The browser mentioned is only one example. Their main question about changing good proprietary software to FOSS licenses is the main topic.
Convincing proprietary software devs to make their project FOSS?
You're all a bunch of fucking idiots
vivaldi.com
That doesn't answer OP's question. The goal is to convince the owners to make the official FOSS, as the fact that it is so well made yet remains unfree is kinda sad.
Not everyone is interested in communism, go figure.
...
At least before the progressives got involved
Semi-serious answer: buy their business faggot. That's how you "convince" them. Of course, you will drive development into the grave but that's OK because at least the browser will be moral by your standards!
Only by convincing them that doing so would increase their profits, whether that is true is another matter. This is what the OSI does, the FSF tries to convince users to reject proprietary software, because unlike the amoral beings that are corporations not all of them act solely for short-term profit. You could try Otter Browser which is free software and made to be like old opera as well.
Yeah, it's a great browser. It's too bad I can't use my favorite firefox plugins with it, and I don't think it has some kind of sync feature, otherwise it would be perfect.
Vivaldi is a HTML+angularjs UI wrapper around vanilla chromium, there also may be an internal webserver running locally for the settings.
The punchline is that you can easily turn them off and get a vanilla chromium experience, which also saves you like 90% of startup time and 50% of page loading.