Is it permissible for some Christian colleagues to be friends on Facebook and Twitter?

The ruling on befriending disbelievers on social media is determined based on its effect. If it is beneficial and does not harm one's religion or worldly affairs, such as using it for da'wah (inviting to the truth) or exchanging beneficial expertise, then there is no objection to it. However, if it leads to a religiously forbidden corruption, such as raising doubts or showing loyalty to disbelievers, then it is prohibited, due to the Almighty's saying: ﴿O YOU WHO HAVE BELIEVED, DO NOT TAKE THE JEWS AND THE CHRISTIANS AS ALLIES. SOME OF THEM ARE ALLIES OF ONE ANOTHER. AND WHOEVER OF YOU TAKES THEM AS ALLIES – INDEED, HE IS [ONE] OF THEM. INDEED, ALLAH DOES NOT GUIDE THE WRONGDOING PEOPLE﴾ [Al-Ma'idah: 51].