I don't mean to be nit-pickey but just as using electrical terms incorrectly can cause confusion, so can the incorrect use of other building code terms. Here are some difinitions from the IBC (and they are used the same in other building codes):
DRAFTSTOP. A material, device or construction installed to
restrict the movement of air within open spaces of concealed
areas of building components such as crawl spaces, floor/ceiling
assemblies, roof/ceiling assemblies and attics.
FIREBLOCKING. Building materials installed to resist the
free passage of flame to other areas of the building through
PENETRATION FIRESTOP. A through-penetration
firestop or a membrane-penetration firestop.
MEMBRANE-PENETRATION FIRESTOP. A material,
device or construction installed to resist for a prescribed time
period the passage of flame and heat through openings in a protective
membrane in order to accommodate cables, cable trays,
conduit, tubing, pipes or similar items.
THROUGH-PENETRATION FIRESTOP SYSTEM. An
assemblage of specific materials or products that are designed,
tested and fire-resistance rated to resist for a prescribed period
of time the spread of fire through penetrations. The F and T rating
criteria for penetration firestop systems shall be in accordance
with ASTM E 814. See definitions of “F rating” and “T
I think what George is asking about is Fireblocking rather than fire stoping. In the right application and if installed properly, I think fiberglass works as a fireblocking material. The IBC in fact mentions fiberglass as an acceptable fireblocking material. Fiberglass does not burn, but it does melt. I have looked up the melting temperature of glass befor. I can't remember offhand what it is, but it is about the same as sheet metal or gypsum.
Fire Stopping on the other hand is a completley differant animal. Fire stopping is used when a penetration is made through a fire rated wall or other assembly (penetrating a top or bottom plate of a wall is not an example of this). A fire stopping assembly needs to be tested for the required fire rating. I know of no tested fire stop system that consists of fiberglass used to fill up a hole through a rated assembly. It can be used within a tested assembly that uses gypsum board or other materials as the primary material to resist the fire, but I doubt there is a tested assembly that uses fiber glass as the primary material to resist the fire.
NEC 300.21 correctly uses the term fire stopping in conjuction with penetrations through rated assemblies. 334.80 seems to use the term incorrectly because it seems to use that term for any penetration through wood framing. Remember, it is the building code, not the NEC, is the primary authority on where fireblocking or firestopping is required.