The "Windows Classic" environment of "Windows RT" - the name Microsoft has given to Windows running on the ARM processor - prohibits any browser except for Internet Explorer from running, a policy that could have antitrust implications for Microsoft.

Windows RT will have two environments, a "Windows Classic" environment and a "Metro" environment for apps. However, Windows on ARM prohibits any browser except for Internet Explorer from running in the privileged "Windows Classic" environment. This means that only Internet Explorer will be able to perform many of the advanced computing functions vital to modern browsers in terms of speed, stability, and security. Given that IE can run in Windows on ARM, there is no technical reason to conclude other browsers can?t do the same.

Microsoft's browser practices was described by Mozilla as "an unwelcome return to the digital dark ages where users and developers didn't have browser choices."

"Windows on ARM -as currently designed- restricts user choice, reduces competition and chills innovation," Harvey Anderson, Mozilla General Counsel wrote in a blog post.

While ARM chipsets may be primarily built into phones and tablets today, in the future ARM will be significant on the PC hardware platform as well.

Mozilla's counsel added that Microsoft's policy contradicts its own published principles that users and developers have relied upon for years.

"Because Windows on ARM relies upon so many traditional Windows assets, including brand, code, footprint, and experience, the decision to exclude other browsers may also have antitrust implications," he added.

Microsoft's practises may also contradict to the company's commitments to the European Comission in 2009. The European Commission had accepted Microsoft's commitments to boost competition on the web browser market, ending an antitrust dispute with the U.S. software maker.

In announcing the Windows Principles, Microsoft's General Counsel, Brad Smith, stated "As creators of an operating system used so widely around the world, we recognize that we have a special responsibility, both to advance innovation and to help preserve competition in the information technology industry."

"We encourage Microsoft to remain firm on its user choice principles and reject the temptation to pursue a closed path," Anderson added.

Google, maker of the Chrome browser, also detailed concerns on Microsoft's policy.

"We share the concerns Mozilla has raised regarding the Windows 8 environment restricting user choice and innovation. We've always welcomed innovation in the browser space across all platforms and strongly believe that having great competitors makes us all work harder. In the end, consumers and developers benefit the most from robust competition," Google said.

Microsoft declined to comment on the issue.