Yahoo recently updated its del.icio.us Firefox extension to more tightly integrate some of the great features of the del.icio.us bookmarking service into Firefox.

Del.icio.us replaces the venerable folder system of organization with a system of "tags." Tags are the equivalent of being able to put a single bookmark in multiple folders without having to make copies, and they're much better than folders for keeping your bookmarks organized and easy to find.

The del.icio.us service, combined with the Firefox extension, also makes it easy to synchronize bookmarks between multiple PCs -- for example, your PC at the office and the one at home.

All of these things have been available in the del.icio.us bookmarking service for a couple of years; now with the del.icio.us extension version 1.3.59, they're integrated with the Firefox browser and much easier to use. It's a great leap forward in bookmarking and makes browsing significantly faster and easier.Getting Started
To use the del.icio.us Firefox extension, simply download and install it in the standard way. If you have a del.icio.us account, the service prompts you to log in to that; if you don't already have one, the service prompts you to create one. After that, the service uploads all your existing Firefox bookmarks to del.icio.us. Your existing folders become tags. For example, if you had a folder called "search," containing links to Google, Yahoo, MSN, Ask.com, and so forth, each of those bookmarks would be imported into del.icio.us separately, and each one of them would have the tag "search."

The del.icio.us extension completely overwrites the default Firefox bookmarking tool, and your existing bookmarks. You should back up your bookmarks before installing the del.icio.us extension. If you decide you don't like the del.icio.us extension, you can get the old bookmarks back by uninstalling the del.icio.us extension and restoring your bookmarks from the backup. This article shows you how to back up your bookmarks, along with the rest of your Firefox profile.

Using It
Once you install the extension, the operation is similar to the default Firefox bookmarking tool. You call it up from the Firefox menus, from toolbar icons, or or by entering Ctrl-B on your keyboard. You add a new bookmark with Ctrl-D. These are the same keyboard shortcuts that the default Firefox bookmarking tool uses.

The del.icio.us sidebar (above) is a two-pane window, with the top pane for tags and the bottom pane for bookmarks. The window also includes a search box at the top; enter a search term, and the top pane will show you all the tags containing that term, and all the bookmarks associated with those tags. The bottom pane contains a list of all the bookmarks containing the search text in the title, URL, description, or tags.

The extension synchs your browser bookmarks with the bookmarks on the del.icio.us service regularly -- I'm not sure what the schedule is, but I haven't noticed my bookmarks to be out-of-date on either of the two PCs I've been using the extension on. It's probably about once a day. You can also do a manual synch by clicking a link on the configuration page in your browser.

The tagging organization system for del.icio.us is pretty easy to get used to. As I said earlier, you can just think of it as having a single bookmark in multiple folders, without making copies of the bookmark. For example, consider this page of articles and resources related to last week's big Microsoft announcement of Windows Vista, 2007 Office, and Exchange 2007. I've got that tagged "informationweek," "Microsoft," "Windows," "Vista," "Exchange," and "Office." That's not hard to figure out, is it?

Potential Problems
One thing that's difficult to get used to: The del.icio.us extension changes how browser bookmarks toolbar works. That's the toolbar below the address bar, at the top of the browser window, where you can park frequently used bookmarks for one-click access.

Here's the problem: The standard Firefox lets you put folders in the browser toolbar, with each folder containing multiple bookmarks. I kept several folders on my browser toolbar. For example, one of them was called "read_later," for articles I'd found on the Web that I wanted to read later.

The del.icio.us extension doesn't use folders at all, so you can't have folders on your toolbar. That'll take some getting used to.

Instead of folder, the del.icio.us Firefox extension lets you designate as many button toolbars as you want. Here's how that works: You designate particular tags as favorite tags, and can pick from the dropdown list of favorites to park all the buttons with a given tag in the browser toolbar.

For example, you might add the tag "search" to various search engines, and designate the "search" tag as a favorite. Then, simply by calling up the "search" tag from a drop-down list of your favorite tags, you can populate your browser bookmarks toolbar with a bunch of different search engines: Google, Yahoo, Ask.com, etc. That's useful.

Another problem -- search on the extension is pretty rudimentary. You can't do "and" searches -- for example, you can't search for bookmarks tagged both "Microsoft" and "browser."

You can only display your bookmarks in alphabetical order in the sidebar, although, in the browser toolbar, you can also display them in the order added, most recent first.

But if you go to the del.icio.us Web site, you can vary the order in which bookmarks are displayed, and do more sophisticated searches.

Security? We've Heard Of It
By default, all del.icio.us bookmarks are viewable by the entire world -- that's one of the main points of del.icio.us; it's a "social bookmarking" service, to allow you to share bookmarks with others. But don't worry if your existing Firefox bookmarks are confidential; del.icio.us will automatically mark bookmarks imported from Firefox as private. (Your secret collection of My Little Pony links is safe from the prying eyes of the world, tough guy.)

I don't know how secure the privacy is on private del.icio.us bookmarks; I haven't examined the terms of service. If you've bookmarked the secret nuclear launch codes, then you don't want to trust that to del.icio.us. But marking bookmarks private on that service should be good enough security for most purposes, especially if the site you bookmark is encrypted and password-protected, which it should be anyway.

I haven't really discussed the social bookmarking aspects of del.icio.us in this review, mainly because the Firefox browser extension doesn't address those. The extension doesn't make it any easier to share bookmarks, or locate bookmarks that others have shared. That's not what it's about. Del.icio.us has other tools for that.

Conclusion
I don't expect del.icio.us bookmarks will be for everyone. It's the kind of thing I expect people will either love or hate, depending on if the tagging system matches the way your brain works. I've only been using it a couple of days now, but it looks great so far, and if you think you might like it too, give it a try.

By the way, developer John Marshall has a Firefox extension for the Google Bookmarks online bookmarking service, which is Google's del.icio.us competitor. I just spotted the GMarks extension this morning on the Firefox Add-Ons page. I the feature list makes it look like the user interface for GMarks might be better than for the del.icio.us Firefox extension. But I haven't downloaded it and looked for myself.