FlashGot is a free Mozilla/Firefox/Thunderbird extension, meant to handle single and massive ("all" and "selection") downloads with several external Download Managers.
FlashGot turns every supported download manager in a download manager for Firefox!
Works with Firefox: 1.5 3.1a1pre.x
What's New in version 1.0.5:
Speed Download Lite support
Moved changelog online to reduce XPI size
(Dar)Wine support turned off by default to avoid annoyances on some configurations (e.g. X11 starting on Mac OS X). It can be turned on by setting the flashgot.useWine about:config preference to true
Added option for "Built in" download manager to overwrite files, rather than renaming with numbers (thanks Lawrence O. Johnstone for suggestion)