Projecting IE's slide using Net Applications' data, Computerworld now estimates that the browser will fall under the 50% share mark as early as mid-May if the dramatic negative trend of the last three months holds true.

Like Microsoft, Mozilla did a good job last month converting users to its newest browser, Firefox 3.5. Fewer than 7% of all browser users ran Firefox 3.0 in December, for example, a decline of 1.2 point2, the largest dip since September 2009. The jump in Firefox 3.5 usage may be in reaction to the impending retirement of version 3.0 later this month, when Mozilla will stop serving up security updates for the older application.

Net Applications measures browser usage share by tracking the systems used to visit the 40,000 sites it monitors for clients, which results in a pool of about 160 million unique visitors per month.

is available on Net Applications' site.

Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld . Follow Gregg on Twitter @gkeizer , send e-mail at gkeizer@ix.netcom.com or subscribe to Gregg's RSS feed .