Changing the bucket size seems to have made a difference. Wonder why nobody from Curious Labs suggested this when I was reporting my rendering crashes and posting screenshots when the Beta Forum was up. I'm not sure if all the Firefly hangups can be controlled by changing the bucket size but I was able to even render the scene with shadows enabled for all the lights, use raytracing for the scene that I never even dreamed of for such a big scene before afraid to have a crash. Still the version of the scene I'm using I had already deleated some figures trying to cure the problem that I might need to add again but this results are very hopeful. I used 2 for bucket size which was painfully slow and then moved to 8 which is still slow but I can work with it.