Is styrofoam board insulation as good as fiberglass insulation?

depends on your definition of "as good" if you mean does it insulate as well as fiberglass the answer would be that styrofoam board insulates much better and that it will dramatically reduce your heating cooling cost. I viewed a film on the subject where a church pastor commented that he sometimes has to run the AC in the winter at the church because the heat from all the people will warm the building up too much.
As far as structural support styrofoam board is currently used in countries like Afghanistan because it makes buildings virtually earthquake proof.

The only downside of styrofoam board is that in the event of a rapid fire you would need to get out immediately to avoid all the toxins that would be released into the air and could kill you before the fire. We currently ingest these toxins when you allow styrofoam to be used as a take home box and more if the food you put into it is warm as that styrofoam will rapidly melt into your food.

So I believe we should take it out of our plates and cups and into our walls much better trade of risks and benefits