Jackie, can you clarify? What do you mean by "did not install one between the floor joists and the new wall" Where exactly is the firestop supposedly being required? Are the floor joist above exposed or concealed?
Local juridictions vary, but typically fire blocking is required within concealed cavities, such as vertical walls and horizontal joists & soffits at 10 foot intervals, AND at transitions between vertical and horizontal cavities.
A wall would normally be constructed with least one top plate (typically there are two). The top plate would prevent any smoke and fire from spreading from between a stud cavity to the cavities between the joists. While blocking between the joists directly over the wall might be a good idea, unless the wall is separating a different occupancy (i.e. a garage), I don't beleive would typically be a requirement.
Unless a local inspector or lender is requiring you to correct something specific, I wouldn't be too concerned. I would suggest that you direct your efforts toward making sure that all sleeping rooms and spaces directly outside of sleeping rooms have functioning smoke alarms. If at all possible alarms run on house AC current that are interconnected so that if one sounds, they all sounds.