I use Firefox 3.0b2. Firefox has improved the Bookmarking, which is now called Places Organizer. Places contains your bookmarks, tags and history. You can search in all bookmarks, a selected folder, or even the history. You do not need to install any add-ons for using this functionality.
You can create a new bookmark, or add a new folder or add a separator, or organize your existing bookmarks in the places organizer. From the Places menu in the toolbar, you can access recently starred pages, most visited started pages, most visited pages, etc.. Places Organizer also help you take backup of the bookmarks, restore it, export the bookmark to a bookmark.html and import bookmarks from a file or Internet Explorer.
There are still bugs in this feature. First and important one is that you cannot drag and drop the bookmarks within the places. You will need to cut/copy and paste the bookmark to other folders when organizing. I hope this will be fixed in the nest stable release.
Second bug is, places organizer does not remember the columns selected in the views. By default it shows Name, Tags and Location. I can select other options like Keyword, Visit Date, Visit Count, Description, Last Modified, etc. from the Views -> Show Columns menu. If I close the Places Organizer and open it again, my previous column selections are all gone!