Mozilla will "probably not bother" building a version of Firefox for Windows RT if Microsoft does not allow other browser makers to call important APIs for the new operating system, according to a Mozilla product director.
Asa Dotzler slammed Microsoft for not allowing third-party browsers access to Win32 APIs, or application programming interfaces, in the upcoming Windows RT.
Windows RT, once called Windows on ARM, or WOA, is the operating system Microsoft is developing for devices - tablets primarily, but also lightweight laptops - that rely on processors designed for the ARM architecture.
"If we built Firefox for Windows ARM Metro, we would not have access to those powerful Win32 APIs and so we would be at an extreme disadvantage when compared to IE10 for Metro," said Dotzler, referring to Microsoft's own browser, which will be able to call the banned APIs.
"We could build a beautiful Firefox that looked really nice on Metro, but Firefox would be so crippled in terms of power and speed that it's probably not worth it to even bother," Dotzler added. "No sane user would want to surf today's web and use today's modern websites with that kind of crippled browser."
Although Dotzler's "not worth it" comment may hint at the likelihood that Mozilla will step away from Windows RT, it is not the company's official position.
Last week, Harvey Anderson, Mozilla's chief counsel, said that company engineers were "still evaluating the best course of action" to take with Windows RT.
Anderson and Dotzler took to the web last week to publicly knock Microsoft for barring third-party developers access to the Win32 APIs in Windows RT, and for letting its own software, especially IE10, call those same APIs.
Under Microsoft's current rules for Windows RT, only IE10 will be allowed to call the APIs necessary to execute a JIT compiler.
"Without a JIT compiler modern websites like Facebook, Twitter and Gmail would be painfully slow for users, unusably slow." Dotzler said.
Microsoft originally had a similar restriction in place on Windows 8, the more traditional operating system for x86/64 processors like those made by Intel and AMD, but relaxed the API-access rules there in February.
At that time, Microsoft issued some basic documentation that put browsers in a special category on Windows 8, and showed how developers could access the Win32 APIs from Metro versions of their applications.
Mozilla and Google, which makes Chrome, have both said they will create a browser that runs in the Metro environment on Windows 8; those Metro-app versions will call the Win32 APIs from the traditional desktop side of the OS.
Dotzler argued that Microsoft should do the same in Windows RT.
"Microsoft can solve this problem for Windows on ARM the exact same way they solved it for Windows on Intel. They can give third-party browsers the same access they give Internet Explorer," said Dotzler.
Microsoft has repeatedly declined to comment on Mozilla's allegations concerning API access in Windows RT. Google has said it stands with Mozilla on the issue.
European Union antitrust regulator have made it clear that Windows 8 must abide by a 2009 deal that requires the operating system to offer users a choice of browsers other than IE. Those regulators, however, but have not made the same assertion for Windows RT.
By the language of the landmark settlement Microsoft reached in 2002 with the US Department of Justice, Microsoft may be free to ban access to Win32 APIs in Windows RT, as the settlement repeatedly limited the deal to "Intel-compatible PCs."
Microsoft stepped out from under most US government scrutiny related to the case in 2007.