What a fantastic little game you made, this is platforming done right! The controls are responsive and the levels are designed well with thought and care. Even little things down to the forgiveness of falling on to fire and spraying last minute or hugging the wall as you ascend and the fire on the floor above the wall you are ascending doesn’t hit you. You have taken a lot of care and understand what makes platformers like this work, especially with the restart button being also tied to the jump button, so no funky finger dancing around the keyboard. I would think the only improvement would be registering the next jump as you hit the floor, its like a pre jump before you land which helps register any jumps you may have pressed a little bit too soon (again more forgiveness but also feels great)
Good job with this one!