nsIContentPrefObserver Interface

 Called when a content pref is removed.
 
 @param    aGroup      the group to which the pref belongs, or null
                       if it's a global pref (applies to all URIs)
 @param    aName       the name of the pref that was removed

void onContentPrefRemoved(in AString aGroup, in AString aName)

 Called when a content pref is set to a different value.
 
 @param    aGroup      the group to which the pref belongs, or null
                       if it's a global pref (applies to all URIs)
 @param    aName       the name of the pref that was set
 @param    aValue      the new value of the pref

void onContentPrefSet(in AString aGroup, in AString aName, in nsIVariant aValue)