Integrating Firefox & Yahoo! Mail

I am trying to configure Firefox so that it will open Yahoo! Mail (the webmail version) and parse mailto URIs. But I can't seem to find the right string.

I found the way to select Yahoo! in Tools --> Options --> Applications

But when I click on complex mailto links, all of the fields are combined into the To field of the form.

I even found the string in about:config that I need to change:

gecko.handlerService.schemes.mailto.0.uriTemplate

The default being : http://compose.mail.yahoo.com/?To=%s

which seems to explain why it's all in the To field.

I've also tried: http://compose.mail.yahoo.com/?To=%t&Subject=%s&Body=%

to no avail.

Now how do I change that so that it parses correctly to To, Subject and Body?