The overall global usage share for all versions of IE fell from 55.92% in March to 55.11% in April, according to NetApplications, a firm that tracks Internet metrics.
If Microsoft continues to lose browser market share, it will become less relevant in the Internet standards process and less relevant to developers of Web applications. Already a follower in the tablet business and the smartphone business, Microsoft can't afford to be driven back from the Internet to its two strongholds--Windows and Office. The company is already hemorrhaging cash through its online services division--a $726 million loss last quarter--and its ability to sustain its Bing search engine is likely to be closely related to the popularity of Internet Explorer.
IE 9, released in March, has actually been doing well, thanks to strong demand for Windows 7. In one month, its usage share among Windows 7 users has doubled, from 3.6% in March to 7.5% in April, or 9.95% on the last day of April, as opposed to averaged across the month.
About a week ago, Microsoft said it had sold 350 million Windows 7 licenses in 18 months.
Yet the popularity of Windows 7 hasn't proven to be enough to keep users of older versions of Internet Explorer from defecting to the competition. Internet Explorer 8, 7, and 6 all saw usage declines from March to April.
Overall usage of Firefox declined too, from 21.8% in March to 21.63% in April, despite the March launch of Firefox 4.
Who has been gaining at the expense of Microsoft and Mozilla? Google and Apple, NetApplications said. Google's Chrome browser, the heart of its forthcoming Chrome operating system, saw its global usage share rise from 11.57% in March to 11.94% in April.
Apple's Safari browser jumped from 6.61% in March to 7.15% in April. Apple saw usage gains for Safari in both its Mac OS and iOS product lines, but iOS usage of mobile Safari grew more than twice as fast as Mac OS usage of the desktop version of Safari. iOS usage increased by 0.37 percentage points while Mac OS increased by 0.15 percentage points.
Microsoft isn't giving up, however. Two weeks ago, the company posted a preview of Internet Explorer 10.