NEW APP: Facebook Inc. has updated its app for iPhones and iPads. Rather than add a slew of new features, the company rebuilt it to make it speedier and less clunky.

GONE: Facebook says programmers removed some lesser-used features, such as a way to view the app horizontally, to help speed it up.

SIGNIFICANCE: The mobile arena presents Facebook with its biggest challenge —and its biggest opportunity. That's where its user base is growing the most. But Facebook is still figuring out mobile ads.