Opera's main competitors are open-source projects. You are suggesting that they create another competitor right before putting the company up for sale, and I'm suggesting that they are unlikely to do that.

Yes, a different for-profit company did create an open-source browser project, but that was a rare situation in which the for-profit company dominated a very lucrative market (search) and the open-source project had the effect of undermining one of the few strategic advantages (namely, Internet Explorer's usage share) enjoyed by their only serious competitor.

In other words, in certain situations it might make sense for a for-profit company to use an open-source project to take users away from a proprietary software product of one of its competitors if the competitor would have been able to use its control over the proprietary software product as a lever on consumer behavior in a huge and lucrative market. But those situations are rare and do not apply here.

Google's open-sourcing Chromium resembles Russia's "scorched-earth policy": the move destroyed some of Google's options or resources, but made sense because it simultaneously took those resources away from Google's biggest threat. But the circumstances in which a scorched-earth policy make sense are rare and do not apply in Opera's situation.

It may be dead weight, but there's still Opera Mini with its hundreds of millions of users, and then there's plenty of embedded products using it which will never move to the Chromium Content API (because, hey, they're last year's model!).