Facebook has been all over the press recently where users have signed up to various apps and found that their personal information (and some of their friends) has leaked without their authorisation. Facebook's answer is that personal information will be shared if you sign up to third-party apps from your account.
Mozilla has released an official app which attempts to safeguard your personal information by using a container to store data, whilst you interact with Facebook.
The container works by ring-fencing your data, so limited information is shared with Facebook. Mozilla does not have any access to this data, either. When you open your Facebook page, you'll see a blue hue around your tab showing that it's being contained.
The only issue with using this container will be where you use your Facebook account to login to a third-party website. As your Facebook data is contained, this means it cannot be shared with other websites. Also, another issue will be attempting to like a Facebook post or anything similar from outside your contained environment - you can't. So you're limited to all Facebook activity within the contained tab and nothing more.
You'll need to ask yourself are you that paranoid about Facebook sharing your personal information to need to ring-fence and safeguard your Facebook content in such fashion.
Excellent for people who are paranoid about Facebook taking their personal information, but very limiting if you want third-party websites to interact with your Facebook account.