Really "Downloads" Them All! Rated 5 out of 5 stars
I can hardly remember a time without this add-on; the moment I see Firefox installed on a system without this, I'm tempted to get it. And it goes without saying that this little application has saved my life a million times now.
Now, as a download manager, it's obvious that it manages your downloads, aids in pausing them if the internet link is broken, and has an option to auto-rename all the files before actually getting them. Download Managers are especially useful when downloads in various major browsers tend to get corrupted, either because of the server hosting them or because you have slow internet. But very few people know of its many interesting uses.
For instance, in a Third World like India, internet disconnection out of the blue is commmon place. That doesn't help when you're spending hours of research online and need the other related pages. Simply rightclicking and selecting "DownThemAll" helps downloading ALL the related pages and content within seconds for offline viewing, just in case, or even on the move (in short: yes, this works better than manual "Save Page As" on every open tab).
Must have add-on in every system!