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Computerworld - Opera Software on Thursday announced that it will add support for extensions to its flagship browser, mimicking the functionality of more popular rivals such as Mozilla's Firefox and Google's Chrome.

Opera 11 will support add-ons created using a variety of Web standards -- including HTML5 and JavaScript -- as well as Opera-specific APIs, or application programming interfaces, said Arnstein Teigene, the company's product manager for desktop add-ons.

"We've always focused on having a very customized browser," said Teigene in a Thursday interview, "and extensions have been one of the most frequently-requested additions from users and developers alike."

Opera 11 will be the first version of the Norwegian-made browser to support extensions. Teigene declined to set a specific launch date for the upgrade, saying only that an alpha preview would be released "sometime soon."

Details for developers interested in writing Opera extensions will be published at the same time, Teigene said.

Other browsers, most notably Firefox -- which last summer boasted that users had downloaded 2 billion of its add-ons -- have thousands of available extensions. But while Firefox popularized the concept, rivals like Chrome and Apple's Safari also offer feature-adding extensions. Microsoft's Internet Explorer, which still accounts for a majority of the browsers used each month, relies on the company's proprietary ActiveX technology to provide some of the functionality of extensions.

But Teigene argued that Opera wasn't playing catch-up by introducing extensions, and instead pointed out that the company has offered widgets -- small, single-purpose Web applications that run outside the browser -- since the 2006 introduction of Opera 9.

He also touted what he called Opera's "open standards" approach to extensions. "We've always been a keen participant in open standards, including CSS, HTML5 and JavaScript, which is why we're focusing on those for extensions," Teigene said.

Opera's extensions will use HTML5 for rendering content, CSS (cascading style sheets) for formatting, and JavaScript for processing.

Teigene was hesitant to go into details of Opera's extension strategy, saying that many were still in flux. Opera 11's extensions, however, will be offered to users in a gallery or download center, as are those designed to run in Firefox, Chrome or Safari. And they will be vetted, he said, to provide some modicum of quality control.

"In order to submit an extension, the developer will have to be a registered Opera developer, and we'll go through the code to make sure that there's no malicious stuff in it," Teigene said.

However, he declined to spell out how Opera will ensure that rogue extensions don't slip through the cracks, or whether Opera will be able to remotely uninstall potentially dangerous extensions. Mozilla has employed such a blocklist-based "kill switch" feature several times, most recently last July, as a last-ditch defense against malicious add-ons.

"We take security concerns very seriously," said Teigene as he refused to go into details of how Opera will protect users. "We're looking at what has worked with competitors and what hasn't, and we'll focus on something that's really strong."

While most developers will only get a crack at writing extensions for Opera when the alpha release of Version 11 hits the street, a small number have been given what Teigene called early "snapshots" of the browser and they will have extensions ready when the preview goes public. One early extension will be for StumbleUpon.com, Teigene confirmed.

Although Opera is late to the extension party, Hakon Wium Lie, the company's CTO, claimed that add-ons were "ripe for standardization," and said Opera wants to collaborate with other browser builders to make that happen.

"We'd like to work with other vendors to make sure that extensions become a true part of the Web," Lie said at an Olso press conference that was also webcast Thursday. "We should work together, as we've done with other standards, to make extensions part of that repertoire, that buffet, of standards."

Currently, an extension crafted for Firefox won't run on Chrome, nor will a Chrome add-on run on Safari. Standardizing extensions would let developers write an extension once, then distribute it to users of multiple browsers.

Opera's extensions will be based on the World Wide Web Consortium's Widget specification, which has not yet been finalized. The W3C is the primary international standards organization for the Web.

Opera accounted for just 2.4% of the browsers used last month, according to U.S. metrics firm Net Applications. Of the top five browsers, Opera has long been mired in fifth place, with less than half the usage share of Safari, and under one-third that of Chrome, the No. 4 and No. 3 browsers, respectively.

When it's released, Opera 11 will be available from this page on Opera Software's site.

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 e-mail address is gkeizer@ix.netcom.com.

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