apparently safari won't parse that particular date format; i think the "GMT" needs to follow the time.
you'll have to use a different format, e.g.:
use POSIX;
my $expDate = strftime "%a %b %e %Y %H:%M:%S GMT", gmtime;
or use javascript to reformat the string.
of course you could also request that safari support native gmtime() format. i think
bug 3366 is the one you want.
iBook g4 OS X.4.x