Can't answer for parent post, but I do my living room browsing on a 1360x768 dumb TV and having the bookmarks toolbar open in any tab other than a blank new tab eats a noticeable amount of screen real state, so I default to new tab & click on bookmark.

It's a bummer that Firefox is not respecting its own compact layout by needlessly enlarging the address bar while on focus, but the shadow dropped from the new monstrosity obscures the bookmarks toolbar in my desktop with default layout, too, and that's a real usability concern.

Because GUIs have have more then one workflow since their invention. Same reason that there are multiple designs of physical tools, user preference.