Whenever you go to close a folder from the bookmark menu in the browser sidebar, having scrolled down due to a long list, the menu will not only close the folder but also make you click whatever was in that mouse position on the menu with the menu closed. This means closing a folder having scrolled down will cause you to potentially click open another folder or bookmark unintentionally. This is not an issue on the old bookmark menu, but using that isn't as convenient as the sidebar is.