Personally I'd say 1000 no thanks if they implemented that. The scrollbars are part of the application chrome, not content. I should choose how to style them, through my OS, not a website I visit.

Anyway, you can apply own user CSS styles in Chrome.

Yes, and I assume Firefox would let you turn it off, in about:config at least. So I'm fine with it being implemented ;-)

It's actually 17y old, that bug or a dupe of https://bugzilla.mozilla.org/show_bug.cgi?id=77790.

Why do you want it - if you really need it then you can have a skin so the user can alter the user chrome to match a specific website.

Personally I consider it one of IE5s many horrors that websites were given control over the users UI. (IIRC you could turn it off at least?)

Bugs are different, 77790 is about color, 547260 is about CSS styling(+size control). Default scrollbar width is very thick and its color is out of web developer control. It's a pain for developer to make a good admin panel with several scrollable areas. JS-scrolling is not stable for all browsers and CPU-intensive for mobiles.