The pref that disables the ugly behaviour is going away. Indeed, in some sense it's already gone: ["Remove the megabar pref"](https://bugzilla.mozilla.org/show_bug.cgi?id=1627969) is already marked as `closed`.
I think the UI change is not merely ugly, but actively harmful. When the user's attention is elsewhere, but the focus of the urlbar changes there's a nasty UI animation that occurs in the user's peripheral vision. As any real UI designer should know, human peripheral vision is primarily for motion detection, directly tied to fight-or-flight stress reactions and triggers an adrenal stress reaction which in this case is not merely "undesirable" but downright harmfully misleading. The last thing the world needs is more stress just because some delusional UI designers thought an animation upon receiving/losing focus was a good thing to implement.
This abomination has to die, and today would not be soon enough.