Actually this discussion is wrong here. Please always create GitHub Issues for such things so a proper discussion is possible.

I don't know anything about "network.cookie.cookieBehavior.pbmode". And I could not find good documentation on the web.

I could try to find out something about this topic, but it is very likely that I can't do anything about this as I can not change any preferences at all. I can only change the few Mozilla has exposed to the Add-on programming interface.