Download management is one of the larger categories on the Firefox Add-ons site, but while hundreds of extensions fall under this category, they are a mixed lot at best. Many have yet to release versions compatible with Firefox 3.0, and others are designed to work with Windows programs. However, with patience, you can find some programs worth exploring -- and even a few small treasures -- in this category.

Several add-ons offer small improvements to Firefox's default download manager (the window in which you choose to open a download or save it to disk, and the other dialog in which you can view and control each download). Using Custom Download Manager, you can add buttons and toolbars to the download window, and change the position of existing ones -- a reasonable idea, given that by default the buttons are at the bottom and the progress bars are at the top, and you can easily overlook the options in the right-click menu.

Custom Download Manager also gives you options for handling Windows files with executable extensions -- if you care -- and allows you to display the download manager in a window like the default or to display it instead in a sidebar or tab.

More Here