It seems to a bug with Firefox as the HTTP_USER_AGENT doesn't indicate Ubuntu at all. From the logs on apt.ubuntu.com:
[28/Jan/2011:22:39:50 +0000] "GET /p/python-wxtools HTTP/1.0" 200 343 "-" "Mozilla/5.0 (X11; Linux x86_64; rv:2.0b10) Gecko/20100101 Firefox/4.0b10"
It seems to a bug with Firefox as the HTTP_USER_AGENT doesn't indicate Ubuntu at all. From the logs on apt.ubuntu.com:
[28/Jan/ 2011:22: 39:50 +0000] "GET /p/python-wxtools HTTP/1.0" 200 343 "-" "Mozilla/5.0 (X11; Linux x86_64; rv:2.0b10) Gecko/20100101 Firefox/4.0b10"