Firefox 4 managed to double IE9&39's download total in less than 24 hours after its release.

Firefox may be under fire from Microsoft's newly competitive browser, but with more than twice the downloads in its first day, Firefox 4 today soared over its rival by one measurement.

Microsoft, not without reason, boasted that IE9 was downloaded 2.35 million times in the first 24 hours after its release last week. And that is indeed a big number, especially for a browser that tech enthusiasts had scoffed at for years.

But less than 24 hours after its own launch, Firefox 4 cleared 4.7 million, according to the Mozilla Glow site that logs downloads.

That's a lot less than the 8 million copies of Firefox 3 downloaded in that version's 24-hour debut in 2008, but that event was a heavily promoted "Download Day," and it should be noted that Firefox 4's full day hasn't finished yet.

And it does signal that at least a very sizable chunk of the Net-connected population is, in Firefox's apt phrase, choosing to "upgrade the Web." New browsers bring new Web standards, new performance, and often a new auto-update ethos that likely will lead to browsers staying continuously updated. That could simplify lives for Web developers who constantly wrangle with the difficulties of supporting old browsers.

Firefox 4 brings a raft of new features--new security and privacy options, faster loading and JavaScript, support for a variety of new standards including WebM video and WebGL 3D graphics, and 3D acceleration that extends even to Windows XP.

Mozilla expects that its arrival will lead to an increase in usage. The browser maker said it has 400 million Firefox users and counting, but as a percentage of worldwide browser use it has lost share to Chrome, which now accounts for more than 10 percent of usage worldwide.