!Egads . . . I sure hope it's not toxic since I teach fire extinguisher classes and have ended up with this stuff on my uniform and inhaling who knows how much of the stuff over the years.
Unfortunately, I'm not at work so I cannot consult my "Fire Bible" -- two volumes that are the final word on all things related to fire and fire science. If I'm reminded tomorrow and have some time I can look up the info on the toxicity . . . I do know however from memory that the ammonium phosphate is slightly corrosive . . . emphasis on slightly . . . we're not talking battery acid or Alien blood corrosive here.
I think I might try some good hot fires . . . razor . . . maybe even a Magic Eraser to see if that might help.
I am not concerned about toxicity. As for the good hot fire option, well, no luck there. I have not let the fire go out even right after the incident. I am going try soaking the glass during the warm up this week. We shall see what happens.