sealing air gaps around a light fixture? (not recessed light)

Hello.

I'm about to replace my ceiling light fixture. It is not a recessed light.

I know there are some air gaps around the ceiling wire box. I will try to fill the big gaps via some settling joint compound.

But for the small gaps, can Great Stuff fireblock foam be used? I know you are not suppose to use it with recessed light, but for flush or ceiling flush mounted ceiling lights, are those okay?

Or should I just mud the crap out of the box and the drywall surrounding it. Doesn't matter since it is ugly, since it will be blocked by the light anyway.

Thanks.

 

How big are the gaps? Setting compound might be ok but you might need drywall tape also. I'd just caulk minor cracks/gaps.