Scroll right and select "Facebook." A download prompt appears.
Choose "Confirm Download." The Facebook application downloads to your Xbox 360.
Press "B" when a "Download Complete" notification appears.
Choose "Facebook."
Enter your Facebook login information into the corresponding fields and choose "Login." A "Settings" screen opens.
Place a check in the box next to "Automatically log in." Select "Display my Live info" if you want Facebook to post your Xbox Live gamertag in your profile.
Choose "Continue" to start using Facebook on your Xbox 360.