I found a cookie in the Cookie Manager that had been stored from the .co.uk top level domain. I haven't tested to see if mozilla actually sends this back to all .co.uk websites as I haven't got access to a suitable server at the moment. The name of the cookie was "RMID", but I've no idea which organisation it came from. It's possible that .com.au and other multiple top level domains are effected, possibly even .com and .org etc.

Yes, the cookie will be sent to all hosts in the .co.uk domain. This is an old problem that we have known about for some time and which, unfortunately, does not have any solution. For all the gory details of why we can't fix it, see bug 8743 and the discussion there about the .co.nz domain

You asked about .com and .org. No, they are not affected -- the domain name must have at least two dots in it.

verified WONTFIX

*** Bug 252342 has been marked as a duplicate of this bug. ***

see bug 252342 comment 66 *** This bug has been marked as a duplicate of 252342 ***