Microsoft.'s refusal or inability to fully support three web standards has cost Opera Software users, the Norwegian browser maker's chief technology officer said Friday.

"They participated in the development of standards, even promised to implement them, but their products contain both bugs and unimplemented features that create problems for other browsers, like Opera," said Hakon Wium Lie, chief technology officer of the Oslo-based developer, referring to Microsoft.

On Thursday Opera Software filed a complaint with the European Union's antitrust agency, accusing Microsoft of stifling competition by tying its Internet Explorer (IE) browser to Windows, and by hindering interoperability by not following internet standards.

In a follow-up interview, Lie provided more detail on the second of the two arguments against Microsoft. "We listed core standards in the complaint, including [cascading style sheets], XHTML and [document object model]," said Lie when asked to specify which standards Microsoft's IE browser doesn't comply with. "[But] we could have added more to this list."

According to Lie, IE's quirky support for those and other standards gives web site designers and web application developers fits. "Developers must work around those bugs and undocumented features [in IE]," he said, "because of IE's high usage numbers."

IE, while off its peak market share, still accounts for more than 77 per cent of all browsers used, according to the latest data from web metrics vendor Net Applications. Naturally, site and web app developers want to reach the largest audience, so if tweaks are necessary to make their work render or run properly, that's what they do.

That is the core of Lie's claim that Microsoft's lack of standards support has hurt Opera. "We've been forced to decode the errors in IE and try to duplicate its rendering mode," said Lie, so sites look good when viewed in Opera. Those efforts have not always been successful, he acknowledged.

"Often, those pages won't render properly for Opera," he said. "We've lost many users who used Opera and liked it, but abandoned it because some pages wouldn't render correctly."

That's not right, he argued. "Web developers shouldn't have to create special versions of their sites or applications. Standards are what everyone should be coding for, but by following the standards we're being punished."

Ironically, developers have been saying somewhat the same thing in a rash of comments to recent posts placed on the official IE blog. There, developers have blasted Microsoft for not properly supporting standards, with some claiming that they must spend significant time and money making sure their sites and applications work properly with IE6 and IE7.

While proving that Microsoft is deliberately skirting standards to stymie rivals may be very difficult for Opera, Lie brushed aside the concerns. He pointed out that Opera had not filed a lawsuit, but only a complaint with the EU's Competition Commission. "It's up to the commission to consider the complaint's merits," he said.

At the same time, however, he thought that talk of possible Microsoft defenses - some pundits and bloggers have suggested, for instance, that Microsoft could simply say it wasn't technically able to make IE compliant - was ridiculous. "Microsoft has a lot of [development] talent and knows all the standards because [it has] sat on the committees," Lie said. "Microsoft clearly knows what standards are about."

And he also rejected claims by detractors who have said Opera only filed the complaint because it couldn't compete in the marketplace. "That's not true," he said. We have a very successful browser on the mobile platform. But on the desktop it's clearly very, very hard, and that's because there is no fair competition."

By Net Applications' numbers, Opera has never broken the 1 per cent market share mark. Last month, it accounted for 0.65 per cent of all browsers used to connect to the web sites of Net Applications' customers, up from 0.48 per cent in January 2007 and just slightly above the 0.64 per cent of August 2006.

"All we want is a way to compete in a fair and square way," said Lie.