A start page can be configured to contain any number of selected folders of local hard drives and other devices. Firefox tries to discover the available devices automatically at first start but all of them can be edited or removed from the list. Each device is listed with a system path, an alias and other information like type.

The user can then browse those folders and devices normally by clicking on them. The functionality is basically the same than that of Windows Explorer. Several file types can be previewed by hoovering the mouse over them. Most multimedia files can be played right in the browser

Windows can be split and a folder structure can be displayed in the left sidebar as well. I would say that it is a sophisticated file manager, great for everyone who needs something like this in Firefox. I see it more as a nice proof of concept of what can be done with Firefox add-ons.