It's uncertain whether the pair will submit their Modern apps to the Windows Store, the Microsoft-curated online outlet that is the sole source of Windows RT software.

The European Commission's decision not to pursue complaints about Windows RT drew a carefully-worded comment from Mozilla on Wednesday. "We hope the European Commission is correct in its conclusions and users are not deprived of browser choice in Window RT operating systems," said Harvey Anderson, Mozilla's general counsel, in an email.

Google did not reply to a request for comment on Almunia's decision.

Along with the pass given to Windows RT, the Commission also said that Windows 8 must include the browser choice screen that Microsoft agreed to in 2009.

"We have raised issues to Microsoft relating to Windows 8, which is to be released soon," Almunia said. "If a user decides to set a rival browser as the default browser, there should not be unnecessary warning windows or confirmations by the user, and the Internet Explorer icon should also be unpinned from the Start screen."