There’s a scrollbar for the page contents, but not for the list of pages on the left side. To scroll the list you either need to have a mouse with a scrollwheel (scrollwheel technology still sucks), or you need to have a notebook with a touchpad and use a two-finger scrolling (on Windows), (notebook touchpad technology still sucks).
We really need a scrollbar for the list, most of the time the list is too large to fit the window and you either need to use a scroll wheel or two finger touchpad scrolling. Both are inaccurate tech and that’s just not how any other sites do this. And the user has to guess that.
Looks like it has been added. Works great on Windows on Firefox and Edge browsers.
On Android phones on Firefox Mobile works fine in “Desktop view” mode, and the sidebar is completely hidden when in normal portrait view, kind of like when the window on Windows is made very narrow. I think that’s fine and by design.