This Glue Chart Guides You Through Which Glue to Use Where
* These glues are not ideal for adhering the material but can be sufficient if the project is small and lightweight. When using hot glue for styrofoam projects, choose a low-temperature glue gun only. High-temperature hot glue will most likely refuse to bond and melt the plastic, which gives off harmful fumes. cheat-sheets
Put warm water into the dirty pan or cookie sheet, lay the dryer sheet (or sheets) flat in the water and leave it to sit overnight. In the morning, the baked-on stuff will either have lifted off, or will be very easy to slough off with a spatula or other flat object.
As a side note, I happened to be at Home Depot over the weekend and noticed that they sell some of these glass tile in their tile aisle. They come in sheets of about 144 and come in several different mixed colors (with some clear ones). All you would have to do is cut them apart and use some adhesive remover to get the stuff off the back of them. You could use those tiles in much the same way and have some cute colored ones as well!