Only todays time is showing for new emails

I have recently installed Thunderbird as my default mail client, and I love it. However, the problem I'm having is that Thunderbird displays only the time for today's email without the date. In order to change this I'll have to change the configuration in the preferences file, according to this link;

http://kb.mozillazine.org/Date_displa....2Ftime_system_settings_on_your_computer

Nevertheless, I'm unable to find the preference line that controls today's date format on Thunderbird 3.

Can someone tell me what's the name of this line in Thunderbird 3?

Thanks,