I tried the "Log in" button when looking at the page:
https://wiki.postgresql.org/wiki/What%27s_new_in_PostgreSQL_9.3
and got a 403 Forbidden error (at the target URL
<https://wiki.postgresql.org/index.php?title=Special:UserLogin&returnto=What%27s+new+in+PostgreSQL+9.3>).
I'm able to reproduce this problem in a Chrome incognito window and in
Safari.
Trying the same Log in button from a handful of other wiki pages seems
to work OK, so it seems to be a problem with that page in particular.
Josh