There is a Google Chrome plugins that allow you to save all your Facebook contacts and export it into Google+. Unfortunately, this has been disabled by Facebook as of now. Facebook fears that this will make it too easy for users to save their contacts and load in to Google+.
The only other alternative way that we know is to use the Yahoo! Mail trick.
First, you will need to log into your Yahoo! Mail account. If you do not have one, you can easily sign up one by going to the mail.yahoo.com site. Once you are logged into the Yahoo! Mail account, click on the “Tools” button for the drop down. Look for the “Import…” option and click on it. This will bring you to the import contacts page and you will see several icons to choose from. Select the “Facebook” icon and a popup will prompt you to login with your Facebook account credential. Once the Facebook address book is imported to your Yahoo Mail account, you can now use the “Export” option from the “Tools” menu to export it as a CSV file. You can now use this file and import it in to your Google+ account. Go to the Circles section and use the “Find and Invite” option.