After upgrade to 13.04 neither Firefox or Chromium browsers will access localhost. Chromium says "Chromium's connection attempt to localhost was rejected".
This is not a problem when I go back to 12.10.
It may be a 64bit specific problem 'cos it happens on my desktop (64-bit installation) but not on a laptop (32-bit).
The contents of /etc/hosts,host.conf,hostname,hosts.allow,hosts.deny are the same in my 12.10 & 13.04