Microsoft on Friday issued an official reply to a complaint by browser maker Opera that the inclusion of Internet Explorer (IE) in Windows is somehow anti-competitive. According to the software giant, the proliferation of browsers in the market place, including a new Windows-compatible version of Apple's Safari in the past year, proves that Opera's complaint is baseless.

"Computer users have freedom of choice to use and set as default any browser they wish, including Opera, and PC manufacturers can also preinstall any browser as the default on any Windows machine they sell," a Microsoft spokesperson said. "Microsoft is committed to ensuring that freedom through our Windows Principles."

The Windows Principles, incidentally, are a set of "guiding principles" that Microsoft established in the wake of its antitrust issues in the US and Europe: They establish three key principles under which Windows is developed: Choice (for consumers and computer manufacturers), Opportunity (for software developers), and Interoperability (for Microsoft customers).

From a competitive standpoint, IE is still the dominant browser. But Microsoft has been unable to stem its falling market share over the past few years, thanks largely to the success of Mozilla Firefox, a browser that, in some markets, is actually catching up to IE. Worldwide, IE is down to about 63 percent of the market as of October 2007; in 2002, IE controlled over 85 percent. Firefox, meanwhile, is closing in on 20 percent. Opera controls less than 2 percent of the market.

Microsoft also notes that IE has been part of the Windows operating system for over a decade. The implication here is that IE has withstood several antitrust complaints already, and no government or legal body has ever required or even asked Microsoft to decouple the browser from Windows.

As for Opera's complaint that IE does not conform to Web standards, Microsoft claims that its browser "supports a wide range of Web standards." A bigger issue, of course, is whether a company should be legally required to change its product to support a nebulous set of standards, regardless of the impact that change would have on customers. Microsoft has struggled with its support of Web standards specifically because of this compatibility requirement, which is expected by its largest corporate customers.