DisplayFusion's never had the ability to force it to a new position before the window is visible. We wait until after it's visible to move it, because a lot of applications don't behave correctly if you try to move them before they're visible.

What may have been happening before, is that the application was already opening in the correct spot, due to Windows remembering the position it was in when it was last closed.

Firefox seems to have a bug where if it was maximized, and you moved it to a new monitor, then closed it, it wouldn't remember its last position. So the trick is to restore it, drag it to the new monitor, then maximize it and close it. Windows should then remember the position for Firefox

Hope that helps!