George,

Yes, I agree. And I have spoken with a representative of ICC about this. No official interpretation, so take it for what it is worth, but the individual I spoke with concurred that fire caulk is not required when the only issue involved is maintaining the integrity of fire blocking. He stated that expanding foam would not be acceptable because it is too insubstantial, and I would add, burns too well. But a good silicone caulk, or as you say, fiberglass insulation would work. I have seen some expanding foam that is fire resistant. I think this would be acceptable as well. How do you feel about that?