AJAX :: Update Panel Not Working In Firefox

Environment used : asp.net 2008 webapplication with c#

problem : here is my code :

default.aspx
<form id="form1" runat="server">
<iframe id ="captchaframe" src="test.aspx"></iframe>
<asp:ScriptManager ID="ScriptManager1" runat="server">
</asp:ScriptManager>
<asp:UpdatePanel ID="UpdatePanel1" runat="server">
<ContentTemplate>
<asp:Button id="Button1" runat="server" Text="refresh" onclick="Button1_Click"></asp:Button>
</ContentTemplate>
</asp:UpdatePanel>
</form>
default.aspx.cs
protected void Button1_Click(object sender, ImageClickEventArgs e)
{
Session["CaptchaImageText"] = GenerateRandomCode();
StringBuilder sb = new StringBuilder();
sb.AppendLine("$(document).ready(function() {");
sb.AppendLine(@"document.frames['captchaframe'].location.reload(true);");
sb.AppendLine(" });");
ScriptManager requestSM = ScriptManager.GetCurrent(this);
if (requestSM != null && requestSM.IsInAsyncPostBack)
{
ScriptManager.RegisterClientScriptBlock(this,
typeof(Page),
Guid.NewGuid().ToString(),
sb.ToString(),
true);
}
else
{
ClientScript.RegisterClientScriptBlock(typeof(Page),
Guid.NewGuid().ToString(),
sb.ToString(),
true);
}
}

I want to just refresh the iframe on button click without whole page postback.so i have used update panel for removing postback and easily refresh iframe .I works in IE, but not working in firefox.