program 'firefox1.exe' does not contain a static 'Main' method suitable for an entry point

using System;
using System.Linq;
using System.IO;

namespace firefox1
{
class Reader
{
    public static  string ReadFirefoxProfile()
    {
        string apppath = Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData);

        string mozilla = System.IO.Path.Combine(apppath, "Mozilla");

        bool exist = System.IO.Directory.Exists(mozilla);

        if (exist)
        {

            string firefox = System.IO.Path.Combine(mozilla, "firefox");

            if (System.IO.Directory.Exists(firefox))
            {
                string prof_file = System.IO.Path.Combine(firefox, "profiles.ini");

                bool file_exist = System.IO.File.Exists(prof_file);

                if (file_exist)
                {
                    StreamReader rdr = new StreamReader(prof_file);

                    string resp = rdr.ReadToEnd();

                    string[] lines = resp.Split(new string[] { "\r\n" }, StringSplitOptions.None);

                    string location = lines.First(x => x.Contains("Path=")).Split(new string[] { "=" }, StringSplitOptions.None)[1];

                    string prof_dir = System.IO.Path.Combine(firefox, location);

                    return prof_dir;
                }
            }
        }
        return "";
    }
}
}

thanks in advance