The old cooking refrain that "hot pan, cold oil, food won't stick" may be true, but I have another bit to add: "plastic bowl, hot oil, food falls through bottom."
My first two attempts at making homemade microwave popcorn didn't go so well. The first time, Saran Wrap melted to the sides of the plastic bowl and wouldn't come off. The second time, the plastic bowl started melting, and when I took it out of the microwave, unpopped kernels started dropping through the bottom.
So take my advice: use a Pyrex casserole dish if you're going to make homemade microwave popcorn.