Wishes on Download Manager

I wish,
(1) "Add a comment filed": each items in DM has an editable text field as
description, and the Clear List bottom should clear only items whose text
field is empty.
(2)"Synchronize items in DM and temp folder": When deleting the items, also
deleting the associated files in the temp directory.
(3)"Avoid redundant download": When visiting a visited link which would
triggers DM and the downloaded file had not been cleared yet, FF would open
the file directly from the temp directory, instead of downloading it again.