There is an excellent extension for firefox called
Download Statusbar that alters the behavior of downloading files. Instead of opening a new window to show the downloads, it creates a small statusbar along the bottom of the browser window that allows the user to monitor, pause, resume, open, and delete downloaded files.
Double click on a file opens it and removes it from the statusbar. When no items are left, the statusbar disappears.
To this day it is probably the single biggest thing I miss from my move from FF, and I'd love to see some version of it implemented in OW, especially since I always have to dig behind the browser to find the download window, and other than checking the download window, there's no quick visual way to determine if a download has finished.