There is still a need to indicate progress when scrolling even with a mouse wheel. So scroll bars are designed with that in mind. And there is still occasion that you may want to use it to brag the bar to a specific part of a page. But this is fairly rare, because how do you know what part of a page you want to go to before you’ve seen it?
Currently on my Firefox there is indeed no scrollbar displayed. If I use my mouse wheel a thin version appears to indicate progress while scrolling. If I move my mouse to the edge of the screen a wider version appears which is easier to interface with on the rare occasion I want to do that. This is an optimal interface given the hardware I have available.
On a phone or table the scrollbar will not be interacted with my clicking on it. It only appears to indicate progress.
The old scrollbar design is obsolete. Doesn’t make any sense on touchscreens and is a waste of screen space on desktops since people have scroll wheels now.
Obsolete doesn’t mean it no longer works, a horse and carriage still functions after all. Obsolete simply means there’s more optimal options available because of improvements in technology. The scrollbar on Firefox right now is more optimal because of newer technology. The scrollbars pictured are obsolete no matter how much nostalgia you might feel for them.