nsContentUtils::UnregisterPrefCallback("network.image.imageBehavior",
nsContentUtils::UnregisterPrefCallback("permissions.default.image",
nsPresContext::~nsPresContext(){  mImageLoaders.Enumerate(destroy_loads);  NS_PRECONDITION(!mShell, "Presshell forgot to clear our mShell pointer");  SetShell(nsnull);  if (mEventManager) {    mEventManager->SetPresContext(nsnull);   // unclear if this is needed, but can't hurt    NS_RELEASE(mEventManager);  }  // Unregister preference callbacks  nsContentUtils::UnregisterPrefCallback("font.",                                         nsPresContext::PrefChangedCallback,                                         this);  nsContentUtils::UnregisterPrefCallback("browser.display.",                                         nsPresContext::PrefChangedCallback,                                         this);  nsContentUtils::UnregisterPrefCallback("browser.underline_anchors",                                         nsPresContext::PrefChangedCallback,                                         this);  nsContentUtils::UnregisterPrefCallback("browser.anchor_color",                                         nsPresContext::PrefChangedCallback,                                         this);  nsContentUtils::UnregisterPrefCallback("browser.active_color",                                         nsPresContext::PrefChangedCallback,                                         this);  nsContentUtils::UnregisterPrefCallback("browser.visited_color",                                         nsPresContext::PrefChangedCallback,                                         this);  nsContentUtils::UnregisterPrefCallback("network.image.imageBehavior",                                         nsPresContext::PrefChangedCallback,                                         this);  nsContentUtils::UnregisterPrefCallback("image.animation_mode",                                         nsPresContext::PrefChangedCallback,                                         this);#ifdef IBMBIDI  nsContentUtils::UnregisterPrefCallback("bidi.", PrefChangedCallback, this);  delete mBidiUtils;#endif // IBMBIDI  NS_IF_RELEASE(mDeviceContext);  NS_IF_RELEASE(mLookAndFeel);  NS_IF_RELEASE(mLangGroup);}