It's just metal clips that hold it on. It's very possible the two sided tape between the windshield trim and metal clip failed. I had to use epoxy on all the clips when I put mine back on to keep them from coming off. and yes I've had mine almost blow completely off going down the road, it's not fun.

Just very carefully start pulling the top piece off first, then the sides. You have to pop them back on pretty forcefully. When you pry them a way a little, you'll see where all the clips are located. There are 3 on each side, and 5 or so on the top peice. Use a flat tip screw driver or something to put in there and pry with. It doesn't take long.