Hmm, 10 gallons is kinda small its hard to say, pick an easy going small marine fish, i dont have any experience but 10 gallons significantly limits you.
there are various gobies and blennys that will go great in a 10g and they stay pretty peaceful, some gobies dont do well mixed with their own species. you can go with a pair of true or false percs or maybe a 6 line wrasse. theres alot more, but maybe someone with more experience can put their input into this. hope this helps.
yeah, a firefish goby, like in your sig, would be ok. Also, I think a true or false perc would be ok and active. I had a true perc in a 20 long, and it was active, it was fine for food just eating off the live rock and algae and stuff. but, I suggest feeding at least every 4 days or so.
Just because you can't have a lot of fish in a small tank does not mean you can't make it look good. You can add corals and invertibrets as well. this can make your tank active and colorful, even in a small tank.
personally I would go with a green, or yellow clown goby to go with the firefish. It would also be possible to get a small goby/pistol shrimp pair. But you would be at your limit after that. Make sure you are doing weekly water changes on that tank.