A change in the way browser usage is calculated led to a decline in web browser market share for Google Chrome, which experienced its second market share slip this year after growing steadily throughout 2011.

Net Applications released its browser usage market share data for February and announced that it has adjusted its calculation methods based on Chrome's pre-rendering feature that tries to determine which sites you're likely to visit when you start typing them into your search bar, then preloads a hidden page or pages (some of which are never seen by the user) in order to speed screen rendering. The pre-rendering feature, which was initially released in Chrome 13 and expanded in the most recent version of Google's browser, known as Chrome 17.

Pre-rendering creates unviewed visits that should not be counted in Chrome's usage share, Net Applications explains. The feature has been shown to inflate Chrome browsing by approximately 4.14% of its usage share, the Web analytics firm asserts. Beginning with its February report, Net Applications is excluding daily unique visits attributed to pre-rendering from Chrome's desktop browser share.

In the big picture, the computational adjustment didn't have an enormous impact on February's desktop browser usage numbers. Microsoft's Internet Explorer maintained its lead in Net Applications' ranking with 52.84% market share, which is down slightly from 52.96% in January. Firefox retained its second-place position with 20.92% (down from 20.88%), followed by Chrome (18.90%, down from 18.94%), Safari (5.24%, up from 4.90%) and Opera (1.71%, up from 1.67%).

Google's Chrome browser saw its global market share slip in January following a self-imposed penalty related to Google violating its own guidelines against paid links. Early in January, Google dropped the page rank for the Chrome site to zero (from nine out of 10), which put an end to the browser's longtime market share climb.