Your last paragraph is what I can't understand. Ignoring OS X for now (wouldn't know a thing about that):

Parental control in Windows just lets me set time limits/limits on what programs/games I can run as far as I know (just double checked microsoft.com and that's what they list as well). Given that and my understanding of the Fx feature means that Fx understands that this is a machine with parental controls enabled and _shares that with the world_.

That is nonsense. It's crap. The world cannot (as I stated before) decide what is okay and what not. Going with your porn example (I .. kinda expected that): I'd be entirely fine with a 16yo kid to look at porn. I might not want that very same kid to use the computer around 2am in the night. For the latter I can use parental control features. You (and Mozilla) force your (weird, from this pov) moral/set of values on me. Enabling parental control does NOT mean that I want the world to know about it. It also doesn't imply that porn isn't okay. On the other hand, maybe I would put the NRA website on the list of things I don't want to see in my household. No one can decide what is okay or not - except for the parent/admin.

"There is no UI in Firefox, because Firefox uses the OS parental control features to enable/disable it" is missing the point. Unless I fail to understand what this does I cannot use the parental controls without Firefox/Mozilla abusing that flag and asking the YouPorn administrators for parental support.

This is a misfeature and at best useless, although I'd lean towards harmful and wrong.

You are just assuming things here. I don't know the parental control features of Windows. And I don't know when this will be enabled. But I don't see a reason why this should be always enabled as soon as parental features are used. In the end Mozilla is implementing a Microsoft proposal here. I would assume that the parental controls have a setting to enable it. So it kinda seems to me that you are building a strawman to attack.

If you want to block specific websites or specific content then you obviously need to use a different tool as well.

Hah. I'm assuming things, you attack my arguments with .. assumptions.

If you look at the code [1], you'll notice that it exists _today_. There is no feature in Windows that says 'I want to restrict this account to a "safe" internet experience' and that wouldn't make a tiny bit of sense as I expressed elsewhere. Again, if you look at the code it seems (Disclaimer: I'm neither familiar with the Fx codebase nor really a C++ guy) easy enough:

    DWORD settings = 0;
    wpcs->GetRestrictions(&settings);
    
    if (settings) { // WPCFLAG_NO_RESTRICTION = 0
      gAdvAPIDLLInst = ::LoadLibrary("Advapi32.dll");
      if(gAdvAPIDLLInst)
      {
        gEventWrite = (decltype(EventWrite)*)GetProcAddress(gAdvAPIDLLInst, "EventWrite");
        gEventRegister = (decltype(EventRegister)*) GetProcAddress(gAdvAPIDLLInst, "EventRegister");
        gEventUnregister = (decltype(EventUnregister)*) GetProcAddress(gAdvAPIDLLInst, "EventUnregister");
      }
      mEnabled = true;
    }

While I admit that I argued based on 'assumptions' (more .. based on what I know about these parental controls and what the article states), these are the facts.

If I translate that into prose (correct me..) that reads as "If the OS supports parental controls and ANY restrictions are active, then set this boolean flag to true". Now, before you argue that these still are just assumptions about how this flag is used ... let me present [2]:

    // add the "Send Hint" header
    if (mSafeHintEnabled || mParentalControlEnabled) {
      rv = request->SetHeader(nsHttp::Prefer, NS_LITERAL_CSTRING("safe"));
      if (NS_FAILED(rv)) return rv;
    }

Ignoring the weird comment: That translates into "If the user _opts in_ to use this header via a setting OR if we detected random parental control restrictions from [1], add the crappy header to the request"

The documentation of the Windows parental control API can be found here [3]. Note that there isn't a feature that says 'add a random useless header' or somesuch nonsense. Glancing over the docs it seems to be possible to register extensions to the parental control environment, and _those_ might offer a 'Get a random different version of the internet, maybe' option in theory. But that doesn't seem to be the case and the check at [1] and [2] seems rather broad.

IF this whole thing would be a configurable (by the responsible admin) feature (and .. ideally opt-in, not a crazy default), THEN I'd just laugh at the people that want that, but wouldn't complain. Based on every fact I can get my hands on that is NOT what they do.

Do you still disagree, at least with the implementation?

1: http://mxr.mozilla.org/mozilla-central/source/toolkit/compon...

2: http://mxr.mozilla.org/mozilla-central/source/netwerk/protoc...

3: http://msdn.microsoft.com/en-us/library/windows/desktop/ms71...

Nice work researching this. Yes, I'd say that always enabling it as soon as some parental control features are enabled is a bad decision. Maybe this should be a bug report. But we should also note that Mozilla follows Microsoft's implementation here.