Hi.
Host Grabber ++ allows to discover and explore pages to find and download files. As an example, downloading galeries from Imagebam our Imagevenue is one of the thing it can do. In fact, this extension is a rewritting of the former Image Host Grabber, with some differences though.
The module is currently in beta version but can be installed from addons.mozilla.org.
Documentation is available on this web site.