Below is a step by step guide on how to make this possible, this method does not require a jailbroken or modified device.
1-Launch your phone's Internet browser
3-Switch to the 'Desktop site'
4-Open up your events on Facebook
5-Somewhere near the top you will find a drop-down menu, click on it
6-You will find an option to export the events, click on it if you would like to export your events, however if you only want to export birthdays click on the birthdays option
7-Repeat step 6 after you have chosen birthdays if you would like to sync birthdays
8-You will get an option to subscribe the the 'Fbcal'
10-Launch your calendar app and you should find them there