John Rotella has just informed me of the following.
"The Thunderbird Registry form on Squarebirds has been removed.... there was a serious problem with a hacker and malicious script. I have no target date for replacing it as I have to work with some web site clients first, people who pay for services I provide. I think for the time being people should use the page on the Registry itself. Thanks"
John also said this was a widespread bot attack with thousands of sites being effected. One of them was his. Whenever John can get the problem fixed he will put the form back up and we should be able to use it again. In the meantime, his website Registry form is working apparently, so if you want to register your Tbird go to his website.