People usually don't compile their browsers from source anyway. And of course, technically, a program can check whether monitoring tools are running and adapt its behaviour accordingly, but this is malware territory and it makes no sense for any reputable browser. Also, technically, one can do that on router level anyway and not have this issue. So yes, I would say that analyzing the network is enough.

Because their entire continued existence depends on maintaining a reputation of preserving privacy?

> Source is closed. Is a network analyzer enough to determine? Or do a search and give arguments why it's not enough ?