Why isnt Firestarter or another kind of Firewall set up by default for Ubuntu? How to fix this manually?

Hello,

i can not answer the first part of your question this is a question for the canonical guys, but for the second part you will find your solution here:
https://help.ubuntu.com/7.04/keeping-safe/C/firewall.html
br
Mathias

Firstly Firestarter is not a firewall. This is a common misconception. Firestarter is simply a nice front end to the ipchains / Netfilter firewall. It used to be that ubuntu did not open any ports at all to the outside world so firewalling wasnt necessary. Dont know if that is still the case. If you want to set your machine as a firewall you can simply install firestarter with the add / remove programs application or configure ipchains yourself which I wont go into here as I could never do it full justice!

Iptables is the firewall that is integrated into the kernel so in a way there is a firewall installed by default. It's just not pretty to use. Firestarter makes it pretty but since a new install of ubuntu doesn't really need a firewall (or at least there doesn't need to be any tweaking of the installed firewall since you are secure to begin with) there is no need for it and it's just one more app to increase the size of the download. Once you start opening ports then you need to learn about iptables or firestarter.

Iptables is the firewall that is integrated into the kernel so in a way there is a firewall installed by default. It's just not pretty to use. Firestarter makes it pretty but since a new install of ubuntu doesn't really need a firewall (or at least there doesn't need to be any tweaking of the installed firewall since you are secure to begin with) there is no need for it and it's just one more app to increase the size of the download. Once you start opening ports then you need to learn about iptables or firestarter.