Facebook Goes Down Amid Rollout of New Brand Pages [UPDATED]

Update #3 (5:18 p.m. ET): Facebook is now back up. The company tweeted an apology, explaining that “some internal prototypes were exposed to people and resulted in us disabling the site briefly. It’s now back to normal.” Facebook Pages have also returned to their earlier (old) formats.
Update #2 (4:58 p.m. ET): FacebookFacebook appears to be going in and out of service.
Update (4:44 p.m. ET): Facebook appears to be back up for most users.
Facebook just began rolling out several new features, including newly redesigned brand Pagespages (first revealed about a week and a half ago), a new Photos section dubbed “Memories” that allows users to view photos by year, and the ability to switch accounts for managing different Facebook Pages without having to log out.
However, at around the time the new features began appearing (4:15 ET), the site went down for many users, including all of us here at MashableMashable. Per usual, hundreds of users have since turned to TwitterTwitter to complain about the outage.
We’ve reached out to Facebook to find out the reason for the downtime and will update the post with any additional information. A source close to Facebook said the outage was related to an issue with customized tabs on Facebook Pages, which disappeared an hour before the site went down. In addition, Page owners were unable to determine which tab visitors landed on. When the site reappeared temporarily, customized tabs and landing pages were restored.