Here is the code:

```
    function onSelectClient(index) {

        var orderNumber = "123";

        $.ajax({
            async: true,
            type: "POST",
            url: "myAspx.aspx/GetPASR",
            data: '{orderNumber: "' + orderNumber + '" }',
            contentType: "application/json; charset=utf-8",
            dataType: "json",
            success: OnSuccess,
            failure: function (response) {
                alert(response.d);
            }
        });
        alert("After Call");
        return false;
    }

function OnSuccess(response) {
       //Do some stuff and then below

        location = "myAspx.aspx";
    }

```

The ajax call works good in IE and chrome.
In Firefox, it works when I have that alert after the call and I take a second to click on "Ok".
It does not work in firefox (V 36.0.1) when I don't have that alert or if I keep my mouse ready at the right place and click on Ok right when it appears.
Also, I see two errors in the console in FF.
1. "Use of getPreventDefault() is deprecated. Use defaultPrevented instead." - I see this in all pages of the application which are working good. So, this is not likely to cause the trouble.
2. "uncaught exception: out of memory". Not sure if it is related.