Is the participation of Muslims in Christmas celebrations and other non-Islamic festivities forbidden in Islamic Sharia?

It is not permissible to participate with disbelievers in their festivals because it involves imitating them and showing affection towards them. Furthermore, their festivals are religious and doctrinal, based on corrupt beliefs, and participating in them falls under the meaning of "falsehood" (al-zur) which Allah has forbidden witnessing. It is also not permissible to give them greeting cards for their festivals, or to sell them such cards, or to sell items associated with their celebrations.