From the description, it looks like they unfucked the layout, then firefox refucked it.
A decade ago it was very easy to make Firefox look like you wanted, even without extensions (if you weren't opinionated about aesthetics, just position and functionality.) Every UI change since Chrome was released has been a regression, and more obnoxiously, each change has been locked in with user adjustment actively prevented or made prohibitively difficult, even for programmers.
They could at least offer a consistent interface to change the UI. Instead they demand the flexibility to make UI changes without having to maintain an interface, while using that flexibility to claw back more and more flexibility from their users.
A decade ago it was very easy to make Firefox look like you wanted, even without extensions (if you weren't opinionated about aesthetics, just position and functionality.) Every UI change since Chrome was released has been a regression, and more obnoxiously, each change has been locked in with user adjustment actively prevented or made prohibitively difficult, even for programmers.
They could at least offer a consistent interface to change the UI. Instead they demand the flexibility to make UI changes without having to maintain an interface, while using that flexibility to claw back more and more flexibility from their users.