Better late than never. This reply is not very timely but you may have interest anyway. There are two foam firestops (Dow and Hilti) but they have very specific uses. Both foams are two part and mix before injecting into the opening. They are pretty liquid like and not like Great Stuff, which is what most people want to use when they ask for a foam. I don't think they will work for your intent. Great stuff is not a firestop it is a fire block. Firestops are for fire-resistance rated assemblies in commercial construction. They are used very little in single family residences. Don't feel bad most people want the foam solution. It may pass inspection as a firestop but is not really compliant.
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