Bill Gates will hold a yard sale to help make ends meet before his company's Internet Explorer is displaced as the world's dominant Web browser.

But that doesn't mean there's nothing meaningful in the browser usage trend data released recently by WebSideStory. According to the Web analytics firm, users of the Mozilla and pre-release Firefox open source browsers grew to 6% of the U.S. online populace as of Oct. 29, up from 3.5% only four months earlier.

That's a solid jump from a modest starting point, yes, and Microsoft still commands a 92.9% market share. But the increased open source use comes almost entirely out of IE's hide and presages nothing but good things for the official release this week of Firefox 1.0, the Mozilla project's almost universally acclaimed entry into the world of alternative browsers.

"When we saw Firefox making a dent, and when we saw IE starting to lose a little market share at the start of the summer, we didn't know if this was going to be a six- or eight-week thing and then all would go back to normal," says Geoff Johnston, an analyst at WebSideStory, which has tracked browser trends since 1998. "What's interesting is that here we are five months [into the movement] and not only have things not flattened but they have continually and steadily grown. Firefox is gaining market share largely at the expense of IE. Now it's not just curiosity seekers; now people are changing and staying."

No one is suggesting that what we are witnessing is the opening salvo in a Browser War II that this time will find Microsoft on the losing end. But Johnston does see forces at work that recall IE's late-'90s knockout of Netscape. (It was only six years ago that Netscape ruled the roost.)

"What really knocked them out in the end was that IE 5.0 was just better than Netscape 4.0," Johnston says. Early adopters are reaching the same conclusion about Firefox, he adds. "You're getting the impression that people are not just trying it but staying with it. Apparently people like it well enough not to switch back."

Firefox has been downloaded more than 7.5 million times, according to the ticker at www.spreadfirefox.com. Hoopla around the official launch of Firefox 1.0 has included a fund-raising effort to publish full-page advertisements in The New York Times and plans for some 280 launch parties worldwide.