Comment 20 for bug 213081

Mack:
You have to get the root privileges to edit /etc/sysctl.conf. To learn about acting as root see for example:
   https://help.ubuntu.com/8.04/administrative/C/
   https://help.ubuntu.com/community/RootSudo

I suppose you use graphical interface, so open a terminal and at the command prompt enter

   sudo gedit /etc/sysctl.conf

Insert the new line as Eric proposed:

   net.ipv4.tcp_frto = 0

save the file and close the editor. To make the system recognize the change enter the command

   sudo /sbin/sysctl -p /etc/sysctl.conf

or reboot your machine.
Good luck

PS. Consider making your e-mail available in your profile, to avoid posting information just for you to the entire forum.