Tuesday's debut of the Mozilla Foundation's new browser, Firefox 3, was a hit.

The browser was downloaded more than 8.3 million times, according to Mozilla CEO John Lilly. Guinness World Records was tracking the record-breaking day, though it's not as though Firefox was bumping up against some unachievable Hank Aaron milestone. Most browsers are usually released gradually, with little fanfare as they work their way through beta-related bugs.

It's still a great day for Firefox. The new browser went from 0% market share to 4% in a single day -- if, of course, those who downloaded the Web-surfing application are actually using it.

Microsoft (NASDAQ:MSFT) probably isn't quivering in its Redmond boots. Its Internet Explorer remains the industry's top dog, and most of this week's downloads are probably coming from existing non-IE users, anyway.

That doesn't mean Microsoft can afford to ignore the threat. Firefox is here to stay. Apple's (NASDAQ:AAPL) Safari is gaining as the company nibbles away at computer market share and blankets the country with iPhones. And although Time Warner's (NYSE:TWX) AOL ceased development of its Netscape browser earlier this year, Firefox, Safari, and Opera are still there to keep Microsoft on its toes.

As the gateway to the Internet, the browser has always been important. That's why companies from Google (NASDAQ:GOOG) to Yahoo! (NASDAQ:YHOO) to even Amazon.com's (NASDAQ:AMZN) Alexa have developed browser toolbars to help guide the surfing experience. There's money to be made in funneling searches and other queries their way.

Microsoft has its MSN toolbars too, of course. Earlier this month, it agreed to replace Yahoo! on Hewlett-Packard (NYSE:HPQ) machines as the pre-installed toolbar of choice. Just because the browsers and toolbars are free downloads, that doesn't mean they're not big businesses.

In a nutshell, browsers matter. If you don't believe me, ask yourself why the Mozilla Foundation is flashing a smile for Guinness this week. 

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