Why "Delete" button in "Certificate manager" is disables? Why certificates are prefilled?

[Yuri]

On 01/04/2013 19:13, J.R. Oldroyd wrote:
> For certificates that were distributed with the browser, you can click
> the "Edit" button and disable the three Trust boxes which essentially
> turns off the certificate.

For the matter of testing, I disabled all Thawte* certificates.
And https://google.com still shows without a problem and says that its 
identity is verified by Thawte SGC CA.

Yuri