It's actually a pretty consistent view. You can use Gecko through a reskinned FF clone like Palemoon or Iceweasel, but can't call it Firefox. Firefox is the UI chrome and corresponding stack. Gecko is the engine.
Some would say they're part and parcel, but it's clear now that Mozilla doesn't agree.
It's entirely inconsistent with Mozilla's past actions.
You can compile Firefox source code of which 100% of it came from released Firefox versions in Mozilla's HG tree and they won't let you call that "Firefox". Part of why IceWeasel exists is Debian wanted to backport security patches from Firefox releases into an older version (eg. apply security patches from Firefox 4 to Firefox 3.5) for Debian-stable and Mozilla wouldn't let them use the name Firefox if they did that.
Therefore your claim that
> Firefox is the UI chrome and corresponding stack
doesn't match the reality of what Mozilla has done. It seems now Firefox is anything that Mozilla calls Firefox.
Some would say they're part and parcel, but it's clear now that Mozilla doesn't agree.