I'm using 1.3a3 with PPPoe and I'm unable to browse some sites (imdb, amazon,digg).
This reminded me of the mss clamping problem in the previous version of
ipfilter. In the new version there is the mssclamp option for the map rule

map ng0 192.168.1.0/24 -> 0.0.0.0/32 proxy port ftp ftp/tcp
map ng0 192.168.1.0/24 -> 0.0.0.0/32 mssclamp 1452

using this now i can browse those sites.