Any “3D effects have to be applied to 2D layers (flat to camera), because AE makes a 3D “movie” that plays on a 2D “screen”. If the layer were 3D, you’d see the flat “screen” at an angle, and the illusion would be lost.
So effects that use a comp camera use the camera info to create the 3D movie that plays on the flat screen. It’s an illusion. If you have “comp camera” selected, the layer is seen accurately by the comp camera. However … you need to set the layer’s position within the effect. All controls for any 3D effect need to be set within the effect — the comp camera button just syncs the effect’s camera with the comp camera.
I haven’t used FF in years … there should be position controls within the effect. However, you may be close to graduating to a real 3D app. 🙂
Hope that makes sense …