You need to add
firefox35, not firefox.
You
could have figured this out quite easily with some research
Code:
[~]% ftp ftp://ftp.openbsd.org/4.7/packages/i386/
[... snip motd etc. ...]
ftp> ls firefox*3.5*
229 Entering Extended Passive Mode (|||62394|)
150 Opening ASCII mode data connection for '/bin/ls'.
-rw-r--r-- 1 0 0 15454185 Mar 23 14:55 firefox35-3.5.8.tgz
226 Transfer complete.