I don't think it's a failure. I prefer not to think of things like that. It's too early to tell really. Building a browser is really hard.

I interviewed at Mighty (now defunct) and turned down an offer because the team seemed burned out. (Kind of a tangent, but I've also worked at companies where the product's main angle was performance - it's a grind.)

Anyway, they are smart people. Even if they haven't succeeded by your standards, it doesn't mean they've failed.