ASPNet AJAX — Works In IE But Not Firefox

It's actually a pretty frustrating problem. You get your WCF service constructed and you get your web.config all perfect and you get your client-side script running smoothly . . . in Internet Explorer. When you go to check it out in Mozilla Firefox, it doesn't work. Your server-side code never gets executed. When you check out the Firefox Error Console, you see something like this:

Error: [Exception... "'Sys.Net.WebServiceFailedException: Sys.Net.WebServiceFailedException:
The server method 'MyMethod' failed with the following error: '
when calling method: [nsIDOMEventListener::handleEvent]
"  nsresult: "0x8057001c (NS_ERROR_XPC_JS_THREW_JS_OBJECT)"
location: "<unknown>"  data: no]

Don't panic. The problem is that Firefox requires both a success and a failure handler. You cannot pass null in for either one — both have to be valid functions:

<script type="text/javascript" language="javascript">
// <![CDATA[
function MyMethod()
{
    var service = new ajaxService();
    service.MyMethod("Data",OnSuccess,OnFailure,null);
}

function OnSuccess(result){ alert(result); }

function OnFailure(err){ alert(err); }

// ]]>
</script>

Add both a valid success and a valid failure handler and Firefox will function as expected.

I hope this helps someone.