downthemall extention
https://addons.mozilla.org/firefox/201/
The first and only download manager/accelerator built inside Firefox!
DownThemAll is all you can desire from a download manager: it features an advanced accelerator that increases speed up to 400% and it allows you to pause and resume downloads at any time!
DownThemAll is fast, reliable and easy-to-use! It lets you download all the links or images contained in a webpage and much more: you can refine your downloads by fully customizable criteria to get only what you really want!
DownThemAll is absolutely freeware and open-source. No Adware, no Spyware.
For more informations,
http://www.downthemall.net/howto/features/