Bookmark Previews adds an album view or cover flow view to Firefox bookmarks as shown in Apple Leopard operating system for viewing browsing files. If you saved websites as bookmarks for future reference, this extension will create a small snapshot of it. This will be used to show a Cover Flow-like interface for flipping through your bookmarks when you open up your bookmark manager.This extension will works in both Firefox 2 and Firefox 3, although it may act a little different between Firefox versions because each has a separate book marking system.. When you first start you will be able to have the extension create previews for you in the background. You can also perform this task later by Choosing 'File>Create Previews' in the Bookmarks Organizer. Your previews are stored as .jpg files in a folder named 'bookmarkpreviews' located in your profile folder. When you uninstall the extension (via the extension manager) this folder should be deleted.
However this extension is still in sandboxed, means in beta stage. To use it you should have an account with Mozilla. You can install it from here.