Yeah. The firefish are very nice fish and do very well from what i've heard in 10G tanks. I have one and i'm glad i bought him. He's an awesome fish to have. You can still get a clown goby.. and a pistol shrimp if you want.. but i don't think those types pair up. Never heard of a clown goby and a pistol shrimp pairing up..
Also, liveaquaria.com has compiled a listing of fish that can fit in small nano tanks. I think you should take a look at it. Maybe you'll find something you like that can go in your 10G
Also, the wheelers watchman goby can fit in a 10G tank.. sooo.. maybe your dreams of a pistol shrimp/goby pair aren't exactly crushed yet.. lol.