In the name of Allah, the most Beneficent, the most Merciful.

Answer

Allah (SWA) in the Holy Quran has said: “O those who believe, eat of the good things we have provided you”.  (Surah Baqarah v.172)

And “O people eat what is in the earth, permissible and good”.  (Surah Baqarah v.168)

Allah (SWA) encourages the Muslims to eat those food products, which are Tayyib and are halal beyond any doubt.  Halal food fried in the same oil as haraam oil is haraam.  Therefore we can only say if it is haraam or halal by assessing how the food is prepared in the kitchen.  If the food is not fried in haraam oil or there is no contamination with haraam things then it will be permissible, otherwise no. However, it is preferable to refrain from eating in McDonalds restaurant.

With regards to your second question it is Makruh Tahrimi (prohibitively disliked) to do business with those at war with Muslims in a way in which the trade will benefit and strengthen them in any way. For example, if a certain company directly funds any army fighting against Muslims, then buying their products is Makruh Tahrimi. However, if the trade does not directly fund against the Muslims, then it is not Makruh Tahrimi to buy and sell with such companies. (Maariful Quran p.58 v.2)

Only Allah Knows Best

Mohammed Tosir Miah

Darul Ifta Birmingham.