What is the difference between the methodology of Ahlus-Sunnah wal-Jama'ah and Salafism, and is everyone who does not believe in Salafism an infidel, and is Salafism a methodology or a movement?

Salafism is a methodology based on returning to what the predecessors of the Ummah (Muslim nation) were upon in knowledge and action. It is not a movement started by Muhammad ibn Abd al-Wahhab; rather, he was a righteous man who followed this methodology. As for the term "Ahl al-Sunnah wa al-Jama'ah" (People of the Sunnah and the Community), it is the antithesis of the term "Ahl al-Bid'ah wa al-Furqah" (People of Innovation and Division). Declaring everyone who deviates from the methodology of the Salaf or Ahl al-Sunnah wa al-Jama'ah to be an unbeliever is not sound, for innovators (mubtadi'ah) are of two types: those whose innovation constitutes disbelief and those whose innovation does not constitute disbelief. Innovation that constitutes disbelief is the denial of a matter that is unanimously agreed upon, transmitted continuously (mutawatir) from the Shari'ah, and known by necessity to be part of the religion, such as the innovation of the Jahmiyyah in denying the attributes of Allah, those who say the Qur'an is created, the innovation of the Qadariyyah in denying Allah's knowledge and decree, and the Mujassimah (anthropomorphists). These are judged to be disbelievers after proof has been established against them. Innovation that does not constitute disbelief is that which does not necessitate a denial of the Book or of anything with which Allah sent His messengers, such as the Marwaniyyah innovation. Al-Azhar remains a beacon of knowledge, and the presence of errors by some of its scholars should not be attributed to Al-Azhar as a whole. Celebrating the Mawlid (Prophet's birthday) is a reprehensible innovation, and singing accompanied by music is forbidden, even if it is called religious.