Web surfing has belonged almost exclusively to Microsoft Corp.'s Internet Explorer ever since it buried Netscape's pioneering browser.

That doesn't seem to have bothered the developers of the Mozilla Firefox, a feisty new kid on the block that's worth a serious look.

Officially released this week, Firefox packs security protections and other welcome features that emphasize just how little Microsoft has innovated its aging Microsoft browser in recent years.

True, Microsoft made significant security improvements to IE when it released Service Pack 2 for Windows XP computers in August. But the improvements aren't available for older Windows systems.

Nor does the updated IE offer a versatile search box feeds of frequently visited Web pages or the ability to open windows within windows. More on that later.

The biggest reason to consider Firefox is security.

To its credit, Microsoft is trying hard to address that. But as long as IE commands more than 90 percent of the world's computers, malicious hackers will continue to target it. The very IE features that Web developers love are also exploited by virus and spyware writers.

That's not to say you can't get spyware or other malicious code using Firefox, but risks are greatly reduced.

Firefox also offers protections against phishing -- those e-mail scams that pretend to be legitimate notices from banks and service providers. A few scams did slip through during my test, but I was warned about others.

Still not sold?

Then check out Firefox's non-security features, which in some cases are available on IE only by downloading third-party toolbars or plug-ins, some of which carry a fee:

• Search. From a toolbar up top, you have instant access to several search engines and can easily switch among them. You can also customize the browser so that typing ``book'' followed by a title automatically performs a search at amazon.com.

• Pop-up blocker. It does the job, while letting you open pop-ups you want.

• News feeds. Firefox supports Really Simple Syndication, or RSS, a technology for pulling headlines from news sites and Web journals so you won't have to keep checking them.

• Tabbed browsing. Instead of constantly opening new windows to browse, cluttering your Windows taskbar, Firefox lets you open new pages as tabs within a single window. Click on the appropriate tab to switch among the pages.

The latest version of Netscape, which shares much of Firefox's core technology, also has many of these features, and Norwegian browser Opera offers all four _ and more.

But both bundle e-mail and other tools that can get in the way. When viewing a Web page on Opera, for instance, clicking on an e-mail link calls up Opera's own e-mail software _ not Microsoft Outlook, which my company requires me to use.

And did I mention that Firefox is free? Opera costs $39 for an ad-free version.

Despite being a ``1.0'' release, Firefox is mature. And the breeding is good. It's the product of more than a thousand full-time engineers and volunteers and is based on the open-source Mozilla suite, which in turn has its roots in Netscape.

Plus, Firefox is available for Linux and Mac computers as well. I tried the Mac version and found all the major features available right away.

The browser was also available in more than a dozen languages on its first day -- a commendable feat.

Of course, no good product comes without a catch. I ran into trouble with a few Web sites designed specifically for IE, mainly those requiring ActiveX controls or the portion of JavaScript in which Microsoft departs from published standards.

So you can forget about watching movies on CinemaNow or Movielink. You also won't be able to update your Windows operating system relying on Firefox alone (Good thing Microsoft bundles IE with its operating systems).

Plug-ins designed for Netscape or Opera should work with Firefox, but you won't be able to use any of the IE toolbars, including Yahoo's spyware scanner and e-mail checker, or fully take advantage of Google's new desktop search software.

Nevertheless, some companies, including Amazon.com, are starting to adapt their tools for Firefox.

Some Web pages won't display correctly -- among the ones I encountered were spam stats from Postini Inc., stock indices for the Bombay Stock Exchange and one AP internal site.

And Firefox mysteriously froze the first time I checked America Online mail. Closing the browser and restarting it fixed it on two different computers.

As for the RSS feeds, though I was impressed with how easy it was to add feeds for sites that let machines automatically detect them, manually adding feeds was overly complicated. I also found the tools for reading feeds quite clunky and inflexible. Opera has much better RSS tools.

In fact, I see little reason to switch from Opera, unless you'd prefer to drop the e-mail integration. The features are comparable.

As an alternative to IE, Firefox is a strong contender. And for the few sites that don't work with Firefox, you can always launch IE.