Daily Firefox downloads decreased by 63 percent during the nearly 15 months that Microsoft failed to show users of Windows 7 Service Pack 1 a court-mandated browser choice screen, according to figures released by Mozilla.

In settlement of a European Union antitrust case, Microsoft agreed to present new Windows users with a screen allowing them to choose a web browser to install instead of, or in addition to, Internet Explorer. Microsoft should have presented the browser choice screen to new and existing Windows users from December 2009, but failed to include it in Windows 7 SP1 on its release in February 2011. Microsoft reinstated the choice screen after a complaint was filed with antitrust regulators at the European Commission.

The absence of the browser choice screen from new or updated installations of Windows 7 had a big impact on downloads of Firefox, according to a blog postby Mozilla's general counsel and vice president of business affairs, Harvey Anderson.

"Cumulatively 6 to 9 million Firefox browser downloads were lost during this period," Anderson wrote. "After the fix, Firefox downloads increased 150 percent to approximately 50,000 per day," he said, adding that when the browser screen was absent, downloads decreased to a low of 20,000 just prior to the fix.

Mozilla isn't the only one to notice the influence of the browser choice screen on browser downloads.

The screen shows the top five browsers by market share on the first page, while seven others can be scrolled into view. When Apple abandoned the Windows version of its Safari browser, little-known competitor Maxthon was catapulted to the front page, boosting downloads of its browser. "We have witnessed an increase," Maxthon spokesman Lewis Fein said at the time, although he did not say how big the increase was.