How to Know Someones Facebook Email ?

1) Login To your Yahoo Mail account.

                                          

2) Goto contacts option.
3) Now their select tools and then you will see there is an option of import on yahoo toolbar.

                               

4) Now goto your facebook account login and hit Facebook here on yahoo, Now they will ask you on facebook to import contacts, allow them.
5) After Five minutes they will import all the contacts and emails of your facebook friends they could be 10-1000, depends on your friends list.

6) Now Yahoo has successfully imports your contacts, Goto Your Yahoo Contacts list there you will see all friends email with details.