What can I do with the Download Manager?

From Mozilla Firefox help

In addition to keeping information on all your downloads in one place, the
Download Manager keeps convenient download actions easily accessible for each
of your downloads.

Pause


You can pause any downloads currently in progress by clicking the
Pause link beside the file entry. This may be useful, for
example, if you need to open a small download started after a large
download. Pausing downloads gives you the choice to decide which of your
downloads are most important. When you want to continue downloading those
files, simply use the Resume link to finish those downloads.


Cancel


If after starting a download you decide you no longer need that file,
canceling the download is simple: just use the Cancel link beside
that file entry to cancel it and free up your connection for your browsing
and other downloads.


Open the File


When a download has finished, the Open link will appear
by the file entry. Use it to open the file.


Remove the File's Entry


If you do not wish to store information on a particular download, removing
the entry is as simple as the click of a mouse. Simply use the
Remove link beside the file entry to delete it.


Retry a Download


If for any reason a download does not complete, it is easy to attempt the
download again. To recover from a failed download and retry it, just use
the Retry link next to the file entry and Firefox will
restart the download for you.


Show Download Folder


If you have set Firefox to save all downloads to a folder in
Download Manager OptionsPreferences,
you can open this folder by clicking the Folder Name at the
bottom of the Download Manager window.