The March launches of Internet Explorer 9 (IE9) and Firefox 4 failed to stop Microsoft's and Mozilla's decline in browser share, new Web usage data published on May 1 showed.

According to California-based Net Applications, one of a handful of companies that regularly publishes browser usage data, IE lost eight-tenths of a percentage point of share in April, falling to 55.1%, a new low for Microsoft.

Meanwhile, Firefox dropped two-tenths of a percentage point to 21.6%, a share equivalent to its December 2008 standing.

Both Microsoft and Mozilla debuted new browsers several weeks ago: The former launched IE9 on March 14, while the latter shipped Firefox 4 on March 22. Neither release stemmed their maker's long-standing slide.

Apple's Safari and Google's Chrome took up the slack in April.

Safari posted an increase of five-tenths of a point to end the month at 7.2%, a record for the browser that ships with Mac OS X, and is integrated with iOS, the mobile operating system that powers the iPhone and iPad. The one-month gain was Safari's biggest-ever by Net Applications' tracking.

Chrome's usage share grew by four-tenths of a percentage point, slightly less than the browser's average increase over the past 12 months. Google's browser accounted for 11.9% of all browsers used in April.

Opera, the Norwegian browser that rounds out the top five, was flat last month at 2.1%, ComputerWorld reported.