If you're not happy with Firefox's favorites manager, and want a visual way to manage your bookmarks, consider Tidy Favorites. This one download is a Firefox and Internet Explorer add-in, and it displays thumbnails of your favorites inside a Firefox tab. You can easily copy, delete, and update them, drag and drop them inside the tab, resize them, rearrange them, and quickly search through them all.
One of the program's nicer touches is that the thumbnails refresh themselves, so that you can see not just a static thumbnail, but one that displays the current information on the page. Also useful is that you can share your favorites among Firefox and Internet Explorer. Use it in one browser, and the favorites you add with be available in the other browser as well. You can also install a portable version that you can install on a USB flash drive. In that way, you can use the same favorites on different PCs.
All that being said, this program is not for everyone. I found it more difficult, not easier, to manage my favorites with it, because the thumbnails quickly overwhelm the screen, and the screen quickly gets cluttered. Still, if you like to manage things visually, it might be what you want.
When you install it, its features become accessible via buttons in Firefox and Internet Explorer. But this buttons might not be visible. If you can't find it in Firefox, restart Firefox, select View-->Toolbars-->Customize, and drag the program's icons to the Firefox toolbar. In Internet Explorer if they're not visible, click the double-arrow at the far right of the toolbar, and you should see them.