i would like to able to focus in on one folder on the sidebar and have nothing else showing. currently when you have things organised in folders and subfolders, the 1st level of subfolders are indented, the 2nd level are indented even more and eventually you have to scroll sideways to see things.
and having shortcuts to get back to frequently used folders, or at least be able to search for a folder in the sidebar. at the moment firefox only searches for bookmarks, not folders
being able to edit bookmark names and links directly without having to open separate editing window. vivaldi's sidebar does a pretty good job of this and also has a note section which can be very useful to remind your future self in a few years why you bookmarked something