I just realized something after spending some time with Namoroka (Firefox 3.6 Alpha 1). Sometimes, the download window doesn't show the remaining time and also the download progress when i'm downloading something. It does give some notification when the download has finished just like the current version of Firefox, but that's it. If you are downloading big files, you won't notice it. Also when you download several files at once, it will not show every files on the dialog window.
Let's just hope it will get fixed in the next Alpha (or Beta)