The statement only addresses the classic style of the Windows 8 desktop, but Mozilla says that this is where Microsoft intends to block other browsers, such as Google's Chrome and Firefox.
As for the Metro touch-optimised panel, Microsoft previously announced that the environment is open to any developer, as long as it fulfils the application requirements.
Harvey Anderson, Mozilla's general counsel, accuses Microsoft of making the same mistake as back in 1998 - when the software creator lost a big lawsuit against browser maker Netscape Communications over the same matter.
Anderson also stated that one browser will not suffice for the tech industry, and Microsoft's move of limiting choices on ARM devices will only pain the consumer: "You're going to look up one day and there's going to be one browser...We'll be right back where we started."
Microsoft's attorney David Heiner told Anderson that the company does not allow other browsers because of the unique security and power needs of the chips used by mobile devices, while adding that the ARM-based Windows RT is not "Windows anymore."
Microsoft declined to comment on the accusation and Anderson suggested that a little pressure may change the company's mind - pressure that could eventually evolve into a legal lawsuit.