firefox scrollbar

Hello: The scrollbars' properties (color, background color, width) are really important things in scrollable windows, normally they are controlled by the window theme. I've recently installed firefox 91.2.0esr and its scroll bars are not like the used theme's scrollbar. They are hard to see, changing color depending on visited site and so thin that it is hard to move the cursor over them. I guess this is a new firefox "improvement", because the previous firefox esr (78) uses the theme's scrollbar. Is there a way to make firefox use the theme defined scrollbars? Thanks, Istvan