Firefox中的Asp.Net Form DefaultButton错误

if (Request.UserAgent.Contains("Firefox"))
{
    Button btn = (Button)FormView1.FindControl("Button1");
    if (btn != null)
    {
        btn.Attributes.Add("onkeydown", "if (event.keyCode == 13) { " + ClientScript.GetPostBackEventReference(btn, "") + "; return false; }");
    }
}

if (navigator.userAgent.indexOf("Firefox") != -1) {
    var defaultButton = document.querySelector('[defaultbutton]');
    if (defaultButton) {
        defaultButton.addEventListener('keydown', function (event) {
            if (event.keyCode === 13) {
                event.preventDefault();
                defaultButton.click();
            }
        });
    }
}