[Solved] DropDownList CSS width issue in different browsers

I am using width attribrute of aspdropdown list

The issue is the width is not constant in firefox and mozilla

its fine in chrome..

So is this a problem with browser..

Please help me out

asp:DropDownList ID="countrydropdown"  Width="160px"  class ="combo"  Height ="23px" onselectedindexchanged="countrydropdown_SelectedIndexChanged" AutoPostBack="true" runat="server"><asp:ListItem>Select country</asp:ListItem></asp:DropDownList>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
    <asp:DropDownList ID="statedropdown"    Width="160px" class = "combo"    Height ="23px" 
    AutoPostBack="true" runat="server" onselectedindexchanged="statedropdown_SelectedIndexChanged"><asp:ListItem>Select state</asp:ListItem></asp:DropDownList>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
    <asp:DropDownList ID="citydropdown"  Width="160px" class = "combo"  Height ="23px" AutoPostBack="true"  runat="server"><asp:ListItem>Select city</asp:ListItem></asp:DropDownList><br /><br /><br />