Two wrongs don't make a right, Mozilla's chief counsel said Thursday when asked why his company hasn't lambasted Apple, as it did Microsoft, for blocking rival browsers from its mobile operating system.

"The similarities to iOS don't justify an outcome on Windows that deprives users of choice, reduces competition and hurts innovation," said Harvey Anderson, Mozilla's top lawyer.

That question -- how is Microsoft's behavior different from Apple's -- came up time and again in comments on the blogs and news stories that reported the claims.

And if both Microsoft and Apple bar competitors' browsers from their operating systems -- Apple refuses to accept rival browsers in its App Store -- why is Mozilla focused on Microsoft?

Anderson's answer: Microsoft is a different beast.

"The difference here is that Microsoft is using its Windows monopoly power in the OS market to exclude competition in the browser market," Anderson said, possibly referring to Microsoft's dominance of the entire operating system space, not only mobile.

According to Web metrics company Net Applications, Windows remains the overwhelming favorite on the Internet. Last month, Windows powered 85% of all Internet-browsing hardware, including personal computers, smartphones and tablets. And while Apple's iOS owns the lion's share of the mobile browsing market, its share of the market made up of all devices was less than 5%.

More important to Mozilla, however, was that Microsoft had pledged in the past to play fair. Its 12 promises, articulated in 2006 as U.S. antitrust supervision was winding down, included one central to Mozilla's argument.

"Going forward, Microsoft will ensure that all interfaces within Windows called by any other Microsoft product ... will be disclosed for use by the developer community generally," the 2006 document titled "Windows Principles" stated. "That means that anything that Microsoft products can do in terms of how they plug into Windows, competing products will be able to do as well."

Although "Windows Principles" is no longer available on Microsoft's website, it appears to have been replaced by a 2008 document dubbed "Interoperability Principles," which has similar, although not identical, language related to APIs.

Microsoft made the 2008 pledge -- and published tens of thousands of pages of protocol documentation -- to meet obligations demanded by the European Union after an antitrust conviction there.

Anderson hammered on the broken promises theme.

"Microsoft [has] published commitments to users, industry and software developers like us that in essence said Microsoft would design Windows to allow choice and provide a level playing field for third-party applications like the browser," said Anderson. "These factors create a situation that is materially different than iOS."

Asa Dotzler, director of Firefox, echoed Anderson in a pair of Wednesday posts on his personal blog.

"Apple is not a convicted monopolist that has legally binding commitments to not block access to browser-related APIs [application programming interfaces], like Microsoft," Dotzler wrote in a comment added to his first post. And in another, he said, "Those [legally-binding] commitments don't go away because Microsoft wishes them away."

The dustup stems from Microsoft's decision to limit access to Win32 APIs on Windows RT to its own software. Mozilla claimed that that gives IE10 an unfair advantage on ARM-powered devices.

Windows RT, once called WOA, for Windows on ARM, will include both a Metro mode that features touch-based apps and a restricted desktop mode, called "Classic Windows" by some.

While the Windows RT desktop seems designed primarily to run new versions of Office's Word, Excel, PowerPoint and OneNote -- the programs will be bundled with the OS -- a special version of IE10 will also run there.

Because IE10 will be the only browser able to call Win32 APIs within Windows RT, it will enjoy functionality others are denied, whether it's running on the "Classic Windows" desktop or in the Metro environment, where all non-Microsoft code must operate.

"IE on ARM has access to Win32 APIs -- even when it's running in Metro mode -- but no other Metro browser has that same access," said Dotzler. "Without that access, no other browser has a prayer of being competitive with IE."

Anderson described some of the Win32 APIs that only IE10 can access.

"Of particular concern are the APIs that IE has access to which Microsoft is denying other browsers, including VirtualAlloc, HeapAlloc and friends; CreateNamedPipe; ConnectNamedPipe; DisconnectNamedPipe; CreateProcess and various others," Anderson said. "These APIs allow for things like making memory executable, a pre-requisite for building a JIT [Just In Time compiler]," Anderson continued. "Without a JIT, it will be impossible to build a modern browser. These APIs also allow for things like spawning additional processes, and communicating between them -- something we use to isolate plug-ins for security and stability purposes, and other browsers, including IE, use to isolate tabs and windows for security and stability purposes."

All the major desktop browsers use a JavaScript JIT compiler -- Firefox's is tagged as "JaegerMonkey," Google Chrome's as "V8," IE10's as "Chakra" -- to quickly render JavaScript, the backbone of many online games, content-rich websites and advanced Web apps.

Mozilla and other browser makers can call Win32 APIs in Windows 8 -- in fact, only browsers are allowed to access the traditional Windows APIs from Metro -- which is why they can build browsers competitive with IE10 on that OS.

Both Mozilla and Google have committed to creating Windows 8 browsers that run on both the desktop and in Metro.

Microsoft has said its decision to bar other vendors from accessing Win32 APIs in Windows RT was driven by security, reliability and performance.

Last February, Windows chief executive Steven Sinofsky spelled it out in no uncertain terms.

"If we enabled the broad porting of existing code [to Windows RT] we would fail to deliver on our commitment to longer battery life, predictable performance, and especially a reliable experience over time," Sinofsky said. "The conventions used by today's Windows apps do not necessarily provide this."

But there's nothing stopping Microsoft from opening the Win32 APIs to other browsers, contended Anderson. "Given that IE can run in Windows on ARM, there is no technical reason to conclude other browsers can't do the same," he said.

On Thursday, Anderson wouldn't say what Mozilla would do if it couldn't change Microsoft's mind, whether it would, for instance, produce a Metro-only Firefox for Windows RT or abandon the platform, as it essentially did with iOS two years ago when it ran into Apple's App Store wall.

"Product management is still evaluating the best course of action," Anderson said.

Even though Anderson called Microsoft's behavior "an unwelcome return to the digital dark ages where users and developers didn't have browser choices," legal action isn't Mozilla's first choice.

"We think the most effective way to resolve this is through critical discussion and transparency of the issues rather than through legal action," Anderson said.

Nor was he ready to say what he thought Mozilla's chances were of changing Microsoft's mind. "It's too early to tell," Anderson said.

Google is in Mozilla's corner -- the maker of Chrome said it "share[s] the concerns Mozilla has raised" -- but Opera Software, the Norwegian browser builder that filed a complaint with EU regulators that forced Microsoft to add a browser choice screen in Windows, declined to comment Thursday.

Microsoft also declined to comment on Mozilla's accusations.

Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer, or subscribe to Gregg's RSS feed . His email address is gkeizer@ix.netcom.com.