As powerful as ever and considerably more polished, Firefox 3 is an improvement on its useful but somewhat clunky predecessor in nearly every respect. However, users may not get all of the dramatic speed boosts its programmers promise.

Everything good about Firefox 2 is present in the new version. Its top-notch Gecko rendering engine displays even the trickiest pages almost flawlessly, and the new version passes the Acid2 test for Web standards compliance with flying colors. The worst errors I noticed in my tests were some flickering in Flash video ads that changed size within the browser window, and one minor glitch in rendering a complex CSS trick. Firefox's many customizable features are back, too, including dozens of invaluable third-party add-ons, like blog editor ScribeFire and code inspector Firebug.

Building on these useful features, Firefox 3 adds a host of welcome improvements. The new Firefox sports the program's most Mac-like look and feel yet, with a sleek silver design and buttons that make it look like Safari's more futuristic cousin. The new location bar, which Mozilla dubs the awesome bar, builds on Web browsers' common autocomplete functions by guessing at your destination based on your bookmarks and user history. The awesome bar also examines any tags users may have added to their bookmarks, another clever new addition. For example, users can tag their bookmark of Apple's Web site with words like "Steve Jobs," "iMac," and "iPhone," then jump directly to the site just by typing any of those words into the URL field.

Bookmarks in general are greatly improved from Firefox 2, thanks to the addition of a star-shaped button that creates a new bookmark for the currently displayed site when clicked. New smart folders can also aggregate bookmarks based on users' search terms. Unfortunately, you'll still have to edit your bookmarks in a separate window, which is awkward compared to Safari's more convenient one-window approach.

Firefox 3 has also amped up its security features. One click on a site's favicon (on the location bar) brings up a handy window that summarizes how secure the site is, and whether Firefox thinks you can trust it with your data. The new version promises to alert users when they surf to phony sites out to steal personal information or attack unsuspecting computers with malicious scripts. These security judgments are based on reports from Firefox users, and on information from Google's phishing protection service, also used for Gmail. Mercifully, power users who don't need such warnings can specify which alerts Firefox should display via the program's Preferences.

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