Is mere doubt concerning the Islamic religion considered apostasy that expels one from the fold of Islam, and what should one do if faced with such doubts?

It is not permissible for a Muslim who is not armed with religious knowledge to browse websites that contain doubts and delusions of misguided people. Instead, he should seek religious knowledge. A Muslim must be certain of the truth of Islam and the word of Tawhid (monotheism), in accordance with the Almighty's saying: "The believers are only those who have believed in Allah and His Messenger and then doubt not but strive with their properties and their lives in the cause of Allah. It is those who are the truthful." And condemning the hypocrites, He says: "And their hearts have doubted, so in their doubt they waver." If the intrusive thoughts are merely fleeting occurrences that do not settle in the heart and are not spoken aloud, they do not expel one from the fold of Islam.