One of the best things about Firefox is its download manager. Download Manager Tweak does what you'd expect, and slightly improves the experience.
Once you've installed and restarted Firefox, you'll have a new Downloads tab in Preferences. Ad well as the usual download options, Download Manager Tweak will have added new abilities. You can now choose to open the download manager in a sidebar or as a new tab, removing the normal extra window that Firefox uses. There's also a download toolbar, which is customizable.
The toolbar has a Launch, Open Folder, Delete File and Remove File buttons. The download information is also expanded slightly.
Download Manager Tweak doesn't add a great deal to Firefox, but being able to choose where the manager shows up is nice. The Opera browser keeps downloads inside the browser, and feels much more modern for it, so having the same option for Firefox can only be a good thing. The other Download Manager Tweak additions are pretty minor.
Download Manager Tweak is useful, but doesn't do enough to become an essential Firefox Add-on