It appears it is/was/could have been a mirror site for Mozilla?
For instance, this page http://mytopfiles.com/programs/file/Firefox-Setup-4-0/431156.htm shows stonekitty.net & below various mirrors. (It does not show the particular port.)
I picked one of the mirrors, "saudi.net.sa".
Going here, http://www.mozilla.org/community/mirrors.html, I find neither "stonekitty" nor "saudi".
Though viewing the source of the page, I do find, "href="http://mozilla.saudi.net.sa", so you would expect that to be legit?
Perhaps stonekitty was at one time a mirror?
In any case, what I surmise above proves nothing.
Do you still have the downloaded file? If so, you can easily verify its validity, ftp://ftp.mozilla.org/pub/firefox/releases/3.6.13/SHA1SUMS.
(And in any case, 3.6.13 is dated & you should update to 3.6.17.)