Internet Explorer 9 was released on March 15, 2011. Two weeks later, on March 29, 2011 (yesterday), Microsoft turned on Windows Update for the new version, but only for existing IE9 Beta and IE9 RC users. The software giant has now confirmed that IE9 will not be broadly rolled out on Windows Update until the end of June.

Mozilla recently released Firefox 4 and Google recently released Chrome 10. Both companies have update mechanisms in their browsers that are turned on automatically as part of the release of a new version.

Microsoft says it cannot do the same because it has hundreds of millions of business customers that rely on Internet Explorer and require an appropriate window of time to plan and test their deployments. At the same time, the company argues it has a responsibility, as the company behind the most popular browser, to ensure that IE9 is introduced in a timeline that allows website developers to make sure their website is compatible.

This is Microsoft's response to the recent news that Firefox 4 is already beating IE9 in market share, despite being released much later. In their respective first 24 hours, IE9 saw 2.35 million downloads and Firefox 4 saw 7.1 million downloads. Microsoft argues that every IE9 download is from a customer actively seeking out the latest version and downloading it, as opposed to getting it after an automatic update (Chrome) or in-product prompt (Firefox).

"The net of all this is that any comparison of browser share adoption at this point is premature at best, and misleading at worst," a Microsoft spokesperson said in a statement. "In a few months we’ll be better placed to look at the share of the latest browser versions and get a sense for relative progress and adoption."