would have been way easier than facing the foam I put in the rim joist with drywall!)

As an ignition/thermal barrier, that's a different use than you are proposing. And it is acceptable. (Check with local agency with jurisdiction to be sure.)

Used as wall insulation, mineral wool has to be covered with an air barrier to be effective.

so its an appropriate fire barrier if I understand you...do you know the difference between the straight roxul and the safe and sound...just curious...

do you know the difference between the straight roxul and the safe and sound.

Only what I read on their website (see link)-- that Safe 'n Sound is for soundproofing and fire protection not energy conservation purposes, as it's denser than the Comfort Batt.

For instance, S&S is 2.5 lbs./ft.3 vs. R-15 Comfort Batts at 2lbs./ft. 3.

Here is a link that might be useful: Roxul

so the comfort roxul appears to offer some rvalue and is fire proof though so I think I should use it under the fp....?

looked on the website....interesting...s&s apparently is for sound deadening + fire retardancy. I assume what I have...regular roxul is something I could use...offers fire retardency (though to what degree I could not tell since the link on the website did not work!---hopefully better than fg) and inslulates...

Agree?

Are you further saying for this roxul to be effective I need to cover the area with a piece of drywall...or its simply less effective without it?

Used as insulation, low density fibrous materials such as mineral wool should be covered by an air barrier. Otherwise, convective looping and air pressure moving through the product from wind can subvert its performance. (See link.)

Here is a link that might be useful: Building Science Corp.: Cavity Insulation

interesting stuff....I had fg in there..made a huge difference...I am going to fireproof caulk the gaps and put the roxul in....it should be safer and be can be no worse insulation wise than the fg..I'd prefer not to drywall that spot.