Throwing JS errors inside event listeners - FireFox

Hiya guys.
I'm trying to throw errors in on of my functions. I am using this syntax:

---
var myFunction = function() {throw new Error('a new error')}
myFunction();
---

This works in both FireFox and IE. In FireFox JS console if gives you a nice pretty error with the line number and a reference to where the error occurred in the document.

However, if you try to throw this error from inside an event listener:

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var myFunction = function() {throw new Error('a new error')}
if(window.addEventListener) window.addEventListener('load',myFunction,false);
else if(window.attachEvent) window.attachEvent('onload',myFunction);
---

Then while it behaves exactly the same in IE, in FireFox you get an ugly "[Exception... "'Error: a new error' when calling method: " style error message. This offends me, I want the nice pretty and functional error message.

It must be possible, because if I generate a default error, e.g.:

---
var myFunction = function() {alert(afgad.adfg)}
if(window.addEventListener) window.addEventListener('load',myFunction,false);
else if(window.attachEvent) window.attachEvent('onload',myFunction);
---

It works properly again.

Does anyone know if there is a technique for throwing this error properly from within an event listener for FireFox?

Thanks.
Robin.