Mulberry - look at the leaves in pic 2. There are at least two different shaped leaves, one of which is shaped kind of like a glove. That, and the flowers say Mulberry to me. Mulberry and Sassafras are some of the very few trees that have different shaped leaves on the same tree. Mulberry can have different shaped leaves on the same branch. The pic of the single leaf he's holding does look like basswood - but it doesn't give the complete picture of all the leaves on the tree.
I couldn't say from experience if either mulberry or sass make for good firewood. Sass makes great canoe paddles though...very strong, light weight and rot and insect resistant. I also used to cut Sass saplings to make hiking sticks - tried to sell them. Makes for a great stick...but who's willing to pay for a walking stick?