FlashGot is a free Mozilla/Firefox/Thunderbird extension (compatible with Netscape too), meant to handle single and massive ("all" and "selection") downloads with several external Download Managers.

FlashGot's main commands are:
-FlashGot Link (contextual menu or Ctrl-F1 or Alt+Click on a link) - downloads through the default download manager the link under the mouse pointer.
-FlashGot Selection (menu or Ctrl-F2 or Alt+Click with an active selection) - catches links in hilighted text/images, attempting also pure text to anchors conversion. It performs some "smart" replacement too, like turning "hxxp://" into "http://".
-FlashGot All (menu or Ctrl-F3) - grabs all the links found in the current page and dispatches them to the default download manager, which could offer an easy interface* to filter and select the file that will be downloaded in a batch.
* built-in filter dialog is provided by every Windows download manager except GetRight. On Linux, your best option is Downloader 4 X 2.5.4 or above. An emulated FlashGot filter dialog will be included in 0.6 release, being needed for GetRight, Linux and Mac OS X users.

-FlashGot Tabs (menu or Ctrl-F6) - performs a "FlashGot All" on every tab open in the current window. Notice that this command is hidden by default from the context menu: you can show it using the Menu options.