Wow... You don't know what it means for an idea to be "falsifiable" apparantly.
That's okay, I'll explain - just make sure you remember.
It means that the idea is falsifiable in principle.
It kind of goes hand in hand with being verifiable in some way or another.
It means that the idea makes a couple testable predictions in such a way that if the predictions are tested and if these tests fail, then the idea is falsified.
So an idea being "falsifiable" doesn't mean that it CAN be shown to be false. It means that it COULD be shown to be false, if it is indeed false.
As opposed to an unfalsifiable idea.. such an idea is impossible to being demonstrated as false, even if it is false, because it makes no testable predictions. Because there is nothing to test.
So to summarize, an idea isn't "falsifiable" when it can be shown to be false. An idea is "falsifiable" when it could be shown to be false in case that it is.