cannot login from firefox- asp.net login functionality

Private Sub portalLogin_Init(ByVal sender As Object, ByVal e As System.EventArgs) Handles portalLogin.Init
        If Not IsPostBack Then
            If Request.Cookies("myCookie") IsNot Nothing Then
                Dim cookie As HttpCookie = Request.Cookies.[Get]("myCookie")
                portalLogin.UserName = cookie.Values("username")
 
                portalLogin.RememberMeSet = (Not [String].IsNullOrEmpty(portalLogin.UserName))
            End If
            Dim txtUser As TextBox = TryCast(portalLogin.FindControl("UserName"), TextBox)
            If txtUser IsNot Nothing Then
                'Me.SetFocus(txtUser)
            End If
        End If
 
        ' Note this
        Response.Cache.SetNoStore()
 
    End Sub
 
    'redirect the user to the HOME page when he logs in
    Private Sub portalLogin_LoggedIn(ByVal sender As Object, ByVal e As System.EventArgs) Handles portalLogin.LoggedIn
        'get user name
        Dim usern As String = portalLogin.UserName.ToString
 
        Dim myCookie As New HttpCookie("myCookie")
        Dim remember As Boolean = portalLogin.RememberMeSet
 
        If remember Then
            Dim persistDays As Int32 = 60 'cookie set toe expire in 60 days
            myCookie.Values.Add("username", portalLogin.UserName)
            myCookie.Expires = DateTime.Now.AddDays(persistDays)
            'you can add years and months too here
        Else
            myCookie.Values.Add("username", String.Empty)
            ' overwrite empty string is safest
            myCookie.Expires = DateTime.Now.AddMinutes(5)
            'you can add years and months too here
        End If
 
        Response.Cookies.Add(myCookie)
 
        
        
    End Sub
 
 
    Protected Sub portalLogin_LoginError(ByVal sender As Object, ByVal e As System.EventArgs) Handles portalLogin.LoginError
        'determine why the user could not login...
        portalLogin.FailureText = "Your login attempt was not sucessful. Please try again"
 
        'does that user account Exist ?
        Dim usrInfo As MembershipUser = Membership.GetUser(portalLogin.UserName)
 
 
        If usrInfo IsNot Nothing Then
            'is this user Locked out?
            If usrInfo.IsLockedOut Then
                portalLogin.FailureText = "Your account has been locked out because of too many invalid login attempts. Please contact administrator to re-activate it"
 
                'has user been Approved yet?
            ElseIf Not usrInfo.IsApproved Then
                portalLogin.FailureText = "Your account has not been approved yet. You cannot login until an administrator has approved your account"
            End If
 
        End If
    End Sub