Mozilla has accused Microsoft of failing in its commitment to give Windows users a choice in browsers, a charge that previously saw Microsoft become the subject of a U.S. antitrust case.
The accusations relate to Microsoft's upcoming Windows 8 operating system and in particular, the version that will be built into ARM-based mobile devices, known as Windows RT.
Windows RT, along with other Windows 8 versions, will effectively have two distinct environments; one for Metro-style applications and a "classic" desktop, which is needed to support legacy applications on x86 systems.
However, Mozilla claims that Internet Explorer (IE) will be the only browser able to run in the classic environment under Windows RT, at the expense of rival browsers like Firefox, Safari and Chrome.
"Windows on ARM - as currently designed - restricts user choice, reduces competition and chills innovation," said Mozilla General Counsel Harvey Anderson in a company blog post.
"By allowing only IE to perform the advanced functions of a modern Web browser, third-party browsers are effectively excluded from the platform."
Anderson argued that since IE can run in Windows on ARM, there is no technical reason to conclude other browsers can't do the same.
"We encourage Microsoft to remain firm on its user choice principles and reject the temptation to pursue a closed path," said Anderson.
Google's Chrome browser division has issued a statement of support for Mozilla's accusations.
"We share the concerns Mozilla has raised regarding the Windows 8 environment restricting user choice and innovation," said a Google spokesman. "We've always welcomed innovation in the browser space across all platforms and strongly believe that having great competitors makes us all work harder."
Microsoft published aset of Windows Principles in 2006 for users and developers that commit the firm to fostering competition and innovation.
Such commitments followed the DOJ vs Microsoft settlement in 2001, which forced Microsoft to allow PC vendors to include non-Microsoft software on systems.
Further action by the European Commission led to an agreement whereby Windows users get offered a choice of browsers in Europe.
The blog post from Anderson is not the first time this year that Mozilla has accused Microsoft Windows 8 of being anti-competitive.