Praise be to Allaah.
It is not permissible for the Muslim to join the kuffaar in their festivals and to express joy and happiness on these occasions, or to take the day off work, whether the occasion is religious or secular, because this is a kind of imitating the enemies of Allaah, which is forbidden, and a kind of co-operating with them in falsehood. It was proven that the Messenger of Allaah (peace and blessings of Allaah be upon him) said: Whoever imitates a people is one of them. And Allaah says (interpretation of the meaning):
Help you one another in AlâBirr and AtâTaqwa (virtue, righteousness and piety); but do not help one another in sin and transgression. And fear Allaah. Verily, Allaah is Severe in punishment[al-Maa'idah 5:2]
We advise you to refer to the book Iqtidaa' al-Siraat al-Mustaqeem by Shaykh al-Islam Ibn Taymiyah (may Allaah have mercy on him), for it is very useful on this topic. [Translator's note: This book is available in English under the title The Right Way, published by Darussalam, Riyadh].
And Allaah is the source of strength. May Allaah bless our Prophet Muhammad and his family and companions, and grant them peace.