php - 登录系统：不同浏览器php中的不同错误

Question

我正在尝试开发一个登录系统。这是我检查用户是否登录的文件：

<?php 
require_once("config.inc.php"); 

session_start();

if( isset($_SESSION['username']) ) { header('location:' . $website_url . '/home.php'); }
?>

<?php
date_default_timezone_set("Europe/Tirane");
$todaydate3 = date("Y-m-d H:i:s");

$myusername7=$_POST['usernameform']; 
$mypassword7=$_POST['passwordform'];

$myusername7=stripslashes($myusername7);
$mypassword7=stripslashes($mypassword7);

$myusername7=mysqli_real_escape_string($con, $myusername7);
$mypassword7=mysqli_real_escape_string($con, $mypassword7);

$encrypted_mypassword234=hash('sha512', $mypassword7);

$logimi46 = mysqli_query($con,"SELECT * FROM users WHERE username = '$myusername7' AND password = '$encrypted_mypassword234' AND oauth_provider != 'facebook' AND verifikuar = 'po'");
$logimi225 = mysqli_num_rows($logimi46);

if($logimi225 > '0') {

$myusername71=$_POST['usernameform'];
$myusername71=stripslashes($myusername71);
$myusername71=mysqli_real_escape_string($con, $myusername71);

$mypassword71=$_POST['passwordform'];
$mypassword71=stripslashes($mypassword71);
$mypassword71=mysqli_real_escape_string($con, $mypassword71);
$encrypted_mypassword231=hash('sha512', $mypassword71);

$tedhenateperdoruesit21=mysqli_query($con,"SELECT * FROM users WHERE username = '$myusername71' AND password = '$encrypted_mypassword231' AND oauth_provider != 'facebook' AND verifikuar = 'po'");
$userdata2 = mysqli_fetch_array($tedhenateperdoruesit21);

session_start();
$_SESSION['id'] = $userdata2['id'];
$_SESSION['oauth_id'] = "nuk_ka_id";
$_SESSION['username'] = $userdata2['username'];
$_SESSION['email'] = $userdata2['email'];
$_SESSION['oauth_provider'] = "log_in_form";

if($userdata2['disabled'] == "po") {  
$sqlcojejo = "UPDATE users SET disabled = 'jo' WHERE username = '$myusername7'";
$querycojejo = mysqli_query($con, $sqlcojejo);
} 

header("Location: " . $website_url . "/checkifloggedin.php");

} else {

header("Location: " . $website_url . "/signup.php?action=loginerror");
exit();

}

?>

现在，我的问题是，如果我尝试使用 google chrome 登录，它可以工作并且我登录我的网站，但是如果我尝试使用 Firefox，它不会让我登录，而是将我重定向到signup.php?action=loginerror并且我尝试登录这 2 个不同的具有相同帐户详细信息的浏览器。

任何想法？

谢谢