Facebook Friends Exporter as this extension is called, allows you to transfer details that your Facebook friends have shared with you (i.e. their names, email addresses, phone numbers, websites, addresses and birthdays). The information should be saved as a CSV file or imported directly into your Gmail address book as a folder labeled "Facebook contacts Imported"
A user’s Google+ connections are based upon his or her Gmail address book. To get started, users are encouraged to sift through their Google contacts to add them to “Circles” for friends, family, classmates, co-workers and other custom groups. Circles is Google’s attempt to help users interact better with specific social groups.
According to CNET reporter Stephen Shankland he noted that that this tool probably won’t rub well with Facebook, citing Section 3.2 of Facebook’s terms of service: “You will not collect users’ content or information, or otherwise access Facebook, using automated means (such as harvesting bots, robots, spiders, or scrapers) without our permission.”
Apparently there will be some sort of opposition between the two social giants, because Google has for long held the philosophy of users been able to extract their data (i mean their entire data, including Google contacts using Google Takeout). And Facebook on the other hand, attest to this as a very "serious privacy concerns".
Now i ought to warn you that using this extension is at your own risk according to the programmer Mohamed Mansour. Currently 30k + users have used it and not one of them have received ban notice from Facebook.