Firefox is more valuable though. They have a revshare agreement with Google and others. People actively use Firefox to search for things, at least a few dozen times a day, not to mention are more apt to click on ads based on their current mindset.
I don't think that same behavior is going to be exhibited in a Unity lens, certainly not with the same frequency. I also doubt the click rate too.
If we consider they have about 15 million users, that's about 45 million dollars. But maybe they have other sources of revenue.