onbeforeonload call on iframe window

[Madhumita]

Hi,
I cannot get the onbeforeonload call on a iframe window to fire when I
change the src of the iframe. Any clues on this will be appreciated:

So if I have an iframe called myIframe and set a onbefore handler and
change the location, I don't see it being triggered.

myIframe = createIframe();
myIframe.contentWindow.onbeforeunload = fr_unload;

myIframe.contentWindow.location = url1;
myIframe.contentWindow.location = url2;

When I am changing the location I don't see the alert statement that I
have in the function fr_unload being triggered.

I tried testing this on both IE (6.0) and Firefox (2.0).

Any ideas on this?

Thanks,
Madhumita