Google may intend to produce a Chrome Frame plug-in for Firefox, Mozilla's chief engineer said.

"The code is certainly there," said Mike Shaver, Mozilla's vice president of engineering, referring to parts of the Chrome Frame source code that indicate Google could crank out a Firefox plug-in similar to what Google released last week for Microsoft's Internet Explorer (IE).

"But source code doesn't speak to intent," Shaver added Wednesday, saying he had no inside knowledge whether Google would, in fact, expand its browser-in-a-browser plug-in concept to Firefox.

Chrome Frame, which Google launched 23 Sept., currently only supports IE6, IE7 and IE8, and lets those Microsoft browsers utilise the Chrome browser's WebKit rendering engine, as well as its V8 JavaScript engine. Google pitched the plug-in as a way to instantly boost the speed of the notoriously slow IE and as a means for web developers to support standards IE can't handle, including HTML 5.

Specifically, Google said it had created Chrome Frame because it decided it wasn't worth the time and trouble to make its new collaboration and communications tool, Google Wave, work with IE. Google developers claimed they had spent "countless hours" tweaking Wave for IE, but gave up in favor of producing a plug-in instead.

Shaver said that Chrome Frame, which is open source, includes technologies that could be destined for Firefox as well as Opera Software's Opera browser. "They've chosen not to ship yet," said Shaver, talking about plug-ins for those two browsers. "I hope they won't."

Mozilla staked out its position on Chrome Frame this week, when both Shaver and Mitchell Baker, the former CEO of Mozilla and currently the chairman of the Mozilla Foundation, took swipes at Google for releasing the plug-in.

Both Shaver and Baker called the plug-in a bad idea, with Baker arguing that it would confuse readers over which browser was rendering a site, divide personal details like site passwords and browsing history between two applications and cede control over users' browsing experience to site designers.

Shaver, meanwhile, panned Chrome Frame for some of the same things that Microsoft used to hammer Google earlier, including breaking IE's private browsing mode.

Shaver acknowledged that some of Mozilla's motivation for taking Chrome Frame to the woodshed was in its own interest. "We started to get some inbound [feedback] from our community about Chrome Frame, and the more we did, the more we decided that we'd rather have people using Chrome the browser rather than Chrome Frame.

"And we wouldn't want Google to do for us what they did for Microsoft," Shaver said.

Google's intentions are unclear, Shaver admitted, and Mozilla has not talked directly with Google about Chrome Frame. For its part, Google did not reply to queries made early Wednesday asking whether it plans to craft a plug-in for browsers other than IE and why.