Comment 13 for bug 896060

The only logical solution to this issue is making the Curtain'd unit be stuck inside the Firestorm.

While the Iron Curtain makes a unit invulnerable, it doesn't magically let it pass through walls, no matter their material.
And while the Firestorm Wall does kill everything that's on it on activation, it shouldn't magically be able to overrule invulnerability.

Thus, the reasonably solution is to just make the two end up in a stalemate: The Firestorm Wall doesn't kill the object, but it doesn't let it pass, either. The Iron Curtain'd unit isn't killed, but it doesn't magically transcend walls, either.

And as you may have guessed, that's a whole lot of special case coding of low priority that's not gonna be done for 0.2.