IT people normally make silly mistakes which u can exploit....https://www.facebook.com go to this link....only difference is additional "S" which by pass firewall (if not already blocked).....
remember company has full authority for its asset and u r bound to follow those policies....
Go to A/c stttings then Security Tab Left hand side-second option..Secured browsing.tick the box and then save changes...
This will make ur fb even more safer and bypass firewall too....but for log in u have to type https...................wala address...https://www.facebook.com/ u can also book mark this which will relieve u for typing