Firefox is one very hot browser, pardon the pun, and your computer will be safer if you switch to this free software that's heating up the charts.

There's been a seismic shift during November, with Firefox emerging as the first credible competitive threat in a decade to Microsoft's aging Internet Explorer browser for Windows.

The rush started on Nov. 9, when the non-profit Mozilla Foundation, based in Mountain View, released the finished 1.0 version of Firefox after many months of pre-release ``beta'' development.

Millions of Internet users have since installed Firefox 1.0, which is available as a free download. OneStat.com, a Web research firm based in Amsterdam, said last week that Firefox and related browsers from the Mozilla Foundation now account for 7 percent of global Internet usage -- up from just 2 percent in May.

Internet Explorer's market share has dropped by an equal amount, to 89 percent from 94 percent.

There are two reasons why you should care about this:

First, Internet Explorer's outdated design is full of security flaws, despite some major patching in the recent Windows XP Service Pack 2 upgrade. IE's huge market share also makes the browser a major target for cyber-criminals.

Second, Microsoft has been asleep at the switch in adding features and design improvements. While the current version of IE was a state-of-the-art browser when released three years ago, Firefox has now pulled ahead with several clever improvements.

Switching to Firefox is surprisingly easy. You start by downloading the 4.7-megabyte install file from Mozilla's Web site (www.mozilla.org/firefox). It's available for every version of Windows back to Windows 98, as well as the Macintosh and Linux. Mac users, however, are best served by Apple's own Safari browser.

Then you run the install file, which takes little more than a minute.

Importing bookmarks

If you follow the default choices when you first open Firefox -- and you should -- the browser will import your favorites, also known as bookmarks, from IE, along with other stored information such as the addresses of sites you've recently visited. Firefox will also become your default browser, meaning that Firefox will open instead of IE whenever you click a Web link in an e-mail or other document.

The first thing I noticed after launching Firefox was how little I noticed.

Familiar menus and control buttons from IE are found in the same positions along the top of the Firefox screen, altered only slightly. The ``Forward'' and ``Back'' buttons, for example are green arrows in Firefox, instead of IE's green circles with white arrows inside. The ``Home'' button in both browsers is a white house with a yellow roof, the only difference is that IE's house has a tiny chimney.

Normal people outside the tech community -- who don't obsess about browser market share, the future of open-source vs. commercial software and similar arcane subjects -- would hardly notice the switch from IE to Firefox. The learning curve is zero, unless you want to take the optional step of mastering the extra features missing from IE.

Those extra features certainly are worth exploring, especially for power users.

The most important is tabbed browsing. You can open multiple pages within a single browser window in Firefox, with each page becoming a file-folder-like tab across the top of the screen. To move from one page to another, you just click on the tabs. This is much faster and more efficient way to cope with multiple pages than opening separate browser windows in IE, littering incomprehensible icons along the Windows taskbar.

Firefox also has a nifty integrated search box in the upper right corner of the screen. You can type a search term into the box and get an immediate Google search, without going to Google's Web site. You can click the Google icon in the box for a pull-down menu of other search sites, such as Yahoo and Amazon, and can even add search sites of your own choosing.

A geek's playground

There's more, which I don't have room to cover here, making Firefox a kind of playground for Net geeks. Firefox also is slightly faster than IE in loading pages.

But the real reason to switch is security. I called three experts last week: R. Scott Granneman, a computer security consultant in St. Louis who's also writing a Firefox how-to book; Eric T. Peterson, a Web analyst in San Diego for the firm JupiterResearch; and Johannes B. Ullrich, chief technical officer of the SANS Internet Storm Center security service in Quincy, Mass. All three recommended that home computer users running Windows make the shift to Firefox.

That's because the Internet is swarming with viruses, worms, Trojans, spyware and phishing traps. IE is a conveyor for some of these maladies, while Firefox so far is falling below the bad guys' radar. Another non-IE alternative is the free Opera browser (www.opera.com), which I reviewed favorably in March.

I'll close with two very important pieces of advice:

Firefox is not a cure for cancer. You still need to take all the burdensome steps required for safe computing: installing anti-virus software and keeping it up to date, using firewall software if you have a broadband connection, running an anti-spyware program, and making sure not to fall for phishing e-mail that tries to talk you out of personal information. If your computer runs Windows XP, you should also upgrade to Microsoft's free Service Pack 2, despite the very slight risk it will hurt your system.

Also, you don't have to give up on IE entirely. Some Web sites require IE for certain functions, or just look better with IE. There's no big security risk in using IE to visit sites you know and trust, as long as Firefox is fixed as your default browser.

By day, Alexander Vincent is a mild-mannered secretary for a Vallejo real estate broker. By night, he's an online crusader protecting users of a new Internet browser from glitches and security bugs. If he were a superhero, you might call him Mozilla Man.

In fact, Vincent is part of a worldwide army of Mozilla men and women who believe in freedom, progress and the inalienable right to an open source browser.

Their weapon of faith is Fire- fox, a free browser created by the non-profit Mozilla Foundation as an alternative to Microsoft's ubiquitous Internet Explorer. Officially released this month, Firefox is converting a growing number of Internet users -- and nibbling away at Microsoft's dominance.

Vincent is one of roughly 2,000 volunteer evangelists who see their mission as freeing millions of computer users from the tyranny of Internet Explorer. Mountain View-based Mozilla -- with a paid staff of 12 software developers -- depends on volunteers like Vincent to help write code, fix software bugs and market the browser.

``A lot of people out there are not aware of what is possible on the Internet,'' said Vincent. ``Firefox is waking up a lot of people.''

Firefox missionaries promise an Internet experience that's faster, more secure and free from pop-up ads. And that's just the beginning of their Utopian vision. To hear many of the faithful talk, their ministry stops nothing short of changing the lives of Internet users.

``You hear a lot of tales about people having very bad online experiences. Life can be better,'' said Mitchell Baker, Mozilla's president. ``Our end goal is to have real choice and innovation on the Web.''

Test versions of Firefox were released in February. Since Firefox's official release Nov. 9, users have downloaded the browser 6 million times.

Explorer's market share has slid for the first time ever, to 92 percent from 95 percent in June, according to WebSideStory, a Web analytics firm. Firefox has gained one-half percent a month in the same period, giving it a 3.6 percent market share.

Firefox owes its growing celebrity to new converts, many of whom become preachers themselves. Take Katie Kimball, a choreographer who got fed up with pop-up ads on Explorer. Her brother-in-law suggested Firefox -- and Kimball is surfing the Internet like never before, she says. Now when others complain about their computers, she offers her own testimonial. ``It was a Eureka moment for me,'' said Kimball, who lives in South San Francisco. ``I will never go back to Internet Explorer.''

Strength of the collective

The Mozilla mania is part of a broader movement toward free, open source software, in which no company owns the code. Open source draws upon the strength of the collective. Anyone can add features and fix flaws. Not beholden to any commercial interests, developers argue they only have users' interests at heart.

The Mozilla Project began under Netscape in 1998, when it publicly released the blueprint for its Navigator browser. Netscape was purchased by AOL, which in turn merged with Time Warner. Last year, Mozilla was established as a non-profit and Time Warner seeded it with $2 million. The foundation is also supported by donations and partnerships from companies such as Red Hat and Sun Microsystems, which ship the free, open source Linux operating system that rivals Microsoft's Windows.

Aside from its team of 12 developers, many of whom are former Netscape employees, Mozilla depends on a crew of approximately 80 programmers to do heavy-duty coding. These programmers are employed by other technology companies that work on Mozilla projects because it benefits them.

Another 1,000 or so programmers work for free. They have developed roughly 200 add-on features for Firefox, from a program to detect fake Web sites to a spoofed Homeland Security alert.

Vincent, the real estate broker's secretary, volunteers 20 hours a week of his time rooting out bugs and documenting code for Firefox, he said. He specializes in one task many developers hate: checking the spelling of code.

His biggest contribution, said Vincent, is finding and reporting security bug #259708, which ``blew away my download directory and could have deleted files on my desktop.'' His reward: $500 from Mozilla's Bug Bounty program, a T-shirt and bragging rights. ``My goal is to make a a better browser for others to use, to make their lives better,'' he said.

It's that sense of ownership and civic participation that help fuel the success of open source projects, said Haim Mendelson, professor at the Stanford Graduate School of Business.

Open source advocates criticize Microsoft's lock on technology, pointing out that a new version of Explorer has not been released since 2001.

For its part, Microsoft said it released this year a ``major upgrade'' to Explorer that ``focused solely on security enhancements,'' and reduced spyware, Gary Schare, director of product management for Windows said in an e-mail. The upgrade, however, covers only the browser that is used in the XP operating system and not older systems.

While Internet Explorer is the choice of hundreds of millions because of the unique value it provides, ``we respect that some customers will choose an alternative,'' said Schare. ``We also know that choosing a browser is about more than a handful of features. Microsoft continues to make major investments in Internet Explorer.''

Analysts and some in the open source community say Firefox's success will be the catalyst for Microsoft to kick into high gear. ``When you have an open source software competing with a commercial software, it pushes the commercial developer to develop faster and come out with a competitive product,'' said Mendelson. Firefox ``will help push Microsoft into more innovation on the Explorer, which they have neglected a bit.''

In the meantime, Mozilla faithful are out proselytizing. The grass-roots marketing is done almost entirely by volunteers. A group of Canadian designers came up with the concept for the Firefox logo, an orange fox with a flaming tail curled around the a globe of the world. A British graphics artist then sketched and illustrated it.

Volunteers have formed a user and marketing community of 30,000 at SpreadFirefox.com. Some keep Firefox blogs there while others offer marketing ideas to attract users. One Japanese devotee at the site has depicted Firefox as a fierce female human-fox in comic mangas. The site also sponsored Firefox launch parties the past few weeks. Vincent of Vallejo hosted a San Francisco party one recent Saturday night, attended by about 50 party goers.

`Virus free, innovative and useful'

Rob Davis, who works for a public relations firm in Minneapolis, switched to Firefox last summer after his Explorer browser was attacked by a virus that crashed his computer. He became so hooked that he personally installed it on other people's computers for them.

``I was delighted to have a virus free, innovative and useful browser for free,'' said Davis. Firefox ``completely changes the way you interact with the Internet.''

Feeling ``indebted'' to the Mozilla Foundation, he pitched in. His experience in grass-roots organizing, most recently for Moveon.org, gave him the idea to take out an ad for Firefox, paid for by users. In less than a day, 10,000 contributors donated $250,000 dollars.

The ad, a full page in the New York Times, will run early next month. A single guy, Davis has canceled two first dates recently because he's too busy helping to design the ad.

One woman agreed to a rain check. The other discovered his ``work'' was really a volunteer effort. Says Davis: ``I won't be hearing from her. And that's fine.''