Microsoft's Internet Explorer (IE) again lost ground to Apple's Safari and Google's Chrome last month, even as the company launched its newest browser, Web metrics data showed today.
But Microsoft stands behind its decision to limit IE9 to users running Windows Vista and Windows 7.
"It was a very deliberate decision," said Ryan Gavin, senior director of IE, talking about the move to exclude XP users from IE9. "You simply can't build on something that is 10 years ago."
Gavin said that Microsoft "has no second thoughts" about its decision.
According to California-based Net Applications, one of several companies that regularly publishes browser usage data, IE lost nine-tenths of a percentage point of share in March, falling to 55.9%, another record low.
IE9, which debuted more than two weeks ago, accounted for 1% of all browsers, a five-tenths of a point jump over February.
But older editions of IE dropped by more than what IE9 gained.
IE6, the browser Microsoft wants to kill, fell by four-tenths of a point to 11%, while IE7 slipped by two-tenths of a percentage point to 7.9%. And IE8, until last month Microsoft's current browser, dropped half a point to end March at 34.4%.
IE8's slip was the first for that browser since Net Applications began tracking it three years ago, a full year before it shipped in final form in March 2009.
Some rivals, meanwhile, continued to gain share at Microsoft's expense.
Google's Chrome grew its share by six-tenths of a point to account for 11.6% of all browsers used worldwide last month, a record. And Apple's Safari posted a gain of three-tenths of a point to end the month at 6.6%.
Even Mozilla's Firefox, which has lost share eight out of the last 12 months, managed a slight increase of one-tenth of a point, the first increase since December 2010, to account for 21.8% of all browsers.
The March 22 launch of Firefox 4 contributed to Mozilla's small turn-around. Net Applications' statistics show that Firefox 4 boosted its share to 1.7% last month, a 1.1-point increase over February.
Microsoft and Mozilla have each touted the number of downloads of their newest browsers, but the latter has clearly won that battle, claiming 7.1 million downloads on Firefox 4's first day of availability and a record 8.75 million the following day.
Gavin has argued that IE9's numbers should be calculated solely by its use on Vista and Windows 7, and its success or failure judged accordingly.
Net Applications put IE9's share of browsers running on Windows 7 at 3.6%, more than three times the overall average, a fact that Gavin stressed during an interview today. "That's about five times the rate of adoption in a comparable period for IE8," Gavin said.
But Net Applications' data also shows that the newest IE9 rivals -- Chrome 10 and Firefox 4 -- have significant chunks of the Windows 7 browser market. Chrome 10, which Google began pushing to current Chrome users via the browser's silent update mechanism almost a month ago, accounted for 10.2% of Windows 7 browsers in March. Firefox 4, on the other hand, lagged behind IE9 with a 2.8% share on Windows 7.