After adding this one it's work for all browsers
if (Request.UserAgent.IndexOf("AppleWebKit") > 0)
{
Request.Browser.Adapters.Clear();
}
for IE8...
Add css Proferty in StyleSheet
.IE8Fix
{
z-index: 1000;
}
and add the css property as follows...
<asp:Menu runat="server" >
<DynamicMenuStyle CssClass="IE8Fix" />
</asp:Menu>