He was the third of Tughlaq dynasty, ruled for 38 years ( 1351 - 88 AD ) and his reign was the longest of the Delhi Sultanate.
All Muslim chronicles of that period refer to him as the most kindest, generous, religious and justice oriented Sultan among all the Sultans of Delhi. Elliot, the British historian who supervised over translations of many Persian chronicles giving accounts of India during Muslim rule, has high praise for Firoz Shah and calls him as Akbar of his times ( Delhi Sultanate ).
He was neither a barbarian nor uncivilized and was a very illustrious King. Sure, he was a very devout Muslim, even though he took wine, and that outlook based on Islam towards his Hindu subjects, which is no diff. from rulings of Sharia, was the force behind his actions.
The story behind his birth gives insight in to the affairs of those days. His father, Sipah salar Rajjab was a brother of Ghiyasuddeen Tughlaq, the founder of Tughlaq dynasty. At the time of his birth, Ghiyasuddeen was a noble in the court of Alauddin Khilji and assigned to Dipalpur ( in present day Pakistan's Punjab ) as fief-holder ( iqtadar ). Wanting to amass wealth, he wanted his brother obtain a daughter of one of Hindu kings there in marriage. Having found a daughter of a small Hindu king, Ranamall Bhatti, he sends a proposal which was rejected by Ranamall. On this rejection, Ghiyasuddeen brings his army to villages belonging to Ranamall and starts harassing villagers by demanding full payment of one year's revenue and helpless Ranamall agrees to the marriage proposal. After the marriage, her name ' Bibi Naila ' was changed to ' Sultan Bibi Kadbanu '. She gave birth to Firoz Shah in the year 1309 AD. ( Shams-I Siraj Afif's Tarikhi Firoz Shahi ; Elliot Vol. 3, pp 271-273)
So, what impact Hindu ancestry of his mother could have made on him ?
The very first lines from his autobiography, Fatuhat i Firoz Shahi, would point to the answer to the above question and his rejection of any religion other than Islam and his belief of superiority of lives of Muslims over others :
".....First I would praise Him [ Allah ] because when irreligion [ Hinduism ] and sins opposed to the Law [ Sharia ] prevailed in Hindustan, and men's habits and dispositions were inclined towards them, and were averse to the restraints of religion, He [ Allah ] inspired me His humble servant with an earnest desire to repress irreligion and wickedness, so that I was able to labour diligently until with HIS blessing the vanities of the world, and things repugnat to religion, were set aside, and the truthwas distinuguished from the false. "
"In the reigns of former Kings the blood of many Musslamans has been shed and many varieties of torture were employed...... [ he named the few of those tortures ] ......The Great and Merciful God [ Allah ] made me, His servant, hope and seek for His Mercy by devoting myself to prevent the unlawful killing of Musslamans."