Firefox just keeps getting better and better with the help of the community and some very well designed extensions. My two favourites currently is the excellent download manager DownloadThemAll! and the tab navigation tool Tab Catalog.
DownloadThemAll not only provides much needed download management functionality missing in Firefox but also does an excellent job of speeding the task up through simultaneous segmented downloads. This process maximises bandwidth usage and provides a hefty speed increase over traditional single stream downloads.
Tab Catalog is a very handy tool for Tab-power users by providing a quick thumbnail overview of the tabs that are open. Compared to similar tools it doesn't suffer the variable speed or resource hungriness of alternatives and is ideal in situations where there are too many tabs and not enough time.