I have no experience with firebelly toads, in fact I have never heard of them. However I spent countless hours as a child in the tadpole ponds near the beach. I know 'regular' frog and toad eggs come in a long string, like Christmas rope lights, and are clear with black centers. They are also very jelly-like and durable. You can pick up a strand of eggs at any place in the strand without breaking them. As I said, this is not firebelly specific, but I would think that most toads and frogs would be generally similar?
I would assume Toirtis would be your best bet for an answer. Good luck