According to theory, there were no molecules in the very beginning of the universe. There weren’t even atoms yet, only energy and an assortment of fundamental particles.
Well something had to bring all that together to ignite or whatever. Then too, how can energy (of what sort) could assemble the odd assortment of fundamental particles and compress them enough to explode out; then it also follows how large was the mass considering what’s out there in the universe now?