[jQuery] jQuery Ajax Error in Firefox 3.0.8

[Geo..]

Hi friends
I tried to develop an ajax request using jQuery
It works fine with IE and Even Chrome
But I always getting same error in firefox "411 Length Required" On
firebug
error shows on jquery.js line no 19

my code is given below
$.ajax({
                type:'POST',
                url:'ajax.php',
                dataType:"html",
                cache:false,
                timeout:10000,
                beforeSend:function(){
                                $('#searchresult').html("<div align='center' 
valign='middle'
style:'height:300px;position:fixed;'><img src='loading.gif' /
>&nbsp;&nbsp;<img src='text.gif' /></div>");
                },
                error:function(){
                        $('#searchresult').text("Server Not Responding ,Try 
again ").show
().fadeOut(2000);
                },
                success:function(data){
                                $('#searchresult').html(data);
                }
});


Is there any common error with jquery + firefox + ajax

I tried versions of jquery 1.2.6 and 1.3.2

expecting your help

Geo ..