Ever since I downloaded and updated Firefox to the current latest version 20.01, the Download window is missing, which I think is very troublesome to users.
After some googling, I managed to find the solution to make the download window shows after downloading a file:
1. Open Firefox and type “about:config” and enter. You may see a warning saying this may void the warranty, click continue if you are ok with it.
2. On the search field under the address field, type “browser.download.useToolkitUI” and double click on the entry to change the “value” to true.
3. Restart your Firefox and hopefully the download window appear.