Basically, instant immolate is for the shadowburn spec and 200% CB is for the CB spec, guess firestone will rarely be picked now that it's subpar to it's peers in any of the respective playstyles, especially considering that firestone is dispellable.
Good changes nonetheless, now as for UA I feel like it's transitioning into something but they haven't quite figured out what to do with it so we only get to see half the notes, I'd expect buffs coming soon to aff if they plan on limiting UA stacks to targets.