"When Firefox 2.12 came out on Feb. 7, it brought with it fixes
for three critical security holes and seven that were not quite so
serious. According to the security advisories, many of these
problems were also fixed in the Thunderbird 2.12 e-mail client.
Unfortunately, there is no Thunderbird 2.12.
"The Mozilla Foundation's press release focused on the Firefox
2.12 security fixes. The Foundation also reported, though, in its
MFSA (Mozilla Foundation Security Advisory), that these same bugs
had been fixed in the fictitious Thunderbird 2.12..."