Since mine is about 12' tall and grows faster than I can chop it back I am not sure how they do in a pot.
I suggest no black pots, the sun just bakes them here in the south, a BIG pot and water fairly frequently-if it looks droopy water it, if the soil feels dry when you stick your finger in it then water it.
Good luck!
Tally HO!

That's good advice from Tally. I saw some blooming beautifully in a pot at a plant nursery, so I know they will bloom in a pot. Firebush likes LOTS of sun.

I have had one in a pot for years. I didn't like where DH planted it, so I dug it up and stuck it in a black garden center pot. Granted, it isn't very big, but it lives. (The pot is where the bottom is shaded by other pots, so I'm not discounting the advice above to not use black pots.)

I have 2 in pots. One is in part sun and a brown pottery pot. It gets more fertilizer and it is bigger than the one in part sun in a beige plastic pot. Both are blooming and I love them. Also have 2 in ground, but don't get as much sun and are much smaller. Never noticed any heat problems. They seem to like it. Even when one was in a beige pot on concrete all summer long.

Mine grows in partial shade and always has. It dies back with any freeze but will reach over 6-8 feet by the middle of July but do start late after many other plants have been sprouting up. The only starts I have been able to get were from plants coming up from the roots. Tried cuttings but nothing worked. I never do anything for this plant it does just great all by its self no matter how bad our weather is including the drought we had last year.